draft-ietf-eap-keying-18.txt   draft-ietf-eap-keying-19.txt 
EAP Working Group Bernard Aboba EAP Working Group Bernard Aboba
INTERNET-DRAFT Dan Simon Internet Draft Dan Simon
Category: Standards Track Microsoft Updates: 3748 Microsoft Corporation
<draft-ietf-eap-keying-18.txt> P. Eronen Category: Standards Track P. Eronen
7 February 2007 Nokia Expires: April 23, 2008 Nokia
H. Levkowetz 23 October 2007
Ericsson Research
Extensible Authentication Protocol (EAP) Key Management Framework Extensible Authentication Protocol (EAP) Key Management Framework
draft-ietf-eap-keying-19.txt
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
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This Internet-Draft will expire on August 8, 2007. This Internet-Draft will expire on April 23, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). All rights reserved. Copyright (C) The IETF Trust (2007). All rights reserved.
Abstract Abstract
The Extensible Authentication Protocol (EAP), defined in [RFC3748], The Extensible Authentication Protocol (EAP), defined in RFC 3748,
enables extensible network access authentication. This document enables extensible network access authentication. This document
specifies the EAP key hierarchy and provides a framework for the specifies the EAP key hierarchy and provides a framework for the
transport and usage of keying material generated by EAP transport and usage of keying material and parameters generated by
authentication algorithms, known as "methods". It also provides a EAP authentication algorithms, known as "methods". It also provides
system-level security analysis. a detailed system-level security analysis, demonstrating compliance
with the key management guidelines described in RFC 4962.
Table of Contents Table of Contents
1. Introduction .......................................... 3 1. Introduction .......................................... 3
1.1 Requirements Language ........................... 3 1.1 Requirements Language ........................... 3
1.2 Terminology ..................................... 3 1.2 Terminology ..................................... 3
1.3 Overview ........................................ 6 1.3 Overview ........................................ 7
1.4 EAP Key Hierarchy ............................... 9 1.4 EAP Key Hierarchy ............................... 9
1.5 Security Goals .................................. 13 1.5 Security Goals .................................. 13
1.6 EAP Invariants .................................. 14 1.6 EAP Invariants .................................. 14
2. Lower Layer Operation ................................. 17 2. Lower Layer Operation ................................. 18
2.1 Transient Session Keys .......................... 18 2.1 Transient Session Keys .......................... 18
2.2 Authenticator and Peer Architecture ............. 19 2.2 Authenticator and Peer Architecture ............. 20
2.3 Server Identification ........................... 24 2.3 Authenticator Identification ..................... 21
3. Security Association Management ....................... 26 2.4 Peer Identification ............................. 25
3.1 Secure Association Protocol ..................... 27 2.5 Server Identification ........................... 26
3.2 Key Scope ....................................... 30 3. Security Association Management ....................... 28
3.3 Parent-Child Relationships ...................... 30 3.1 Secure Association Protocol ..................... 29
3.4 Local Key Lifetimes ............................. 31 3.2 Key Scope ....................................... 32
3.5 Exported and Calculated Key Lifetimes ........... 32 3.3 Parent-Child Relationships ...................... 32
3.6 Key Cache Synchronization ....................... 34 3.4 Local Key Lifetimes ............................. 33
3.7 Key Strength .................................... 34 3.5 Exported and Calculated Key Lifetimes ........... 34
3.8 Key Wrap ........................................ 35 3.6 Key Cache Synchronization ....................... 36
4. Handoff Vulnerabilities ............................... 35 3.7 Key Strength .................................... 37
4.1 EAP Pre-authentication .......................... 36 3.8 Key Wrap ........................................ 37
4.2 Proactive Key Distribution ...................... 38 4. Handoff Vulnerabilities ............................... 38
4.3 AAA Bypass ...................................... 39 4.1 EAP Pre-authentication .......................... 39
5. Security Considerations .............................. 43 4.2 Proactive Key Distribution ...................... 40
5.1 Peer and Authenticator Compromise ............... 44 4.3 AAA Bypass ...................................... 42
5.2 Cryptographic Negotiation ....................... 45 5. Security Considerations .............................. 46
5.3 Confidentiality and Authentication .............. 46 5.1 Peer and Authenticator Compromise ............... 47
5.4 Key Binding ...................................... 51 5.2 Cryptographic Negotiation ....................... 48
5.5 Authorization ................................... 52 5.3 Confidentiality and Authentication .............. 50
5.6 Replay Protection ............................... 53 5.4 Key Binding ..................................... 55
5.7 Key Freshness ................................... 54 5.5 Authorization ................................... 56
5.8 Key Scope Limitation ............................ 55 5.6 Replay Protection ............................... 58
5.9 Key Naming ...................................... 56 5.7 Key Freshness ................................... 59
5.10 Denial of Service Attacks ....................... 56 5.8 Key Scope Limitation ............................ 61
6. IANA Considerations ................................... 57 5.9 Key Naming ...................................... 62
7. References ............................................ 57 5.10 Denial of Service Attacks ....................... 62
7.1 Normative References ............................ 57 6. IANA Considerations ................................... 63
7.2 Informative References .......................... 57 7. References ............................................ 63
Acknowledgments .............................................. 63 7.1 Normative References ............................ 63
Author's Addresses ........................................... 63 7.2 Informative References .......................... 63
Appendix A - Exported Parameters in Existing Methods ......... 64 Acknowledgments .............................................. 70
Full Copyright Statement ..................................... 66 Author's Addresses ........................................... 70
Intellectual Property ........................................ 66 Appendix A - Exported Parameters in Existing Methods ......... 71
Full Copyright Statement ..................................... 73
Intellectual Property ........................................ 73
1. Introduction 1. Introduction
The Extensible Authentication Protocol (EAP), defined in [RFC3748], The Extensible Authentication Protocol (EAP), defined in [RFC3748],
was designed to enable extensible authentication for network access was designed to enable extensible authentication for network access
in situations in which the Internet Protocol (IP) protocol is not in situations in which the Internet Protocol (IP) protocol is not
available. Originally developed for use with Point-to-Point Protocol available. Originally developed for use with Point-to-Point Protocol
(PPP) [RFC1661], it has subsequently also been applied to IEEE 802 (PPP) [RFC1661], it has subsequently also been applied to IEEE 802
wired networks [IEEE-802.1X], IKEv2 [RFC4306] and wireless networks wired networks [IEEE-802.1X], IKEv2 [RFC4306] and wireless networks
such as [IEEE-802.11i] and [IEEE-802.16e]. such as [IEEE-802.11] and [IEEE-802.16e].
EAP is a two-party protocol spoken between the EAP peer and server. EAP is a two-party protocol spoken between the EAP peer and server.
Within EAP, keying material is generated by EAP authentication Within EAP, keying material is generated by EAP authentication
algorithms, known as "methods". Part of this keying material may be algorithms, known as "methods". Part of this keying material can be
used by EAP methods themselves and part of this material may be used by EAP methods themselves and part of this material can be
exported. In addition to export of keying material, EAP methods may exported. In addition to export of keying material, EAP methods can
also export associated parameters such as authenticated peer and also export associated parameters such as authenticated peer and
server identities and a unique EAP conversation identifier, and may server identities and a unique EAP conversation identifier, and can
import and export lower layer parameters known as "Channel Binding import and export lower layer parameters known as "channel binding
parameters", or simply "channel bindings". parameters", or simply "channel bindings".
This document specifies the EAP key hierarchy and provides a This document specifies the EAP key hierarchy and provides a
framework for the transport and usage of keying material and framework for the transport and usage of keying material and
parameters generated by EAP methods. It also provides a system-level parameters generated by EAP methods. It also provides a detailed
security analysis. security analysis, demonstrating compliance with the requirements
described in "Guidance for Authentication, Authorization and
Accounting (AAA) Key Management" [RFC4962].
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
1.2. Terminology 1.2. Terminology
The terms "Cryptographic binding", "Cryptographic separation", "Key The terms "Cryptographic binding", "Cryptographic separation", "Key
strength" and "Mutual authentication" are defined in [RFC3748] and strength" and "Mutual authentication" are defined in [RFC3748] and
are used with the same meaning in this document, which also are used with the same meaning in this document, which also
frequently uses the following terms: frequently uses the following terms:
4-Way Handshake 4-Way Handshake
A pairwise Authentication and Key Management Protocol (AKMP) A pairwise Authentication and Key Management Protocol (AKMP)
defined in [IEEE-802.11i], which confirms mutual possession of a defined in [IEEE-802.11], which confirms mutual possession of a
Pairwise Master Key by two parties and distributes a Group Key. Pairwise Master Key by two parties and distributes a Group Key.
AAA Authentication, Authorization and Accounting. AAA protocols with AAA Authentication, Authorization and Accounting. AAA protocols with
EAP support include RADIUS [RFC3579] and Diameter [RFC4072]. In EAP support include RADIUS [RFC3579] and Diameter [RFC4072]. In
this document, the terms "AAA server" and "backend authentication this document, the terms "AAA server" and "backend authentication
server" are used interchangeably. server" are used interchangeably.
AAA-Key AAA-Key
The term AAA-Key is synonymous with MSK. Since multiple keys may The term AAA-Key is synonymous with Master Session Key (MSK).
be transported by AAA, the term is potentially confusing and is not Since multiple keys can be transported by AAA, the term is
used in this document. potentially confusing and is not used in this document.
authenticator authenticator
The end of the link initiating EAP authentication. The term The entity initiating EAP authentication.
Authenticator is used in [IEEE-802.1X], and authenticator has the
same meaning in this document.
backend authentication server backend authentication server
A backend authentication server is an entity that provides an A backend authentication server is an entity that provides an
authentication service to an authenticator. When used, this server authentication service to an authenticator. When used, this server
typically executes EAP methods for the authenticator. This typically executes EAP methods for the authenticator. This
terminology is also used in [IEEE-802.1X]. terminology is also used in [IEEE-802.1X].
Channel Binding Channel Binding
A secure mechanism for ensuring that a subset of the parameters A secure mechanism for ensuring that a subset of the parameters
transmitted by the authenticator (such as authenticator identifiers transmitted by the authenticator (such as authenticator identifiers
and properties) are agreed upon by the EAP peer and server. It is and properties) are agreed upon by the EAP peer and server. It is
expected that the parameters are also securely agreed upon by the expected that the parameters are also securely agreed upon by the
EAP peer and authenticator via the lower layer if the authenticator EAP peer and authenticator via the lower layer if the authenticator
advertised the parameters. advertised the parameters.
Derived Keying Material
Keys derived from EAP keying material, such as Transient Session
Keys (TSKs).
EAP Keying Material
Keys derived by an EAP method; this includes exported keying
material (MSK, EMSK, IV) as well as local keying material such as
Transient EAP Keys (TEKs).
EAP pre-authentication EAP pre-authentication
The use of EAP to pre-establish EAP keying material on an The use of EAP to pre-establish EAP keying material on an
authenticator prior to arrival of the peer at the access network authenticator prior to arrival of the peer at the access network
managed by that authenticator. managed by that authenticator.
EAP re-authentication EAP re-authentication
EAP authentication between an EAP peer and a server with whom the EAP authentication between an EAP peer and a server with whom the
EAP peer shares valid unexpired keying material. EAP peer shares valid unexpired EAP keying material.
EAP server EAP server
The entity that terminates the EAP authentication method with the The entity that terminates the EAP authentication method with the
peer. In the case where no backend authentication server is used, peer. In the case where no backend authentication server is used,
the EAP server is part of the authenticator. In the case where the the EAP server is part of the authenticator. In the case where the
authenticator operates in pass-through mode, the EAP server is authenticator operates in pass-through mode, the EAP server is
located on the backend authentication server. located on the backend authentication server.
Exported keying material
The EAP Master Session Key (MSK), Extended Master Session Key
(EMSK), and Initialization Vector (IV).
Extended Master Session Key (EMSK) Extended Master Session Key (EMSK)
Additional keying material derived between the peer and server that Additional keying material derived between the peer and server that
is exported by the EAP method. The EMSK is at least 64 octets in is exported by the EAP method. The EMSK is at least 64 octets in
length, and is never shared with a third party. The EMSK MUST be length, and is never shared with a third party. The EMSK MUST be
at least as long as the MSK in size. at least as long as the MSK in size.
Initialization Vector (IV) Initialization Vector (IV)
A quantity of at least 64 octets, suitable for use in an A quantity of at least 64 octets, suitable for use in an
initialization vector field, that is derived between the peer and initialization vector field, that is derived between the peer and
EAP server. Since the IV is a known value in methods such as EAP- EAP server. Since the IV is a known value in methods such as EAP-
TLS [I-D.simon-emu-rfc2716bis], it cannot be used by itself for TLS [I-D.simon-emu-rfc2716bis], it cannot be used by itself for
computation of any quantity that needs to remain secret. As a computation of any quantity that needs to remain secret. As a
result, its use has been deprecated and EAP methods are not result, its use has been deprecated and it is OPTIONAL for EAP
required to generate it. However, when it is generated it MUST be methods to generate it. However, when it is generated it MUST be
unpredictable. unpredictable.
Keying Material
Unless otherwise qualified, the term "keying material" refers to
EAP keying material as well as derived keying material.
Key Scope Key Scope
The parties to whom a key is available. The parties to whom a key is available.
Keywrap Key Wrap
The encryption of one symmetric cryptographic key in another. The The encryption of one symmetric cryptographic key in another. The
algorithm used for the encryption is called a key wrap algorithm or algorithm used for the encryption is called a key wrap algorithm or
a key encryption algorithm. The key used in the encryption process a key encryption algorithm. The key used in the encryption process
is called a key-encryption key (KEK). is called a key-encryption key (KEK).
Long Term Credential Long Term Credential
EAP methods frequently make use of long term secrets in order to EAP methods frequently make use of long term secrets in order to
enable authentication between the peer and server. In the case of enable authentication between the peer and server. In the case of
a method based on pre-shared key authentication, the long term a method based on pre-shared key authentication, the long term
credential is the pre-shared key. In the case of a public-key credential is the pre-shared key. In the case of a public-key
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Master Session Key (MSK) Master Session Key (MSK)
Keying material that is derived between the EAP peer and server and Keying material that is derived between the EAP peer and server and
exported by the EAP method. The MSK is at least 64 octets in exported by the EAP method. The MSK is at least 64 octets in
length. length.
Network Access Server (NAS) Network Access Server (NAS)
A device that provides an access service for a user to a network. A device that provides an access service for a user to a network.
Pairwise Master Key (PMK) Pairwise Master Key (PMK)
Lower layers use the MSK in lower-layer dependent manner. For Lower layers use the MSK in lower-layer dependent manner. For
instance, in [IEEE-802.11i] Octets 0-31 of the MSK are known as the instance, in IEEE 802.11 [IEEE-802.11] Octets 0-31 of the MSK are
Pairwise Master Key (PMK). In [IEEE-802.11i] the TKIP and AES CCMP known as the Pairwise Master Key (PMK); the TKIP and AES CCMP
ciphersuites derive their Transient Session Keys (TSKs) solely from ciphersuites derive their Transient Session Keys (TSKs) solely from
the PMK, whereas the WEP ciphersuite as noted in [RFC3580], derives the PMK, whereas the WEP ciphersuite as noted in [RFC3580], derives
its TSKs from both halves of the MSK. In [802.16e], the MSK is its TSKs from both halves of the MSK. In [802.16e], the MSK is
truncated to 20 octets for PMK and 20 octets for PMK2. truncated to 20 octets for PMK and 20 octets for PMK2.
peer The end of the link that responds to the authenticator. peer The entity that responds to the authenticator. In [IEEE-802.1X],
this entity is known as the Supplicant.
security association security association
A set of policies and cryptographic state used to protect A set of policies and cryptographic state used to protect
information. Elements of a security association may include information. Elements of a security association include
cryptographic keys, negotiated ciphersuites and other parameters, cryptographic keys, negotiated ciphersuites and other parameters,
counters, sequence spaces, authorization attributes, etc. counters, sequence spaces, authorization attributes, etc.
Secure Association Protocol Secure Association Protocol
An exchange that occurs between the EAP peer and authenticator in An exchange that occurs between the EAP peer and authenticator in
order to manage security associations derived from EAP exchanges. order to manage security associations derived from EAP exchanges.
The protocol establishes unicast and (optionally) multicast The protocol establishes unicast and (optionally) multicast
security associations, which include symmetric keys and a context security associations, which include symmetric keys and a context
for the use of the keys. An example of a Secure Association for the use of the keys. An example of a Secure Association
Protocol is the 4-way handshake defined within [IEEE-802.11i]. Protocol is the 4-way handshake defined within [IEEE-802.11].
Session-Id Session-Id
The EAP Session-Id uniquely identifies an EAP authentication The EAP Session-Id uniquely identifies an EAP authentication
exchange between an EAP peer (as identified by the Peer-Id) and exchange between an EAP peer (as identified by the Peer-Id(s)) and
server (as identified by the Server-Id). For more information, see server (as identified by the Server-Id(s)). For more information,
Section 1.4. see Section 1.4.
Transient EAP Keys (TEKs) Transient EAP Keys (TEKs)
Session keys which are used to establish a protected channel Session keys which are used to establish a protected channel
between the EAP peer and server during the EAP authentication between the EAP peer and server during the EAP authentication
exchange. The TEKs are appropriate for use with the ciphersuite exchange. The TEKs are appropriate for use with the ciphersuite
negotiated between EAP peer and server for use in protecting the negotiated between EAP peer and server for use in protecting the
EAP conversation. The TEKs are stored locally by the EAP method EAP conversation. The TEKs are stored locally by the EAP method
and are not exported. Note that the ciphersuite used to set up the and are not exported. Note that the ciphersuite used to set up the
protected channel between the EAP peer and server during EAP protected channel between the EAP peer and server during EAP
authentication is unrelated to the ciphersuite used to subsequently authentication is unrelated to the ciphersuite used to subsequently
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1b: AAA Key Transport (optional) 1b: AAA Key Transport (optional)
Phase 2: Secure Association Protocol Phase 2: Secure Association Protocol
2a: Unicast Secure Association 2a: Unicast Secure Association
2b: Multicast Secure Association (optional) 2b: Multicast Secure Association (optional)
Of these phases, Phase 0, 1b and Phase 2 are handled external to EAP. Of these phases, Phase 0, 1b and Phase 2 are handled external to EAP.
Phases 0 and 2 are handled by the lower layer protocol and phase 1b Phases 0 and 2 are handled by the lower layer protocol and phase 1b
is typically handled by a AAA protocol. is typically handled by a AAA protocol.
In the discovery phase (phase 0), peers locate authenticators and In the discovery phase (phase 0), peers locate authenticators and
discover their capabilities. A peer may locate an authenticator discover their capabilities. A peer can locate an authenticator
providing access to a particular network, or a peer may locate an providing access to a particular network, or a peer can locate an
authenticator behind a bridge with which it desires to establish a authenticator behind a bridge with which it desires to establish a
Secure Association. Discovery can occur manually or automatically, Secure Association. Discovery can occur manually or automatically,
depending on the lower layer over which EAP runs. depending on the lower layer over which EAP runs.
The authentication phase (phase 1) may begin once the peer and The authentication phase (phase 1) can begin once the peer and
authenticator discover each other. This phase, if it occurs, always authenticator discover each other. This phase, if it occurs, always
includes EAP authentication (phase 1a). Where the chosen EAP method includes EAP authentication (phase 1a). Where the chosen EAP method
supports key derivation, in phase 1a EAP keying material is derived supports key derivation, in phase 1a EAP keying material is derived
on both the peer and the EAP server. on both the peer and the EAP server.
An additional step (phase 1b) is required in deployments which An additional step (phase 1b) is needed in deployments which include
include a backend authentication server, in order to transport keying a backend authentication server, in order to transport keying
material from the backend authentication server to the authenticator. material from the backend authentication server to the authenticator.
In order to obey the principle of mode independence (see Section In order to obey the principle of mode independence (see Section
1.6.1), where a backend server is present, all keying material which 1.6.1), where a backend server is present, all keying material needed
is required by the lower layer needs to be transported from the EAP by the lower layer is transported from the EAP server to the
server to the authenticator. Since existing TSK derivation and authenticator. Since existing TSK derivation and transport
transport techniques depend solely on the MSK, in existing techniques depend solely on the MSK, in existing implementations,
implementations, this is the only keying material replicated in the this is the only keying material replicated in the AAA key transport
AAA key transport phase 1b. phase 1b.
Successful completion of EAP authentication and key derivation by a Successful completion of EAP authentication and key derivation by a
peer and EAP server does not necessarily imply that the peer is peer and EAP server does not necessarily imply that the peer is
committed to joining the network associated with an EAP server. committed to joining the network associated with an EAP server.
Rather, this commitment is implied by the creation of a security Rather, this commitment is implied by the creation of a security
association between the EAP peer and authenticator, as part of the association between the EAP peer and authenticator, as part of the
Secure Association Protocol (phase 2). The Secure Association Secure Association Protocol (phase 2). The Secure Association
Protocol exchange (phase 2) occurs between the peer and authenticator Protocol exchange (phase 2) occurs between the peer and authenticator
in order to manage the creation and deletion of unicast (phase 2a) in order to manage the creation and deletion of unicast (phase 2a)
and multicast (phase 2b) security associations between the peer and and multicast (phase 2b) security associations between the peer and
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the services offered by the concentrator. The discovery phase is the services offered by the concentrator. The discovery phase is
not secured. PPPoE, like PPP, does not include a Secure not secured. PPPoE, like PPP, does not include a Secure
Association Protocol. Association Protocol.
IKEv2 IKEv2
Internet Key Exchange v2 (IKEv2), defined in [RFC4306], includes Internet Key Exchange v2 (IKEv2), defined in [RFC4306], includes
support for EAP and handles the establishment of unicast security support for EAP and handles the establishment of unicast security
associations (phase 2a). However, the establishment of multicast associations (phase 2a). However, the establishment of multicast
security associations (phase 2b) typically does not involve EAP and security associations (phase 2b) typically does not involve EAP and
needs to be handled by a group key management protocol such as GDOI needs to be handled by a group key management protocol such as GDOI
[RFC3547], GSAKMP [GSAKMP], MIKEY [RFC3830], or GKDP [GKDP]. [RFC3547], GSAKMP [RFC4535], MIKEY [RFC3830], or GKDP [GKDP].
Several mechanisms have been proposed for discovery of IPsec Several mechanisms have been proposed for discovery of IPsec
security gateways. [RFC2230] discusses the use of Key eXchange security gateways. [RFC2230] discusses the use of Key eXchange
(KX) Resource Records (RRs) for IPsec gateway discovery; while KX (KX) Resource Records (RRs) for IPsec gateway discovery; while KX
RRs are supported by many Domain Name Service (DNS) server RRs are supported by many Domain Name Service (DNS) server
implementations, they have not yet been widely deployed. implementations, they have not yet been widely deployed.
Alternatively, DNS SRV [RFC2782] can be used for this purpose. Alternatively, DNS SRV RRs [RFC2782] can be used for this purpose.
Where DNS is used for gateway location, DNS security mechanisms Where DNS is used for gateway location, DNS security mechanisms
such as DNSSEC ([RFC4033], [RFC4035]), TSIG [RFC2845], and Simple such as DNSSEC ([RFC4033], [RFC4035]), TSIG [RFC2845], and Simple
Secure Dynamic Update [RFC3007] are available. Secure Dynamic Update [RFC3007] are available.
IEEE 802.11i IEEE 802.11
IEEE 802.11, defined in [IEEE-802.11], handles discovery via the IEEE 802.11, defined in [IEEE-802.11], handles discovery via the
Beacon and Probe Request/Response mechanisms. IEEE 802.11 access Beacon and Probe Request/Response mechanisms. IEEE 802.11 access
points periodically announce their Service Set Identifiers (SSIDs) points periodically announce their Service Set Identifiers (SSIDs)
as well as capabilities using Beacon frames. Stations can query as well as capabilities using Beacon frames. Stations can query
for access points by sending a Probe Request to the broadcast for access points by sending a Probe Request to the broadcast
address. Neither Beacon nor Probe Request/Response frames are address. Neither Beacon nor Probe Request/Response frames are
secured. The 4-way handshake defined in [IEEE-802.11i] enables the secured. The 4-way handshake defined in [IEEE-802.11] enables the
derivation of unicast (phase 2a) and multicast/broadcast (phase 2b) derivation of unicast (phase 2a) and multicast/broadcast (phase 2b)
secure associations. Since the group key exchange transports a secure associations. Since the group key exchange transports a
group key from the access point to the station, two 4-way group key from the access point to the station, two 4-way
handshakes may be required in order to support peer-to-peer handshakes can be needed in order to support peer-to-peer
communications. A proof of the security of the IEEE 802.11i 4-way communications. A proof of the security of the IEEE 802.11 4-way
handshake when used with EAP-TLS is provided in [He]. handshake when used with EAP-TLS is provided in [He].
IEEE 802.1X IEEE 802.1X
IEEE 802.1X-2004, defined in [IEEE-802.1X] does not support IEEE 802.1X-2004, defined in [IEEE-802.1X] does not support
discovery (phase 0), nor does it provide for derivation of unicast discovery (phase 0), nor does it provide for derivation of unicast
or multicast secure associations. or multicast secure associations.
1.4. EAP Key Hierarchy 1.4. EAP Key Hierarchy
As illustrated in Figure 2, the EAP method key derivation has at the As illustrated in Figure 2, the EAP method key derivation has at the
root the long term credential utilized by the selected EAP method. root the long term credential utilized by the selected EAP method.
If authentication is based on a pre-shared key, the parties store the If authentication is based on a pre-shared key, the parties store the
EAP method to be used and the pre-shared key. The EAP server also EAP method to be used and the pre-shared key. The EAP server also
stores the peer's identity as well as additional information. This stores the peer's identity as well as additional information. This
information is typically used outside of the EAP method to determine information is typically used outside of the EAP method to determine
if access to some service should be granted. The peer stores whether to grant access to a service. The peer stores information
information necessary to choose which secret to use for which necessary to choose which secret to use for which service.
service.
If authentication is based on proof of possession of the private key
corresponding to the public key contained within a certificate, the
parties store the EAP method to be used and the trust anchors used to
validate the certificates. The EAP server may also store additional
information associated with the peer's identity and the peer stores
information necessary to choose which certificate to use for which
service.
If authentication is based on proof of possession of the private key If authentication is based on proof of possession of the private key
corresponding to the public key contained within a certificate, the corresponding to the public key contained within a certificate, the
parties store the EAP method to be used and the trust anchors used to parties store the EAP method to be used and the trust anchors used to
validate the certificates. The EAP server also stores the peer's validate the certificates. The EAP server also stores the peer's
identity and the peer stores information necessary to choose which identity and the peer stores information necessary to choose which
certificate to use for which service. Based on the long term certificate to use for which service. Based on the long term
credential established between the peer and the server, EAP methods credential established between the peer and the server, methods
derive two types of keys: derive two types of EAP keying material:
(a) Keys calculated locally by the EAP method but not exported (a) Keying material calculated locally by the EAP method
by the EAP method, such as the Transient EAP Keys (TEKs). but not exported, such as the Transient EAP Keys (TEKs).
(b) Keying material exported by the EAP method: Master Session Key (b) Keying material exported by the EAP method: Master Session Key
(MSK), Extended Master Session Key (EMSK), Initiatlization (MSK), Extended Master Session Key (EMSK), Initialization
Vector (IV). Vector (IV).
As noted in [RFC3748] Section 7.10, EAP methods generating keys are As noted in [RFC3748] Section 7.10:
required to calculate and export the MSK and EMSK, which must be at
least 64 octets in length. EAP methods also may export the IV;
however, the use of the IV is deprecated.
The EMSK MUST NOT be provided to an entity outside the EAP server or
peer, nor is it permitted to pass any quantity to an entity outside
the EAP server or peer from which the EMSK could be computed without
breaking some cryptographic assumption, such as inverting a one-way
function.
EAP methods also MAY export method-specific peer (Peer-Id) and server
(Server-Id) identifiers and a method-specific EAP conversation
identifier known as the Session-Id. EAP methods MAY also support the
import and export of channel binding parameters. New EAP method
specifications MUST define the Peer-Id, Server-Id and Session-Id.
The combination of the Peer-Id and Server-Id uniquely specifies the
endpoints of the EAP method exchange when they are provided. For
existing EAP methods the Peer-Id, Server-Id, and Session-Id are
defined in Appendix A.
Peer-Id
As described in [RFC3748] Section 7.3, the identity provided in In order to provide keying material for use in a subsequently
the EAP-Response/Identity may be different from the peer identity negotiated ciphersuite, an EAP method supporting key derivation
authenticated by the EAP method. For example, the identity MUST export a Master Session Key (MSK) of at least 64 octets, and
provided in the EAP-Response/Identity may be a privacy identifier an Extended Master Session Key (EMSK) of at least 64 octets.
as described in "The Network Access Identifier" [RFC4282] Section
2.3, or may be decorated as described in [RFC4282] Section 2.7.
Where the EAP method authenticates the peer identity, that
identity is exported by the method as the Peer-Id. A suitable EAP
peer name may not always be available. Where an EAP method does
not define a method-specific peer identity, the Peer-Id is the
null string.
Server-Id EAP methods also MAY export the IV; however, the use of the IV is
deprecated. The EMSK MUST NOT be provided to an entity outside the
EAP server or peer, nor is it permitted to pass any quantity to an
entity outside the EAP server or peer from which the EMSK could be
computed without breaking some cryptographic assumption, such as
inverting a one-way function.
Where the EAP method authenticates the server identity, that EAP methods supporting key derivation and mutual authentication
identity is exported by the method as the Server-Id. A suitable SHOULD export a method-specific EAP conversation identifier known as
EAP server name may not always be available. Where an EAP method the Session-Id, as well as one or more method-specific peer
does not define a method-specific server identity, the Server-Id identifiers (Peer-Id(s)) and MAY export one or more method-specific
is the null string. server identifiers (Server-Id(s)). EAP methods MAY also support the
import and export of channel binding parameters. EAP method
specifications developed after the publication of this document MUST
define the Peer-Id, Server-Id and Session-Id. The Peer-Id(s) and
Server-Id(s), when provided, identify the entities involved in
generating EAP keying material. For existing EAP methods the Peer-Id,
Server-Id and Session-Id are defined in Appendix A.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+
| | ^ | | ^
| EAP Method | | | EAP Method | |
| | | | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ | |
| | | | | | | | | | | | | |
| | EAP Method Key |<->| Long-Term | | | | | EAP Method Key |<->| Long-Term | | |
| | Derivation | | Credential | | | | | Derivation | | Credential | | |
| | | | | | | | | | | | | |
skipping to change at page 11, line 41 skipping to change at page 11, line 30
| | | | | | | | | | | |
| | +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+-+ | | | | +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+-+ | |
| | | TEK | |MSK, EMSK | |IV | | | | | | TEK | |MSK, EMSK | |IV | | |
| | |Derivation | |Derivation | |Derivation | | | | | |Derivation | |Derivation | |Derivation | | |
| | | | | | |(Deprecated) | | | | | | | | | |(Deprecated) | | |
| | +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+-+ | | | | +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+-+ | |
| | ^ | | | | | | ^ | | | |
| | | | | | V | | | | | | V
+-+-|-+-+-+-+-+-+-+-|-+-+-+-+-+-+-|-+-+-+-+-+-+-+-|-+-+-+-+ ---+ +-+-|-+-+-+-+-+-+-+-|-+-+-+-+-+-+-|-+-+-+-+-+-+-+-|-+-+-+-+ ---+
| | | | ^ | | | | ^
| Peer-Id, | | | Exported | | | | | Exported |
| Server-Id, | channel | MSK (64+B) | IV (64B) by | | Peer-Id(s), | channel | MSK (64+B) | IV (64B) by |
| Session-Id | bindings | EMSK (64+B) | (Optional) EAP | | Server-Id(s), | bindings | EMSK (64+B) | (Optional) EAP |
| | & Result | | Method | | Session-Id | & Result | | Method |
V V V V V V V V V V
Figure 2: EAP Method Parameter Import/Export Figure 2: EAP Method Parameter Import/Export
Peer-Id
If an EAP method that generates keys authenticates one or more
method-specific peer identities, those identities are exported by
the method as the Peer-Id(s). It is possible for more than one
Peer-Id to be exported by an EAP method. Not all EAP methods
provide a method-specific peer identity; where this is not
defined, the Peer-Id is the null string. In EAP methods that do
not support key generation, the Peer-Id MUST be the null string.
Where an EAP method that derives keys does not provide a Peer-Id,
the EAP server will not authenticate the identity of the EAP peer
with which it derived keying material.
Server-Id
If an EAP method that generates keys authenticates one or more
method-specific server identities, those identities are exported
by the method as the Server-Id(s). It is possible for more than
one Server-Id to be exported by an EAP method. Not all EAP
methods provide a method-specific server identity; where this is
not defined, the Server-Id is the null string. If the EAP method
not generate keying material, the Server-Id MUST be the null
string. Where an EAP method that derives keys does not provide a
Server-Id, the EAP peer will not authenticate the identity of the
EAP server with which it derived EAP keying material.
Session-Id Session-Id
The Session-Id uniquely identifies an EAP session between an EAP The Session-Id uniquely identifies an EAP session between an EAP
peer (as identified by the Peer-Id) and server (as identified by peer (as identified by the Peer-Id) and server (as identified by
the Server-Id). Where the EAP Type Code is less than 255, the EAP the Server-Id). Where non-expanded EAP Type Codes are used (EAP
Session-Id consists of the concatenation of the EAP Type Code and Type Code not equal to 254), the EAP Session-Id is the
a temporally unique identifier obtained from the method (known as concatenation of the single octet EAP Type Code and a temporally
the Method-Id). Where expanded EAP Type Codes are used, the EAP unique identifier obtained from the method (known as the Method-
Session-Id consists of the Expanded Type Code (including the Type, Id). Where expanded EAP Type Codes are used, the EAP Session-Id
Vendor-Id and Vendor-Type fields defined in [RFC3748] Section 5.7) consists of the Expanded Type Code (including the Type, Vendor-Id
and Vendor-Type fields defined in [RFC3748] Section 5.7)
concatenated with a temporally unique identifier obtained from the concatenated with a temporally unique identifier obtained from the
method (Method-Id). This unique identifier is typically method (Method-Id). The Method-Id is typically constructed from
constructed from nonces or counters used within the EAP method nonces or counters used within the EAP method exchange. The
exchange. The inclusion of the Type Code in the EAP Session-Id inclusion of the Type Code or Expanded Type Code in the EAP
ensures that each EAP method has a distinct Session-Id space. Session-Id ensures that each EAP method has a distinct Session-Id
Since an EAP session is not bound to a particular authenticator or space. Since an EAP session is not bound to a particular
specific ports on the peer and authenticator, the authenticator authenticator or specific ports on the peer and authenticator, the
port or identity are not included in the Session-Id. authenticator port or identity are not included in the Session-Id.
Channel Binding Channel Binding
Channel Binding is the process by which lower layer parameters are Channel Binding is the process by which lower layer parameters are
verified for consistency between the EAP peer and server. In verified for consistency between the EAP peer and server. In
order to avoid introducing media dependencies, EAP methods that order to avoid introducing media dependencies, EAP methods that
transport channel binding parameters MUST treat this data as transport channel binding parameters MUST treat this data as
opaque octets. See Section 5.3.3 for further discussion. opaque octets. See Section 5.3.3 for further discussion.
1.4.1. Key Naming 1.4.1. Key Naming
Each key created within the EAP key management framework has a name Each key created within the EAP key management framework has a name
(a unique identifier), as well as a scope (the parties to whom the (a unique identifier), as well as a scope (the parties to whom the
key is available). The scope of exported parameters is defined by key is available). The scope of exported keying material and TEKs is
the EAP Peer-Id (if securely exchanged within the method) and the EAP defined by the authenticated method-specific peer identities (Peer-
Server-Id (also only if securely exchanged). Where a peer or server Id(s)) and the authenticated server identities (Server-Id(s)), where
name is missing the null string is used. available.
MSK and EMSK Names MSK and EMSK Names
These parameters are exported by the EAP peer and EAP server, and The MSK and EMSK are exported by the EAP peer and EAP server, and
can be referred to using the EAP Session-Id and a binary or textual MUST be named using the EAP Session-Id and a binary or textual
indication of the EAP keying material being referred to. indication of the EAP keying material being referred to.
PMK Name PMK Name
This document does not specify a naming scheme for the Pairwise This document does not specify a naming scheme for the Pairwise
Master Key (PMK). The PMK is only identified by the name of the Master Key (PMK). The PMK is only identified by the name of the
key from which it is derived. key from which it is derived.
Note: IEEE 802.11i names the PMK for the purposes of being able to Note: IEEE 802.11 names the PMK for the purposes of being able to
refer to it in the Secure Association protocol; the PMK name (known refer to it in the Secure Association Protocol; the PMK name (known
as the PMKID) is based on a hash of the PMK itself as well as some as the PMKID) is based on a hash of the PMK itself as well as some
other parameters (see [IEEE-802.11i] Section 8.5.1.2). other parameters (see [IEEE-802.11] Section 8.5.1.2).
TEK Name TEK Name
The TEKs may or may not be named. Their naming is specified in the Transient EAP Keys (TEKs) MAY be named; their naming is specified
EAP method. in the EAP method specification.
TSK Name TSK Name
The Transient Session Keys (TSKs) are typically named. Their Transient Session Keys (TSKs) are typically named. Their naming is
naming is specified in the lower layer so that the correct set of specified in the lower layer so that the correct set of TSKs can be
transient session keys can be identified for processing a given identified for processing a given packet.
packet.
1.5. Security Goals 1.5. Security Goals
The goal of the EAP conversation is to derive fresh session keys The goal of the EAP conversation is to derive fresh session keys
between the EAP peer and authenticator that are known only to those between the EAP peer and authenticator that are known only to those
parties, and for both the EAP peer and authenticator to demonstrate parties, and for both the EAP peer and authenticator to demonstrate
that they are authorized to perform their roles either by each other that they are authorized to perform their roles either by each other
or by a trusted third party (the backend authentication server). or by a trusted third party (the backend authentication server).
Completion of an EAP method exchange (Phase 1a) supporting key Completion of an EAP method exchange (Phase 1a) supporting key
derivation results in the derivation of EAP keying material (MSK, derivation results in the derivation of EAP keying material (MSK,
EMSK, TEKs) known only to the EAP peer (identified by the Peer-Id) EMSK, TEKs) known only to the EAP peer (identified by the Peer-Id(s))
and server (identified by the Server-Id). Both the EAP peer and EAP and EAP server (identified by the Server-Id(s)). Both the EAP peer
server know the exported keying material to be fresh. The Peer-Id and EAP server know this keying material to be fresh. The Peer-Id
and Server-Id are discussed in Section 1.4 and Appendix A. Key and Server-Id are discussed in Section 1.4 and Appendix A. Key
freshness is discussed in Sections 3.4, 3.5 and 5.7. freshness is discussed in Sections 3.4, 3.5 and 5.7.
Completion of the AAA exchange (Phase 1b) results in the transport of Completion of the AAA exchange (Phase 1b) results in the transport of
EAP keying material from the EAP server (identified by the Server-Id) keying material from the EAP server (identified by the Server-Id(s))
to the EAP authenticator (identified by the NAS-Identifier) without to the EAP authenticator (identified by the NAS-Identifier) without
disclosure to any other party. Both the EAP server and EAP disclosure to any other party. Both the EAP server and EAP
authenticator know this keying material to be fresh. Disclosure authenticator know this keying material to be fresh. Disclosure
issues are discussed in Sections 3.8 and 5.3; security properties of issues are discussed in Sections 3.8 and 5.3; security properties of
AAA protocols are discussed in Sections 5.1-5.9. AAA protocols are discussed in Sections 5.1-5.9.
The backend authentication server is trusted to only transport EAP The backend authentication server is trusted to transport keying
keying material to the authenticator that was established with the material only to the authenticator that was established with the
peer, and it is trusted to transport that EAP keying material to no peer, and it is trusted to transport that keying material to no other
other parties. In many systems, EAP keying material established by parties. In many systems, EAP keying material established by the EAP
the EAP peer and EAP server are combined with publicly available data peer and EAP server are combined with publicly available data to
to derive other keys. The backend authentication server is trusted derive other keys. The backend authentication server is trusted to
to refrain from deriving these same keys or acting as a man-in-the- refrain from deriving these same keys or acting as a man-in-the-
middle even though it has access to the EAP keying material that is middle even though it has access to the keying material that is
needed to do so. The authenticator is also a trusted party. It is needed to do so. The authenticator is also a trusted party. It is
trusted not to provide EAP keying material it obtains from the trusted not to provide keying material it obtains from the backend
backend authentication server to any other parties. authentication server to any other parties.
Completion of the Secure Association Protocol (Phase 2) results in Completion of the Secure Association Protocol (Phase 2) results in
the derivation or transport of Transient Session Keys (TSKs) known the derivation or transport of Transient Session Keys (TSKs) known
only to the EAP peer (identified by the Peer-Id) and authenticator only to the EAP peer (identified by the Peer-Id(s)) and authenticator
(identified by the NAS-Identifier). Both the EAP peer and (identified by the NAS-Identifier). Both the EAP peer and
authenticator know the TSKs to be fresh. Both the EAP peer and authenticator know the TSKs to be fresh. Both the EAP peer and
authenticator demonstrate that they are authorized to perform their authenticator demonstrate that they are authorized to perform their
roles. Authorization issues are discussed in Sections 4.3.2 and 5.5; roles. Authorization issues are discussed in Sections 4.3.2 and 5.5;
security properties of Secure Association Protocols are discussed in security properties of Secure Association Protocols are discussed in
Section 3.1. Section 3.1.
1.6. EAP Invariants 1.6. EAP Invariants
Certain basic characteristics, known as "EAP Invariants", hold true Certain basic characteristics, known as "EAP Invariants", hold true
for EAP implementations on all media: for EAP implementations:
Mode independence Mode independence
Media independence Media independence
Method independence Method independence
Ciphersuite independence Ciphersuite independence
1.6.1. Mode Independence 1.6.1. Mode Independence
EAP is typically deployed to support extensible network access EAP is typically deployed to support extensible network access
authentication in situations where a peer desires network access via authentication in situations where a peer desires network access via
one or more authenticators. Where authenticators are deployed one or more authenticators. Where authenticators are deployed
standalone, the EAP conversation occurs between the peer and standalone, the EAP conversation occurs between the peer and
authenticator, and the authenticator must locally implement an EAP authenticator, and the authenticator locally implements one or more
method acceptable to the peer. However, when utilized in "pass- EAP methods. However, when utilized in "pass-through" mode, EAP
through" mode, EAP enables deployment of new authentication methods enables deployment of new authentication methods without requiring
without requiring development of new code on the authenticator. development of new code on the authenticator.
While the authenticator may implement some EAP methods locally and While the authenticator can implement some EAP methods locally and
use those methods to authenticate local users, it may at the same use those methods to authenticate local users, it can at the same
time act as a pass-through for other users and methods, forwarding time act as a pass-through for other users and methods, forwarding
EAP packets back and forth between the backend authentication server EAP packets back and forth between the backend authentication server
and the peer. This is accomplished by encapsulating EAP packets and the peer. This is accomplished by encapsulating EAP packets
within the Authentication, Authorization and Accounting (AAA) within the Authentication, Authorization and Accounting (AAA)
protocol, spoken between the authenticator and backend authentication protocol, spoken between the authenticator and backend authentication
server. AAA protocols supporting EAP include RADIUS [RFC3579] and server. AAA protocols supporting EAP include RADIUS [RFC3579] and
Diameter [RFC4072]. Diameter [RFC4072].
It is a fundamental property of EAP that at the EAP method layer, the It is a fundamental property of EAP that at the EAP method layer, the
conversation between the EAP peer and server is unaffected by whether conversation between the EAP peer and server is unaffected by whether
the EAP authenticator is operating in "pass-through" mode. EAP the EAP authenticator is operating in "pass-through" mode. EAP
methods operate identically in all aspects, including key derivation methods operate identically in all aspects, including key derivation
and parameter import/export, regardless of whether the authenticator and parameter import/export, regardless of whether the authenticator
is operating as a pass-through or not. is operating as a pass-through or not.
The successful completion of an EAP method that supports key The successful completion of an EAP method that supports key
derivation results in the export of keying material and parameters on derivation results in the export of EAP keying material and
the EAP peer and server. Even though the EAP peer or server may parameters on the EAP peer and server. Even though the EAP peer or
import channel binding parameters that may include the identity of server can import channel binding parameters that can include the
the EAP authenticator, this information is treated as opaque octets. identity of the EAP authenticator, this information is treated as
As a result, within EAP the only relevant identities are the Peer-Id opaque octets. As a result, within EAP the only relevant identities
and Server-Id. Channel Binding parameters are only interpreted by are the Peer-Id(s) and Server-Id(s). Channel binding parameters are
the lower layer. only interpreted by the lower layer.
Within EAP, the primary function of the AAA protocol is to maintain Within EAP, the primary function of the AAA protocol is to maintain
the principle of mode independence, so that as far as the EAP peer is the principle of mode independence. As far as the EAP peer is
concerned, its conversation with the EAP authenticator, and all concerned, its conversation with the EAP authenticator, and all
consequences of that conversation, are identical, regardless of the consequences of that conversation, are identical, regardless of the
authenticator mode of operation. authenticator mode of operation.
1.6.2. Media Independence 1.6.2. Media Independence
One of the goals of EAP is to allow EAP methods to function on any One of the goals of EAP is to allow EAP methods to function on any
lower layer meeting the criteria outlined in [RFC3748], Section 3.1. lower layer meeting the criteria outlined in [RFC3748], Section 3.1.
For example, as described in [RFC3748], EAP authentication can be run For example, as described in [RFC3748], EAP authentication can be run
over PPP [RFC1661], IEEE 802 wired networks [IEEE-802.1X], and over PPP [RFC1661], IEEE 802 wired networks [IEEE-802.1X], and
wireless networks such as 802.11 [IEEE-802.11i] and 802.16 wireless networks such as 802.11 [IEEE-802.11] and 802.16
[IEEE-802.16e]. [IEEE-802.16e].
In order to maintain media independence, it is necessary for EAP to In order to maintain media independence, it is necessary for EAP to
avoid consideration of media-specific elements. For example, EAP avoid consideration of media-specific elements. For example, EAP
methods cannot be assumed to have knowledge of the lower layer over methods cannot be assumed to have knowledge of the lower layer over
which they are transported, and cannot be restricted to identifiers which they are transported, and cannot be restricted to identifiers
associated with a particular usage environment (e.g. MAC addresses). associated with a particular usage environment (e.g. MAC addresses).
Note that media independence may be retained within EAP methods that Note that media independence can be retained within EAP methods that
support Channel Binding or method-specific identification. An EAP support Channel Binding or method-specific identification. An EAP
method need not be aware of the content of an identifier in order to method need not be aware of the content of an identifier in order to
use it. This enables an EAP method to use media-specific identifiers use it. This enables an EAP method to use media-specific identifiers
such as MAC addresses without compromising media independence. such as MAC addresses without compromising media independence.
Channel Binding parameters are treated as opaque octets by EAP Channel binding parameters are treated as opaque octets by EAP
methods, so that handling them does not require media-specific methods, so that handling them does not require media-specific
knowledge. knowledge.
1.6.3. Method Independence 1.6.3. Method Independence
By enabling pass-through, authenticators can support any method By enabling pass-through, authenticators can support any method
implemented on the peer and server, not just locally implemented implemented on the peer and server, not just locally implemented
methods. This allows the authenticator to avoid implementing code methods. This allows the authenticator to avoid having to implement
for each EAP method required by peers. In fact, since a pass-through the EAP methods configured for use by peers. In fact, since a pass-
authenticator is not required to implement any EAP methods at all, it through authenticator need not implement any EAP methods at all, it
cannot be assumed to support any EAP method-specific code. cannot be assumed to support any EAP method-specific code. As noted
in [RFC3748] Section 2.3:
As a result, as noted in [RFC3748], authenticators must by default be Compliant pass-through authenticator implementations MUST by
capable of supporting any EAP method. This is useful where there is default forward EAP packets of any Type.
no single EAP method that is both mandatory-to-implement and offers
acceptable security for the media in use. For example, the [RFC3748] This is useful where there is no single EAP method that is both
mandatory-to-implement EAP method (MD5-Challenge) does not provide mandatory-to-implement and offers acceptable security for the media
dictionary attack resistance, mutual authentication or key in use. For example, the [RFC3748] mandatory-to-implement EAP method
derivation, and as a result is not appropriate for use in wireless (MD5-Challenge) does not provide dictionary attack resistance, mutual
LAN authentication [RFC4017]. However, despite this it is possible authentication or key derivation, and as a result is not appropriate
for the peer and authenticator to interoperate as long as a suitable for use in Wireless Local Area Network (WLAN) authentication
EAP method is supported on the EAP server. [RFC4017]. However, despite this it is possible for the peer and
authenticator to interoperate as long as a suitable EAP method is
supported both on the EAP peer and server.
1.6.4. Ciphersuite Independence 1.6.4. Ciphersuite Independence
Ciphersuite Independence is a requirement for Media Independence. Ciphersuite Independence is a requirement for Media Independence.
Since lower layer ciphersuites vary between media, media independence Since lower layer ciphersuites vary between media, media independence
requires that EAP keying material needs to be large enough (with requires that exported EAP keying material be large enough (with
sufficient entropy) to handle any ciphersuite. sufficient entropy) to handle any ciphersuite.
While EAP methods may negotiate the ciphersuite used in protection of While EAP methods can negotiate the ciphersuite used in protection of
the EAP conversation, the ciphersuite used for the protection of the the EAP conversation, the ciphersuite used for the protection of the
data exchanged after EAP authentication has completed is negotiated data exchanged after EAP authentication has completed is negotiated
between the peer and authenticator within the lower layer, outside of between the peer and authenticator within the lower layer, outside of
EAP. EAP.
For example, within PPP, the ciphersuite is negotiated within the For example, within PPP, the ciphersuite is negotiated within the
Encryption Control Protocol (ECP) defined in [RFC1968], after EAP Encryption Control Protocol (ECP) defined in [RFC1968], after EAP
authentication is completed. Within [IEEE-802.11i], the AP authentication is completed. Within [IEEE-802.11], the AP
ciphersuites are advertised in the Beacon and Probe Responses prior ciphersuites are advertised in the Beacon and Probe Responses prior
to EAP authentication, and are securely verified during a 4-way to EAP authentication, and are securely verified during a 4-way
handshake exchange. handshake exchange.
Since the ciphersuites used to protect data depend on the lower Since the ciphersuites used to protect data depend on the lower
layer, requiring EAP methods have knowledge of lower layer layer, requiring that EAP methods have knowledge of lower layer
ciphersuites would compromise the principle of Media Independence. ciphersuites would compromise the principle of Media Independence.
Since ciphersuite negotiation occurs in the lower layer, there is no As a result, methods export EAP keying material that is ciphersuite-
need for lower layer ciphersuite negotiation within EAP, and EAP independent. Since ciphersuite negotiation occurs in the lower
methods generate keying material that is ciphersuite-independent. layer, there is no need for lower layer ciphersuite negotiation
within EAP.
In order to allow a ciphersuite to be usable within the EAP keying In order to allow a ciphersuite to be usable within the EAP keying
framework, a specification MUST be provided describing how TSKs framework, the ciphersuite specification needs to describe how TSKs
suitable for use with the ciphersuite are derived from exported EAP suitable for use with the ciphersuite are derived from exported EAP
keying parameters. To maintain Method Independence, algorithms for keying material. To maintain Method Independence, algorithms for
deriving TSKs MUST NOT depend on the EAP method, although algorithms deriving TSKs MUST NOT depend on the EAP method, although algorithms
for TEK derivation MAY be specific to the EAP method. for TEK derivation MAY be specific to the EAP method.
Advantages of ciphersuite-independence include: Advantages of ciphersuite-independence include:
Reduced update requirements Reduced update requirements
If EAP methods were to specify how to derive transient session keys Ciphersuite independence enables EAP methods to be used with new
for each ciphersuite, they would need to be updated each time a new ciphersuites without requiring the methods to be updated. If EAP
methods were to specify how to derive transient session keys for
each ciphersuite, they would need to be updated each time a new
ciphersuite is developed. In addition, backend authentication ciphersuite is developed. In addition, backend authentication
servers might not be usable with all EAP-capable authenticators, servers might not be usable with all EAP-capable authenticators,
since the backend authentication server would also need to be since the backend authentication server would also need to be
updated each time support for a new ciphersuite is added to the updated each time support for a new ciphersuite is added to the
authenticator. authenticator.
Reduced EAP method complexity Reduced EAP method complexity
Requiring each EAP method to include ciphersuite-specific code for Ciphersuite independence enables EAP methods to avoid having to
transient session key derivation would increase method complexity include ciphersuite-specific code. Requiring each EAP method to
and result in duplicated effort. include ciphersuite-specific code for transient session key
derivation would increase method complexity and result in
duplicated effort.
Simplified configuration Simplified configuration
The ciphersuite is negotiated between the peer and authenticator Ciphersuite independence enables EAP method implementations on the
outside of EAP. Where the authenticator operates in "pass-through" peer and server to avoid having to configure ciphersuite-specific
mode, the EAP server is not a party to this negotiation, nor is it parameters. The ciphersuite is negotiated between the peer and
involved in the data flow between the EAP peer and authenticator. authenticator outside of EAP. Where the authenticator operates in
As a result, the EAP server may not have knowledge of the "pass-through" mode, the EAP server is not a party to this
ciphersuites and negotiation policies implemented by the peer and negotiation, nor is it involved in the data flow between the EAP
authenticator, or be aware of the ciphersuite negotiated between peer and authenticator. As a result, the EAP server does not have
them. For example, since ECP negotiation occurs after knowledge of the ciphersuites and negotiation policies implemented
authentication, when run over PPP, the EAP peer and server may not by the peer and authenticator, nor is it aware of the ciphersuite
anticipate the negotiated ciphersuite and therefore this negotiated between them. For example, since Encryption Control
information cannot be provided to the EAP method. Protocol (ECP) negotiation occurs after authentication, when run
over PPP, the EAP peer and server cannot anticipate the negotiated
ciphersuite and therefore this information cannot be provided to
the EAP method.
2. Lower Layer Operation 2. Lower Layer Operation
On completion of EAP authentication, keying material and material and On completion of EAP authentication, EAP keying material and
parameters exported by the EAP method are provided to the lower layer parameters exported by the EAP method are provided to the lower layer
and AAA layer (if present). These include the Master Session Key and AAA layer (if present). These include the Master Session Key
(MSK), Extended Master Session Key (EMSK), Peer-Id, Server-Id and (MSK), Extended Master Session Key (EMSK), Peer-Id(s), Server-Id(s)
Session-Id. The Initialization Vector (IV) is deprecated. and Session-Id. The Initialization Vector (IV) is deprecated, but
might be provided.
In order to preserve the security of keys derived within EAP methods, In order to preserve the security of EAP keying material derived
lower layers MUST NOT export keys passed down by EAP methods. This within methods, lower layers MUST NOT export keys passed down by EAP
implies that EAP keying material passed down to a lower layer is for methods. This implies that EAP keying material passed down to a
the exclusive use of that lower layer and MUST NOT be used within lower layer is for the exclusive use of that lower layer and MUST NOT
another lower layer. This prevents compromise of one lower layer be used within another lower layer. This prevents compromise of one
from compromising other applications using EAP keying parameters. lower layer from compromising other applications using EAP keying
material.
EAP keying material provided to a lower layer MUST NOT be transported EAP keying material provided to a lower layer MUST NOT be transported
to another entity. For example, EAP keying material passed down to to another entity. For example, EAP keying material passed down to
the EAP peer lower layer MUST NOT leave the peer; EAP keying the EAP peer lower layer MUST NOT leave the peer; EAP keying
material passed down or transported to the EAP authenticator lower material passed down or transported to the EAP authenticator lower
layer MUST NOT leave the authenticator. layer MUST NOT leave the authenticator.
On the EAP server, keying material and parameters requested by and On the EAP server, keying material and parameters requested by and
passed down to the AAA layer may be replicated to the AAA layer on passed down to the AAA layer MAY be replicated to the AAA layer on
the authenticator (with the exception of the EMSK). On the the authenticator (with the exception of the EMSK). On the
authenticator, the AAA layer provides the replicated keying material authenticator, the AAA layer provides the replicated keying material
and parameters to the lower layer over which the EAP authentication and parameters to the lower layer over which the EAP authentication
conversation took place. This enables mode independence to be conversation took place. This enables mode independence to be
maintained. maintained.
The EAP layer as well as the peer and authenticator layers MUST NOT The EAP layer as well as the peer and authenticator layers MUST NOT
modify or cache keying material or parameters (including Channel modify or cache keying material or parameters (including Channel
Bindings) passing in either direction between the EAP method layer Bindings) passing in either direction between the EAP method layer
and the lower layer or AAA layer. and the lower layer or AAA layer.
2.1. Transient Session Keys 2.1. Transient Session Keys
Where explicitly supported by the lower layer, lower layers MAY cache Where explicitly supported by the lower layer, lower layers MAY cache
the exported EAP keying material and parameters and/or TSKs. The keying material, including exported EAP keying material and/or TSKs;
structure of this key cache is defined by the lower layer. So as to the structure of this key cache is defined by the lower layer. So as
enable interoperability, new lower layer specifications MUST describe to enable interoperability, new lower layer specifications MUST
EAP key caching behavior. Unless explicitly specified by the lower describe key caching behavior. Unless explicitly specified by the
layer, the EAP peer, server and authenticator MUST assume that peers lower layer, the EAP peer, server and authenticator MUST assume that
and authenticators do not cache exported EAP keying parameters or peers and authenticators do not cache keying material. Existing EAP
TSKs. Existing EAP lower layers and AAA layers handle the caching of lower layers and AAA layers handle the generation of transient
EAP keying material and the generation of transient session keys in session keys and caching of EAP keying material in different ways:
different ways:
IEEE 802.1X-2004 IEEE 802.1X-2004
IEEE 802.1X-2004, defined in [IEEE-802.1X] does not support caching When used with wired networks, IEEE 802.1X-2004 [IEEE-802.1X] does
of EAP keying material or parameters. Once EAP authentication not support link layer ciphersuites and a result, it does not
completes, it is assumed that EAP keying material and parameters provide for generation of TSKs, or caching of EAP keying material
are discarded. and parameters. Once EAP authentication completes, it is assumed
that EAP keying material and parameters are discarded; on IEEE 802
wired networks there is no subsequent Secure Association Protocol
exchange. Perfect Forward Secrecy (PFS) is only possible if the
negotiated EAP method supports this.
PPP PPP, defined in [RFC1661] does not support caching of EAP keying PPP PPP, defined in [RFC1661] does not include support for a Secure
Association Protocol; nor does it support caching of EAP keying
material or parameters. PPP ciphersuites derive their TSKs material or parameters. PPP ciphersuites derive their TSKs
directly from the MSK, as described in [I-D.simon-emu-rfc2716bis]. directly from the MSK, as described in [RFC2716]. This is NOT
This method is NOT RECOMMENDED, since if PPP were to support RECOMMENDED, since if PPP were to support caching of EAP keying
caching, this could result in TSK reuse. As a result, once the PPP material, this could result in TSK reuse. As a result, once the
session is terminated, EAP keying material and parameters MUST be PPP session is terminated, EAP keying material and parameters MUST
discarded. Since caching of EAP keying material is not permitted, be discarded. Since caching of EAP keying material is not
within PPP there is no way to handle TSK re-key without EAP re- permitted within PPP, there is no way to handle TSK re-key without
authentication. Perfect Forward Secrecy (PFS) is only possible if EAP re-authentication. Perfect Forward Secrecy (PFS) is only
the negotiated EAP method supports this. possible if the negotiated EAP method supports this.
IKEv2 IKEv2
IKEv2, defined in [RFC4306] only uses the MSK for authentication IKEv2, defined in [RFC4306] only uses the MSK for authentication
purposes and not key derivation. The EMSK, IV, Peer-Id, Server-Id purposes and not key derivation. The EMSK, IV, Peer-Id, Server-Id
or Session-Id are not used. As a result, the keying material or Session-Id are not used. As a result, the TSKs derived by IKEv2
derived within IKEv2 is independent of the EAP keying material and are cryptographically independent of the EAP keying material and
re-key of IPsec SAs can be handled without requiring EAP re- re-key of IPsec SAs can be handled without requiring EAP re-
authentication. Since generation of keying material is independent authentication. Within IKEv2 it is possible to negotiate PFS,
of EAP, within IKEv2 it is possible to negotiate PFS, regardless of regardless of which EAP method is negotiated. IKEv2 as specified
the EAP method that is used. IKEv2 as specified in [RFC4306] does in [RFC4306] does not cache EAP keying material or parameters; once
not cache EAP keying material or parameters; once IKEv2 IKEv2 authentication completes it is assumed that EAP keying
authentication completes it is assumed that EAP keying material and material and parameters are discarded. The Session-Timeout
parameters are discarded. The Session-Timeout attribute is attribute is therefore interpreted as a limit on the VPN session
therefore interpreted as a limit on the VPN session time, rather time, rather than an indication of the MSK key lifetime.
than an indication of the MSK key lifetime.
IEEE 802.11i IEEE 802.11
IEEE 802.11i enables caching of the MSK, but not the EMSK, IV, IEEE 802.11 enables caching of the MSK, but not the EMSK, IV, Peer-
Peer-Id, Server-Id, or Session-Id. More details about the Id, Server-Id, or Session-Id. More details about the structure of
structure of the cache are available in [IEEE-802.11i]. In IEEE the cache are available in [IEEE-802.11]. In IEEE 802.11, TSKs are
802.11i, TSKs are derived from the MSK using the 4-way handshake, derived from the MSK using a Secure Association Protocol known as
which includes a nonce exchange. This guarantees TSK freshness the 4-way handshake, which includes a nonce exchange. This
even if the MSK is reused. The 4-way handshake also enables TSK guarantees TSK freshness even if the MSK is reused. The 4-way
re-key without EAP re-authentication. PFS is only possible within handshake also enables TSK re-key without EAP re-authentication.
IEEE 802.11i if caching is not enabled and the negotiated EAP PFS is only possible within IEEE 802.11 if caching is not enabled
method supports PFS. and the negotiated EAP method supports PFS.
IEEE 802.16e IEEE 802.16e
IEEE 802.16e, defined in [IEEE-802.16e] supports caching of the IEEE 802.16e, defined in [IEEE-802.16e] supports caching of the
MSK, but not the EMSK, IV, Peer-Id, Server-Id or Session-Id. In MSK, but not the EMSK, IV, Peer-Id, Server-Id or Session-Id. IEEE
IEEE 802.16e, TSKs are generated by the authenticator without any 802.16e support a Secure Association Protocol in which TSKs are
contribution by the peer. The TSKs are encrypted, authenticated chosen by the authenticator without any contribution by the peer.
and integrity protected using the MSK. As a result, TSK re-key is The TSKs are encrypted, authenticated and integrity protected using
possible without EAP re-authentication. PFS is not possible even the MSK and are transported from the authenticator to the peer.
if the negotiated EAP method supports it. TSK re-key is possible without EAP re-authentication. PFS is not
possible even if the negotiated EAP method supports it.
AAA Existing implementations of RADIUS/EAP [RFC3579] or Diameter EAP AAA Existing implementations and specifications for RADIUS/EAP
[RFC4072] do not support caching of EAP keying material or [RFC3579] or Diameter EAP [RFC4072] do not support caching of
parameters. In existing AAA client, proxy and server keying material or parameters. In existing AAA client, proxy and
implementations, exported EAP keying material (MSK, EMSK and IV) as server implementations, exported EAP keying material (MSK, EMSK and
well as parameters and derived keys are not cached and MUST be IV) as well as parameters and derived keys are not cached and MUST
presumed lost after the AAA exchange completes. be presumed lost after the AAA exchange completes.
In order to avoid key reuse, the AAA layer MUST delete transported In order to avoid key reuse, the AAA layer MUST delete transported
keys once they are sent. The AAA layer MUST NOT retain keys that keys once they are sent. The AAA layer MUST NOT retain keys that
it has previously sent. For example, a AAA layer that has it has previously sent. For example, a AAA layer that has
transported the MSK MUST delete it, and keys MUST NOT be derived transported the MSK MUST delete it, and keys MUST NOT be derived
from the MSK from that point forward. from the MSK from that point forward.
2.2. Authenticator and Peer Architecture 2.2. Authenticator and Peer Architecture
This specification does not impose constraints on the architecture of This specification does not impose constraints on the architecture of
the EAP authenticator or peer. Any of the authenticator the EAP authenticator or peer. For example, any of the authenticator
architectures described in [RFC4118] can be used. As a result, lower architectures described in [RFC4118] can be used. As a result, lower
layers need to identify EAP peers and authenticators unambiguously, layers need to identify EAP peers and authenticators unambiguously,
without incorporating implicit assumptions about peer and without incorporating implicit assumptions about peer and
authenticator architectures. authenticator architectures.
For example, it is possible for multiple base stations and a For example, it is possible for multiple base stations and a
"controller" (e.g. WLAN switch) to comprise a single EAP "controller" (e.g. WLAN switch) to comprise a single EAP
authenticator. In such a situation, the "base station identity" is authenticator. In such a situation, the "base station identity" is
irrelevant to the EAP method conversation, except perhaps as an irrelevant to the EAP method conversation, except perhaps as an
opaque blob to be used in Channel Binding. Many base stations can opaque blob to be used in Channel Binding. Many base stations can
share the same authenticator identity. It should be understood that share the same authenticator identity. An EAP authenticator or peer:
an EAP authenticator or peer:
(a) may contain one or more physical or logical ports; (a) can contain one or more physical or logical ports;
(b) may advertise itself as one or more "virtual" (b) can advertise itself as one or more "virtual"
authenticators or peers; authenticators or peers;
(c) may utilize multiple CPUs; (c) can utilize multiple CPUs;
(d) may support clustering services for load balancing or failover. (d) can support clustering services for load balancing or failover.
Both the EAP peer and authenticator may have more than one physical Both the EAP peer and authenticator can have more than one physical
or logical port. A peer may simultaneously access the network via or logical port. A peer can simultaneously access the network via
multiple authenticators, or via multiple physical or logical ports on multiple authenticators, or via multiple physical or logical ports on
a given authenticator. Similarly, an authenticator may offer network a given authenticator. Similarly, an authenticator can offer network
access to multiple peers, each via a separate physical or logical access to multiple peers, each via a separate physical or logical
port. When a single physical authenticator advertises itself as port. When a single physical authenticator advertises itself as
multiple "virtual authenticators", it is possible for a single multiple virtual authenticators, it is possible for a single physical
physical port to belong to multiple "virtual authenticators". port to belong to multiple virtual authenticators.
An authenticator may be configured to communicate with more than one An authenticator can be configured to communicate with more than one
EAP server, each of which is configured to communicate with a subset EAP server, each of which is configured to communicate with a subset
of the authenticators. The situation is illustrated in Figure 3. of the authenticators. The situation is illustrated in Figure 3.
2.2.1. Authenticator and Peer Identification
The EAP method conversation is between the EAP peer and server. The
authenticator identity, if considered at all by the EAP method, is
treated as an opaque blob for the purpose of Channel Binding (see
Section 5.3.3). However, the authenticator identity is important in
two other exchanges - the AAA protocol exchange and the Secure
Association Protocol conversation.
The AAA conversation is between the EAP authenticator and the backend
authentication server. From the point of view of the backend
authentication server, EAP keying material and parameters are
transported to the EAP authenticator identified by the NAS-Identifier
attribute. Since an EAP authenticator MUST NOT share EAP keying
material or parameters with another party, if the EAP peer or backend
authentication server detects use of EAP keying material and
parameters outside the scope defined by the NAS-Identifier, the
keying material MUST be considered compromised.
+-+-+-+-+ +-+-+-+-+
| EAP | | EAP |
| Peer | | Peer |
+-+-+-+-+ +-+-+-+-+
| | | Peer Ports | | | Peer Ports
/ | \ / | \
/ | \ / | \
/ | \ / | \
/ | \ / | \
/ | \ / | \
skipping to change at page 21, line 39 skipping to change at page 21, line 48
\ | \ | \ | \ |
\ | \ | \ | \ |
\ | \ | \ | \ |
+-+-+-+-+-+ +-+-+-+-+-+ Backend +-+-+-+-+-+ +-+-+-+-+-+ Backend
| EAP | | EAP | Authentication | EAP | | EAP | Authentication
| Server1 | | Server2 | Servers | Server1 | | Server2 | Servers
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
Figure 3: Relationship between EAP peer, authenticator and server Figure 3: Relationship between EAP peer, authenticator and server
2.3. Authenticator Identification
The EAP method conversation is between the EAP peer and server. The
authenticator identity, if considered at all by the EAP method, is
treated as an opaque blob for the purpose of Channel Binding (see
Section 5.3.3). However, the authenticator identity is important in
two other exchanges - the AAA protocol exchange and the Secure
Association Protocol conversation.
The AAA conversation is between the EAP authenticator and the backend
authentication server. From the point of view of the backend
authentication server, keying material and parameters are transported
to the EAP authenticator identified by the NAS-Identifier attribute.
Since an EAP authenticator MUST NOT share EAP keying material or
parameters with another party, if the EAP peer or backend
authentication server detects use of EAP keying material and
parameters outside the scope defined by the NAS-Identifier, the
keying material MUST be considered compromised.
The Secure Association Protocol conversation is between the peer and The Secure Association Protocol conversation is between the peer and
the authenticator. For lower layers which support key caching it is the authenticator. For lower layers which support key caching it is
particularly important for the EAP peer, authenticator and backend particularly important for the EAP peer, authenticator and backend
server to have a consistent view of the usage scope of the server to have a consistent view of the usage scope of the
transported EAP keying material. In order to enable this, it is transported keying material. In order to enable this, it is
RECOMMENDED that the Secure Association Protocol explicitly RECOMMENDED that the Secure Association Protocol explicitly
communicate the usage scope of the EAP keying material passed down to communicate the usage scope of the EAP keying material passed down to
the lower layer, rather than implicitly assuming that this is defined the lower layer, rather than implicitly assuming that this is defined
by the authenticator and peer endpoint addresses. by the authenticator and peer endpoint addresses.
Since an authenticator may have multiple ports, the scope of the Since an authenticator can have multiple ports, the scope of the
authenticator key cache may not be described by a single endpoint authenticator key cache cannot be described by a single endpoint
address. Similarly, where a peer may have multiple ports and sharing address. Similarly, where a peer can have multiple ports and sharing
of EAP keying material and parameters between peer ports of the same of EAP keying material and parameters between peer ports of the same
link type is allowed, the extent of the peer key cache cannot be link type is allowed, the extent of the peer key cache cannot be
communicated by using a single endpoint address. Instead, it is communicated by using a single endpoint address. Instead, it is
RECOMMENDED that the EAP peer and authenticator consistently identify RECOMMENDED that the EAP peer and authenticator consistently identify
themselves utilizing explicit identifiers, rather than endpoint themselves utilizing explicit identifiers, rather than endpoint
addresses or port identifiers. addresses or port identifiers.
AAA protocols such as RADIUS [RFC3579] and Diameter [RFC4072] provide AAA protocols such as RADIUS [RFC3579] and Diameter [RFC4072] provide
a mechanism for the identification of AAA clients; since the EAP a mechanism for the identification of AAA clients; since the EAP
authenticator and AAA client are always co-resident, this mechanism authenticator and AAA client MUST be co-resident, this mechanism is
is applicable to the identification of EAP authenticators. applicable to the identification of EAP authenticators.
RADIUS [RFC2865] requires that an Access-Request packet contain one RADIUS [RFC2865] requires that an Access-Request packet contain one
or more of the NAS-Identifier, NAS-IP-Address and NAS-IPv6-Address or more of the NAS-Identifier, NAS-IP-Address and NAS-IPv6-Address
attributes. Since a NAS may have more than one IP address, the NAS- attributes. Since a NAS can have more than one IP address, the NAS-
Identifier attribute is RECOMMENDED for explicit identification of Identifier attribute is RECOMMENDED for explicit identification of
the authenticator, both within the AAA protocol exchange and the the authenticator, both within the AAA protocol exchange and the
Secure Association Protocol conversation. Secure Association Protocol conversation.
Problems which may arise where the peer and authenticator implicitly Problems which can arise where the peer and authenticator implicitly
identify themselves using endpoint addresses include the following: identify themselves using endpoint addresses include the following:
(a) It may not be obvious to the peer which authenticator ports are (a) It is possible that the peer will not be able to determine which
associated with which authenticators. The EAP peer will be unable authenticator ports are associated with which authenticators. As a
to determine whether EAP keying material has been shared outside result, the EAP peer will be unable to utilize the authenticator
its authorized scope, and needs to be considered compromised. The key cache in an efficient way, and will also be unable to determine
EAP peer may also be unable to utilize the authenticator key cache whether EAP keying material has been shared outside its authorized
in an efficient way. scope, and therefore needs to be considered compromised.
(b) It may not be obvious to the authenticator which peer ports are (b) It is possible that the authenticator will not be able to determine
associated with which peers. As a result, the authenticator may which peer ports are associated with which peers, preventing the
not be able to enable a peer to communicate with it utilizing peer from communicating with it utilizing multiple peer ports.
multiple peer ports.
(c) It may not be obvious to the peer which "virtual authenticator" it (c) It is possible that the peer will not be able to determine which
is communicating with. For example, multiple "virtual virtual authenticator it is communicating with. For example,
authenticators" may share a MAC address, but utilize different NAS- multiple virtual authenticators can share a MAC address, but
Identifiers. utilize different NAS-Identifiers.
(d) It may not be obvious to the authenticator which "virtual peer" it (d) It is possible that the authenticator will not be able to determine
is communicating with. Multiple "virtual peers" may share a MAC which virtual peer it is communicating with. Multiple virtual
address, but utilize different Peer-Ids. peers can share a MAC address, but utilize different Peer-Ids.
(e) It may not be possible for the EAP peer and server to verify the (e) It is possible that the EAP peer and server will not be able to
authenticator identity via Channel Binding. verify the authenticator identity via Channel Binding.
For example, problems (a), (c) and (e) occur in [IEEE-802.11i], which For example, problems (a), (c) and (e) occur in [IEEE-802.11], which
utilizes peer and authenticator MAC addresses within the 4-way utilizes peer and authenticator MAC addresses within the 4-way
handshake. Problems (b) and (d) do not occur since [IEEE-802.11i] handshake. Problems (b) and (d) do not occur since [IEEE-802.11]
only allows a peer to utilize a single port. only allows a virtual peer to utilize a single port.
The following steps enable lower layer identities to be securely The following steps enable lower layer identities to be securely
verified by all parties: verified by all parties:
(f) Specifying the lower layer parameters used to identify the (f) Specify the lower layer parameters used to identify the
authenticator and peer. As noted earlier, endpoint or port authenticator and peer. As noted earlier, endpoint or port
identifiers are not recommended for identification of the identifiers are not recommended for identification of the
authenticator or peer when it is possible for them to have multiple authenticator or peer when it is possible for them to have multiple
ports. ports.
(g) Communicating the lower layer identities between the peer and (g) Communicate the lower layer identities between the peer and
authenticator within phase 0. This allows the peer and authenticator within phase 0. This allows the peer and
authenticator to determine the key scope if a key cache is authenticator to determine the key scope if a key cache is
utilized. utilized.
(h) Communicating the lower layer authenticator identity between the (h) Communicate the lower layer authenticator identity between the
authenticator and backend server within the NAS-Identifier authenticator and backend server within the NAS-Identifier
attribute. attribute.
(i) Including the lower layer identities within Channel Bindings (if (i) Include the lower layer identities within Channel Bindings (if
supported) in phase 1a, ensuring that they are communicated between supported) in phase 1a, ensuring that they are communicated between
the EAP peer and server. the EAP peer and server.
(j) Supporting the integrity-protected exchange of identities within (j) Support the integrity-protected exchange of identities within phase
phase 2a. 2a.
(k) Utilizing the advertised lower layer identities to enable the peer (k) Utilize the advertised lower layer identities to enable the peer
and authenticator to verify that keys are maintained within the and authenticator to verify that keys are maintained within the
advertised scope. advertised scope.
2.2.2. Virtual Authenticators 2.3.1. Virtual Authenticators
When a single physical authenticator advertises itself as multiple When a single physical authenticator advertises itself as multiple
"virtual authenticators", if the virtual authenticators do not virtual authenticators, if the virtual authenticators do not maintain
maintain logically separate key caches, then by authenticating to one logically separate key caches, then by authenticating to one virtual
virtual authenticator, the peer can gain access to the other virtual authenticator, the peer can gain access to the other virtual
authenticators sharing a key cache. authenticators sharing a key cache.
For example, where a physical authenticator implements "Guest" and For example, where a physical authenticator implements "Guest" and
"Corporate Intranet" virtual authenticators, an attacker acting as a "Corporate Intranet" virtual authenticators, an attacker acting as a
peer could authenticate with the "Guest" "virtual authenticator" and peer could authenticate with the "Guest" virtual authenticator and
derive EAP keying material. If the "Guest" and "Corporate Intranet" derive EAP keying material. If the "Guest" and "Corporate Intranet"
virtual authenticators share a key cache, then the peer can utilize virtual authenticators share a key cache, then the peer can utilize
the EAP keying material derived for the "Guest" network to obtain the EAP keying material derived for the "Guest" network to obtain
access to the "Corporate Intranet" network. access to the "Corporate Intranet" network.
In order to address this vulnerability: The following steps can be taken to mitigate this vulnerability:
(a) Authenticators are REQUIRED to cache associated authorizations (a) Authenticators are REQUIRED to cache associated authorizations
along with EAP keying material and parameters and to apply along with EAP keying material and parameters and to apply
authorizations consistently. This ensures that an attacker cannot authorizations to the peer on each network access, regardless of
obtain elevated privileges even where the key cache is shared which virtual authenticator is being accessed. This ensures that
between "virtual authenticators". an attacker cannot obtain elevated privileges even where the key
cache is shared between virtual authenticators, and a peer obtains
access to one virtual authenticator utilizing a key cache entry
created for use with another virtual authenticator.
(b) It is RECOMMENDED that physical authenticators maintain separate (b) It is RECOMMENDED that physical authenticators maintain separate
key caches for each "virtual authenticator". key caches for each virtual authenticator. This ensures that a
cache entry created for use with one virtual authenticator cannot
be used for access to another virtual authenticator. Since a key
cache entry can no longer be shared between virtual
authentications, this step provides protection beyond that offered
in (a). This is valuable in situations where authorizations are
not used to enforce access limitations. For example, where access
is limited using a filter installed on a router rather than using
authorizations provided to the authenticator, a peer can gain
unauthorized access to resources by exploiting a shared key cache
entry.
(c) It is RECOMMENDED that each "virtual authenticator" identify itself (c) It is RECOMMENDED that each virtual authenticator identify itself
consistently to the peer and to the backend authentication server, consistently to the peer and to the backend authentication server,
so as to enable the peer to verify the authenticator identity via so as to enable the peer to verify the authenticator identity via
Channel Binding (see Section 5.3.3). Channel Binding (see Section 5.3.3).
(d) It is RECOMMENDED that each "virtual authenticator" identify itself (d) It is RECOMMENDED that each virtual authenticator identify itself
distinctly, in order to enable the peer and backend server to tell distinctly, in order to enable the peer and backend server to tell
them apart. For example, this can be accomplished by utilizing a them apart. For example, this can be accomplished by utilizing a
distinct NAS-Identifier attribute. distinct NAS-Identifier attribute.
2.3. Server Identification 2.4. Peer Identification
The EAP method conversation is between the EAP peer and server, as As described in [RFC3748] Section 7.3, the peer identity provided in
identified by the Peer-Id and Server-Id. As shown in Figure 3, an the EAP-Response/Identity can be different from the peer identities
authenticator may be configured to communicate with multiple EAP authenticated by the EAP method. For example, the identity provided
servers; the EAP server that an authenticator communicates with may in the EAP-Response/Identity can be a privacy identifier as described
vary according to configuration and network and server availability. in "The Network Access Identifier" [RFC4282] Section 2. As noted in
While the EAP peer can assume that all EAP servers within a realm [RFC4284], it is also possible to utilize a Network Access Identifier
have access to the credentials necessary to validate an (NAI) for the purposes of source routing; an NAI utilized for source
authentication attempt, it cannot assume that all EAP servers share routing is said to be "decorated" as described in [RFC4282] Section
persistent state. 2.7.
Authenticators may be configured with different primary or secondary When EAP peer provides the Network Access Identity (NAI) within the
EAP-Response/Identity, as described in [RFC3579], the authenticator
copies the NAI included in the EAP-Response/Identity into the User-
Name attribute included within the Access-Request. As the Access-
Request is forwarded toward the backend authentication server, AAA
proxies remove decoration from the NAI included in the User-Name
Attribute; the NAI included within the EAP-Response/Identity
encapsulated in the Access-Request remains unchanged. As a result,
when the Access-Request arrives at the backend authentication server,
the EAP-Response/Identity can differ from the User-Name Attribute
(which can have some or all of the decoration removed). In the
absence of a Peer-Id, the backend authentication server SHOULD use
the contents of the User-Name Attribute, rather than the EAP-
Response/Identity as the peer identity.
It is possible for more than one Peer-Id to be exported by an EAP
method. For example, a peer certificate can contain more than one
peer identity; in a tunnel method peer identities can be
authenticated both within an outer and inner exchange and these
identities could be different in type and contents. For example, an
outer exchange could provide a Peer-Id in the form of an RDN, whereas
an inner exchange could identify the peer via its NAI or MAC address.
Where EAP keying material is determined solely from the outer
exchange, only the outer Peer-Id(s) are exported; where the EAP
keying material is determined from both the inner and outer
exchanges, then both the inner and outer Peer-Id(s) are exported by
the tunnel method.
2.5. Server Identification
It is possible for more than one Server-Id to be exported by an EAP
method. For example, a server certificate can contain more than one
server identity; in a tunnel method server identities could be
authenticated both within an outer and inner exchange and these
identities could be different in type and contents. For example, an
outer exchange could provide a Server-Id in the form of an IP
address, whereas an inner exchange could identify the server via its
FQDN or hostname. Where EAP keying material is determined solely
from the outer exchange, only the outer Server-Id(s) are exported by
the EAP method; where the EAP keying material is determined from both
the inner and outer exchanges, then both the inner and outer Server-
Id(s) are exported by the EAP method.
As shown in Figure 3, an authenticator can be configured to
communicate with multiple EAP servers; the EAP server that an
authenticator communicates with can vary according to configuration
and network and server availability. While the EAP peer can assume
that all EAP servers within a realm have access to the credentials
necessary to validate an authentication attempt, it cannot assume
that all EAP servers share persistent state.
Authenticators can be configured with different primary or secondary
EAP servers, in order to balance the load. Also, the authenticator EAP servers, in order to balance the load. Also, the authenticator
can dynamically determine the EAP server to which requests will be can dynamically determine the EAP server to which requests will be
sent; in event of a communication failure, the authenticator may fail sent; in event of a communication failure, the authenticator can fail
over to another EAP server. For example, in Figure 3, Authenticator2 over to another EAP server. For example, in Figure 3, Authenticator2
may be initially configured with EAP server1 as its primary backend can be initially configured with EAP server1 as its primary backend
authentication server, and EAP server2 as the backup, but if EAP authentication server, and EAP server2 as the backup, but if EAP
server1 becomes unavailable, EAP server2 may become the primary server1 becomes unavailable, EAP server2 can become the primary
server. server.
In general, the EAP peer cannot direct an authentication attempt to a In general, the EAP peer cannot direct an authentication attempt to a
particular EAP server within a realm; this decision is made solely by particular EAP server within a realm; this decision is made by AAA
the authenticator. Nor can it determine which EAP server it will be clients. Nor can the peer determine which EAP server it will be
communicating with, prior to the start of the EAP method communicating with, prior to the start of the EAP method
conversation. The Server-Id is not included in the EAP- conversation. The Server-Id is not included in the EAP-
Request/Identity, and since the authenticator determines the EAP Request/Identity, and since the EAP server may be determined
server dynamically, it typically is not possible for the dynamically, it typically is not possible for the authenticator to
authenticator to advertise the Server-Id during the discovery phase. advertise the Server-Id during the discovery phase. Some EAP methods
EAP methods may or may not export the Server-Id, and as a result, the do not export the Server-Id so that is is possible that the EAP peer
EAP peer may not even learn which server it was conversing with after will not learn which server it was conversing with after the EAP
the EAP conversation completes successfully. conversation completes successfully.
As a result, an EAP peer, on connecting to a new authenticator or As a result, an EAP peer, on connecting to a new authenticator or
reconnecting to the same authenticator, may find itself communicating reconnecting to the same authenticator, can find itself communicating
with a different EAP server. Fast reconnect, defined in [RFC3748] with a different EAP server. Fast reconnect, defined in [RFC3748]
Section 7.2, may fail if the EAP server that the peer communicates Section 7.2, can fail if the EAP server that the peer communicates
with is not the same one with which it initially established a with is not the same one with which it initially established a
security association. For example, an EAP peer attempting an EAP-TLS security association. For example, an EAP peer attempting an EAP-TLS
session resume may find that the new EAP-TLS server will not have session resume can find that the new EAP-TLS server will not have
access to the TLS Master Key identified by the TLS Session-Id, and access to the TLS Master Key identified by the TLS Session-Id, and
therefore the session resumption attempt will fail, requiring therefore the session resumption attempt will fail, requiring
completion of a full EAP-TLS exchange. completion of a full EAP-TLS exchange.
EAP methods that support mutual authentication may not allow the EAP EAP methods that export the Server-Id MUST authenticate the server.
peer to verify the EAP server identity. For example, the EAP peer However, not all EAP methods supporting mutual authentication provide
may only verify that the EAP server possesses a long-term secret; in a non-null Server-Id; some methods only enable the EAP peer to verify
this case the EAP peer will only know that an authenticator has been that the EAP server possesses a long-term secret, but do not provide
authorized by an EAP server, but will not confirm the identity of the the identity of the EAP server. In this case the EAP peer will know
that an authenticator has been authorized by an EAP server, but will
not confirm the identity of the EAP server. Where the EAP method
does not provide a Server-Id, the peer cannot identify the EAP server
with which it generated keying material. This can make it difficult
for the EAP peer to identity the location of a key possessed by that
EAP server. EAP server.
EAP methods that export the Server-Id MUST verify the server As noted in [I-D.simon-emu-rfc2716bis] Section 5.2, EAP methods
identity. As noted in Appendix A, existing EAP methods exporting the supporting authentication using server certificates can determine the
Server-Id determine this from the subjectAltName in the server Server-Id from the subject or subjectAltName fields in the server
certificate, and as a result, the peer determines the identity of the certificate. Validating the EAP server identity can help the EAP
server (expressed as a Fully Qualified Domain Name (FQDN)) by peer to decide whether a specific EAP server is authorized. In some
validating the server certificate. cases, such as where the certificate extensions defined in [RFC4334]
are included in the server certificate, it can even be possible for
Validating the EAP server identity may help the EAP peer to decide the peer to verify some Channel Binding parameters from the server
whether a specific EAP server is authorized, and to determine whether certificate.
the EAP server is sharing keying material outside the intended scope.
In some cases, such as where the certificate extensions defined in
[RFC4334] are included in the server certificate, it may even be
possible for the peer to verify some Channel Binding parameters from
the server certificate. Where the EAP peer does not verify the EAP
server identity, it is not possible for the peer to determine whether
the EAP server has shared keying material outside its authorized
scope.
It is possible for problems to arise in situations where the EAP It is possible for problems to arise in situations where the EAP
server identifies itself differently to the EAP peer and server identifies itself differently to the EAP peer and
authenticator. For example, the Server-Id exported by EAP methods authenticator. For example, it is possible that the Server-Id
may not be identical to the Fully Qualified Domain Name (FQDN) of the exported by EAP methods will not be identical to the Fully Qualified
backend authentication server. Where certificate-based Domain Name (FQDN) of the backend authentication server. Where
authentication is used within RADIUS or Diameter, the subjectAltName certificate-based authentication is used within RADIUS or Diameter,
used in the backend server certificate may not be identical to the it is possible that the subjectAltName used in the backend
Server-Id or backend server FQDN. authentication server certificate will not be identical to the
Server-Id or backend authentication server FQDN.
Where the backend server FQDN differs from the subjectAltName in the Where the backend authentication server FQDN differs from the
certificate, the AAA client may not be able to successfully determine subjectAltName in the backend authentication server certificate, it
whether it is talking to the correct backend authentication server. is possible that the AAA client will not be able to determine whether
Where the Server-Id and backend server FQDN differ, the combination it is talking to the correct backend authentication server. Where
of the key scope (Peer-Id, Server-Id) and EAP conversation identifier the Server-Id and backend server FQDN differ, it is possible that the
(Session-Id) may not be sufficient for the authenticator to determine combination of the key scope (Peer-Id(s), Server- Id(s)) and EAP
where the key resides. For example, the authenticator may identify conversation identifier (Session-Id) will not be sufficient to
backend servers by their IP address (as occurs in RADIUS), or using a determine where the key resides. For example, the authenticator can
Fully Qualified Domain Name (as in Diameter). If the Server-Id does identify backend servers by their IP address (as occurs in RADIUS),
not correspond to the IP address or FQDN of a known backend or using a Fully Qualified Domain Name (as in Diameter). If the
authentication server, then the authenticator will not know which Server-Id does not correspond to the IP address or FQDN of a known
backend authentication server possesses the key. backend authentication server, then it may not be possible to locate
which backend authentication server possesses the key.
3. Security Association Management 3. Security Association Management
EAP as defined in [RFC3748] supports key derivation, but does not EAP as defined in [RFC3748] supports key derivation, but does not
provide for the management of lower layer security associations. provide for the management of lower layer security associations.
Missing functionality includes: Missing functionality includes:
(a) Security Association negotiation. EAP does not negotiate lower (a) Security Association negotiation. EAP does not negotiate lower
layer unicast or multicast security associations, including layer unicast or multicast security associations, including
cryptographic algorithms or traffic profiles. EAP methods only cryptographic algorithms or traffic profiles. EAP methods only
negotiate cryptographic algorithms for their own use, not for the negotiate cryptographic algorithms for their own use, not for the
underlying lower layers. EAP also does not negotiate the traffic underlying lower layers. EAP also does not negotiate the traffic
profiles to be protected with the negotiated ciphersuites; in some profiles to be protected with the negotiated ciphersuites; in some
cases the traffic to be protected may have lower layer source and cases the traffic to be protected can have lower layer source and
destination addresses different from the lower layer peer or destination addresses different from the lower layer peer or
authenticator addresses. authenticator addresses.
(b) Re-key. EAP does not support re-key of exported keys without EAP (b) Re-key. EAP does not support re-key of exported EAP keying
re-authentication, although EAP methods may support "fast material without EAP re-authentication, although EAP methods can
reconnect" as defined in [RFC3748] Section 7.2.1. support "fast reconnect" as defined in [RFC3748] Section 7.2.1.
(c) Key delete/install semantics. EAP does not synchronize (c) Key delete/install semantics. EAP does not synchronize
installation or deletion of keying material on the EAP peer and installation or deletion of keying material on the EAP peer and
authenticator. authenticator.
(d) Lifetime negotiation. EAP does not support lifetime negotiation (d) Lifetime negotiation. EAP does not support lifetime negotiation
for exported keys, and existing EAP methods also do not support key for exported EAP keying material, and existing EAP methods also do
lifetime negotiation. not support key lifetime negotiation.
(e) Guaranteed TSK freshness. Without a post-EAP handshake, TSKs can (e) Guaranteed TSK freshness. Without a post-EAP handshake, TSKs can
be reused if EAP keying material is cached. be reused if EAP keying material is cached.
These deficiencies are typically addressed via a post-EAP handshake These deficiencies are typically addressed via a post-EAP handshake
known as the Secure Association Protocol. known as the Secure Association Protocol.
3.1. Secure Association Protocol 3.1. Secure Association Protocol
Since neither EAP nor EAP methods provide for establishment of lower Since neither EAP nor EAP methods provide for establishment of lower
layer security associations, it is RECOMMENDED that these facilities layer security associations, it is RECOMMENDED that these facilities
be provided within the Secure Association Protocol. This includes: be provided within the Secure Association Protocol, including:
(a) Entity Naming. A basic feature of a Secure Association Protocol is (a) Entity Naming. A basic feature of a Secure Association Protocol is
the explicit naming of the parties engaged in the exchange. the explicit naming of the parties engaged in the exchange.
Without explicit identification, the parties engaged in the Without explicit identification, the parties engaged in the
exchange are not identified and the scope of the EAP keying exchange are not identified and the scope of the EAP keying
parameters negotiated during the EAP exchange is undefined. parameters negotiated during the EAP exchange is undefined.
(b) Mutual proof of possession of EAP keying material. During the (b) Mutual proof of possession of EAP keying material. During the
Secure Association Protocol the EAP peer and authenticator MUST Secure Association Protocol the EAP peer and authenticator MUST
demonstrate possession of the keying material transported between demonstrate possession of the keying material transported between
the backend authentication server and authenticator (e.g. MSK), in the backend authentication server and authenticator (e.g. MSK), in
order to demonstrate that the peer and authenticator have been order to demonstrate that the peer and authenticator have been
authorized. Since mutual proof of possession is not the same as authorized. Since mutual proof of possession is not the same as
mutual authentication, the peer cannot verify authenticator mutual authentication, the peer cannot verify authenticator
assertions (including the authenticator identity) as a result of assertions (including the authenticator identity) as a result of
this exchange. Identity verification is discussed in Section this exchange. Authenticator identity verification is discussed in
2.2.1. Section 2.3.
(c) Secure capabilities negotiation. In order to protect against (c) Secure capabilities negotiation. In order to protect against
spoofing during the discovery phase, ensure selection of the "best" spoofing during the discovery phase, ensure selection of the "best"
ciphersuite, and protect against forging of negotiated security ciphersuite, and protect against forging of negotiated security
parameters, the Secure Association Protocol MUST support secure parameters, the Secure Association Protocol MUST support secure
capabilities negotiation. This includes the secure negotiation of capabilities negotiation. This includes the secure negotiation of
usage modes, session parameters (such as security association usage modes, session parameters (such as security association
identifiers (SAIDs) and key lifetimes), ciphersuites and required identifiers (SAIDs) and key lifetimes), ciphersuites and required
filters, including confirmation of security-relevant capabilities filters, including confirmation of security-relevant capabilities
discovered during phase 0. The Secure Association Protocol MUST discovered during phase 0. The Secure Association Protocol MUST
support integrity and replay protection of all capability support integrity and replay protection of all capability
negotiation messages. negotiation messages.
(d) Key naming and selection. Where key caching is supported, it may (d) Key naming and selection. Where key caching is supported, it is
be possible for the EAP peer and authenticator to share more than possible for the EAP peer and authenticator to share more than one
one key of a given type. As a result, the Secure Association key of a given type. As a result, the Secure Association Protocol
Protocol MUST explicitly name the keys used in the proof of MUST explicitly name the keys used in the proof of possession
possession exchange, so as to prevent confusion when more than one exchange, so as to prevent confusion when more than one set of
set of keying material could potentially be used as the basis for keying material could potentially be used as the basis for the
the exchange. Use of the key naming mechanism described in Section exchange. Use of the key naming mechanism described in Section
1.4.1 is RECOMMENDED. 1.4.1 is RECOMMENDED.
In order to support the correct processing of phase 2 security In order to support the correct processing of phase 2 security
associations, the Secure Association (phase 2) protocol MUST associations, the Secure Association (phase 2) protocol MUST
support the naming of phase 2 security associations and associated support the naming of phase 2 security associations and associated
transient session keys, so that the correct set of transient transient session keys, so that the correct set of transient
session keys can be identified for processing a given packet. The session keys can be identified for processing a given packet. The
phase 2 Secure Association Protocol also MUST support transient phase 2 Secure Association Protocol also MUST support transient
session key activation and SHOULD support deletion, so that session key activation and SHOULD support deletion, so that
establishment and re-establishment of transient session keys can be establishment and re-establishment of transient session keys can be
synchronized between the parties. synchronized between the parties.
(e) Generation of fresh transient session keys (TSKs). Where the lower (e) Generation of fresh transient session keys (TSKs). Where the lower
layer supports caching of exported EAP keying material, the EAP layer supports caching of keying material, the EAP peer lower layer
peer lower layer may initiate a new session using keying material can initiate a new session using keying material that was derived
that was derived in a previous session. Were the TSKs to be in a previous session. Were the TSKs to be derived solely from a
derived from a portion of the exported EAP keying material, this portion of the exported EAP keying material, this would result in
would result in reuse of the session keys which could expose the reuse of the session keys which could expose the underlying
underlying ciphersuite to attack. ciphersuite to attack.
In lower layers where caching of EAP keying material is supported, In lower layers where caching of keying material is supported, the
the Secure Association Protocol phase is REQUIRED, and MUST support Secure Association Protocol phase is REQUIRED, and MUST support the
the derivation of fresh unicast and multicast TSKs, even when the derivation of fresh unicast and multicast TSKs, even when the
keying material provided by the backend authentication server is transported keying material provided by the backend authentication
not fresh. This is typically supported via the exchange of nonces server is not fresh. This is typically supported via the exchange
or counters, which are then mixed with the exported keying material of nonces or counters, which are then mixed with the keying
in order to generate fresh unicast (phase 2a) and possibly material in order to generate fresh unicast (phase 2a) and possibly
multicast (phase 2b) session keys. By not using EAP keying multicast (phase 2b) session keys. By not using exported EAP
material directly to protect data, the Secure Association Protocol keying material directly to protect data, the Secure Association
protects it against compromise. Protocol protects it against compromise.
(f) Key lifetime management. This includes explicit key lifetime (f) Key lifetime management. This includes explicit key lifetime
negotiation or seamless re-key. EAP does not support re-key negotiation or seamless re-key. EAP does not support re-key of EAP
without re-authentication and existing EAP methods do not support keying material without re-authentication and existing EAP methods
key lifetime negotiation. As a result, the Secure Association do not support key lifetime negotiation. As a result, the Secure
Protocol may handle re-key and determination of the key lifetime. Association Protocol MAY handle re-key and determination of the key
Where key caching is supported, secure negotiation of key lifetimes lifetime. Where key caching is supported, secure negotiation of
is RECOMMENDED. Lower layers that support re-key, but not key key lifetimes is RECOMMENDED. Lower layers that support re-key,
caching, may not require key lifetime negotiation. For example, a but not key caching, may not require key lifetime negotiation. For
difference between IKEv1 [RFC2409] and IKEv2 [RFC4306] is that in example, a difference between IKEv1 [RFC2409] and IKEv2 [RFC4306]
IKEv1 SA lifetimes were negotiated; in IKEv2, each end of the SA is is that in IKEv1 SA lifetimes were negotiated; in IKEv2, each end
responsible for enforcing its own lifetime policy on the SA and re- of the SA is responsible for enforcing its own lifetime policy on
keying the SA when necessary. the SA and re-keying the SA when necessary.
(g) Key state resynchronization. It is possible for the peer or (g) Key state resynchronization. It is possible for the peer or
authenticator to reboot or reclaim resources, clearing portions or authenticator to reboot or reclaim resources, clearing portions or
all of the key cache. Therefore, key lifetime negotiation cannot all of the key cache. Therefore, key lifetime negotiation cannot
guarantee that the key cache will remain synchronized, and the peer guarantee that the key cache will remain synchronized, and it may
may not be able to determine before attempting to use a key whether not be possible for the peer to determine before attempting to use
it exists within the authenticator cache. It is therefore a key whether it exists within the authenticator cache. It is
RECOMMENDED for the Secure Association Protocol to provide a therefore RECOMMENDED for the EAP lower layer to provide a
mechanism for key state resynchronization. Since in this situation mechanism for key state resynchronization, either via the SAP or
one or more of the parties initially do not possess a key with using a lower layer indication (see [RFC3748] Section 3.4). Where
which to protect the resynchronization exchange, securing this the peer and authenticator do not jointly possess a key with which
mechanism may be difficult. to protect the resynchronization exchange, secure resynchronization
is not possible and alternatives (such as a initiation of EAP re-
authentication after expiration of a timer) is needed to ensure
timely resynchronization.
(h) Key scope synchronization. To support key scope determination, the (h) Key scope synchronization. To support key scope determination, the
Secure Association Protocol SHOULD provide a mechanism by which the Secure Association Protocol SHOULD provide a mechanism by which the
peer can determine the scope of the key cache on each peer can determine the scope of the key cache on each
authenticator, and by which the authenticator can determine the authenticator, and by which the authenticator can determine the
scope of the key cache on a peer. This includes negotiation of scope of the key cache on a peer. This includes negotiation of
restrictions on key usage. restrictions on key usage.
(i) Traffic profile negotiation. The traffic to be protected by a (i) Traffic profile negotiation. The traffic to be protected by a
lower layer security association may not necessarily have the same lower layer security association will not necessarily have the same
lower layer source or destination address as the EAP peer and lower layer source or destination address as the EAP peer and
authenticator, and it is possible for the peer and authenticator to authenticator, and it is possible for the peer and authenticator to
negotiate multiple security associations, each with a different negotiate multiple security associations, each with a different
traffic profile. Where this is the case, the profile of protected traffic profile. Where this is the case, the profile of protected
traffic SHOULD be explicitly negotiated. For example, in IKEv2 it traffic SHOULD be explicitly negotiated. For example, in IKEv2 it
is possible for an Initiator and Responder to utilize EAP for is possible for an Initiator and Responder to utilize EAP for
authentication, then negotiate a Tunnel Mode Security Association authentication, then negotiate a Tunnel Mode Security Association
(SA) which permits passing of traffic originating from hosts other (SA) which permits passing of traffic originating from hosts other
than the Initiator and Responder. Similarly, in IEEE 802.16e a than the Initiator and Responder. Similarly, in IEEE 802.16e a
Subscriber Station (SS) may forward traffic to the Base Station Subscriber Station (SS) can forward traffic to the Base Station
(BS) which originates from the Local Area Network (LAN) to which it (BS) which originates from the Local Area Network (LAN) to which it
is attached. To enable this, Security Associations within IEEE is attached. To enable this, Security Associations within IEEE
802.16e are identified by the Connection Identifier (CID), not by 802.16e are identified by the Connection Identifier (CID), not by
the EAP peer and authenticator MAC addresses. In both IKEv2 and the EAP peer and authenticator MAC addresses. In both IKEv2 and
IEEE 802.16e, multiple security associations may exist between the IEEE 802.16e, multiple security associations can exist between the
EAP peer and authenticator, each with their own traffic profile and EAP peer and authenticator, each with their own traffic profile and
quality of service parameters. quality of service parameters.
(j) Direct operation. Since the phase 2 Secure Association Protocol is (j) Direct operation. Since the phase 2 Secure Association Protocol is
concerned with the establishment of security associations between concerned with the establishment of security associations between
the EAP peer and authenticator, including the derivation of the EAP peer and authenticator, including the derivation of
transient session keys, only those parties have "a need to know" transient session keys, only those parties have "a need to know"
the transient session keys. The Secure Association Protocol MUST the transient session keys. The Secure Association Protocol MUST
operate directly between the peer and authenticator, and MUST NOT operate directly between the peer and authenticator, and MUST NOT
be passed-through to the backend authentication server, or include be passed-through to the backend authentication server, or include
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directions, other ciphersuites require a unique set of transient directions, other ciphersuites require a unique set of transient
session keys in each direction. The phase 2 Secure Association session keys in each direction. The phase 2 Secure Association
Protocol SHOULD provide for the derivation of unicast and multicast Protocol SHOULD provide for the derivation of unicast and multicast
keys in each direction, so as not to require two separate phase 2 keys in each direction, so as not to require two separate phase 2
exchanges in order to create a bi-directional phase 2 security exchanges in order to create a bi-directional phase 2 security
association. See [RFC3748] Section 2.4 for more discussion. association. See [RFC3748] Section 2.4 for more discussion.
3.2. Key Scope 3.2. Key Scope
Absent explicit specification within the lower layer, after the Absent explicit specification within the lower layer, after the
completion of phase 1b, EAP keying material and parameters are bound completion of phase 1b, transported keying material and parameters
to the EAP peer and authenticator, but are not bound to a specific are bound to the EAP peer and authenticator, but are not bound to a
peer or authenticator port. specific peer or authenticator port.
While EAP Keying Material passed down to the lower layer is not While EAP keying material passed down to the lower layer is not
intrinsically bound to particular authenticator and peer ports, intrinsically bound to particular authenticator and peer ports, TSKs
Transient Session Keys MAY be bound to particular authenticator and MAY be bound to particular authenticator and peer ports by the Secure
peer ports by the Secure Association Protocol. However, a lower Association Protocol. However, a lower layer MAY also permit TSKs to
layer MAY also permit TSKs to be used on multiple peer and/or be used on multiple peer and/or authenticator ports, providing that
authenticator ports, providing that TSK freshness is guaranteed (such TSK freshness is guaranteed (such as by keeping replay counter state
as by keeping replay counter state within the authenticator). within the authenticator).
In order to further limit the key scope the following measures are In order to further limit the key scope the following measures are
suggested: suggested:
(a) The lower layer MAY specify additional restrictions on key usage, (a) The lower layer MAY specify additional restrictions on key usage,
such as limiting the use of EAP keying material and parameters on such as limiting the use of EAP keying material and parameters on
the EAP peer to the port over which on the EAP conversation was the EAP peer to the port over which on the EAP conversation was
conducted. conducted.
(b) The backend authentication server and authenticator MAY implement (b) The backend authentication server and authenticator MAY implement
additional attributes in order to further restrict the scope of EAP additional attributes in order to further restrict the scope of
keying material. For example, in 802.11, the backend keying material. For example, in IEEE 802.11, the backend
authentication server may provide the authenticator with a list of authentication server can provide the authenticator with a list of
authorized Called or Calling-Station-Ids and/or SSIDs for which EAP authorized Called or Calling-Station-Ids and/or SSIDs for which
keying material is valid. keying material is valid.
(c) Where the backend authentication server provides attributes (c) Where the backend authentication server provides attributes
restricting the key scope, it is RECOMMENDED that restrictions be restricting the key scope, it is RECOMMENDED that restrictions be
securely communicated by the authenticator to the peer. This can securely communicated by the authenticator to the peer. This can
be accomplished using the Secure Association Protocol, but also be accomplished using the Secure Association Protocol, but also
can be accomplished via the EAP method or the lower layer. can be accomplished via the EAP method or the lower layer.
3.3. Parent-Child Relationships 3.3. Parent-Child Relationships
When an EAP re-authentication takes place, new keying material is When an EAP re-authentication takes place, new EAP keying material is
derived and exported by the EAP method, which eventually results in exported by the EAP method. In EAP lower layers where EAP re-
replacement of TSKs, regardless of the way they are derived (see authentication eventually results in TSK replacement, the maximum
Section 2.1). While the maximum lifetime of TSKs or child keys can lifetime of derived keying material (including TSKs) can be less than
be less than or equal to that of the MSK/EMSK, it cannot be greater. or equal to that of EAP keying material (MSK/EMSK), but it cannot be
This is true even where exported EAP keying material is only used for greater.
entity authentication and is not used for key derivation (such as in
IKEv2), so that compromise of exported EAP keying material does not Where TSKs are derived from or are wrapped by exported EAP keying
imply compromise of the TSKs or child keys. However, where child material, compromise of that exported EAP keying material implies
keys are derived from or are wrapped by EAP keying material, compromise of TSKs. Therefore if EAP keying material is considered
compromise of the MSK/EMSK does imply compromise of the child keys. stale, not only SHOULD EAP re-authentication be initiated, but also
replacement of child keys, including TSKs.
Where EAP keying material is used only for entity authentication but
not for TSK derivation (as in IKEv2), compromise of exported EAP
keying material does not imply compromise of the TSKs. Nevertheless,
the compromise of EAP keying material could enable an attacker to
impersonate an authenticator, so that EAP re-authentication and TSK
re-key are RECOMMENDED.
With respect to IKEv2, "IKEv2 Clarifications and Implementation
Guidelines" [RFC4718] Section 5.2 states:
Rekeying the IKE-SA and reuathentication are different concepts in
IKEv2. Rekeying the IKE_SA establishes new keys for the IKE_SA
and resets the Message ID counters, but it does not authenticate
the parties again (no AUTH or EAP payloads are involved)... This
means that reauthentication also establishes new keys for the
IKE_SA and CHILD_SAs. Therefore while rekeying can be performed
more often than reauthentication, the situation where
"authentication lifetime" is shorter than "key lifetime" does not
make sense.
Child keys that are used frequently (such as TSKs which are used for Child keys that are used frequently (such as TSKs which are used for
traffic protection) can expire sooner than the exported EAP keying traffic protection) can expire sooner than the exported EAP keying
material they are dependent on, so that it is advantageous to support material they are dependent on, so that it is advantageous to support
re-key of child keys prior to EAP re-authentication. Note that re-key of child keys prior to EAP re-authentication. Note that
deletion of the MSK/EMSK does not necessarily imply deletion of TSKs deletion of the MSK/EMSK does not necessarily imply deletion of TSKs
or child keys. or child keys.
Failure to mutually prove possession of exported EAP keying material Failure to mutually prove possession of exported EAP keying material
during the Secure Association Protocol exchange need not be grounds during the Secure Association Protocol exchange need not be grounds
for deletion of the keying material by both parties; rate-limiting for deletion of keying material by both parties; rate-limiting Secure
Secure Association Protocol exchanges could be used to prevent a Association Protocol exchanges could be used to prevent a brute force
brute force attack. attack.
3.4. Local Key Lifetimes 3.4. Local Key Lifetimes
The Transient EAP Keys (TEKs) are session keys used to protect the The Transient EAP Keys (TEKs) are session keys used to protect the
EAP conversation. The TEKs are internal to the EAP method and are EAP conversation. The TEKs are internal to the EAP method and are
not exported. TEKs are typically created during an EAP conversation, not exported. TEKs are typically created during an EAP conversation,
used until the end of the conversation and then discarded. However, used until the end of the conversation and then discarded. However,
methods may re-key TEKs during an EAP conversation. methods can re-key TEKs during an EAP conversation.
When using TEKs within an EAP conversation or across conversations, When using TEKs within an EAP conversation or across conversations,
it is necessary to ensure that replay protection and key separation it is necessary to ensure that replay protection and key separation
requirements are fulfilled. For instance, if a replay counter is requirements are fulfilled. For instance, if a replay counter is
used, TEK re-key MUST occur prior to wrapping of the counter. used, TEK re-key MUST occur prior to wrapping of the counter.
Similarly, TSKs MUST remain cryptographically separate from TEKs Similarly, TSKs MUST remain cryptographically separate from TEKs
despite TEK re-keying or caching. This prevents TEK compromise from despite TEK re-keying or caching. This prevents TEK compromise from
leading directly to compromise of the TSKs and vice versa. leading directly to compromise of the TSKs and vice versa.
EAP methods may cache local keying material which may persist for EAP methods MAY cache local EAP keying material (TEKs) which can
multiple EAP conversations when fast reconnect is used [RFC3748]. persist for multiple EAP conversations when fast reconnect is used
For example, EAP methods based on TLS (such as EAP-TLS [I-D.simon- [RFC3748]. For example, EAP methods based on TLS (such as EAP-TLS
emu-rfc2716bis]) derive and cache the TLS Master Secret, typically [I-D.simon-emu-rfc2716bis]) derive and cache the TLS Master Secret,
for substantial time periods. The lifetime of other local keying typically for substantial time periods. The lifetime of other local
material calculated within the EAP method is defined by the method. EAP keying material calculated within the EAP method is defined by
Note that in general, when using fast reconnect, there is no the method. Note that in general, when using fast reconnect, there
guarantee to that the original long-term credentials are still in the is no guarantee to that the original long-term credentials are still
possession of the peer. For instance, a card hold holding the in the possession of the peer. For instance, a smart-card holding
private key for EAP-TLS may have been removed. EAP servers SHOULD the private key for EAP-TLS can have been removed. EAP servers
also verify that the long-term credentials are still valid, such as SHOULD also verify that the long-term credentials are still valid,
by checking that certificate used in the original authentication has such as by checking that certificate used in the original
not yet expired. authentication has not yet expired.
3.5. Exported and Calculated Key Lifetimes 3.5. Exported and Calculated Key Lifetimes
The following mechanisms are available for communicating the lifetime The following mechanisms are available for communicating the lifetime
of exported and calculated keying material between the EAP peer, of keying material between the EAP peer, server and authenticator:
server and authenticator:
AAA protocols (backend server and authenticator) AAA protocols (backend server and authenticator)
Lower layer mechanisms (authenticator and peer) Lower layer mechanisms (authenticator and peer)
EAP method-specific negotiation (peer and server) EAP method-specific negotiation (peer and server)
Where the EAP method does not support the negotiation of the lifetime Where the EAP method does not support the negotiation of the lifetime
of exported keys, and a key lifetime negotiation mechanism is not of exported EAP keying material, and a key lifetime negotiation
provided by the lower layer, there may be no way for the peer to mechanism is not provided by the lower layer, it is possible that
learn the lifetime of exported and calculated keys. This can leave there will not be a way for the peer to learn the lifetime of keying
the peer uncertain how long the authenticator will maintain EAP material. This can leave the peer uncertain how long the
keying material within the key cache. In this case the lifetime of authenticator will maintain keying material within the key cache. In
exported keys can be managed as a system parameter on the peer and this case the lifetime of keying material can be managed as a system
authenticator; a default lifetime of 8 hours is RECOMMENDED. parameter on the peer and authenticator; a default lifetime of 8
hours is RECOMMENDED.
3.5.1. AAA Protocols 3.5.1. AAA Protocols
AAA protocols such as RADIUS [RFC2865] and Diameter [RFC4072] can be AAA protocols such as RADIUS [RFC2865] and Diameter [RFC4072] can be
used to communicate the maximum exported key lifetime from the used to communicate the maximum key lifetime from the backend
backend authentication server to the authenticator. authentication server to the authenticator.
The Session-Timeout attribute is defined for RADIUS in [RFC2865] and The Session-Timeout attribute is defined for RADIUS in [RFC2865] and
for Diameter in [RFC4005]. Where EAP is used for authentication, for Diameter in [RFC4005]. Where EAP is used for authentication,
[RFC3580] Section 3.17 indicates that a Session-Timeout attribute [RFC3580] Section 3.17 indicates that a Session-Timeout attribute
sent in an Access-Accept along with a Termination-Action value of sent in an Access-Accept along with a Termination-Action value of
RADIUS-Request specifies the maximum number of seconds of service RADIUS-Request specifies the maximum number of seconds of service
provided prior to EAP re-authentication. provided prior to EAP re-authentication.
However, there is also a need to be able to specify the maximum However, there is also a need to be able to specify the maximum
lifetime of cached keying material. Where EAP pre-authentication is lifetime of cached keying material. Where EAP pre-authentication is
supported, cached keys can be pre-established on the authenticator supported, cached keying material can be pre-established on the
prior to session start, and will remain there until they expire. EAP authenticator prior to session start, and will remain there until
lower layers supporting caching of exported keying material may also expiration. EAP lower layers supporting caching of keying material
persist that material after the end of a session, enabling the peer MAY also persist that material after the end of a session, enabling
to subsequently resume communication utilizing the cached keying the peer to subsequently resume communication utilizing the cached
material. In these situations it may be desirable for the backend keying material. In these situations it can be desirable for the
authentication server to specify the maximum lifetime of cached backend authentication server to specify the maximum lifetime of
keying material. cached keying material.
To accomplish this, [IEEE-802.11i] overloaded the Session-Timeout To accomplish this, [IEEE-802.11] overloads the Session-Timeout
attribute, assuming that it represents the maximum time after which attribute, assuming that it represents the maximum time after which
transported EAP keying material will expire on the authenticator, transported keying material will expire on the authenticator,
regardless of whether transported keying material is cached. regardless of whether transported keying material is cached.
An IEEE 802.11 authenticator receiving keying material is expected to An IEEE 802.11 authenticator receiving transported keying material is
initialize a timer to the Session-Timeout value, and once the timer expected to initialize a timer to the Session-Timeout value, and once
expires, the exported keying material expires. Whether this results the timer expires, the transported keying material expires. Whether
in session termination or EAP re-authentication is controlled by the this results in session termination or EAP re-authentication is
value of the Termination-Action attribute. Where EAP re- controlled by the value of the Termination-Action attribute. Where
authentication occurs the exported keying material is replaced, and EAP re-authentication occurs the transported keying material is
with it, new calculated keys are put in place. Where session replaced, and with it, new calculated keys are put in place. Where
termination occurs, exported and calculated keying material is session termination occurs, transported and derived keying material
deleted. is deleted.
Overloading the Session-Timeout attribute is problematic in Overloading the Session-Timeout attribute is problematic in
situations where it is necessary to control the maximum session time situations where it is necessary to control the maximum session time
and key lifetime independently. For example, it might be desirable and key lifetime independently. For example, it might be desirable
to limit the lifetime of cached keys to 5 minutes while permitting a to limit the lifetime of cached keying material to 5 minutes while
user once authenticated to remain connected for up to an hour without permitting a user once authenticated to remain connected for up to an
re-authenticating. As a result, in the future additional attributes hour without re-authenticating. As a result, in the future
may be specified to control the lifetime of cached keys; these additional attributes can be specified to control the lifetime of
attributes may modify the meaning of the Session-Timeout attribute in cached keys; these attributes MAY modify the meaning of the Session-
specific circumstances. Timeout attribute in specific circumstances.
Since the TSK lifetime is often determined by authenticator Since the TSK lifetime is often determined by authenticator
resources, and the backend authentication server has no insight into resources, and the backend authentication server has no insight into
the TSK derivation process, by the principle of ciphersuite the TSK derivation process, by the principle of ciphersuite
independence, it is not appropriate for the backend authentication independence, it is not appropriate for the backend authentication
server to manage any aspect of the TSK derivation process, including server to manage any aspect of the TSK derivation process, including
the TSK lifetime. the TSK lifetime.
3.5.2. Lower Layer Mechanisms 3.5.2. Lower Layer Mechanisms
Lower layer mechanisms can be used to enable the lifetime of exported Lower layer mechanisms can be used to enable the lifetime of keying
and calculated keys to be negotiated between the peer and material to be negotiated between the peer and authenticator. This
authenticator. This can be accomplished either using the Secure can be accomplished either using the Secure Association Protocol or
Association Protocol or within the lower layer transport. within the lower layer transport.
Where TSKs are established as the result of a Secure Association Where TSKs are established as the result of a Secure Association
Protocol exchange, it is RECOMMENDED that the Secure Association Protocol exchange, it is RECOMMENDED that the Secure Association
Protocol include support for TSK re-key. Where the TSK is taken Protocol include support for TSK re-key. Where the TSK is taken
directly from the MSK, there is no need to manage the TSK lifetime as directly from the MSK, there is no need to manage the TSK lifetime as
a separate parameter, since the TSK lifetime and MSK lifetime are a separate parameter, since the TSK lifetime and MSK lifetime are
identical. identical.
3.5.3. EAP Method-Specific Negotiation 3.5.3. EAP Method-Specific Negotiation
All EAP methods generating keys are required to generate the MSK and As noted in [RFC3748] Section 7.10:
EMSK, and may optionally generate the IV. However, EAP, defined in
[RFC3748], does not itself support the negotiation of lifetimes for In order to provide keying material for use in a subsequently
exported keying material such as the MSK, EMSK and IV. negotiated ciphersuite, an EAP method supporting key derivation
MUST export a Master Session Key (MSK) of at least 64 octets, and
an Extended Master Session Key (EMSK) of at least 64 octets. EAP
Methods deriving keys MUST provide for mutual authentication
between the EAP peer and the EAP Server.
However, EAP does not itself support the negotiation of lifetimes for
exported EAP keying material such as the MSK, EMSK and IV.
While EAP itself does not support lifetime negotiation, it would be While EAP itself does not support lifetime negotiation, it would be
possible to specify methods that do. However, systems that rely on possible to specify methods that do. However, systems that rely on
such negotiation for exported keys would only function with these key lifetime negotiation within EAP methods would only function with
methods. Also, there is no guarantee that the lifetime negotiated these methods. Also, there is no guarantee that the key lifetime
within the EAP method would be compatible with backend authentication negotiated within the EAP method would be compatible with backend
server policy. In the interest of method independence and authentication server policy. In the interest of method independence
compatibility with backend server implementations, key management of and compatibility with backend server implementations, management of
exported or derived keys SHOULD NOT be provided within EAP methods. the lifetime of keying material SHOULD NOT be provided within EAP
methods.
3.6. Key Cache Synchronization 3.6. Key Cache Synchronization
Key lifetime negotiation alone cannot guarantee key cache Key lifetime negotiation alone cannot guarantee key cache
synchronization. Even where a lower layer exchange is run synchronization. Even where a lower layer exchange is run
immediately after EAP in order to determine the lifetime of EAP immediately after EAP in order to determine the lifetime of keying
keying material, it is still possible for the authenticator to purge material, it is still possible for the authenticator to purge all or
all or part of the key cache prematurely (e.g. due to reboot or need part of the key cache prematurely (e.g. due to reboot or need to
to reclaim memory). reclaim memory).
The lower layer may utilize the Discovery phase 0 to improve key The lower layer can utilize the Discovery phase 0 to improve key
cache synchronization. For example, if the authenticator manages the cache synchronization. For example, if the authenticator manages the
key cache by deleting the oldest key first, the relative creation key cache by deleting the oldest key first, the relative creation
time of the last key to be deleted could be advertised within the time of the last key to be deleted could be advertised within the
Discovery phase, enabling the peer to determine whether keying Discovery phase, enabling the peer to determine whether keying
material had been prematurely expired from the authenticator key material had been prematurely expired from the authenticator key
cache. cache.
3.7. Key Strength 3.7. Key Strength
As noted in Section 2.1, EAP lower layers determine TSKs in different As noted in Section 2.1, EAP lower layers determine TSKs in different
ways. Where EAP keying material is utilized in the derivation, ways. Where exported EAP keying material is utilized in the
encryption or authentication of TSKs, it is possible for EAP key derivation, encryption or authentication of TSKs, it is possible for
generation to represent the weakest link. EAP key generation to represent the weakest link.
In order to ensure that EAP methods produce keying material of an In order to ensure that methods produce EAP keying material of an
appropriate symmetric key strength, it is RECOMMENDED that EAP appropriate symmetric key strength, it is RECOMMENDED that EAP
methods utilizing public key cryptography choose a public key that methods utilizing public key cryptography choose a public key that
has a cryptographic strength providing the required level of attack has a cryptographic strength providing the required level of attack
resistance. This is typically provided by configuring EAP methods, resistance. This is typically provided by configuring EAP methods,
since there is no coordination between the lower layer and EAP method since there is no coordination between the lower layer and EAP method
with respect to minimum required symmetric key strength. with respect to minimum required symmetric key strength.
BCP 86 [RFC3766] Section 5 offers advice on the required RSA or DH BCP 86 [RFC3766] Section 5 offers advice on the required RSA or DH
module and DSA subgroup size in bits, for a given level of attack module and DSA subgroup size in bits, for a given level of attack
resistance in bits. The National Institute for Standards and resistance in bits. The National Institute for Standards and
skipping to change at page 35, line 27 skipping to change at page 38, line 7
As discussed in [RFC3579] Section 4.3, the security vulnerabilities As discussed in [RFC3579] Section 4.3, the security vulnerabilities
of RADIUS are extensive, and therefore development of an alternative of RADIUS are extensive, and therefore development of an alternative
key wrap technique based on the RADIUS shared secret would not key wrap technique based on the RADIUS shared secret would not
substantially improve security. As a result, [RFC3579] Section 4.2 substantially improve security. As a result, [RFC3579] Section 4.2
recommends running RADIUS over IPsec. The same approach is taken in recommends running RADIUS over IPsec. The same approach is taken in
Diameter EAP [RFC4072], which defines clear-text key attributes, to Diameter EAP [RFC4072], which defines clear-text key attributes, to
be protected by IPsec or TLS. be protected by IPsec or TLS.
4. Handoff Vulnerabilities 4. Handoff Vulnerabilities
A handoff occurs when an EAP peer moves to a new authenticator.
Several mechanisms have been proposed for reducing handoff latency Several mechanisms have been proposed for reducing handoff latency
within networks utilizing EAP. These include: within networks utilizing EAP. These include:
EAP pre-authentication EAP pre-authentication
In EAP pre-authentication, an EAP peer pre-establishes EAP keying In EAP pre-authentication, an EAP peer pre-establishes EAP keying
material with an authenticator prior to arrival. EAP pre- material with an authenticator prior to arrival. EAP pre-
authentication only affects the timing of EAP authentication, but authentication only affects the timing of EAP authentication, but
does not shorten or eliminate EAP (phase 1a) or AAA (phase 1b) does not shorten or eliminate EAP (phase 1a) or AAA (phase 1b)
exchanges; Discovery (phase 0) and Secure Association Protocol exchanges; Discovery (phase 0) and Secure Association Protocol
(phase 2) exchanges occur as described in Section 1.3. As a (phase 2) exchanges occur as described in Section 1.3. As a
result, the primary benefit is to enable EAP authentication to be result, the primary benefit is to enable EAP authentication to be
removed from the handoff critical path, thereby reducing latency. removed from the handoff critical path, thereby reducing latency.
Use of EAP pre-authentication within IEEE 802.11 is described in Use of EAP pre-authentication within IEEE 802.11 is described in
[8021XPreAuth] and [IEEE-802.11i]. [IEEE-802.11] and [8021XPreAuth].
Proactive key distribution Proactive key distribution
In proactive key distribution, derived keying material and In proactive key distribution, keying material and authorizations
authorizations are transported from the backend authentication are transported from the backend authentication server to a
server to a candidate authenticator in advance of a handoff. As a candidate authenticator in advance of a handoff. As a result, EAP
result, EAP (phase 1a) is not required, but the Discovery (phase (phase 1a) is not needed, but the Discovery (phase 0), and Secure
0), and Secure Association Protocol exchanges (phase 2) are still Association Protocol exchanges (phase 2) are still necessary.
necessary. Within the AAA exchange (phase 1b), authorization and Within the AAA exchange (phase 1b), authorization and key
key distribution functions are typically supported, but not distribution functions are typically supported, but not
authentication. Proactive key distribution is described in authentication. Proactive key distribution is described in
[MishraPro], [IEEE-03-084] and [I-D.irtf-aaaarch-handoff]. [MishraPro], [IEEE-03-084] and [I-D.irtf-aaaarch-handoff].
Key caching Key caching
Caching of EAP keying material enables an EAP peer to re-attach to Caching of EAP keying material enables an EAP peer to re-attach to
an authenticator without requiring EAP (phase 1a) or AAA (phase 1b) an authenticator without requiring EAP (phase 1a) or AAA (phase 1b)
exchanges. However, Discovery (phase 0) and Secure Association exchanges. However, Discovery (phase 0) and Secure Association
Protocol (phase 2) exchanges are still required. Use of key Protocol (phase 2) exchanges are still needed. Use of key caching
caching within IEEE 802.11 is described in [IEEE-802.11i]. within IEEE 802.11 is described in [IEEE-802.11].
Context transfer Context transfer
In context transfer schemes, keying material and authorizations are In context transfer schemes, keying material and authorizations are
transferred between a previous authenticator and a new transferred between a previous authenticator and a new
authenticator. This can occur in response to a handoff request by authenticator. This can occur in response to a handoff request by
the EAP peer, or in advance, as in proactive key distribution. As the EAP peer, or in advance, as in proactive key distribution. As
a result, EAP (phase 1a) is eliminated, but not the Discovery a result, EAP (phase 1a) is eliminated, but not the Discovery
(phase 0) or Secure Association Protocol exchanges (phase 2). If a (phase 0) or Secure Association Protocol exchanges (phase 2). If a
secure channel can be established between the new and previous secure channel can be established between the new and previous
authenticator without assistance from the backend authentication authenticator without assistance from the backend authentication
server, then the AAA exchange (phase 1b) can be eliminated; server, then the AAA exchange (phase 1b) can be eliminated;
otherwise, it is still required, although it may be shortened. otherwise, it is still needed, although it can be shortened.
Context transfer protocols are described in [IEEE-802.11F] (now Context transfer protocols are described in [IEEE-802.11F] (now
deprecated) and "Context Transfer Protocol (CXTP)" [RFC4067]. deprecated) and "Context Transfer Protocol (CXTP)" [RFC4067].
"Fast Authentication Methods for Handovers between IEEE 802.11 "Fast Authentication Methods for Handovers between IEEE 802.11
Wireless LANs" [Bargh] analyzes fast handoff techniques, including Wireless LANs" [Bargh] analyzes fast handoff techniques, including
context transfer mechanisms. context transfer mechanisms.
Token distribution Token distribution
In token distribution schemes the EAP peer is provided with a In token distribution schemes the EAP peer is provided with a
credential, subsequently enabling it to authenticate with one or credential, subsequently enabling it to authenticate with one or
more additional authenticators. During the subsequent more additional authenticators. During the subsequent
authentications, EAP (phase 1a) is eliminated or shortened; the authentications, EAP (phase 1a) is eliminated or shortened; the
Discovery (phase 0) and Secure Association Protocol exchanges Discovery (phase 0) and Secure Association Protocol exchanges
(phase 2) still occur, although the latter may be shortened. If (phase 2) still occur, although the latter can be shortened. If
the token includes authorizations and can be validated by an the token includes authorizations and can be validated by an
authenticator without assistance from the backend authentication authenticator without assistance from the backend authentication
server, then the AAA exchange (phase 1b) can be eliminated; server, then the AAA exchange (phase 1b) can be eliminated;
otherwise it is still required, although it may be shortened. otherwise it is still needed, although it can be shortened. Token-
Token-based schemes are described in [Token] and [I-D.friedman-ike- based schemes, initially proposed in early drafts of IEEE 802.11i
short-term-certs]. [IEEE-802.11i], are described in [Token], [Tokenk] and
[I-D.friedman-ike-short-term-certs].
The sections that follow discuss the security vulnerabilities The sections that follow discuss the security vulnerabilities
introduced by the above schemes. introduced by the above schemes.
4.1. EAP Pre-authentication 4.1. EAP Pre-authentication
EAP pre-authentication differs from a normal EAP conversation EAP pre-authentication differs from a normal EAP conversation
primarily with respect to the lower layer encapsulation. For primarily with respect to the lower layer encapsulation. For
example, in [IEEE-802.11i], EAP pre-authentication frames utilize a example, in [IEEE-802.11], EAP pre-authentication frames utilize a
distinct Ethertype, but otherwise conform to the encapsulation distinct Ethertype, but otherwise conforms to the encapsulation
described in [IEEE-802.1X]. As a result, an EAP pre-authentication described in [IEEE-802.1X]. As a result, an EAP pre-authentication
conversation differs little from the model described in Section 1.3, conversation differs little from the model described in Section 1.3,
other than the introduction of a delay between phase 1 and phase 2. other than the introduction of a delay between phase 1 and phase 2.
EAP pre-authentication relies on lower layer mechanisms for discovery EAP pre-authentication relies on lower layer mechanisms for discovery
of candidate authenticators. Where discovery can provide information of candidate authenticators. Where discovery can provide information
on candidate authenticators outside the immediate listening range, on candidate authenticators outside the immediate listening range,
and the peer can determine whether it already possesses valid keying and the peer can determine whether it already possesses valid EAP
material with candidate authenticators, the peer can avoid keying material with candidate authenticators, the peer can avoid
unnecessary EAP pre-authentications and can establish keying material unnecessary EAP pre-authentications and can establish EAP keying
well in advance, regardless of the coverage overlap between material well in advance, regardless of the coverage overlap between
authenticators. However, if the peer can only discover candidate authenticators. However, if the peer can only discover candidate
authenticators within listening range and cannot determine whether it authenticators within listening range and cannot determine whether it
can reuse existing key material, then peer may not be able to can reuse existing EAP keying material, then it is possible that the
complete EAP pre-authentication prior to connectivity loss or may peer will not be able to complete EAP pre-authentication prior to
pre-authenticate multiple times with the same authenticator, connectivity loss or that it can pre-authenticate multiple times with
increasing backend authentication server load. the same authenticator, increasing backend authentication server
load.
Since a peer may complete EAP pre-authentication with an Since a peer can complete EAP pre-authentication with an
authenticator without eventually attaching to it, phase 2 may never authenticator without eventually attaching to it, it is possible that
occur. As a result, an Accounting-Request signifying the start of phase 2 will not occur. In this case an Accounting-Request
service may never be sent, or may only be sent with a substantial signifying the start of service will not be sent, or will only be
delay after the completion of authentication. sent with a substantial delay after the completion of authentication.
As noted in "IEEE 802.1X RADIUS Usage Guidelines" [RFC3580], the AAA As noted in "IEEE 802.1X RADIUS Usage Guidelines" [RFC3580], the AAA
exchange resulting from EAP pre-authentication differs little from an exchange resulting from EAP pre-authentication differs little from an
ordinary exchange described in "RADIUS Support for EAP" [RFC3579]. ordinary exchange described in "RADIUS Support for EAP" [RFC3579].
For example, since in IEEE 802.11i an Association exchange does not For example, since in IEEE 802.11 [IEEE-802.11] an Association
occur prior to EAP pre-authentication, the SSID is not known by the exchange does not occur prior to EAP pre-authentication, the SSID is
authenticator at authentication time, so that an Access-Request not known by the authenticator at authentication time, so that an
cannot include the SSID within the Called-Station-Id attribute as Access-Request cannot include the SSID within the Called-Station-Id
described in [RFC3580] Section 3.20. attribute as described in [RFC3580] Section 3.20.
Since only the absence of an SSID in the Called-Station-Id attribute Since only the absence of an SSID in the Called-Station-Id attribute
distinguishes an EAP pre-authentication attempt, if the authenticator distinguishes an EAP pre-authentication attempt, if the authenticator
does not always include the SSID for a normal EAP authentication does not always include the SSID for a normal EAP authentication
attempt, the backend authentication server may not be able to attempt, it is possible that the backend authentication server will
determine whether a session constitutes an EAP pre-authentication not be able to determine whether a session constitutes an EAP pre-
attempt, potentially resulting in authorization or accounting authentication attempt, potentially resulting in authorization or
problems. Where the number of simultaneous sessions is limited, the accounting problems. Where the number of simultaneous sessions is
backend authentication server may refuse to authorize a valid EAP limited, the backend authentication server can refuse to authorize a
pre-authentication attempt or may enable the peer to engage in more valid EAP pre-authentication attempt or can enable the peer to engage
simultaneous sessions than they are authorized for. Where EAP pre- in more simultaneous sessions than they are authorized for. Where
authentication occurs with an authenticator which the peer never EAP pre-authentication occurs with an authenticator which the peer
attaches to, the backend accounting server may not be able to never attaches to, it is possible that the backend accounting server
determine whether the absence of an Accounting-Request was due to will not be able to determine whether the absence of an Accounting-
packet loss or a session that never started. Request was due to packet loss or a session that never started.
In order to enable pre-authentication requests to be handled more In order to enable pre-authentication requests to be handled more
reliably, it is RECOMMENDED that AAA protocols explicitly identify reliably, it is RECOMMENDED that AAA protocols explicitly identify
EAP pre-authentication. In order to suppress unnecessary EAP pre- EAP pre-authentication. In order to suppress unnecessary EAP pre-
authentication exchanges, it is RECOMMENDED that authenticators authentication exchanges, it is RECOMMENDED that authenticators
unambiguously identify themselves as described in Section 2.2.1. unambiguously identify themselves as described in Section 2.3.
4.2. Proactive Key Distribution 4.2. Proactive Key Distribution
In proactive key distribution schemes, the backend authentication In proactive key distribution schemes, the backend authentication
server transports keying material and authorizations to an server transports keying material and authorizations to an
authenticator in advance of the arrival of the peer. The authenticator in advance of the arrival of the peer. The
authenticators selected to receive the transported key material are authenticators selected to receive the transported key material are
selected based on past patterns of peer movement between selected based on past patterns of peer movement between
authenticators known as the "neighbor graph". Since proactive key authenticators known as the "neighbor graph". In order to reduce
distribution schemes typically only demonstrate proof of possession handoff latency, proactive key distribution schemes typically only
of transported keying material between the EAP peer and demonstrate proof of possession of transported keying material
authenticator, the backend authentication server may not be provided between the EAP peer and authenticator. During a handoff, the
with proof that the peer successfully authenticated to an backend authentication server is not provided with proof that the
authenticator. To compute the "neighbor graph" the backend peer successfully authenticated to an authenticator; instead, the
authentication server therefore may need to rely on a stream of authenticator generates a stream of accounting messages without a
accounting messages without a corresponding set of authentication corresponding set of authentication exchanges. As described in
exchanges. [MishraPro], knowledge of the neighbor graph can be established via
static configuration or analysis of authentication exchanges. In
order to prevent corruption of the neighbor graph, new neighbor graph
entries can only be created as the result of a successful EAP
exchange, and accounting packets with no corresponding authentication
exchange need to be verified to correspond to neighbor graph entries
(e.g. corresponding to handoffs between neighbors).
In order to prevent compromise of one authenticator from resulting in In order to prevent compromise of one authenticator from resulting in
compromise of other authenticators, cryptographic separation needs compromise of other authenticators, cryptographic separation needs
to be maintained between the keying material transported to each to be maintained between the keying material transported to each
authenticator. However, even where cryptographic separation is authenticator. However, even where cryptographic separation is
maintained, an attacker compromising an authenticator may still maintained, an attacker compromising an authenticator can still
disrupt the operation of other authenticators. Since proactive key disrupt the operation of other authenticators. As noted in [RFC3579]
distribution schemes typically only demonstrate proof of possession Section 4.3.7, in the absence of spoofing detection within the AAA
of transported keying material between the EAP peer and infrastructure, it is possible for EAP authenticators to impersonate
authenticator, the backend authentication server is typically not each other. By forging NAS identification attributes within
provided with proof that the peer actually connected to an authentication messages, an attacker compromising one authenticator
authenticator. To compute the "neighbor graph" it therefore may be could corrupt the neighbor graph, tricking the backend authentication
necessary to rely on a stream of accounting messages without a server into transporting keying material to arbitrary authenticators.
corresponding set of authentication exchanges to verify against. While this would not enable recovery of EAP keying material without
breaking fundamental cryptographic assumptions, it could enable
As noted in [RFC3579] Section 4.3.7, in the absence of spoofing subsequent fraudulent accounting messages, or allow an attacker to
detection within the AAA infrastructure, it is possible for EAP disrupt service by increasing load on the backend authentication
authenticators to impersonate each other. By forging NAS server or thrashing the authenticator key cache.
identification attributes within accounting messages, an attacker
compromising one authenticator could corrupt the neighbor graph,
tricking the backend authentication server into transporting keying
material to arbitrary authenticators. While this would not enable
recovery of EAP keying material without breaking fundamental
cryptographic assumptions, it could enable fraudulent charges or
allow an attacker to disrupt service by increasing load on the
backend authentication server or thrashing the authenticator key
cache.
Since proactive key distribution requires the distribution of derived Since proactive key distribution requires the distribution of derived
keying material to candidate authenticators, the effectiveness of keying material to candidate authenticators, the effectiveness of
this scheme depends on the ability of backend authentication server this scheme depends on the ability of backend authentication server
to anticipate the movement of the EAP peer. As described in [Mishra- to anticipate the movement of the EAP peer. Since proactive key
Pro], knowledge of the "neighbor graph" can be established via static distribution relies on backend authentication server knowledge of the
configuration or analysis of accounting messages. Since proactive neighbor graph it is most applicable to intra-domain handoff
key distribution relies on backend authentication server knowledge of scenarios. However, in inter-domain handoff where there can be many
the "neighbor graph" it is most applicable to intra-domain handoff authenticators, peers can frequently connect to authenticators that
scenarios. However, in inter-domain handoff where there may be many have not been previously encountered, making it difficult for the
authenticators, the "neighbor graph" may not be readily derived on backend authentication server to derive a complete neighbor graph.
the backend authentication server, since peers may frequently connect
to authenticators that have not previously been encountered.
Since proactive key distribution schemes typically require Since proactive key distribution schemes typically require
introduction of server-initiated messages as described in [RFC3576] introduction of server-initiated messages as described in
and [I-D.irtf-aaaarch-handoff], security issues described in [RFC3576bis] and [I-D.irtf-aaaarch-handoff], security issues
[RFC3576] Section 5 are applicable, including authorization (Section described in [RFC3576bis] Section 6 are applicable, including
5.1) and replay detection (Section 5.4) problems. authorization (Section 6.1) and replay detection (Section 6.3)
problems.
4.3. AAA Bypass 4.3. AAA Bypass
Fast handoff techniques which enable elimination of the AAA exchange Fast handoff techniques which enable elimination of the AAA exchange
(phase 1b) differ fundamentally from typical network access scenarios (phase 1b) differ fundamentally from typical network access scenarios
(dial-up, wired LAN, etc.) which include user authentication as well (dial-up, wired LAN, etc.) which include user authentication as well
as authorization for the offered service. Where the AAA exchange as authorization for the offered service. Where the AAA exchange
(phase 1b) is omitted, authorizations and keying material are not (phase 1b) is omitted, authorizations and keying material are not
provided by the backend authentication server, and as a result they provided by the backend authentication server, and as a result they
need to be supplied by other means. This section describes some of need to be supplied by other means. This section describes some of
the implications. the implications.
4.3.1. Key Transport 4.3.1. Key Transport
Where transported keying material is not supplied by the backend Where transported keying material is not supplied by the backend
authentication server, it needs to be provided by another party authentication server, it needs to be provided by another party
authorized to access that keying material. As noted in Section 1.5, authorized to access that keying material. As noted in Section 1.5,
only the EAP peer, authenticator and server are authorized to possess only the EAP peer, authenticator and server are authorized to possess
transported EAP keying material. Since EAP peers do not trust each transported keying material. Since EAP peers do not trust each
other, if the backend authentication server does not supply other, if the backend authentication server does not supply
transported keying material to a new authenticator, it can only be transported keying material to a new authenticator, it can only be
provided by a previous authenticator. provided by a previous authenticator.
As noted in Section 1.5, the goal of the EAP conversation is to As noted in Section 1.5, the goal of the EAP conversation is to
derive session keys known only to the peer and the authenticator. If derive session keys known only to the peer and the authenticator. If
EAP keying material is replicated between a previous authenticator keying material is replicated between a previous authenticator and a
and a new authenticator, then the previous authenticator may new authenticator, then the previous authenticator can possess
potentially know the session keys used between the peer and new session keys used between the peer and new authenticator. Also, the
authenticator. Also, the new authenticator may potentially know the new authenticator can possess session keys used between the peer and
session keys used between the peer and the previous authenticator. the previous authenticator.
If a one-way function is used to derive the keying material to be If a one-way function is used to derive the keying material to be
transported to the new authenticator, then the new authenticator is transported to the new authenticator, then the new authenticator
not longer able to know previous session keys without breaking a cannot possess previous session keys without breaking a fundamental
fundamental cryptographic assumption. cryptographic assumption.
4.3.2. Authorization 4.3.2. Authorization
As a part of the authentication process, the backend authentication As a part of the authentication process, the backend authentication
server determines the user's authorization profile and transmits the server determines the user's authorization profile and transmits the
authorizations to the authenticator along with the transported EAP authorizations to the authenticator along with the transported keying
key material. Typically, the profile is determined based on the user material. Typically, the profile is determined based on the user
identity, but a certificate presented by the user may also provide identity, but a certificate presented by the user can also provide
authorization information. authorization information.
The backend authentication server is responsible for making a user The backend authentication server is responsible for making a user
authorization decision, which requires answering the following authorization decision, which requires answering the following
questions: questions:
(a) Is this a legitimate user of this network? (a) Is this a legitimate user of this network?
(b) Is the user allowed to access this network? (b) Is the user allowed to access this network?
(c) Is the user permitted to access this network on this day and at (c) Is the user permitted to access this network on this day and at
this time? this time?
(d) Is the user within the concurrent session limit? (d) Is the user within the concurrent session limit?
(e) Are there any fraud, credit limit, or other concerns indicating (e) Are there any fraud, credit limit, or other concerns that could
that access should be denied? lead to access denial?
(f) If access is to be granted, what are the service parameters (f) If access is to be granted, what are the service parameters
(mandatory tunneling, bandwidth, filters, and so on) to be (mandatory tunneling, bandwidth, filters, and so on) to be
provisioned for the user? provisioned for the user?
While the authorization decision is in principle simple, the While the authorization decision is in principle simple, the
distributed decision making process may add complexity. Where distributed decision making process can add complexity. Where
brokers or proxies are involved, all of the AAA entities in the chain brokers or proxies are involved, all of the AAA entities in the chain
from the authenticator to the home backend authentication server are from the authenticator to the home backend authentication server are
involved in the decision. For example, a broker can deny access even involved in the decision. For example, a broker can deny access even
if the home backend authentication server would allow it, or a proxy if the home backend authentication server would allow it, or a proxy
can add authorizations (e.g., bandwidth limits). can add authorizations (e.g., bandwidth limits).
Decisions can be based on static policy definitions and profiles as Decisions can be based on static policy definitions and profiles as
well as dynamic state (e.g. time of day or concurrent session well as dynamic state (e.g. time of day or concurrent session
limits). In addition to the Accept/Reject decisions made by AAA limits). In addition to the Accept/Reject decisions made by AAA
entities, service parameters or constraints may be communicated to entities, service parameters or constraints can be communicated to
the authenticator. the authenticator.
The criteria for Accept/Reject decisions or the reasons for choosing The criteria for Accept/Reject decisions or the reasons for choosing
particular authorizations are typically not communicated to the particular authorizations are typically not communicated to the
authenticator, only the final result. As a result, the authenticator authenticator, only the final result. As a result, the authenticator
has no way to know what the decision was based on. Was a set of has no way to know what the decision was based on. Was a set of
authorization parameters sent because this service is always provided authorization parameters sent because this service is always provided
to the user, or was the decision based on the time of day and the to the user, or was the decision based on the time of day and the
capabilities of the authenticator? capabilities of the authenticator?
4.3.3. Correctness 4.3.3. Correctness
When the AAA exchange (phase 1b) is bypassed, several challenges When the AAA exchange (phase 1b) is bypassed, several challenges
arise in ensuring correct authorization: arise in ensuring correct authorization:
Theft of service Theft of service
Bypassing the AAA exchange (phase 1b) should not enable a user to Bypassing the AAA exchange (phase 1b) SHOULD NOT enable a user to
extend their network access or gain access to services they are not extend their network access or gain access to services they are not
entitled to. entitled to.
Consideration of network-wide state Consideration of network-wide state
Handoff techniques should not render the backend authentication Handoff techniques SHOULD NOT render the backend authentication
server incapable of keeping track of network-wide state. For server incapable of keeping track of network-wide state. For
example, a backend authentication server may need to keep track of example, a backend authentication server can need to keep track of
simultaneous user sessions. simultaneous user sessions.
Elevation of privilege Elevation of privilege
Backend authentication servers often perform conditional Backend authentication servers often perform conditional
evaluation, in which the authorizations returned in an Access- evaluation, in which the authorizations returned in an Access-
Accept message are contingent on the authenticator or on dynamic Accept message are contingent on the authenticator or on dynamic
state such as the time of day. In this situation, bypassing the state such as the time of day. In this situation, bypassing the
AAA exchange could enable unauthorized access unless the AAA exchange could enable unauthorized access unless the
restrictions are explicitly encoded within the authorizations restrictions are explicitly encoded within the authorizations
provided by the backend authentication server. provided by the backend authentication server.
skipping to change at page 42, line 29 skipping to change at page 45, line 10
In order to perform a correct handoff, if a new authenticator is In order to perform a correct handoff, if a new authenticator is
provided with RADIUS authorizations for a known but unavailable provided with RADIUS authorizations for a known but unavailable
service, then it MUST process these authorizations the same way it service, then it MUST process these authorizations the same way it
would handle a RADIUS Access-Accept requesting an unavailable would handle a RADIUS Access-Accept requesting an unavailable
service; this MUST cause the handoff to fail. However, if a new service; this MUST cause the handoff to fail. However, if a new
authenticator is provided with authorizations including unknown authenticator is provided with authorizations including unknown
attributes, then these attributes MAY be ignored. The definition of attributes, then these attributes MAY be ignored. The definition of
a "known but unsupported service" MUST encompass requests for a "known but unsupported service" MUST encompass requests for
unavailable security services. This includes vendor-specific unavailable security services. This includes vendor-specific
attributes related to security, such as those described in [RFC2548]. attributes related to security, such as those described in [RFC2548].
Although it may seem somewhat counter-intuitive, failure is indeed Although it can seem somewhat counter-intuitive, failure is indeed
the "correct" result where a known but unsupported service is the "correct" result where a known but unsupported service is
requested. requested.
Presumably a correctly configured backend authentication server would Presumably a correctly configured backend authentication server would
not request that an authenticator provide a service that it does not not request that an authenticator provide a service that it does not
implement. This implies that if the new authenticator were to implement. This implies that if the new authenticator were to
complete a AAA conversation, it would be likely to receive different complete a AAA conversation, it would be likely to receive different
service instructions. Failure of the handoff is the desired result service instructions. Failure of the handoff is the desired result
since it will cause the new authenticator to go back to the backend since it will cause the new authenticator to go back to the backend
server in order to receive the appropriate service definition. server in order to receive the appropriate service definition.
Handoff mechanisms which bypass the backend authentication server are Handoff mechanisms which bypass the backend authentication server are
most likely to be successful when employed in a homogeneous most likely to be successful when employed in a homogeneous
deployment within a single administrative domain. In a heterogeneous deployment within a single administrative domain. In a heterogeneous
deployment, the backend authentication server may return different deployment, the backend authentication server can return different
authorizations depending on the authenticator making the request, in authorizations depending on the authenticator making the request, in
order to make sure that the requested service is consistent with the order to make sure that the requested service is consistent with the
authenticator capabilities. Where a backend authentication server authenticator capabilities. Where a backend authentication server
would send different authorizations to the new authenticator than would send different authorizations to the new authenticator than
were sent to a previous authenticator, transferring authorizations were sent to a previous authenticator, transferring authorizations
between the previous authenticator and the new authenticator will between the previous authenticator and the new authenticator will
result in incorrect authorization. result in incorrect authorization.
Virtual LAN (VLAN) support is defined in [IEEE-802.1Q]; RADIUS Virtual LAN (VLAN) support is defined in [IEEE-802.1Q]; RADIUS
support for dynamic VLANs is described in [RFC3580] and [RFC4675]. support for dynamic VLANs is described in [RFC3580] and [RFC4675].
skipping to change at page 43, line 18 skipping to change at page 45, line 47
then attributes present in the Access-Request (such as the NAS-Port- then attributes present in the Access-Request (such as the NAS-Port-
Type, NAS-IP-Address, NAS-IPv6-Address and NAS-Identifier) could be Type, NAS-IP-Address, NAS-IPv6-Address and NAS-Identifier) could be
examined by the backend authentication server to determine when VLAN examined by the backend authentication server to determine when VLAN
attributes will be returned, and if so, which ones. However, if the attributes will be returned, and if so, which ones. However, if the
backend authenticator is bypassed, then a handoff occurring between backend authenticator is bypassed, then a handoff occurring between
authenticators supporting different VLAN capabilities could result in authenticators supporting different VLAN capabilities could result in
a user obtaining access to an unauthorized VLAN (e.g. a user with a user obtaining access to an unauthorized VLAN (e.g. a user with
access to a guest VLAN being given unrestricted access to the access to a guest VLAN being given unrestricted access to the
network). network).
Similarly, a handoff between an authenticator providing Similarly, it is preferable for a handoff between an authenticator
confidentiality and another that does not should fail, since if the providing confidentiality and another that does not to fail, since if
handoff were successful, the user would be moved from a secure to an the handoff were successful, the user would be moved from a secure to
insecure channel without permission from the backend authentication an insecure channel without permission from the backend
server. authentication server.
5. Security Considerations 5. Security Considerations
The EAP threat model is described in [RFC3748] Section 7.1. The The EAP threat model is described in [RFC3748] Section 7.1. The
security properties of EAP methods (known as "security claims") are security properties of EAP methods (known as "security claims") are
described in [RFC3748] Section 7.2.1. EAP method requirements for described in [RFC3748] Section 7.2.1. EAP method requirements for
applications such as Wireless LAN authentication are described in applications such as Wireless LAN authentication are described in
[RFC4017]. The RADIUS threat model is described in [RFC3579] Section [RFC4017]. The RADIUS threat model is described in [RFC3579] Section
4.1, and responses to these threats are described in [RFC3579] 4.1, and responses to these threats are described in [RFC3579]
Sections 4.2 and 4.3. Sections 4.2 and 4.3.
However, in addition to threats against EAP and AAA, there are other However, in addition to threats against EAP and AAA, there are other
system level threats. In developing the threat model, it is assumed system level threats. In developing the threat model, it is assumed
that: that:
All traffic is visible to the attacker. All traffic is visible to the attacker.
The attacker can alter, forge or replay messages. The attacker can alter, forge or replay messages.
The attacker can reroute messages to another principal. The attacker can reroute messages to another principal.
The attacker may be a principal or an outsider. The attacker can be a principal or an outsider.
The attacker can compromise any key that is sufficiently old. The attacker can compromise any key that is sufficiently old.
Threats arising from these assumptions include: Threats arising from these assumptions include:
(a) An attacker may compromise or steal an EAP peer or authenticator, (a) An attacker can compromise or steal an EAP peer or authenticator,
in an attempt to gain access to other EAP peers or authenticators in an attempt to gain access to other EAP peers or authenticators
or to obtain long-term secrets. or to obtain long-term secrets.
(b) An attacker may attempt a downgrade attack in order to exploit (b) An attacker can attempt a downgrade attack in order to exploit
known weaknesses in an authentication method or cryptographic known weaknesses in an authentication method or cryptographic
algorithm. algorithm.
(c) An attacker may try to modify or spoof packets, including Discovery (c) An attacker can try to modify or spoof packets, including Discovery
or Secure Association Protocol frames, EAP or AAA packets. or Secure Association Protocol frames, EAP or AAA packets.
(d) An attacker may attempt to induce an EAP peer, authenticator or (d) An attacker can attempt to induce an EAP peer, authenticator or
server to disclose keying material to an unauthorized party, or server to disclose keying material to an unauthorized party, or
utilize keying material outside the context that it was intended utilize keying material outside the context that it was intended
for. for.
(e) An attacker may alter, forge or replay packets. (e) An attacker can alter, forge or replay packets.
(f) An attacker may cause an EAP peer, authenticator or server to reuse (f) An attacker can cause an EAP peer, authenticator or server to reuse
a stale key. Use of stale keys may also occur unintentionally. a stale key. Use of stale keys can also occur unintentionally.
For example, a poorly implemented backend authentication server may For example, a poorly implemented backend authentication server can
provide stale keying material to an authenticator, or a poorly provide stale keying material to an authenticator, or a poorly
implemented authenticator may reuse nonces. implemented authenticator can reuse nonces.
(g) An authenticated attacker may attempt to obtain elevated privilege (g) An authenticated attacker can attempt to obtain elevated privilege
in order to access information that it does not have rights to. in order to access information that it does not have rights to.
(h) An attacker may attempt a man-in-the-middle attack in order to gain (h) An attacker can attempt a man-in-the-middle attack in order to gain
access to the network. access to the network.
(i) An attacker may compromise an EAP authenticator in an effort to (i) An attacker can compromise an EAP authenticator in an effort to
commit fraud. For example, a compromised authenticator may provide commit fraud. For example, a compromised authenticator can provide
incorrect information to the EAP peer and/or server via out-of-band incorrect information to the EAP peer and/or server via out-of-band
mechanisms (such as via a AAA or lower layer protocol). This mechanisms (such as via a AAA or lower layer protocol). This
includes impersonating another authenticator, or providing includes impersonating another authenticator, or providing
inconsistent information to the peer and EAP server. inconsistent information to the peer and EAP server.
(j) An attacker may launch a denial of service attack against the EAP (j) An attacker can launch a denial of service attack against the EAP
peer, authenticator or backend authentication server. peer, authenticator or backend authentication server.
In order to address these threats, [I-D.housley-aaa-key-mgmt] Section In order to address these threats, [RFC4962] Section 3 describes
3 provides a description of mandatory system security properties. required and recommended security properties. The sections that
These requirements are discussed in the sections that follow. follow analyze the compliance of EAP methods, AAA protocols and
Secure Association Protocols with those guidelines.
5.1. Peer and Authenticator Compromise 5.1. Peer and Authenticator Compromise
Requirement: In the event that an authenticator is compromised or Requirement: In the event that an authenticator is compromised or
stolen, an attacker may gain access to the network through that stolen, an attacker can gain access to the network through that
authenticator, or may obtain the credentials required for the authenticator, or can obtain the credentials needed for the
authenticator/AAA client to communicate with one or more backend authenticator/AAA client to communicate with one or more backend
authentication servers. Similarly, if a peer is compromised or authentication servers. Similarly, if a peer is compromised or
stolen, an attacker may obtain credentials required to communicate stolen, an attacker can obtain credentials needed to communicate with
with one or more authenticators. Compromise of a single peer MUST one or more authenticators. Mandatory requirement from [RFC4962]
NOT compromise keying material held by any other peer within the Section 3:
system, including session keys and long-term keys, with the possible
exception of group keys. Likewise, compromise of a single Prevent the Domino effect
authenticator MUST NOT compromise keying material held by any other
authenticator within the system. In the context of a key hierarchy, Compromise of a single peer MUST NOT compromise keying material
this means that the compromise of one node in the key hierarchy must held by any other peer within the system, including session keys
not disclose the information necessary to compromise other branches and long-term keys. Likewise, compromise of a single
in the key hierarchy. Obviously, the compromise of the root of the authenticator MUST NOT compromise keying material held by any
key hierarchy will compromise all of the keys; however, a compromise other authenticator within the system. In the context of a key
in one branch MUST NOT result in the compromise of other branches. hierarchy, this means that the compromise of one node in the key
There are many implications of this requirement; however, two hierarchy must not disclose the information necessary to
implications deserve highlighting. First, the scope of the keying compromise other branches in the key hierarchy. Obviously, the
material must be defined and understood by all parties that compromise of the root of the key hierarchy will compromise all of
communicate with a party that holds that keying material. Second, a the keys; however, a compromise in one branch MUST NOT result in
party that holds keying material in a key hierarchy must not share the compromise of other branches. There are many implications of
that keying material with parties that are associated with other this requirement; however, two implications deserve highlighting.
branches in the key hierarchy. First, the scope of the keying material must be defined and
understood by all parties that communicate with a party that holds
that keying material. Second, a party that holds keying material
in a key hierarchy must not share that keying material with
parties that are associated with other branches in the key
hierarchy.
Group keys are an obvious exception. Since all members of the
group have a copy of the same key, compromise of any one of the
group members will result in the disclosure of the group key.
Some of the implications of the requirement are as follows: Some of the implications of the requirement are as follows:
No Key Sharing No Key Sharing
An EAP authenticator MUST NOT share any keying material with An EAP authenticator MUST NOT share any keying material with
another EAP authenticator, since if one EAP authenticator were another EAP authenticator, since if one EAP authenticator were
compromised, this would enable the compromise of keying material on compromised, this would enable the compromise of keying material on
another authenticator. In order to be able to determine whether another authenticator. In order to be able to determine whether
keying material has been shared, it is necessary for the identity keying material has been shared, it is necessary for the identity
of the EAP authenticator to be defined and understood by all of the EAP authenticator (NAS-Identifier) to be defined and
parties that communicate with it. Similarly, an EAP peer MUST NOT understood by all parties that communicate with it. Similarly, an
share any keying material with another EAP peer. EAP peer MUST NOT share any keying material with another EAP peer.
EAP lower layer specifications such as [IEEE-802.11],
[IEEE-802.16e], [IEEE-802.1X], IKEv2 [RFC4306] and PPP [RFC1661] do
not involve key sharing.
No AAA Credential Sharing No AAA Credential Sharing
AAA credentials (such as RADIUS shared secrets, IPsec pre-shared AAA credentials (such as RADIUS shared secrets, IPsec pre-shared
keys or certificates) MUST NOT be shared between AAA clients, since keys or certificates) MUST NOT be shared between AAA clients, since
if one AAA client were compromised, this would enable an attacker if one AAA client were compromised, this would enable an attacker
to impersonate other AAA clients to the backend authentication to impersonate other AAA clients to the backend authentication
server, or even to impersonate a backend authentication server to server, or even to impersonate a backend authentication server to
other AAA clients. other AAA clients.
No Compromise of Long-Term Credentials No Compromise of Long-Term Credentials
An attacker obtaining TSKs, TEKs or EAP keying material such as the An attacker obtaining keying material (such as TSKs, TEKs or the
MSK MUST NOT be able to obtain long-term user credentials such as MSK) MUST NOT be able to obtain long-term user credentials such as
pre-shared keys, passwords or private-keys without breaking a pre-shared keys, passwords or private-keys without breaking a
fundamental cryptographic assumption. fundamental cryptographic assumption. The mandatory requirements
of [RFC4017] Section 2.2 include generation of EAP keying material,
capability to generate EAP keying material with 128-bits of
effective strength, resistance to dictionary attacks, shared state
equivalence and protection against man-in-the-middle attacks.
5.2. Cryptographic Negotiation 5.2. Cryptographic Negotiation
Requirement: The ability to negotiate cryptographic algorithms Mandatory requirements from [RFC4962] Section 3:
resilience against compromise of a particular algorithm. This is
usually accomplished by including an algorithm identifier and
parameters in the protocol, and by specifying the algorithm
requirements in the protocol specification. While highly desirable,
the ability to negotiate key derivation functions (KDFs) is not
required. For interoperability, at least one suite of mandatory-to-
implement algorithms MUST be selected. The selection of the "best"
cryptographic algorithm SHOULD be securely confirmed. The mechanism
SHOULD detect attempted roll back attacks.
EAP methods satisfying [RFC4017] requirements and AAA protocols Cryptographic algorithm independent
utilizing transmission layer security are capable of addressing
downgrade attacks. [RFC3748] Section 7.2.1 describes the "protected The AAA key management protocol MUST be cryptographic algorithm
ciphersuite negotiation" security claim that refers to the ability of independent. However, an EAP method MAY depend on a specific
an EAP method to negotiate the ciphersuite used to protect the EAP cryptographic algorithm. The ability to negotiate the use of a
method conversation, as well as to integrity protect the ciphersuite particular cryptographic algorithm provides resilience against
negotiation. [RFC4017] requires EAP methods satisfying this security compromise of a particular cryptographic algorithm. Algorithm
claim. However, EAP methods may not enable the negotiation of all independence is also REQUIRED with a Secure Association Protocol
cryptographic algorithms, such as Key Distribution Functions (KDFs). if one is defined. This is usually accomplished by including an
algorithm identifier and parameters in the protocol, and by
specifying the algorithm requirements in the protocol
specification. While highly desirable, the ability to negotiate
key derivation functions (KDFs) is not required. For
interoperability, at least one suite of mandatory-to-implement
algorithms MUST be selected. Note that without protection by
IPsec as described in [RFC3579] Section 4.2, RADIUS [RFC2865] does
not meet this requirement, since the integrity protection
algorithm cannot be negotiated.
This requirement does not mean that a protocol must support both
public-key and symmetric-key cryptographic algorithms. It means
that the protocol needs to be structured in such a way that
multiple public-key algorithms can be used whenever a public-key
algorithm is employed. Likewise, it means that the protocol needs
to be structured in such a way that multiple symmetric-key
algorithms can be used whenever a symmetric-key algorithm is
employed.
Confirm ciphersuite selection
The selection of the "best" ciphersuite SHOULD be securely
confirmed. The mechanism SHOULD detect attempted roll-back
attacks.
EAP methods satisfying [RFC4017] Section 2.2 mandatory requirements
and AAA protocols utilizing transmission layer security are capable
of addressing downgrade attacks. [RFC3748] Section 7.2.1 describes
the "protected ciphersuite negotiation" security claim that refers to
the ability of an EAP method to negotiate the ciphersuite used to
protect the EAP method conversation, as well as to integrity protect
the ciphersuite negotiation. [RFC4017] Section 2.2 requires EAP
methods satisfying this security claim. Since TLS v1.2 [I-D.ietf-
tls-rfc4346-bis] supports negotiation of Key Distribution Functions
(KDFs), EAP methods based on TLS will, if properly designed, inherit
this capability. However, negotiation of KDFs is not required by RFC
4962 [RFC4962], and EAP methods not based on TLS typically do not
support KDF negotiation.
Diameter [RFC3588] provides support for cryptographic algorithm Diameter [RFC3588] provides support for cryptographic algorithm
negotiation via use of IPsec [RFC4301] or TLS [RFC4346]. RADIUS negotiation via use of IPsec [RFC4301] or TLS [RFC4346]. Since IKEv2
[RFC3579] does not support the negotiation of cryptographic [RFC4306] does not support KDF negotiation, support for KDF
algorithms, and relies on MD5 for integrity protection, negotiation is only available when Diameter runs over TLS v1.2.
authentication and confidentiality, despite known weaknesses in the RADIUS [RFC3579] does not support cryptographic algorithm negotiation
algorithm [MD5Collision]. This issue can be addressed via use of and relies on MD5 for integrity protection, authentication and
RADIUS over IPsec, as described in [RFC3579] Section 4.2. However, confidentiality. Given the known weaknesses in MD5 [MD5Collision]
TLS and IKEv2 currently do not enable negotiation of the Key this is undesirable, and can be addressed via use of RADIUS over
Distribution Function (KDF). IPsec, as described in [RFC3579] Section 4.2.
To ensure against downgrade attacks within lower layer protocols, To ensure against downgrade attacks within lower layer protocols,
algorithm independence is REQUIRED with lower layers using EAP for algorithm independence is REQUIRED with lower layers using EAP for
key derivation. For interoperability, at least one suite of key derivation. For interoperability, at least one suite of
mandatory-to-implement algorithm MUST be selected. Lower layer mandatory-to-implement algorithm MUST be selected. Lower layer
protocols supporting EAP for key derivation SHOULD also support protocols supporting EAP for key derivation SHOULD also support
secure ciphersuite negotiation. As described in [RFC1968], PPP ECP secure ciphersuite negotiation as well as KDF negotiation.
does not provide support for secure ciphersuite negotiation. While
[IEEE-802.16e] and [IEEE-802.11i] support selection of ciphersuites As described in [RFC1968], PPP ECP does not support secure
for protection of data, they do not support negotiation of the ciphersuite negotiation. While [IEEE 802.16e] and [IEEE-802.11]
cryptographic primitives used within the Secure Association Protocol, support ciphersuite negotiation for protection of data, they do not
such as message integrity checks (MICs) and KDFs. support negotiation of the cryptographic primitives used within the
Secure Association Protocol, such as message integrity checks (MICs)
and KDFs.
5.3. Confidentiality and Authentication 5.3. Confidentiality and Authentication
Requirement: Each party in the EAP, AAA and Secure Association Requirement: Each party in the EAP, AAA and Secure Association
Protocol conversations MUST be authenticated to the other parties Protocol conversations MUST be authenticated to the other parties
with whom they communicate. Authentication mechanisms MUST maintain with whom they communicate. Mandatory requirements from [RFC4962]
the confidentiality of any secret values used in the authentication Section 3:
process. When a Secure Association Protocol is used to establish
session keys, the parties involved in the secure association protocol Authenticate all parties
MUST identify themselves using identities that are meaningful in the
lower layer protocol environment that will employ the session keys. Authentication mechanisms MUST maintain the confidentiality of any
secret values used in the authentication process. When a secure
association protocol is used to establish session keys, the
parties involved in the secure association protocol MUST identify
themselves using identities that are meaningful in the lower-layer
protocol environment that will employ the session keys. In this
situation, the authenticator and peer may be known by different
identifiers in the AAA protocol environment and the lower-layer
protocol environment, making authorization decisions difficult
without a clear key scope. If the lower-layer identifier of the
peer will be used to make authorization decisions, then the pair
of identifiers associated with the peer MUST be authorized by the
authenticator and/or the AAA server.
AAA protocols, such as RADIUS [RFC2865] and Diameter [RFC3588],
provide a mechanism for the identification of AAA clients; since
the EAP authenticator and AAA client are always co- resident, this
mechanism is applicable to the identification of EAP
authenticators.
When multiple base stations and a "controller" (such as a WLAN
switch) comprise a single EAP authenticator, the "base station
identity" is not relevant; the EAP method conversation takes place
between the EAP peer and the EAP server. Also, many base stations
can share the same authenticator identity. The authenticator
identity is important in the AAA protocol exchange and the secure
association protocol conversation.
Authentication mechanisms MUST NOT employ plaintext passwords.
Passwords may be used provided that they are not sent to another
party without confidentiality protection.
Keying material confidentiality and integrity
While preserving algorithm independence, confidentiality and While preserving algorithm independence, confidentiality and
integrity of all keying material MUST be maintained. integrity of all keying material MUST be maintained.
Conformance to these requirements are analyzed in the sections that
follow.
5.3.1. Spoofing 5.3.1. Spoofing
Per-packet authentication and integrity protection provides Per-packet authentication and integrity protection provides
protection against spoofing attacks. protection against spoofing attacks.
Diameter [RFC3588] provides support for per-packet authentication and Diameter [RFC3588] provides support for per-packet authentication and
integrity protection via use of IPsec or TLS. RADIUS/EAP [RFC3579] integrity protection via use of IPsec or TLS. RADIUS/EAP [RFC3579]
provides for per-packet authentication and integrity protection via provides for per-packet authentication and integrity protection via
use of the Message-Authenticator attribute. use of the Message-Authenticator attribute.
[RFC3748] Section 7.2.1 describes the "integrity protection" security [RFC3748] Section 7.2.1 describes the "integrity protection" security
claim and [RFC4017] requires use of EAP methods supporting this claim and [RFC4017] Section 2.2 requires EAP methods supporting this
claim. claim.
In order to prevent forgery of Secure Association Protocol frames, In order to prevent forgery of Secure Association Protocol frames,
per-frame authentication and integrity protection is RECOMMENDED on per-frame authentication and integrity protection is RECOMMENDED on
all messages. IKEv2 [RFC4306] supports per-frame integrity all messages. IKEv2 [RFC4306] supports per-frame integrity
protection and authentication, as does [IEEE-802.16e]. protection and authentication, as does the Secure Association
[IEEE-802.11i] supports per-frame integrity protection and Protocol defined in [IEEE-802.16e]. [IEEE-802.11] supports per-frame
authentication on all messages within the 4-way handshake except the integrity protection and authentication on all messages within the
first message. An attack leveraging this omission is described in 4-way handshake except the first message. An attack leveraging this
[Analysis]. omission is described in [Analysis].
5.3.2. Impersonation 5.3.2. Impersonation
Both the RADIUS [RFC2865] and Diameter [RFC3588] protocols are Both RADIUS [RFC2865] and Diameter [RFC3588] implementations are
potentially vulnerable to a rogue authenticator impersonating another potentially vulnerable to a rogue authenticator impersonating another
authenticator. While both protocols support mutual authentication authenticator. While both protocols support mutual authentication
between the AAA client/authenticator and the backend authentication between the AAA client/authenticator and the backend authentication
server, the security mechanisms vary. server, the security mechanisms vary.
In RADIUS, the shared secret used for authentication is determined by In RADIUS, the shared secret used for authentication is determined by
the source address of the RADIUS packet. As noted in [RFC3579] the source address of the RADIUS packet. However, when RADIUS
Section 4.3.7, it is highly desirable that the source address be Access-Requests are forwarded by a proxy, the NAS-IP-Address, NAS-
checked against one or more Network Access Server (NAS) client Identifier or NAS-IPv6-Address attributes received by the RADIUS
identification attributes so as to detect and prevent impersonation server will not correspond to the source address. As noted in
attacks. [RFC3579] Section 4.3.7, if the first-hop proxy does not check the
NAS identification attributes against the source address in the
When RADIUS Access-Requests are forwarded by a proxy, the NAS-IP- Access-Request packet, it is possible for a rogue authenticator to
Address or NAS-IPv6-Address attributes may not correspond to the forge NAS-IP-Address [RFC2865], NAS-IPv6-Address [RFC3162] or NAS-
source address. Since the NAS-Identifier attribute need not contain Identifier [RFC2865] attributes in order to impersonate another
an FQDN, it also may not correspond to the source address, even authenticator; attributes such as the Called-Station-Id [RFC2865] and
indirectly. [RFC2865] Section 3 states: Calling-Station-Id [RFC2865] can be forged as well. Among other
things, this can result in messages (and transported keying material)
A RADIUS server MUST use the source IP address of the RADIUS UDP being sent to the wrong authenticator.
packet to decide which shared secret to use, so that RADIUS
requests can be proxied.
This implies that it is possible for a rogue authenticator to forge
NAS-IP-Address, NAS-IPv6-Address or NAS-Identifier attributes within
a RADIUS Access-Request in order to impersonate another
authenticator. Among other things, this can result in messages (and
transported keying material) being sent to the wrong authenticator.
Since the rogue authenticator is authenticated by the RADIUS proxy or
server purely based on the source address, other mechanisms are
required to detect the forgery. In addition, it is possible for
attributes such as the Called-Station-Id and Calling-Station-Id to be
forged as well.
[RFC3579] Section 4.3.7 describes how an EAP pass-through
authenticator acting as a AAA client can be detected if it attempts
to impersonate another authenticator (such by sending incorrect
Called-Station-Id [RFC2865], NAS-Identifier [RFC2865], NAS-IP-Address
[RFC2865] or NAS-IPv6-Address [RFC3162] attributes via the AAA
protocol). This vulnerability can be mitigated by having RADIUS
proxies check NAS identification attributes against the source
address.
While [RFC3588] requires use of the Route-Record AVP, this utilizes While [RFC3588] requires use of the Route-Record AVP, this utilizes
Fully Qualified Domain Names (FQDNs), so that impersonation detection Fully Qualified Domain Names (FQDNs), so that impersonation detection
requires DNS A, AAAA and PTR Resource Records (RRs) to be properly requires DNS A, AAAA and PTR Resource Records (RRs) to be properly
configured. As a result, Diameter is as vulnerable to this attack as configured. As a result, Diameter is as vulnerable to this attack as
RADIUS, if not more so. To address this vulnerability, it is RADIUS, if not more so. [RFC3579] Section 4.3.7 recommends
necessary to allow the backend authentication server to communicate mechanisms for impersonation detection; to prevent access to keying
with the authenticator directly, such as via the redirect material by proxies without a "need to know", it is necessary to
functionality supported in [RFC3588]. allow the backend authentication server to communicate with the
authenticator directly, such as via the redirect functionality
supported in [RFC3588].
5.3.3. Channel Binding 5.3.3. Channel Binding
It is possible for a compromised or poorly implemented EAP It is possible for a compromised or poorly implemented EAP
authenticator to communicate incorrect information to the EAP peer authenticator to communicate incorrect information to the EAP peer
and/or server. This may enable an authenticator to impersonate and/or server. This can enable an authenticator to impersonate
another authenticator or communicate incorrect information via out- another authenticator or communicate incorrect information via out-
of-band mechanisms (such as via AAA or the lower layer). of-band mechanisms (such as via AAA or the lower layer).
Where EAP is used in pass-through mode, the EAP peer does not verify Where EAP is used in pass-through mode, the EAP peer does not verify
the identity of the pass-through authenticator within the EAP the identity of the pass-through authenticator within the EAP
conversation. Within the Secure Association Protocol, the EAP peer conversation. Within the Secure Association Protocol, the EAP peer
and authenticator only demonstrate mutual possession of the and authenticator only demonstrate mutual possession of the
transported EAP keying material; they do not mutually authenticate. transported keying material; they do not mutually authenticate. This
This creates a potential security vulnerability, described in creates a potential security vulnerability, described in [RFC3748]
[RFC3748] Section 7.15. Section 7.15.
As described in the previous section, it is possible for a AAA proxy As described in [RFC3579] Section 4.3.7, it is possible for a first-
to detect a AAA client attempting to impersonate another hop AAA proxy to detect a AAA client attempting to impersonate
authenticator (such by sending incorrect Called-Station-Id [RFC2865], another authenticator. However, it is possible for a pass-through
NAS-Identifier [RFC2865], NAS-IP-Address [RFC2865] or NAS- authenticator acting as a AAA client to provide correct information
IPv6-Address [RFC3162] attributes via the AAA protocol). However, it to the backend authentication server while communicating misleading
is possible for a pass-through authenticator acting as a AAA client information to the EAP peer via the lower layer.
to provide correct information to the backend authentication server
while communicating misleading information to the EAP peer via the
lower layer.
For example, a compromised authenticator can utilize another For example, a compromised authenticator can utilize another
authenticator's Called-Station-Id or NAS-Identifier in communicating authenticator's Called-Station-Id or NAS-Identifier in communicating
with the EAP peer via the lower layer. Also, a pass-through with the EAP peer via the lower layer. Also, a pass-through
authenticator acting as a AAA client can provide an incorrect peer authenticator acting as a AAA client can provide an incorrect peer
Calling-Station-Id [RFC2865][RFC3580] to the backend authentication Calling-Station-Id [RFC2865][RFC3580] to the backend authentication
server via the AAA protocol. server via the AAA protocol.
As noted in [RFC3748] Section 7.15, this vulnerability can be As noted in [RFC3748] Section 7.15, this vulnerability can be
addressed by EAP methods that support a protected exchange of channel addressed by EAP methods that support a protected exchange of channel
properties such as endpoint identifiers, including (but not limited properties such as endpoint identifiers, including (but not limited
to): Called-Station-Id [RFC2865][RFC3580], Calling-Station-Id to): Called-Station-Id [RFC2865][RFC3580], Calling-Station-Id
[RFC2865][RFC3580], NAS-Identifier [RFC2865], NAS-IP-Address [RFC2865][RFC3580], NAS-Identifier [RFC2865], NAS-IP-Address
[RFC2865], and NAS-IPv6-Address [RFC3162]. [RFC2865], and NAS-IPv6-Address [RFC3162].
Using such a protected exchange, it is possible to match the channel Using such a protected exchange, it is possible to match the channel
properties provided by the authenticator via out-of-band mechanisms properties provided by the authenticator via out-of-band mechanisms
against those exchanged within the EAP method. Typically the EAP against those exchanged within the EAP method. Typically the EAP
method imports Channel Binding parameters from the lower layer on the method imports channel binding parameters from the lower layer on the
peer, and transmits them securely to the EAP server, which exports peer, and transmits them securely to the EAP server, which exports
them to the lower layer or AAA layer. However, transport may occur them to the lower layer or AAA layer. However, transport can occur
from EAP server to peer, or may be bi-directional. On the side of from EAP server to peer, or can be bi-directional. On the side of
the exchange (peer or server) where Channel Binding is verified, the the exchange (peer or server) where Channel Binding is verified, the
lower layer or AAA layer passes the result of the verification (TRUE lower layer or AAA layer passes the result of the verification (TRUE
or FALSE) up to the EAP method. While the verification can be done or FALSE) up to the EAP method. While the verification can be done
either by the peer or the server, typically only the server has the either by the peer or the server, typically only the server has the
knowledge to determine the correctness of the values, as opposed to knowledge to determine the correctness of the values, as opposed to
merely verifying their equality. For further discussion, see [I- merely verifying their equality. For further discussion, see
D.arkko-eap-service-identity-auth]. [I-D.arkko-eap-service-identity-auth].
It is also possible to perform Channel Binding without transporting It is also possible to perform Channel Binding without transporting
data over EAP. For example, see [I-D.draft-ohba-eap-channel- data over EAP, as described in [I-D.ohba-eap-channel-binding]. In
binding]. In this approach the EAP method includes Channel Binding this approach the EAP method includes channel binding parameters in
parameters in the calculation of exported EAP keying material, making the calculation of exported EAP keying material, making it impossible
it impossible for the peer and authenticator to complete the Secure for the peer and authenticator to complete the Secure Association
Association Protocol if there is a mismatch in the Channel Binding Protocol if there is a mismatch in the channel binding parameters.
parameters. However, this approach can only be applied where EAP However, this approach can only be applied where methods generating
methods generating key material are used along with lower layers that EAP keying material are used along with lower layers that utilize EAP
utilize the keying material. For example, this mechanism would not keying material. For example, this mechanism would not enable
enable verification of Channel Binding on wired IEEE 802 networks verification of Channel Binding on wired IEEE 802 networks using
using [IEEE 802.1X]. [IEEE-802.1X].
5.3.4. Mutual Authentication 5.3.4. Mutual Authentication
[RFC3748] Section 7.2.1 describes the "mutual authentication" and [RFC3748] Section 7.2.1 describes the "mutual authentication" and
"dictionary attack resistance" claims, and [RFC4017] requires EAP "dictionary attack resistance" claims, and [RFC4017] requires EAP
methods satisfying these claims. EAP methods complying with methods satisfying these claims. EAP methods complying with
[RFC4017] therefore provide for mutual authentication between the EAP [RFC4017] therefore provide for mutual authentication between the EAP
peer and server. peer and server.
[RFC3748] Section 7.2.1 also describes the "Cryptographic binding" [RFC3748] Section 7.2.1 also describes the "Cryptographic binding"
security claim, and [RFC4017] requires support for this claim. As security claim, and [RFC4017] Section 2.2 requires support for this
described in [I-D.puthenkulam-eap-binding], EAP method sequences and claim. As described in [I-D.puthenkulam-eap-binding], EAP method
compound authentication mechanisms may be subject to man-in-the- sequences and compound authentication mechanisms can be subject to
middle attacks. When such attacks are successfully carried out, the man-in-the-middle attacks. When such attacks are successfully
attacker acts as an intermediary between a victim and a legitimate carried out, the attacker acts as an intermediary between a victim
authenticator. This allows the attacker to authenticate successfully and a legitimate authenticator. This allows the attacker to
to the authenticator, as well as to obtain access to the network. authenticate successfully to the authenticator, as well as to obtain
access to the network.
In order to prevent these attacks, [I-D.puthenkulam-eap-binding] In order to prevent these attacks, [I-D.puthenkulam-eap-binding]
recommends derivation of a compound key by which the EAP peer and recommends derivation of a compound key by which the EAP peer and
server can prove that they have participated in the entire EAP server can prove that they have participated in the entire EAP
exchange. Since the compound key must not be known to an attacker exchange. Since the compound key MUST NOT be known to an attacker
posing as an authenticator, and yet must be derived from quantities posing as an authenticator, and yet must be derived from EAP keying
that are exported by EAP methods, it may be desirable to derive the material, it MAY be desirable to derive the compound key from a
compound key from a portion of the EMSK. In order to provide proper portion of the EMSK. Where this is done, in order to provide proper
key hygiene, it is recommended that the compound key used for man-in- key hygiene, it is RECOMMENDED that the compound key used for man-in-
the-middle protection be cryptographically separate from other keys the-middle protection be cryptographically separate from other keys
derived from the EMSK. derived from the EMSK.
Diameter [RFC3588] provides for per-packet authentication and Diameter [RFC3588] provides for per-packet authentication and
integrity protection via IPsec or TLS, and RADIUS/EAP [RFC3579] also integrity protection via IPsec or TLS, and RADIUS/EAP [RFC3579] also
provides for per-packet authentication and integrity protection. provides for per-packet authentication and integrity protection.
Where the authenticator/AAA client and backend authentication server Where the authenticator/AAA client and backend authentication server
communicate directly and credible keywrap is used (see Section 3.8), communicate directly and credible keywrap is used (see Section 3.8),
this ensures that the AAA Key Transport (phase 1b) achieves its this ensures that the AAA Key Transport (phase 1b) achieves its
security objectives: mutually authenticating the AAA security objectives: mutually authenticating the AAA
client/authenticator and backend authentication server and providing client/authenticator and backend authentication server and providing
EAP keying material to the EAP authenticator and to no other party. transported keying material to the EAP authenticator and to no other
party.
[RFC2607] Section 7 describes the security issues occurring when the [RFC2607] Section 7 describes the security issues occurring when the
authenticator/AAA client and backend authentication server do not authenticator/AAA client and backend authentication server do not
communicate directly. Where a AAA intermediary is present (such as a communicate directly. Where a AAA intermediary is present (such as a
RADIUS proxy or a Diameter agent), and data object security is not RADIUS proxy or a Diameter agent), and data object security is not
used, transported keying material may be recovered by an attacker in used, transported keying material can be recovered by an attacker in
control of the intermediary. As discussed in Section 2.1, unless the control of the intermediary. As discussed in Section 2.1, unless the
TSKs are derived independently from EAP keying material (as in TSKs are derived independently from EAP keying material (as in
IKEv2), possession of transported keying material enables decryption IKEv2), possession of transported keying material enables decryption
of data traffic sent between the peer and the authenticator to whom of data traffic sent between the peer and the authenticator to whom
the keying material was transported. It also allows the AAA the keying material was transported. It also allows the AAA
intermediary to impersonate the authenticator or the peer. Since the intermediary to impersonate the authenticator or the peer. Since the
peer does not authenticate to a AAA intermediary it has no ability to peer does not authenticate to a AAA intermediary it has no ability to
determine whether it is authentic or authorized to obtain keying determine whether it is authentic or authorized to obtain keying
material. material.
However, as long as EAP keying material or keys derived from it are However, as long as transported keying material or keys derived from
only utilized by a single authenticator, compromise of the it are only utilized by a single authenticator, compromise of the
transported keying material does not enable an attacker to transported keying material does not enable an attacker to
impersonate the peer to another authenticator. Vulnerability to impersonate the peer to another authenticator. Vulnerability to
compromise of a AAA intermediary can be mitigated by implementation compromise of a AAA intermediary can be mitigated by implementation
of redirect functionality, as described in [RFC3588] and [RFC4072]. of redirect functionality, as described in [RFC3588] and [RFC4072].
The Secure Association Protocol does not provide for mutual The Secure Association Protocol does not provide for mutual
authentication between the EAP peer and authenticator, only mutual authentication between the EAP peer and authenticator, only mutual
proof of possession of transported EAP keying material. In order for proof of possession of transported keying material. In order for the
the peer to verify the identity of the authenticator, mutual proof peer to verify the identity of the authenticator, mutual proof of
of possession needs to be combined with impersonation prevention and possession needs to be combined with impersonation prevention and
Channel Binding. Impersonation prevention (described in Section Channel Binding. Impersonation prevention (described in Section
5.3.2) enables the backend authentication server to determine that 5.3.2) enables the backend authentication server to determine that
the transported EAP keying material has been provided to the correct the transported keying material has been provided to the correct
authenticator. When utilized along with impersonation prevention, authenticator. When utilized along with impersonation prevention,
Channel Binding (described in Section 5.3.3) enables the EAP peer to Channel Binding (described in Section 5.3.3) enables the EAP peer to
verify that the EAP server has authorized the authenticator to verify that the EAP server has authorized the authenticator to
possess the transported EAP keying material. Completion of the possess the transported keying material. Completion of the Secure
Secure Association Protocol exchange demonstrates that the EAP peer Association Protocol exchange demonstrates that the EAP peer and the
and the authenticator possess the transported EAP keying material. authenticator possess the transported keying material.
5.4. Key Binding 5.4. Key Binding
Requirement: Keying material MUST be bound to the appropriate Mandatory requirement from [RFC4962] Section 3:
context. Any party with legitimate access to keying material can
determine its context. In addition, the protocol MUST ensure that Bind key to its context
all parties with legitimate access to keying material have the same
context for the keying material. This requires that the parties are Keying material MUST be bound to the appropriate context. The
properly identified and authenticated, so that all of the parties
that have access to the keying material can be determined. The
context includes the following: context includes the following:
o The manner in which the keying material is expected to be used. o The manner in which the keying material is expected to
be used.
o The other parties that are expected to have access to the keying o The other parties that are expected to have access to
material. the keying material.
o The maximum lifetime of the keying material. The maximum o The expected lifetime of the keying material. Lifetime
lifetime of a child key SHOULD NOT be greater than the maximum of a child key SHOULD NOT be greater than the lifetime of
lifetime of its parent in the key hierarchy. its parent in the key hierarchy.
Within EAP, keying material (MSK, EMSK) is bound to the Peer-Id and Any party with legitimate access to keying material can determine
Server-Id which are exported along with the keying material. its context. In addition, the protocol MUST ensure that all
However, not all EAP methods support authenticated server identities parties with legitimate access to keying material have the same
(see Appendix A). context for the keying material. This requires that the parties
are properly identified and authenticated, so that all of the
parties that have access to the keying material can be determined.
The context will include the peer and NAS identities in more than
one form. One (or more) name form is needed to identify these
parties in the authentication exchange and the AAA protocol.
Another name form may be needed to identify these parties within
the lower layer that will employ the session key.
Within EAP, exported keying material (MSK, EMSK,IV) is bound to the
Peer-Id(s) and Server-Id(s) which are exported along with the keying
material. However, not all EAP methods support authenticated server
identities (see Appendix A).
Within the AAA protocol, transported keying material is destined for Within the AAA protocol, transported keying material is destined for
the EAP authenticator identified by the NAS-Identifier attribute the EAP authenticator identified by the NAS-Identifier Attribute
within the request, and is for use by the EAP peer identified by the within the request, and is for use by the EAP peer identified by the
Peer-Id, User-Name [RFC2865] or Chargeable User Identity (CUI) Peer-Id(s), User-Name [RFC2865] or Chargeable User Identity (CUI)
[RFC4372] attributes. The maximum lifetime of the transported keying [RFC4372] attributes. The maximum lifetime of the transported keying
material may be provided, as discussed in Section 3.5.1. Key usage material can be provided, as discussed in Section 3.5.1. Key usage
restrictions may also be included as described in Section 3.2. Key restrictions can also be included as described in Section 3.2. Key
lifetime issues are discussed in Sections 3.3, 3.4 and 3.5. lifetime issues are discussed in Sections 3.3, 3.4 and 3.5.
5.5. Authorization 5.5. Authorization
Requirement: Peer and authenticator authorization MUST be performed. Requirement: The Secure Association Protocol (phase 2) conversation
These entities MUST demonstrate possession of the appropriate keying may utilize different identifiers from the EAP conversation (phase
material, without disclosing it. Authorization is REQUIRED whenever 1a), so that binding between the EAP and Secure Association Protocol
a peer associates with a new authenticator. The authorization identities is REQUIRED.
checking prevents an elevation of privilege attack, and it ensures
that an unauthorized authenticator is detected. Authorizations
SHOULD be synchronized between the EAP peer, server, and
authenticator. Once all protocol exchanges are complete, all of
these parties should hold a common view of the authorizations
associated the other parties. The Secure Association Protocol (phase
2) conversation may utilize different identifiers from the EAP
conversation (phase 1a), so that binding between the EAP and Secure
Association Protocol identities is REQUIRED.
As described in Section 2.2.1, consistent identification of the EAP Mandatory requirement from [RFC4962] Section 3:
authenticator enables the EAP peer to determine whether EAP keying
material has been shared between EAP authenticators as well as to Peer and authenticator authorization
confirm with the backend authentication server that an EAP
authenticator proving possession of EAP keying material during the Peer and authenticator authorization MUST be performed. These
Secure Association Protocol was authorized to obtain it. entities MUST demonstrate possession of the appropriate keying
material, without disclosing it. Authorization is REQUIRED
whenever a peer associates with a new authenticator. The
authorization checking prevents an elevation of privilege attack,
and it ensures that an unauthorized authenticator is detected.
Authorizations SHOULD be synchronized between the peer, NAS, and
backend authentication server. Once the AAA key management
protocol exchanges are complete, all of these parties should hold
a common view of the authorizations associated the other parties.
In addition to authenticating all parties, key management
protocols need to demonstrate that the parties are authorized to
possess keying material. Note that proof of possession of keying
material does not necessarily prove authorization to hold that
keying material. For example, within an IEEE 802.11, the 4-way
handshake demonstrates that both the peer and authenticator
possess the same EAP keying material. However, by itself, this
possession proof does not demonstrate that the authenticator was
authorized by the backend authentication server to possess that
keying material. As noted in [RFC3579] in Section 4.3.7, where
AAA proxies are present, it is possible for one authenticator to
impersonate another, unless each link in the AAA chain implements
checks against impersonation. Even with these checks in place, an
authenticator may still claim different identities to the peer and
the backend authentication server. As described in [RFC3748]
Section 7.15, channel binding enables the peer to verify that the
authenticator claim of identity is both consistent and correct.
Recommendation from [RFC4962] Section 3:
Authorization restriction
If peer authorization is restricted, then the peer SHOULD be made
aware of the restriction. Otherwise, the peer may inadvertently
attempt to circumvent the restriction. For example, authorization
restrictions in an IEEE 802.11 environment include:
o Key lifetimes, where the keying material can only be used
for a certain period of time;
o SSID restrictions, where the keying material can only be
used with a specific IEEE 802.11 SSID;
o Called-Station-ID restrictions, where the keying material
can only be used with a single IEEE 802.11 BSSID; and
o Calling-Station-ID restrictions, where the keying
material can only be used with a single peer IEEE 802 MAC
address.
As described in Section 2.3, consistent identification of the EAP
authenticator enables the EAP peer to determine the scope of keying
material provided to an authenticator, as well as to confirm with the
backend authentication server that an EAP authenticator proving
possession of EAP keying material during the Secure Association
Protocol was authorized to obtain it.
Within the AAA protocol, the authorization attributes are bound to Within the AAA protocol, the authorization attributes are bound to
the transported keying material. While the AAA exchange provides the the transported keying material. While the AAA exchange provides the
AAA client/authenticator with authorizations relating to the EAP AAA client/authenticator with authorizations relating to the EAP
peer, neither the EAP nor AAA exchanges provides authorizations to peer, neither the EAP nor AAA exchanges provide authorizations to the
the EAP peer. In order to ensure that all parties hold the same view EAP peer. In order to ensure that all parties hold the same view of
of the authorizations it is RECOMMENDED that the Secure Association the authorizations it is RECOMMENDED that the Secure Association
Protocol enable communication of authorizations between the EAP Protocol enable communication of authorizations between the EAP
authenticator and peer. authenticator and peer.
In lower layers where the authenticator consistently identifies In lower layers where the authenticator consistently identifies
itself to the peer and backend authentication server and the EAP peer itself to the peer and backend authentication server and the EAP peer
completes the Secure Association Protocol exchange with the same completes the Secure Association Protocol exchange with the same
authenticator through which it completed the EAP conversation, authenticator through which it completed the EAP conversation,
authorization of the authenticator is demonstrated to the peer by authorization of the authenticator is demonstrated to the peer by
mutual authentication between the peer and authenticator as discussed mutual authentication between the peer and authenticator as discussed
in the previous section. Identification issues are discussed in in the previous section. Identification issues are discussed in
Section 2.2 and key scope issues are discussed in Section 3.2. Sections 2.3, 2.4 and 2.5 and key scope issues are discussed in
Section 3.2.
Where the EAP peer utilizes different identifiers within the EAP Where the EAP peer utilizes different identifiers within the EAP
method and Secure Association Protocol conversations, peer method and Secure Association Protocol conversations, peer
authorization may be difficult to demonstrate to the authenticator authorization can be difficult to demonstrate to the authenticator
without additional restrictions. This problem does not exist in without additional restrictions. This problem does not exist in
IKEv2 where the Identity Payload is used for peer identification both IKEv2 where the Identity Payload is used for peer identification both
within IKEv2 and EAP, and where the EAP conversation is within IKEv2 and EAP, and where the EAP conversation is
cryptographically protected within IKEv2 packets, binding the EAP and cryptographically protected within IKEv2 binding the EAP and IKEv2
Secure Association Protocol/IKEv2 exchanges. However within exchanges. However within [IEEE-802.11] the EAP peer identity is not
[IEEE-802.11i] the EAP peer identity is not used within the 4-way used within the 4-way handshake, so that it is necessary for the
handshake, so that it is necessary for the authenticator to require authenticator to require that the EAP peer utilize the same MAC
that the EAP peer utilize the same MAC address for EAP authentication address for EAP authentication as for the 4-way handshake.
as for the 4-way handshake.
5.6. Replay Protection 5.6. Replay Protection
Requirement: Exchanges MUST be replay protected, including AAA, EAP Mandatory requirement from [RFC4962] Section 3:
and Secure Association Protocol exchanges. Replay protection allows
a protocol message recipient to discard any message that was recorded Replay detection mechanism
during a previous legitimate dialogue and presented as though it
belonged to the current dialogue. The AAA key management protocol exchanges MUST be replay
protected, including AAA, EAP and Secure Association Protocol
exchanges. Replay protection allows a protocol message recipient
to discard any message that was recorded during a previous
legitimate dialogue and presented as though it belonged to the
current dialogue.
[RFC3748] Section 7.2.1 describes the "replay protection" security [RFC3748] Section 7.2.1 describes the "replay protection" security
claim and [RFC4017] requires use of EAP methods supporting this claim and [RFC4017] Section 2.2 requires use of EAP methods
claim. supporting this claim.
Diameter [RFC3588] provides support for replay protection via use of Diameter [RFC3588] provides support for replay protection via use of
IPsec or TLS. RADIUS/EAP [RFC3579] protects against replay of keying IPsec or TLS. RADIUS/EAP [RFC3579] protects against replay of keying
material via the Request Authenticator. However, some RADIUS packets material via the Request Authenticator. However, some RADIUS packets
are not replay protected. In Accounting, Disconnect and CoA-Request are not replay protected. In Accounting, Disconnect and CoA-Request
packets the Request Authenticator contains a keyed MAC rather than a packets the Request Authenticator contains a keyed MAC rather than a
Nonce. The Response Authenticator in Accounting, Disconnect and CoA Nonce. The Response Authenticator in Accounting, Disconnect and CoA
Response packets also contains a keyed MAC whose calculation does not Response packets also contains a keyed MAC whose calculation does not
depend on a Nonce in either the Request or Response packets. depend on a Nonce in either the Request or Response packets.
Therefore unless an Event-Timestamp attribute is included or IPsec is Therefore unless an Event-Timestamp attribute is included or IPsec is
used, the recipient may not be able to determine whether these used, it is possible that the recipient will not be able to determine
packets have been replayed. whether these packets have been replayed.
In order to prevent replay of Secure Association Protocol frames, In order to prevent replay of Secure Association Protocol frames,
replay protection is REQUIRED on all messages. [IEEE-802.11i] replay protection is REQUIRED on all messages. [IEEE-802.11]
supports replay protection on all messages within the 4-way supports replay protection on all messages within the 4-way
handshake; IKEv2 [RFC4306] also supports this. handshake; IKEv2 [RFC4306] also supports this.
5.7. Key Freshness 5.7. Key Freshness
Requirement: While preserving algorithm independence, session keys Requirement: A session key SHOULD be considered compromised if it
MUST be strong and fresh. A session key SHOULD be considered remains in use beyond its authorized lifetime. Mandatory requirement
compromised if it remains in use beyond its authorized lifetime. from [RFC4962] Section 3:
Each session deserves an independent session key; disclosure of one
session key MUST NOT aid the attacker in discovering any other Strong, fresh session keys
session keys. Fresh keys are required even when a long replay
counter (that is, one that "will never wrap") is used to ensure that While preserving algorithm independence, session keys MUST be
loss of state does not cause the same counter value to be used more strong and fresh. Each session deserves an independent session
than once with the same session key. A fresh cryptographic key is key. Fresh keys are required even when a long replay counter
one that is generated specifically for the intended use. In this (that is, one that "will never wrap") is used to ensure that loss
situation, a secure association protocol is used to establish session of state does not cause the same counter value to be used more
keys. The AAA protocol and EAP method MUST ensure that the keying than once with the same session key.
material supplied as an input to session key derivation is fresh, and
the secure association protocol MUST generate a separate session key Some EAP methods are capable of deriving keys of varying strength,
for each session, even if the keying material provided by EAP is and these EAP methods MUST permit the generation of keys meeting a
cached. minimum equivalent key strength. BCP 86 [RFC3766] offers advice
on appropriate key sizes. The National Institute for Standards
and Technology (NIST) also offers advice on appropriate key sizes
in [SP800-57].
A fresh cryptographic key is one that is generated specifically
for the intended use. In this situation, a secure association
protocol is used to establish session keys. The AAA protocol and
EAP method MUST ensure that the keying material supplied as an
input to session key derivation is fresh, and the secure
association protocol MUST generate a separate session key for each
session, even if the keying material provided by EAP is cached. A
cached key persists after the authentication exchange has
completed. For the AAA/EAP server, key caching can happen when
state is kept on the server. For the NAS or client, key caching
can happen when the NAS or client does not destroy keying material
immediately following the derivation of session keys.
Session keys MUST NOT be dependent on one another. Multiple
session keys may be derived from a higher-level shared secret as
long as a one-time value, usually called a nonce, is used to
ensure that each session key is fresh. The mechanism used to
generate session keys MUST ensure that the disclosure of one
session key does not aid the attacker in discovering any other
session keys.
EAP, AAA and the lower layer each bear responsibility for ensuring EAP, AAA and the lower layer each bear responsibility for ensuring
the use of fresh, strong session keys. EAP methods need to ensure the use of fresh, strong session keys. EAP methods need to ensure
the freshness and strength of EAP keying material provided as an the freshness and strength of EAP keying material provided as an
input to session key derivation. [RFC3748] Section 7.10 states that input to session key derivation. [RFC3748] Section 7.10 states:
"EAP methods SHOULD ensure the freshness of the MSK and EMSK, even in
cases where one party may not have a high quality random number EAP methods SHOULD ensure the freshness of the MSK and EMSK, even
generator. A RECOMMENDED method is for each party to provide a nonce in cases where one party may not have a high quality random number
of at least 128 bits, used in the derivation of the MSK and EMSK." generator. A RECOMMENDED method is for each party to provide a
nonce of at least 128 bits, used in the derivation of the MSK and
EMSK.
The contribution of nonces enables the EAP peer and server to ensure The contribution of nonces enables the EAP peer and server to ensure
that exported EAP keying material is fresh. that exported EAP keying material is fresh.
[RFC3748] Section 7.2.1 describes the "key strength" and "session [RFC3748] Section 7.2.1 describes the "key strength" and "session
independence" security claims, and [RFC4017] requires EAP methods independence" security claims, and [RFC4017] requires EAP methods
supporting these claims as well as methods capable of providing supporting these claims as well as methods capable of providing
equivalent key strength of 128 bits or greater. See Section 3.7 for equivalent key strength of 128 bits or greater. See Section 3.7 for
more information on key strength. more information on key strength.
The AAA protocol needs to ensure that transported keying material is The AAA protocol needs to ensure that transported keying material is
fresh and is not utilized outside its recommended lifetime. Replay fresh and is not utilized outside its recommended lifetime. Replay
protection is necessary for key freshness, but an attacker can protection is necessary for key freshness, but an attacker can
deliver a stale (and therefore potentially compromised) key in a deliver a stale (and therefore potentially compromised) key in a
replay-protected message, so replay protection is not sufficient. As replay-protected message, so replay protection is not sufficient. As
discussed in Section 3.5, the Session-Timeout attribute enables the discussed in Section 3.5, the Session-Timeout attribute enables the
backend authentication server to limit the exposure of transported backend authentication server to limit the exposure of transported
EAP keying material. keying material.
The EAP Session-Id, described in Section 1.4, enables the EAP peer, The EAP Session-Id, described in Section 1.4, enables the EAP peer,
authenticator and server to distinguish EAP conversations. However, authenticator and server to distinguish EAP conversations. However,
unless the authenticator keeps track of EAP Session-Ids, the unless the authenticator keeps track of EAP Session-Ids, the
authenticator cannot use the Session-Id to guarantee the freshness of authenticator cannot use the Session-Id to guarantee the freshness of
EAP keying material. keying material.
The Secure Association Protocol, described in Section 3.1, MUST The Secure Association Protocol, described in Section 3.1, MUST
generate a fresh session key for each session, even if the keying generate a fresh session key for each session, even if the EAP keying
material and parameters provided by EAP methods are cached, or either material and parameters provided by methods are cached, or either the
the peer or authenticator lack a high entropy random number peer or authenticator lack a high entropy random number generator. A
generator. A RECOMMENDED method is for the peer and authenticator to RECOMMENDED method is for the peer and authenticator to each provide
each provide a nonce or counter used in session key derivation. If a a nonce or counter used in session key derivation. If a nonce is
nonce is used, it is RECOMMENDED that it be at least 128 bits. While used, it is RECOMMENDED that it be at least 128 bits. While
[IEEE-802.11i] and IKEv2 [RFC4306] satisfy this requirement, [IEEE-802.11] and IKEv2 [RFC4306] satisfy this requirement,
[IEEE-802.16e] does not, since randomness is only contributed from [IEEE-802.16e] does not, since randomness is only contributed from
the Base Station. the Base Station.
5.8. Key Scope Limitation 5.8. Key Scope Limitation
Requirement: Following the principle of least privilege, parties MUST Mandatory requirement from [RFC4962] Section 3:
NOT have access to keying material that is not needed to perform
their role. A party has access to a particular key if it has access
to all of the secret information needed to derive it. Any protocol
that is used to establish session keys, MUST specify the scope for
session keys, clearly identifying the parties to whom the session key
is available.
Transported EAP keying material is permitted to be accessed by the Limit key scope
EAP peer, authenticator and server. The EAP peer and server derive
EAP keying material during the process of mutually authenticating Following the principle of least privilege, parties MUST NOT have
each other using the selected EAP method. During the Secure access to keying material that is not needed to perform their
Association Protocol exchange, the EAP peer utilizes derived EAP role. A party has access to a particular key if it has access to
keying material to demonstrate to the authenticator that it is the all of the secret information needed to derive it.
same party that authenticated to the EAP server and was authorized by
it. The EAP authenticator utilizes the transported EAP keying Any protocol that is used to establish session keys MUST specify
material to prove to the peer not only that the EAP conversation was the scope for session keys, clearly identifying the parties to
transported through it (this could be demonstrated by a man-in-the- whom the session key is available.
middle), but that it was uniquely authorized by the EAP server to
provide the peer with access to the network. Unique authorization Transported keying material is permitted to be accessed by the EAP
can only be demonstrated if the EAP authenticator does not share the peer, authenticator and server. The EAP peer and server derive EAP
transported keying material with a party other than the EAP peer and keying material during the process of mutually authenticating each
server. other using the selected EAP method. During the Secure Association
Protocol exchange, the EAP peer utilizes keying material to
demonstrate to the authenticator that it is the same party that
authenticated to the EAP server and was authorized by it. The EAP
authenticator utilizes the transported keying material to prove to
the peer not only that the EAP conversation was transported through
it (this could be demonstrated by a man-in-the-middle), but that it
was uniquely authorized by the EAP server to provide the peer with
access to the network. Unique authorization can only be demonstrated
if the EAP authenticator does not share the transported keying
material with a party other than the EAP peer and server.
TSKs are permitted to be accessed only by the EAP peer and TSKs are permitted to be accessed only by the EAP peer and
authenticator (see Section 1.5); TSK derivation is discussed in authenticator (see Section 1.5); TSK derivation is discussed in
Section 2.1. Since demonstration of authorization within the Secure Section 2.1. Since demonstration of authorization within the Secure
Association Protocol exchange depends on possession of transported Association Protocol exchange depends on possession of transported
EAP keying material, the backend authentication server can possibly keying material, the backend authentication server can obtain TSKs
to obtain the TSKs unless the backend server deletes the transported unless it deletes the transported keying material after sending it.
EAP keying material after sending it.
5.9. Key Naming 5.9. Key Naming
Requirement: A robust key naming scheme is REQUIRED, particularly Mandatory requirement from [RFC4962] Section 3:
where key caching is supported. The key name provides a way to refer
to a key in a protocol so that it is clear to all parties which key
is being referenced. Objects that cannot be named cannot be managed.
All keys MUST be uniquely named, and the key name MUST NOT directly
or indirectly disclose the keying material. If the key name is not
based on the keying material, then one can be sure that it cannot be
used to assist in a search for the key value.
EAP key names (defined in Section 1.4.1), along with the Peer-Id and Uniquely named keys
Server-Id, uniquely identify EAP keying material, and do not directly
or indirectly expose the keying material. AAA key management proposals require a robust key naming scheme,
particularly where key caching is supported. The key name
provides a way to refer to a key in a protocol so that it is clear
to all parties which key is being referenced. Objects that cannot
be named cannot be managed. All keys MUST be uniquely named, and
the key name MUST NOT directly or indirectly disclose the keying
material. If the key name is not based on the keying material,
then one can be sure that it cannot be used to assist in a search
for the key value.
EAP key names (defined in Section 1.4.1), along with the Peer-Id(s)
and Server-Id(s), uniquely identify EAP keying material, and do not
directly or indirectly expose EAP keying material.
Existing AAA server implementations do not distribute key names along Existing AAA server implementations do not distribute key names along
with the transported EAP keying material, although Diameter EAP with the transported keying material, although Diameter EAP
[RFC4072], provides the EAP-Key-Name AVP for this purpose. Since the [RFC4072], provides the EAP-Key-Name AVP for this purpose. Since the
EAP-Key-Name AVP is defined within the RADIUS attribute space, it may EAP-Key-Name AVP is defined within the RADIUS attribute space, it can
be used either with RADIUS or Diameter. be used either with RADIUS or Diameter.
Since the authenticator is not provided with the name of the Since the authenticator is not provided with the name of the
transported keying material by existing backend authentication server transported keying material by existing backend authentication server
implementations, existing Secure Association Protocols do not utilize implementations, existing Secure Association Protocols do not utilize
EAP key names. For example, [IEEE-802.11i] supports PMK caching; to EAP key names. For example, [IEEE-802.11] supports PMK caching; to
enable the peer and authenticator to determine the cached PMK to enable the peer and authenticator to determine the cached PMK to
utilize within the 4-way handshake the PMK needs to be named. For utilize within the 4-way handshake the PMK needs to be named. For
this purpose [IEEE-802.11i] utilizes a PMK naming scheme which is this purpose [IEEE-802.11] utilizes a PMK naming scheme which is
based on the key. Since IKEv2 [RFC4306] does not cache transported based on the key. Since IKEv2 [RFC4306] does not cache transported
EAP keying material, it does not need to refer to transported keying keying material, it does not need to refer to transported keying
material. material.
5.10. Denial of Service Attacks 5.10. Denial of Service Attacks
Key caching may result in vulnerability to denial of service attacks. Key caching can result in vulnerability to denial of service attacks.
For example, EAP methods that create persistent state may be For example, EAP methods that create persistent state can be
vulnerable to denial of service attacks on the EAP server by a rogue vulnerable to denial of service attacks on the EAP server by a rogue
EAP peer. EAP peer.
To address this vulnerability, EAP methods creating persistent state To address this vulnerability, EAP methods creating persistent state
may wish to limit the persistent state created by an EAP peer. For can limit the persistent state created by an EAP peer. For example,
example, for each peer an EAP server may choose to limit persistent for each peer an EAP server can choose to limit persistent state to a
state to a few EAP conversations, distinguished by the EAP Session- few EAP conversations, distinguished by the EAP Session-Id. This
Id. This prevents a rogue peer from denying access to other peers. prevents a rogue peer from denying access to other peers.
Similarly, to conserve resources an authenticator may choose to limit Similarly, to conserve resources an authenticator can choose to limit
the persistent state corresponding to each peer. This can be the persistent state corresponding to each peer. This can be
accomplished by limiting each peer to persistent state corresponding accomplished by limiting each peer to persistent state corresponding
to a few EAP conversations, distinguished by the EAP Session-Id. to a few EAP conversations, distinguished by the EAP Session-Id.
Depending on the media, creation of new TSKs may or may not imply Whether creation of new TSKs implies deletion of previously derived
deletion of previously derived TSKs. Where there is no implied TSKs depends on the EAP lower layer. Where there is no implied
deletion, the authenticator may choose to limit the number of TSKs deletion, the authenticator can choose to limit the number of TSKs
and associated state that can be stored for each peer. and associated state that can be stored for each peer.
6. IANA Considerations 6. IANA Considerations
This specification does not request the creation of any new parameter This specification does not request the creation of any new parameter
registries, nor does it require any other IANA assignments. registries, nor does it require any other IANA assignments.
7. References 7. References
7.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H.
Lefkowetz, "Extensible Authentication Protocol (EAP)", Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004. RFC 3748, June 2004.
[RFC4962] Housley, R. and B. Aboba, "Guidance for AAA Key
Management", RFC 4962, July 2007.
7.2. Informative References 7.2. Informative References
[8021XPreAuth] Pack, S. and Y. Choi, "Pre-Authenticated Fast Handoff in
a Public Wireless LAN Based on IEEE 802.1x Model",
Proceedings of the IFIP TC6/WG6.8 Working Conference on
Personal Wireless Communications, p.175-182, October
23-25, 2002.
[Analysis] He, C. and J. Mitchell, "Analysis of the 802.11i 4-Way [Analysis] He, C. and J. Mitchell, "Analysis of the 802.11i 4-Way
Handshake", Proceedings of the 2004 ACM Workshop on Handshake", Proceedings of the 2004 ACM Workshop on
Wireless Security, pp. 43-50, ISBN: 1-58113-925-X. Wireless Security, pp. 43-50, ISBN: 1-58113-925-X.
[Bargh] Bargh, M., Hulsebosch, R., Eertink, E., Prasad, A., Wang, [Bargh] Bargh, M., Hulsebosch, R., Eertink, E., Prasad, A., Wang,
H. and P. Schoo, "Fast Authentication Methods for H. and P. Schoo, "Fast Authentication Methods for
Handovers between IEEE 802.11 Wireless LANs", Proceedings Handovers between IEEE 802.11 Wireless LANs", Proceedings
of the 2nd ACM international workshop on Wireless mobile of the 2nd ACM international workshop on Wireless mobile
applications and services on WLAN hotspots, October, applications and services on WLAN hotspots, October,
2004. 2004.
[GKDP] Dondeti, L., Xiang, J. and S. Rowles, "GKDP: Group Key [GKDP] Dondeti, L., Xiang, J. and S. Rowles, "GKDP: Group Key
Distribution Protocol", Internet draft (work in Distribution Protocol", Internet draft (work in
progress), draft-ietf-msec-gkdp-01, March 2006. progress), draft-ietf-msec-gkdp-01, March 2006.
[GSAKMP] Harney, H., Meth, U., Colegrove, A., and G. Gross,
"GSAKMP: Group Secure Association Group Management
Protocol", Internet draft (work in progress), draft-ietf-
msec-gsakmp-sec-10, May 2005.
[He] He, C., Sundararajan, M., Datta, A. Derek, A. and J. C. [He] He, C., Sundararajan, M., Datta, A. Derek, A. and J. C.
Mitchell, "A Modular Correctness Proof of TLS and IEEE Mitchell, "A Modular Correctness Proof of TLS and IEEE
802.11i", ACM Conference on Computer and Communications 802.11i", ACM Conference on Computer and Communications
Security (CCS '05), November, 2005. Security (CCS '05), November, 2005.
[IEEE-802.11] Institute of Electrical and Electronics Engineers, [IEEE-802.11] Institute of Electrical and Electronics Engineers,
"Information technology - Telecommunications and "Information technology - Telecommunications and
information exchange between systems - Local and information exchange between systems - Local and
metropolitan area networks - Specific Requirements Part metropolitan area networks - Specific Requirements Part
11: Wireless LAN Medium Access Control (MAC) and 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications", IEEE IEEE Standard Physical Layer (PHY) Specifications", IEEE IEEE Standard
802.11-2003, 2003. 802.11-2007, 2007.
[IEEE-802.1X] Institute of Electrical and Electronics Engineers, "Local [IEEE-802.1X] Institute of Electrical and Electronics Engineers, "Local
and Metropolitan Area Networks: Port-Based Network Access and Metropolitan Area Networks: Port-Based Network Access
Control", IEEE Standard 802.1X-2004, December 2004. Control", IEEE Standard 802.1X-2004, December 2004.
[IEEE-802.1Q] Institute of Electrical and Electronics Engineers, "IEEE [IEEE-802.1Q] IEEE Standards for Local and Metropolitan Area Networks:
Standards for Local and Metropolitan Area Networks: Draft Draft Standard for Virtual Bridged Local Area Networks,
Standard for Virtual Bridged Local Area Networks", IEEE P802.1Q-2003, January 2003.
Standard 802.1Q/D8, January 1998. [IEEE802.11i]
Institute of Electrical and Electronics Engineers, [IEEE-802.11i] Institute of Electrical and Electronics Engineers,
"Supplement to Standard for Telecommunications and "Supplement to Standard for Telecommunications and
Information Exchange Between Systems - LAN/MAN Specific Information Exchange Between Systems - LAN/MAN Specific
Requirements - Part 11: Wireless LAN Medium Access Requirements - Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) Specifications: Control (MAC) and Physical Layer (PHY) Specifications:
Specification for Enhanced Security", IEEE 802.11i, July Specification for Enhanced Security", IEEE 802.11i/D1,
2004. 2001.
[IEEE-802.11F] Institute of Electrical and Electronics Engineers, [IEEE-802.11F] Institute of Electrical and Electronics Engineers,
"Recommended Practice for Multi-Vendor Access Point "Recommended Practice for Multi-Vendor Access Point
Interoperability via an Inter-Access Point Protocol Interoperability via an Inter-Access Point Protocol
Across Distribution Systems Supporting IEEE 802.11 Across Distribution Systems Supporting IEEE 802.11
Operation", IEEE 802.11F, July 2003 (now deprecated). Operation", IEEE 802.11F, July 2003 (now deprecated).
[IEEE-802.16e] Institute of Electrical and Electronics Engineers, "IEEE [IEEE-802.16e] Institute of Electrical and Electronics Engineers, "IEEE
Standard for Local and Metropolitan Area Networks: Part Standard for Local and Metropolitan Area Networks: Part
16: Air Interface for Fixed and Mobile Broadband Wireless 16: Air Interface for Fixed and Mobile Broadband Wireless
Access Systems: Amendment for Physical and Medium Access Access Systems: Amendment for Physical and Medium Access
Control Layers for Combined Fixed and Mobile Operations Control Layers for Combined Fixed and Mobile Operations
in Licensed Bands" IEEE 802.16e, August 2005. in Licensed Bands" IEEE 802.16e, August 2005.
[IEEE-03-084] Mishra, A., Shin, M., Arbaugh, W., Lee, I. and K. Jang, [IEEE-03-084] Mishra, A., Shin, M., Arbaugh, W., Lee, I. and K. Jang,
"Proactive Key Distribution to support fast and secure "Proactive Key Distribution to support fast and secure
roaming", IEEE 802.11 Working Group, IEEE-03-084r1-I, roaming", IEEE 802.11 Working Group, IEEE-03-084r1-I,
http://www.ieee802.org/11/Documents/DocumentHolder/ http://www.ieee802.org/11/Documents/DocumentHolder/
3-084.zip, January 2003. 3-084.zip, January 2003.
[I-D.puthenkulam-eap-binding]
Puthenkulam, J., "The Compound Authentication Binding
Problem", draft-puthenkulam-eap-binding-04, Internet
draft (work in progress), October 2003.
[I-D.arkko-eap-service-identity-auth] [I-D.arkko-eap-service-identity-auth]
Arkko, J. and P. Eronen, "Authenticated Service Arkko, J. and P. Eronen, "Authenticated Service
Information for the Extensible Authentication Protocol Information for the Extensible Authentication Protocol
(EAP)", draft-arkko-eap-service-identity-auth-02.txt (EAP)", draft-arkko-eap-service-identity-auth-04.txt
Internet draft (work in progress), May 2005. Internet draft (work in progress), October 2005.
[I-D.friedman-ike-short-term-certs] [I-D.friedman-ike-short-term-certs]
Friedman, A., Sheffer, Y. and A. Shaqed, "Short Term Friedman, A., Sheffer, Y. and A. Shaqed, "Short-Term
Certificates", draft-friedman-ike-short-term-certs-01, Certificates", draft-friedman-ike-short-term-certs-02,
Internet draft (work in progress), December 2006. Internet draft (work in progress), June 2007.
[I-D.housley-aaa-key-mgmt]
Housley, R. and B. Aboba, "Guidance for AAA Key
Management", draft-housley-aaa-key-mgmt-06.txt, Internet
draft (work in progress), November 2006.
[I-D.irtf-aaaarch-handoff] [I-D.irtf-aaaarch-handoff]
Arbaugh, W. and B. Aboba, "Handoff Extension to RADIUS", Arbaugh, W. and B. Aboba, "Handoff Extension to RADIUS",
draft-irtf-aaaarch-handoff-04.txt, Internet Draft (work draft-irtf-aaaarch-handoff-04.txt, Internet Draft (work
in progress), October 2003. in progress), October 2003.
[I-D.ohba-eap-channel-binding] [I-D.ohba-eap-channel-binding]
Ohba, Y., Parthasrathy, M. and M. Yanagiya, "Channel Ohba, Y., Parthasrathy, M. and M. Yanagiya, "Channel
Binding Mechanism Based on Parameter Binding in Key Binding Mechanism Based on Parameter Binding in Key
Derivation", draft-ohba-eap-channel-binding-00.txt, Derivation", draft-ohba-eap-channel-binding-02.txt,
Internet draft (work in progress), January 2006. Internet draft (work in progress), December 2006.
[I-D.puthenkulam-eap-binding]
Puthenkulam, J., Lortz, V., Palekar, A. and D. Simon,
"The Compound Authentication Binding Problem", draft-
puthenkulam-eap-binding-04, Internet draft (work in
progress), October 2003.
[I-D.simon-emu-rfc2716bis] [I-D.simon-emu-rfc2716bis]
Simon, D. and B. Aboba, "EAP TLS Authentication Simon, D., Aboba, B. and R. Hurst, "The EAP TLS
Protocol", draft-simon-emu-rfc2716bis-07.txt, Internet Authentication Protocol", draft-simon-emu-
Draft (work in progress), January 2007. rfc2716bis-11.txt, Internet Draft (work in progress),
July 2007.
[I-D.ietf-tls-rfc4346-bis]
Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", draft-ietf-tls-
rfc4346-bis-05.txt, Internet draft (work in progress),
September 2007.
[MD5Collision] Klima, V., "Tunnels in Hash Functions: MD5 Collisions [MD5Collision] Klima, V., "Tunnels in Hash Functions: MD5 Collisions
Within a Minute", Cryptology ePrint Archive, March 2006, Within a Minute", Cryptology ePrint Archive, March 2006,
http://eprint.iacr.org/2006/105.pdf http://eprint.iacr.org/2006/105.pdf
[MishraPro] Mishra, A., Shin, M. and W. Arbaugh, "Pro-active Key [MishraPro] Mishra, A., Shin, M. and W. Arbaugh, "Pro-active Key
Distribution using Neighbor Graphs", IEEE Wireless Distribution using Neighbor Graphs", IEEE Wireless
Communications, vol. 11, February 2004. Communications, vol. 11, February 2004.
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
skipping to change at page 60, line 24 skipping to change at page 66, line 32
[RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D. [RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D.
and R. Wheeler, "A Method for Transmitting PPP Over and R. Wheeler, "A Method for Transmitting PPP Over
Ethernet (PPPoE)", RFC 2516, February 1999. Ethernet (PPPoE)", RFC 2516, February 1999.
[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes", [RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes",
RFC 2548, March 1999. RFC 2548, March 1999.
[RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
Implementation in Roaming", RFC 2607, June 1999. Implementation in Roaming", RFC 2607, June 1999.
[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication
Protocol", RFC 2716, October 1999.
[RFC2782] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for [RFC2782] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
February 2000. February 2000.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake, D. and B. [RFC2845] Vixie, P., Gudmundsson, O., Eastlake, D. and B.
Wellington, "Secret Key Transaction Authentication for Wellington, "Secret Key Transaction Authentication for
DNS (TSIG)", RFC 2845, May 2000. DNS (TSIG)", RFC 2845, May 2000.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson, [RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", "Remote Authentication Dial In User Service (RADIUS)",
skipping to change at page 60, line 45 skipping to change at page 67, line 8
[RFC3007] Wellington, B., "Simple Secure Domain Name System (DNS) [RFC3007] Wellington, B., "Simple Secure Domain Name System (DNS)
Dynamic Update", RFC 3007, November 2000. Dynamic Update", RFC 3007, November 2000.
[RFC3162] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC [RFC3162] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC
3162, August 2001. 3162, August 2001.
[RFC3547] Baugher, M., Weis, B., Hardjono, T. and H. Harney, "The [RFC3547] Baugher, M., Weis, B., Hardjono, T. and H. Harney, "The
Group Domain of Interpretation", RFC 3547, July 2003. Group Domain of Interpretation", RFC 3547, July 2003.
[RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 3576,
July 2003.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003. Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G. and J. Roese, [RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G. and J. Roese,
"IEEE 802.1X Remote Authentication Dial In User Service "IEEE 802.1X Remote Authentication Dial In User Service
(RADIUS) Usage Guidelines", RFC 3580, September 2003. (RADIUS) Usage Guidelines", RFC 3580, September 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J. [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J.
Arkko, "Diameter Base Protocol", RFC 3588, September Arkko, "Diameter Base Protocol", RFC 3588, September
skipping to change at page 62, line 12 skipping to change at page 68, line 17
Communications (GSM) Subscriber Identity Modules (EAP- Communications (GSM) Subscriber Identity Modules (EAP-
SIM)", RFC 4186, January 2006. SIM)", RFC 4186, January 2006.
[RFC4187] Arkko, J. and H. Haverinen, "Extensible Authentication [RFC4187] Arkko, J. and H. Haverinen, "Extensible Authentication
Protocol Method for 3rd Generation Authentication and Key Protocol Method for 3rd Generation Authentication and Key
Agreement (EAP-AKA)", RFC 4187, January 2006. Agreement (EAP-AKA)", RFC 4187, January 2006.
[RFC4282] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The [RFC4282] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The
Network Access Identifier", RFC 4282, December 2005. Network Access Identifier", RFC 4282, December 2005.
[RFC4284] Adrangi, F., Lortz, V., Bari, F. and P. Eronen, "Identity
Selection Hints for the Extensible Authentication
Protocol", RFC 4284, January 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the [RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005. Internet Protocol", RFC 4301, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005. RFC 4306, December 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006. (TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4372] Adrangi, F., Lior, A., Korhonen, J. and J. Loughney, [RFC4372] Adrangi, F., Lior, A., Korhonen, J. and J. Loughney,
"Chargeable User Identity", RFC 4372, January 2006. "Chargeable User Identity", RFC 4372, January 2006.
[RFC4334] Housley, R. and T. Moore, "Certificate Extensions and [RFC4334] Housley, R. and T. Moore, "Certificate Extensions and
Attributes Suporting Authentication in Point-to-Point Attributes Supporting Authentication in Point-to-Point
Protocol (PPP) and Wireless Local Area Neworks (WLAN)", Protocol (PPP) and Wireless Local Area Networks (WLAN)",
RFC 4334, February 2006. RFC 4334, February 2006.
[RFC4535] Harney, H., Meth, U., Colegrove, A. and G. Gross,
"GSAKMP: Group Secure Association Group Management
Protocol", RFC 4535, June 2006.
[RFC4763] Vanderveen, M. and H. Soliman, "Extensible Authentication [RFC4763] Vanderveen, M. and H. Soliman, "Extensible Authentication
Protocol Method for Shared-secret Authentication and Key Protocol Method for Shared-secret Authentication and Key
Establishment (EAP-SAKE)", RFC 4763, November 2006. Establishment (EAP-SAKE)", RFC 4763, November 2006.
[RFC4675] Congdon, P., Sanchez, M. and B. Aboba, "RADIUS Attributes [RFC4675] Congdon, P., Sanchez, M. and B. Aboba, "RADIUS Attributes
for Virtual LAN and Priority Support", RFC 4675, for Virtual LAN and Priority Support", RFC 4675,
September 2006. September 2006.
[RFC4718] Eronen, P. and P. Hoffman, "IKEv2 Clarifications and
Implementation Guidelines", RFC 4718, October 2006.
[RFC4764] Bersani, F. and H. Tschofenig, "The EAP-PSK Protocol: a [RFC4764] Bersani, F. and H. Tschofenig, "The EAP-PSK Protocol: a
Pre-Shared Key Extensible Authentication Protocol (EAP) Pre-Shared Key Extensible Authentication Protocol (EAP)
Method", RFC 4764, January 2007. Method", RFC 4764, January 2007.
[RFC3576bis] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", draft-
ietf-radext-rfc3576bis-13.txt, Internet draft (work in
progress), October 2007.
[SP800-57] National Institute of Standards and Technology, [SP800-57] National Institute of Standards and Technology,
"Recommendation for Key Management", Special Publication "Recommendation for Key Management", Special Publication
800-57, May 2006. 800-57, May 2006.
[Token] Fantacci, R., Maccari, L., Pecorella, T. and F. Frosali, [Token] Fantacci, R., Maccari, L., Pecorella, T. and F. Frosali,
"A secure and performant token-based authentication for "A secure and performant token-based authentication for
infrastructure and mesh 802.1X networks", IEEE infrastructure and mesh 802.1X networks", IEEE
Conference on Computer Communications, June 2006. Conference on Computer Communications, June 2006.
[8021XPreAuth] Pack, S. and Y. Choi, "Pre-Authenticated Fast Handoff in [Tokenk] Ohba, Y., Das, S. and A. Duttak, "Kerberized Handover
a Public Wireless LAN Based on IEEE 802.1x Model", Keying: A Media-Independent Handover Key Management
Proceedings of the IFIP TC6/WG6.8 Working Conference on Architecture", Mobiarch 2007.
Personal Wireless Communications, p.175-182, October
23-25, 2002.
Acknowledgments Acknowledgments
Thanks to Ashwin Palekar, and Tim Moore of Microsoft, Jari Arkko of Thanks to Ashwin Palekar, Charlie Kaufman and Tim Moore of Microsoft,
Ericsson, Dorothy Stanley of Aruba Networks, Bob Moskowitz of Jari Arkko of Ericsson, Dorothy Stanley of Aruba Networks, Bob
TruSecure, Jesse Walker of Intel, Joe Salowey of Cisco and Russ Moskowitz of TruSecure, Jesse Walker of Intel, Joe Salowey of Cisco
Housley of Vigil Security for useful feedback. and Russ Housley of Vigil Security for useful feedback.
Authors' Addresses Authors' Addresses
Bernard Aboba Bernard Aboba
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
EMail: bernarda@microsoft.com EMail: bernarda@microsoft.com
Phone: +1 425 706 6605 Phone: +1 425 706 6605
skipping to change at page 63, line 43 skipping to change at page 71, line 5
Fax: +1 425 936 7329 Fax: +1 425 936 7329
Pasi Eronen Pasi Eronen
Nokia Research Center Nokia Research Center
P.O. Box 407 P.O. Box 407
FIN-00045 Nokia Group FIN-00045 Nokia Group
Finland Finland
EMail: pasi.eronen@nokia.com EMail: pasi.eronen@nokia.com
Henrik Levkowetz
Ericsson Research
Torshamsgatan 23
SE-164 80 Stockholm
SWEDEN
Phone: +46 7 08 32 16 08
EMail: henrik@levkowetz.com
Appendix A - Exported Parameters in Existing Methods Appendix A - Exported Parameters in Existing Methods
This Appendix specifies Session-Id, Peer-Id, Server-Id and Key- This Appendix specifies Session-Id, Peer-Id, Server-Id and Key-
Lifetime for EAP methods that have been published prior to this Lifetime for EAP methods that have been published prior to this
specification. Future EAP method specifications MUST include a specification. Future EAP method specifications MUST include a
definition of the Session-Id, Peer-Id and Server-Id (could be the definition of the Session-Id, Peer-Id and Server-Id (could be the
empty string). null string).
EAP-Identity EAP-Identity
The EAP-Identity method is defined in [RFC3748]. It does not derive The EAP-Identity method is defined in [RFC3748]. It does not derive
keys, and therefore does not define the Session-Id. The Peer-Id and keys, and therefore does not define the Session-Id. The Peer-Id and
Server-Id are the empty string (zero length). Server-Id are the null string (zero length).
EAP-Notification EAP-Notification
The EAP-Notification method is defined in [RFC3748]. It does not The EAP-Notification method is defined in [RFC3748]. It does not
derive keys and therefore does not define the Session-Id. The Peer- derive keys and therefore does not define the Session-Id. The Peer-
Id and Server-Id are the empty string (zero length). Id and Server-Id are the null string (zero length).
EAP-MD5-Challenge EAP-MD5-Challenge
The EAP-MD5-Challenge method is defined in [RFC3748]. It does not The EAP-MD5-Challenge method is defined in [RFC3748]. It does not
derive keys and therefore does not define the Session-Id. The Peer- derive keys and therefore does not define the Session-Id. The Peer-
Id and Server-Id are the empty string (zero length). Id and Server-Id are the null string (zero length).
EAP-GTC EAP-GTC
The EAP-GTC method is defined in [RFC3748]. It does not derive keys The EAP-GTC method is defined in [RFC3748]. It does not derive keys
and therefore does not define the Session-Id. The Peer-Id and and therefore does not define the Session-Id. The Peer-Id and
Server-Id are the empty string (zero length). Server-Id are the null string (zero length).
EAP-OTP EAP-OTP
The EAP-OTP method is defined in [RFC3748]. It does not derive keys The EAP-OTP method is defined in [RFC3748]. It does not derive keys
and therefore does not define the Session-Id. The Peer-Id and and therefore does not define the Session-Id. The Peer-Id and
Server-Id are the empty string (zero length). Server-Id are the null string (zero length).
EAP-AKA EAP-AKA
EAP-AKA is defined in [RFC4187]. The EAP-AKA Session-Id is the EAP-AKA is defined in [RFC4187]. The EAP-AKA Session-Id is the
concatenation of the EAP Type Code (0x17) with the contents of the concatenation of the EAP Type Code (0x17) with the contents of the
RAND field from the AT_RAND attribute, followed by the contents of RAND field from the AT_RAND attribute, followed by the contents of
the AUTN field in the AT_AUTN attribute. the AUTN field in the AT_AUTN attribute.
The Peer-Id is the contents of the Identity field from the The Peer-Id is the contents of the Identity field from the
AT_IDENTITY attribute, using only the Actual Identity Length octets AT_IDENTITY attribute, using only the Actual Identity Length octets
from the beginning, however. Note that the contents are used as they from the beginning, however. Note that the contents are used as they
are transmitted, regardless of whether the transmitted identity was a are transmitted, regardless of whether the transmitted identity was a
permanent, pseudonym, or fast EAP re-authentication identity. The permanent, pseudonym, or fast EAP re-authentication identity. The
Server-Id is the empty string (zero length). Server-Id is the null string (zero length).
EAP-SIM EAP-SIM
EAP-SIM is defined in [RFC4186]. The EAP-SIM Session-Id is the EAP-SIM is defined in [RFC4186]. The EAP-SIM Session-Id is the
concatenation of the EAP Type Code (0x12) with the contents of the concatenation of the EAP Type Code (0x12) with the contents of the
RAND field from the AT_RAND attribute, followed by the contents of RAND field from the AT_RAND attribute, followed by the contents of
the NONCE_MT field in the AT_NONCE_MT attribute. the NONCE_MT field in the AT_NONCE_MT attribute.
The Peer-Id is the contents of the Identity field from the The Peer-Id is the contents of the Identity field from the
AT_IDENTITY attribute, using only the Actual Identity Length octets AT_IDENTITY attribute, using only the Actual Identity Length octets
from the beginning, however. Note that the contents are used as they from the beginning, however. Note that the contents are used as they
are transmitted, regardless of whether the transmitted identity was a are transmitted, regardless of whether the transmitted identity was a
permanent, pseudonym, or fast EAP re-authentication identity. The permanent, pseudonym, or fast EAP re-authentication identity. The
Server-Id is the empty string (zero length). Server-Id is the null string (zero length).
EAP-PSK EAP-PSK
EAP-PSK is defined in [RFC4764]. The EAP-PSK Session-Id is the EAP-PSK is defined in [RFC4764]. The EAP-PSK Session-Id is the
concatenation of the EAP Type Code (0x2F) with the peer (RAND_P) and concatenation of the EAP Type Code (0x2F) with the peer (RAND_P) and
server (RAND_S) nonces. The Peer-Id is the contents of the ID_P server (RAND_S) nonces. The Peer-Id is the contents of the ID_P
field and the Server-Id is the contents of the ID_S field. field and the Server-Id is the contents of the ID_S field.
EAP-SAKE EAP-SAKE
EAP-SAKE is defined in [RFC4763]. The EAP-SAKE Session-Id is the EAP-SAKE is defined in [RFC4763]. The EAP-SAKE Session-Id is the
concatenation of the EAP Type Code (0x30) with the contents of the concatenation of the EAP Type Code (0x30) with the contents of the
RAND_S field from the AT_RAND_S attribute, followed by the contents RAND_S field from the AT_RAND_S attribute, followed by the contents
of the RAND_P field in the AT_RAND_P attribute. Note that the EAP- of the RAND_P field in the AT_RAND_P attribute. Note that the EAP-
SAKE Session-Id is not the same as the "Session ID" parameter chosen SAKE Session-Id is not the same as the "Session ID" parameter chosen
by the Server, which is sent in the first message, and replicated in by the Server, which is sent in the first message, and replicated in
subsequent messages. The Peer-Id is contained within the value field subsequent messages. The Peer-Id is contained within the value field
of the AT_PEERID attibute and the Server-Id, if available, is of the AT_PEERID attribute and the Server-Id, if available, is
contained in the value field of the AT_SERVERID attribute. contained in the value field of the AT_SERVERID attribute.
EAP-TLS EAP-TLS
For EAP-TLS, the Peer-Id, Server-Id and Session-Id are defined in [I- For EAP-TLS, the Peer-Id, Server-Id and Session-Id are defined in [I-
D.simon-emu-rfc2716bis]. D.simon-emu-rfc2716bis].
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
skipping to change at page 66, line 42 skipping to change at page 73, line 42
Copies of IPR disclosures made to the IETF Secretariat and any Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf- this standard. Please address the information to the IETF at
ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
Open Issues Open Issues
Open issues relating to this specification are tracked on the Open issues relating to this specification are tracked on the
following web site: following web site:
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