draft-ietf-emu-eap-gpsk-01.txt   draft-ietf-emu-eap-gpsk-02.txt 
EMU Working Group T. Clancy EMU Working Group T. Clancy
Internet-Draft LTS Internet-Draft LTS
Intended status: Standards Track H. Tschofenig Intended status: Standards Track H. Tschofenig
Expires: May 4, 2007 Siemens Expires: July 9, 2007 Siemens Networks GmbH & Co KG
October 31, 2006 January 5, 2007
EAP Generalized Pre-Shared Key (EAP-GPSK) EAP Generalized Pre-Shared Key (EAP-GPSK)
draft-ietf-emu-eap-gpsk-01.txt draft-ietf-emu-eap-gpsk-02
Status of this Memo Status of this Memo
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This Internet-Draft will expire on May 4, 2007. This Internet-Draft will expire on July 9, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2007).
Abstract Abstract
This Internet Draft defines an Extensible Authentication Protocol This Internet Draft defines an Extensible Authentication Protocol
method called EAP Generalized Pre-Shared Key (EAP-GPSK). This method method called EAP Generalized Pre-Shared Key (EAP-GPSK). This method
is a lightweight shared-key authentication protocol supporting mutual is a lightweight shared-key authentication protocol supporting mutual
authentication and key derivation. authentication and key derivation.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Ciphersuites . . . . . . . . . . . . . . . . . . . . . . . . . 11 5. Ciphersuites . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Ciphersuites Processing Rules . . . . . . . . . . . . . . . . 13 6. Ciphersuites Processing Rules . . . . . . . . . . . . . . . . 12
6.1. Ciphersuite #1 . . . . . . . . . . . . . . . . . . . . . . 13 6.1. Ciphersuite #1 . . . . . . . . . . . . . . . . . . . . . . 12
6.1.1. Encryption . . . . . . . . . . . . . . . . . . . . . . 13 6.1.1. Encryption . . . . . . . . . . . . . . . . . . . . . . 12
6.1.2. Integrity . . . . . . . . . . . . . . . . . . . . . . 13 6.1.2. Integrity . . . . . . . . . . . . . . . . . . . . . . 12
6.1.3. Key Derivation . . . . . . . . . . . . . . . . . . . . 14 6.1.3. Key Derivation . . . . . . . . . . . . . . . . . . . . 13
6.2. Ciphersuite #2 . . . . . . . . . . . . . . . . . . . . . . 14 6.2. Ciphersuite #2 . . . . . . . . . . . . . . . . . . . . . . 13
6.2.1. Encryption . . . . . . . . . . . . . . . . . . . . . . 14 6.2.1. Encryption . . . . . . . . . . . . . . . . . . . . . . 13
6.2.2. Integrity . . . . . . . . . . . . . . . . . . . . . . 14 6.2.2. Integrity . . . . . . . . . . . . . . . . . . . . . . 13
6.2.3. Key Derivation . . . . . . . . . . . . . . . . . . . . 15 6.2.3. Key Derivation . . . . . . . . . . . . . . . . . . . . 14
7. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 15 7. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Header Format . . . . . . . . . . . . . . . . . . . . . . 15 7.1. Header Format . . . . . . . . . . . . . . . . . . . . . . 14
7.2. Ciphersuite Formatting . . . . . . . . . . . . . . . . . . 16 7.2. Ciphersuite Formatting . . . . . . . . . . . . . . . . . . 15
7.3. Payload Formatting . . . . . . . . . . . . . . . . . . . . 16 7.3. Payload Formatting . . . . . . . . . . . . . . . . . . . . 15
7.4. Protected Data . . . . . . . . . . . . . . . . . . . . . . 20 7.4. Protected Data . . . . . . . . . . . . . . . . . . . . . . 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 8. Packet Processing Rules . . . . . . . . . . . . . . . . . . . 21
8.1. Mutual Authentication . . . . . . . . . . . . . . . . . . 21
8.2. Protected Result Indications . . . . . . . . . . . . . . . 22
8.3. Integrity Protection . . . . . . . . . . . . . . . . . . . 22
8.4. Replay Protection . . . . . . . . . . . . . . . . . . . . 22
8.5. Reflection attacks . . . . . . . . . . . . . . . . . . . . 22
8.6. Dictionary Attacks . . . . . . . . . . . . . . . . . . . . 22
8.7. Key Derivation . . . . . . . . . . . . . . . . . . . . . . 22
8.8. Denial of Service Resistance . . . . . . . . . . . . . . . 22
8.9. Session Independence . . . . . . . . . . . . . . . . . . . 23
8.10. Exposition of the PSK . . . . . . . . . . . . . . . . . . 23
8.11. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 24
8.12. Channel Binding . . . . . . . . . . . . . . . . . . . . . 24
8.13. Fast Reconnect . . . . . . . . . . . . . . . . . . . . . . 24
8.14. Identity Protection . . . . . . . . . . . . . . . . . . . 24
8.15. Protected Ciphersuite Negotiation . . . . . . . . . . . . 24
8.16. Confidentiality . . . . . . . . . . . . . . . . . . . . . 24
8.17. Cryptographic Binding . . . . . . . . . . . . . . . . . . 24
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 25 9.1. Mutual Authentication . . . . . . . . . . . . . . . . . . 22
9.2. Protected Result Indications . . . . . . . . . . . . . . . 22
9.3. Integrity Protection . . . . . . . . . . . . . . . . . . . 23
9.4. Replay Protection . . . . . . . . . . . . . . . . . . . . 23
9.5. Reflection attacks . . . . . . . . . . . . . . . . . . . . 23
9.6. Dictionary Attacks . . . . . . . . . . . . . . . . . . . . 23
9.7. Key Derivation . . . . . . . . . . . . . . . . . . . . . . 23
9.8. Denial of Service Resistance . . . . . . . . . . . . . . . 23
9.9. Session Independence . . . . . . . . . . . . . . . . . . . 24
9.10. Exposition of the PSK . . . . . . . . . . . . . . . . . . 24
9.11. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 24
9.12. Channel Binding . . . . . . . . . . . . . . . . . . . . . 25
9.13. Fast Reconnect . . . . . . . . . . . . . . . . . . . . . . 25
9.14. Identity Protection . . . . . . . . . . . . . . . . . . . 25
9.15. Protected Ciphersuite Negotiation . . . . . . . . . . . . 25
9.16. Confidentiality . . . . . . . . . . . . . . . . . . . . . 25
9.17. Cryptographic Binding . . . . . . . . . . . . . . . . . . 25
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
11. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 25 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 26
12. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 26 12. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 27
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 13. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 27
13.1. Normative References . . . . . . . . . . . . . . . . . . . 26
13.2. Informative References . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Intellectual Property and Copyright Statements . . . . . . . . . . 29 14.1. Normative References . . . . . . . . . . . . . . . . . . . 27
14.2. Informative References . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
Intellectual Property and Copyright Statements . . . . . . . . . . 30
1. Introduction 1. Introduction
EAP Generalized Pre-Shared Key (EAP-GPSK) is an EAP method defining a EAP Generalized Pre-Shared Key (EAP-GPSK) is an EAP method defining a
generalized pre-shared key authentication technique. Mutual generalized pre-shared key authentication technique. Mutual
authentication is achieved through a nonce-based exchange that is authentication is achieved through a nonce-based exchange that is
secured by a pre-shared key. secured by a pre-shared key.
At present, several pre-shared key EAP methods are specified, most At present, several pre-shared key EAP methods are specified, most
notably notably
o EAP-PAX [I-D.clancy-eap-pax] o EAP-PAX [I-D.clancy-eap-pax]
o EAP-PSK [I-D.bersani-eap-psk] o EAP-PSK [I-D.bersani-eap-psk]
o EAP-TLS-PSK [I-D.otto-emu-eap-tls-psk] and o EAP-TLS-PSK [I-D.otto-emu-eap-tls-psk] and
o EAP-SAKE [I-D.vanderveen-eap-sake]. o EAP-SAKE [I-D.vanderveen-eap-sake].
Each proposal has its particular benefits but also its particular Each method has its particular benefits but also its particular
deficiencies. EAP-GPSK is a new EAP method that tries to combine the deficiencies. EAP-GPSK is a new EAP method that tries to combine the
most valuable characteristics of each of these methods and therefore most valuable characteristics of each of these methods and therefore
attempts to address a broad range of usage scenarios. attempts to address a broad range of usage scenarios.
The main design goals of EAP-GPSK are The main design goals of EAP-GPSK are
Simplicity: Simplicity:
EAP-GPSK should be easy to implement and therefore quickly EAP-GPSK should be easy to implement and therefore quickly
available. available.
Wide applicability: Wide applicability:
EAP-GPSK has been designed in a threat model where the attacker EAP-GPSK has been designed in a threat model where the attacker
has full control over the communication channel. This is the EAP has full control over the communication channel. This is the EAP
threat model that is presented in Section 7.1 of [RFC3748]. Thus, threat model that is presented in Section 7.1 of [RFC3748].
it is particularly suited for wireless or battery powered devices.
Efficiency: Efficiency:
EAP-GPSK does not make use of public key cryptography and fully EAP-GPSK does not make use of public key cryptography and fully
relies of symmetric cryptography. The restriction on symmetric relies of symmetric cryptography. The restriction on symmetric
cryptographic computations allows for low computational overhead. cryptographic computations allows for low computational overhead.
Hence, EAP-GPSK is lightweight and well suited for any type of Hence, EAP-GPSK is lightweight and well suited for any type of
device, especially those with little processing power and memory. device, especially those with processing power, memory and battery
constraints.
Flexibility: Flexibility:
EAP-GPSK offers cryptographic flexibility. At the beginning, the EAP-GPSK offers cryptographic flexibility. At the beginning, the
EAP server selects a set of cryptographic algorithms and key EAP server selects a set of cryptographic algorithms and key
sizes, a so called ciphersuite. The current version of EAP-GPSK sizes, a so called ciphersuite. The current version of EAP-GPSK
comprises two ciphersuites, but additional ones can be easily comprises two ciphersuites, but additional ones can be easily
added. added.
Extensibility: Extensibility:
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of the specification. These words are often capitalized. The key of the specification. These words are often capitalized. The key
words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
are to be interpreted as described in [RFC2119]. are to be interpreted as described in [RFC2119].
This section describes the various variables and functions used in This section describes the various variables and functions used in
the EAP-GPSK method. the EAP-GPSK method.
Variables: Variables:
PD_Payload_X: PD_Payload_X: Data carried within the X-th protected data payload
Data carried within the X-th protected data payload
CSuite_List:
An octet array listing available ciphersuites (variable length)
CSuite_Sel:
Ciphersuite selected by the client (1 octet or 7 octets)
ID_Client:
Client NAI [RFC2486bis]
ID_Server:
Server identity as an opaque blob. CSuite_List: An octet array listing available ciphersuites (variable
length)
KS: CSuite_Sel: Ciphersuite selected by the client (6 octets)
Integer representing the key size in octets of the selected ID_Client: Client NAI [RFC2486bis]
ciphersuite CSuite_Sel
RAND_Client: ID_Server: Server identity as an opaque blob.
Random integer generated by the client (256 bits) KS: Integer representing the key size in octets of the selected
ciphersuite CSuite_Sel. The key size is one of the ciphersuite
parameters.
RAND_Server: PL: Integer representing the length of the PSK in octets (2 octets)
Random integer generated by the server (256 bits) RAND_Client: Random integer generated by the client (16 octets)
RAND_Server: Random integer generated by the server (16 octets)
Operations: Operations:
A || B: A || B: Concatenation of octet strings A and B
Concatenation of octet strings A and B
ENC_X(Y):
Encryption of message Y with a symmetric key X, using a defined
block cipher
KDF_X(Y):
Key Derivation Function that generates an arbitrary number of
octets of output using secret X and seed Y
length(X):
Function that returns the length of input X in octets, encoded as
a 16-bit integer in network byte order
MAC_X(Y): ENC_X(Y): Encryption of message Y with a symmetric key X, using a
defined block cipher
Keyed message authentication code computed over Y with symmetric KDF_X(Y): Key Derivation Function that generates an arbitrary number
key X of octets of output using secret X and seed Y
SEC_X(Y): length(X): Function that returns the length of input X in octets,
encoded as a 2-octet integer in network byte order
SEC is a function that provides integrity protection based on the MAC_X(Y): Keyed message authentication code computed over Y with
chosen ciphersuite. The function SEC uses the algorithm defined symmetric key X
by the selected ciphersuite and applies it to the message content
Y with key X. As an output the message returns Y concatenated with
MAC_X(Y).
X[A..B]: SEC_X(Y): SEC is a function that provides integrity protection based
on the chosen ciphersuite. The function SEC uses the algorithm
defined by the selected ciphersuite and applies it to the message
content Y with key X. In short, SEC_X(Y) = Y|MAC_X(Y).
Notation representing octets A through B of octet array X X[A..B]: Notation representing octets A through B of octet array X
The following abbreviations are used for the keying material: The following abbreviations are used for the keying material:
PK: PK: Session key generated from the MK and used during protocol
Session key generated from the MK and used during protocol
exchange to encrypt protected data (size defined by ciphersuite) exchange to encrypt protected data (size defined by ciphersuite)
SK: SK: Session key generated from the MK and used during protocol
exchange to demonstrate knowledge of the PSK (size defined by
Session key generated from the MK and used during protocol ciphersuite)
exchange to prove knowledge of PSK (size defined by ciphersuite)
EMSK:
Extended Master Session Key is exported by the EAP method (512
bits)
MK:
Master Key between the client and EAP server from which all other
EAP method session keys are derived (KS octets)
MSK:
Master Session Key exported by to the EAP method (512 bits)
MID: EMSK: Extended Master Session Key is exported by the EAP method (32
octets)
Method ID exported by the EAP method according to the EAP keying MK: Master Key between the client and EAP server from which all
framework [I-D.ietf-eap-keying] (128 bits) other EAP method session keys are derived (KS octets)
PSK: MSK: Master Session Key exported by the EAP method (32 octets)
MID: Method ID exported by the EAP method according to the EAP
keying framework [I-D.ietf-eap-keying] (16 octets). The EAP
Session-Id uniquely identifies an EAP authentication exchange
between an EAP peer and an EAP server.
Long-term key shared between the client and the server (PL octets) PSK: Long-term key shared between the client and the server (PL
octets)
3. Overview 3. Overview
The EAP framework [RFC3748] defines four basic steps that occur The EAP framework (see Section 1.3 of [RFC3748]) defines three basic
during the execution of an EAP conversation between client and steps that occur during the execution of an EAP conversation between
server. The first phase, discovery, is handled by the underlying the EAP peer, the Authenticator and the EAP server.
protocol. The authentication phase is defined here. The key
distribution and secure association phases are handled differently 1. The first phase, discovery, is handled by the underlying
depending on the underlying protocol, and are not discussed in this protocol.
2. The EAP authentication phase with EAP-GPSK is defined in this
document. document.
3. The secure association distribution and secure association phases
are handled differently depending on the underlying protocol.
+--------+ +--------+ +--------+ +--------+
| | EAP-Request/Identity | | | | EAP-Request/Identity | |
| EAP |<------------------------------------| EAP | | EAP |<------------------------------------| EAP |
| peer | | server | | peer | | server |
| | EAP-Response/Identity | | | | EAP-Response/Identity | |
| |------------------------------------>| | | |------------------------------------>| |
| | | | | | | |
| | EAP-Request/GPSK-1 | | | | EAP-Request/GPSK-1 | |
| |<------------------------------------| | | |<------------------------------------| |
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| | | | | | | |
| | EAP-Response/GPSK-4 | | | | EAP-Response/GPSK-4 | |
| |------------------------------------>| | | |------------------------------------>| |
| | | | | | | |
| | EAP-Success or EAP-Failure | | | | EAP-Success or EAP-Failure | |
| |<------------------------------------| | | |<------------------------------------| |
+--------+ +--------+ +--------+ +--------+
EAP-GPSK performs mutual authentication between EAP peer ("Client") EAP-GPSK performs mutual authentication between EAP peer ("Client")
and EAP server ("Server") based on a pre-shared key (PSK). The and EAP server ("Server") based on a pre-shared key (PSK). The
protocol consists of two EAP message exchanges, in which both sides protocol consists of four message exchanges (GPSK-1, ... GPSK-4), in
which both sides exchange nonces and their identities, compute and
o exchange nonces and their identities and exchange a Message Authentication Code (MAC) over the previously
exchanged values, keyed with the pre-shared key. This MAC is
o compute and exchange a Message Authentication Code (MAC) over the considered as proof of possession of the pre-shared key.
previously exchanged values, keyed with the pre-shared key. This
MAC is considered as proof of possession of the pre-shared key.
The full EAP-GPSK protocol is as follows: The full EAP-GPSK protocol is as follows:
GPSK-1: GPSK-1:
ID_Server, RAND_Server, CSuite_List ID_Server, RAND_Server, CSuite_List
GPSK-2: GPSK-2:
SEC_SK(ID_Client, ID_Server, RAND_Client, RAND_Server, SEC_SK(ID_Client, ID_Server, RAND_Client, RAND_Server, CSuite_Sel,
CSuite_List, CSuite_Sel [, ENC_PK(PD_Payload_1), ... ] ) CSuite_List, [, ENC_PK(PD_Payload_1), ... ] )
GPSK-3 GPSK-3
SEC_SK(RAND_Client, RAND_Server, CSuite_Sel [, SEC_SK(RAND_Client, RAND_Server, CSuite_Sel [,
ENC_PK(PD_Payload_2) ] ) ENC_PK(PD_Payload_2), ... ] )
GPSK-4: GPSK-4:
[ SEC_SK(ENC_PK(PD_Payload_3)) ] [ SEC_SK(ENC_PK(PD_Payload_3)), ... ]
The EAP server begins EAP-GPSK creating a random number RAND_Server The EAP server begins EAP-GPSK by selecting a random number
and by encoding the supported ciphersuites into CSuite_List. A RAND_Server and by encoding the supported ciphersuites into
ciphersuite consists of an encryption algorithm, a key derivation CSuite_List. A ciphersuite consists of an encryption algorithm, a
function and a message authentication code. key derivation function and a message authentication code.
In GPSK-1, the EAP server sends its identity ID_Server, a random In GPSK-1, the EAP server sends its identity ID_Server, a random
number RAND_Server and the identifier of the chosen ciphersuite. The number RAND_Server and a list of supported ciphersuites CSuite_List.
decision which ciphersuite to use is policy-dependent and therefore The decision which ciphersuite to offer and which ciphersuite to pick
outside the scope of this document. is policy- and implementation-dependent and therefore outside the
scope of this document.
In GPSK-2, the peer sends its identity ID_Client, a random number In GPSK-2, the peer sends its identity ID_Client, a random number
RAND_Client. Furthermore, it repeats the received parameters of the RAND_Client. Furthermore, it repeats the received parameters of the
GPSK-1 message and computes a Message Authentication Code over all GPSK-1 message (ID_Server, RAND_Server, CSuite_List), the selected
these parameters. ciphersuite and computes a Message Authentication Code over all these
parameters.
The EAP server verifies the received Message Authentication Code. In The EAP server verifies the received Message Authentication Code. In
case of successful verification, the EAP server computes a Message case of successful verification, the EAP server computes a Message
Authentication Code over the session parameter and returns it to the Authentication Code over the session parameter and returns it to the
client (within GPSK-3). Within GPSK-2 and GPSK-3, peer and EAP client (within GPSK-3). Within GPSK-2 and GPSK-3, peer and EAP
server have the possibility to exchange encrypted protected data server have the possibility to exchange encrypted protected data
parameters. parameters.
The peer verifies the received Message Authentication Code. If the The peer verifies the received Message Authentication Code. If the
verification is successful, GPSK-4 is prepared. This message can verification is successful, GPSK-4 is prepared. This message can
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session keys SK and PK properly. Then, the EAP server sends an EAP session keys SK and PK properly. Then, the EAP server sends an EAP
Success message to indicate the successful outcome of the Success message to indicate the successful outcome of the
authentication. authentication.
4. Key Derivation 4. Key Derivation
EAP-GPSK provides key derivation in compliance to the requirements of EAP-GPSK provides key derivation in compliance to the requirements of
[RFC3748] and [I-D.ietf-eap-keying]. [RFC3748] and [I-D.ietf-eap-keying].
The long-term credential shared between EAP peer and EAP server The long-term credential shared between EAP peer and EAP server
SHOULD be a strong pre-shared key PSK of at least 16 bytes, though SHOULD be a strong pre-shared key PSK of at least 16 octets, though
its length and entropy is variable. While it is possible to use a its length and entropy is variable. While it is possible to use a
password or passphrase, doing so is NOT RECOMMENDED as it would make password or passphrase, doing so is NOT RECOMMENDED as it would make
EAP-GPSK vulnerable to dictionary attacks. EAP-GPSK vulnerable to dictionary attacks.
During an EAP-GPSK authentication, a Master Key MK, a Session Key SK During an EAP-GPSK authentication, a Master Key MK, a Session Key SK
and a Protected Data Encryption Key PK are derived using the and a Protected Data Encryption Key PK are derived using the
ciphersuite-specified KDF and data exchanged during the execution of ciphersuite-specified KDF and data exchanged during the execution of
the protocol, namely 'RAND_Client || ID_Client || RAND_Server || the protocol, namely 'RAND_Client || ID_Client || RAND_Server ||
ID_Server' referred as inputString as its short-hand form. ID_Server' referred as inputString as its short-hand form.
In case of successful completion, EAP-GPSK derives and exports an MSK In case of successful completion, EAP-GPSK derives and exports an MSK
and EMSK both in length of 64 bytes. This keying material is derived and EMSK both in length of 64 octets. This keying material is
using the ciphersuite-specified KDF as follows: derived using the ciphersuite-specified KDF as follows:
o inputString = RAND_Client || ID_Client || RAND_Server || ID_Server o inputString = RAND_Client || ID_Client || RAND_Server || ID_Server
o MK = KDF_Zero-String (PL || PSK || CSuite_Sel || o MK = KDF_Zero-String (PL || PSK || CSuite_Sel ||
inputString)[0..KS-1] inputString)[0..KS-1]
o SK = KDF_MK (inputString)[128..127+KS]
o PK = KDF_MK (inputString)[128+KS..127+2*KS]
o MSK = KDF_MK (inputString)[0..63] o MSK = KDF_MK (inputString)[0..63]
o EMSK = KDF_MK (inputString)[64..127] o EMSK = KDF_MK (inputString)[64..127]
o SK = KDF_MK (inputString)[128..127+KS]
o PK = KDF_MK (inputString)[128+KS..127+2*KS]
o MID = KDF_Zero-String ("Method ID" || EAP_Method_Type || o MID = KDF_Zero-String ("Method ID" || EAP_Method_Type ||
CSuite_Sel || inputString)[0..15] CSuite_Sel || inputString)[0..15]
Note that the term 'Zero-String' refers to a sequence of 0x00 values, Note that the term 'Zero-String' refers to a sequence of 0x00 values,
KS octets in length. EAP_Method_Type refers to the integer value of KS octets in length. EAP_Method_Type refers to the integer value of
the IANA allocated EAP Type code. the IANA allocated EAP Type code.
Figure 2 depicts the key derivation procedure of EAP-GPSK. Figure 2 depicts the key derivation procedure of EAP-GPSK.
+-------------+ +-------------------------------+ +-------------+ +-------------------------------+
| PL-octet | | RAND_Client || ID_Client || | | PL-octet | | RAND_Client || ID_Client || |
| PSK | | RAND_Server || ID_Server | | PSK | | RAND_Server || ID_Server |
+-------------+ +-------------------------------+ +-------------+ +-------------------------------+
| | | | | |
v v | | +------------+ | |
| | CSuite_Sel | | |
| +------------+ | |
| | | |
v v v |
+--------------------------------------------+ | +--------------------------------------------+ |
| KDF | | | KDF | |
+--------------------------------------------+ | +--------------------------------------------+ |
| | | |
v | v |
+-------------+ | +-------------+ |
| KS-octet | | | KS-octet | |
| MK | | | MK | |
+-------------+ | +-------------+ |
| | | |
v v v v
+---------------------------------------------------+ +---------------------------------------------------+
| KDF | | KDF |
+---------------------------------------------------+ +---------------------------------------------------+
| | | | | | | |
v v v v v v v v
+---------+ +---------+ +----------+ +----------+ +---------+ +---------+ +----------+ +----------+
| 512-bit | | 512-bit | | KS-octet | | KS-octet | | 32-octet| | 32-octet| | KS-octet | | KS-octet |
| MSK | | EMSK | | SK | | PK | | MSK | | EMSK | | SK | | PK |
+---------+ +---------+ +----------+ +----------+ +---------+ +---------+ +----------+ +----------+
Figure 2: EAP-GPSK Key Derivation Figure 2: EAP-GPSK Key Derivation
5. Ciphersuites 5. Ciphersuites
The design of EAP-GPSK allows cryptographic algorithms and key sizes, The design of EAP-GPSK allows cryptographic algorithms and key sizes,
called ciphersuites, to be negotiated during the protocol run. The called ciphersuites, to be negotiated during the protocol run. The
ability to specify block-based and hash-based ciphersuites is ability to specify block-based and hash-based ciphersuites is
skipping to change at page 12, line 18 skipping to change at page 11, line 21
+-----------+----+-------------+---------------+--------------------+ +-----------+----+-------------+---------------+--------------------+
| 0x000001 | 16 | AES-CBC-128 | AES_CMAC_128 | GKDF-128 | | 0x000001 | 16 | AES-CBC-128 | AES_CMAC_128 | GKDF-128 |
+-----------+----+-------------+---------------+--------------------+ +-----------+----+-------------+---------------+--------------------+
| 0x000002 | 32 | NULL | HMAC-SHA256 | GKDF-256 | | 0x000002 | 32 | NULL | HMAC-SHA256 | GKDF-256 |
+-----------+----+-------------+---------------+--------------------+ +-----------+----+-------------+---------------+--------------------+
Figure 3: Ciphersuites Figure 3: Ciphersuites
Ciphersuite 1, which is based on AES as a cryptographic primitive, is Ciphersuite 1, which is based on AES as a cryptographic primitive, is
mandatory to implement. This document specifies also a second mandatory to implement. This document specifies also a second
ciphersuite, but its support is only optional. ciphersuite, but its support is optional.
Each ciphersuite needs to specify a key derivation function. The Each ciphersuite needs to specify a key derivation function. The
ciphersuites defined in this document make use of the Generalized Key ciphersuites defined in this document make use of the Generalized Key
Distribution Function (GKDF). Future ciphersuites can use any other Distribution Function (GKDF). Future ciphersuites can use any other
formally specified KDF that takes as arguments a key and a seed formally specified KDF that takes as arguments a key and a seed
value, and produces at least 1024+2*KS bits of output. value, and produces at least 128+2*KS octets of output.
If GKDF is invoked by a MAC-based ciphersuite, then the variable If GKDF is invoked by a MAC-based ciphersuite, then the variable
"size" contains the MAC output size in octets. In case of a block "size" contains the MAC output size in octets. In case of a block
cipher-based ciphersuite, "size" contains the block size in octets. cipher-based ciphersuite, "size" contains the block size in octets.
GKDF has the following structure: GKDF has the following structure:
GKDF-X(Y, Z) GKDF-X(Y, Z)
X length, in octets, of the desired output X length, in octets, of the desired output
Y secret key used to protect the computation Y secret key
Z data specific for the protocol run Z inputstring
hashlen: is the size of hash function output in octets.
Hash-Function: SHA-1 is required, SHAs are recommended.
GKDF-X (Y, Z) {
n = ceiling integer of ( X / hashlen );
/* determine number of output blocks */
GKDF-X (Y, Z)
{
n = int( X / size - 1 ) + 1; /* determine number of
output blocks */
M_0 = ""; M_0 = "";
result = ""; result = "";
for i=1 to n { for i=1 to n {
M_i = MAC_Y (M_{i-1} || Z || i || X); M_i = Hash-Function (i || y || Z);
result = result || M_i; result = result || M_i;
} }
return truncate (result; X) return truncate (result; X)
} }
Note that the variables 'i' and 'X' in M_i are represented as 16-bit
Note that the variables 'i' and 'X' in M_i are represented as 2-octet
values in network byte order. values in network byte order.
6. Ciphersuites Processing Rules 6. Ciphersuites Processing Rules
6.1. Ciphersuite #1 6.1. Ciphersuite #1
6.1.1. Encryption 6.1.1. Encryption
With this ciphersuite all cryptography is built around a single With this ciphersuite all cryptography is built around a single
cryptographic primitive, AES-128. Within the protected data frames, cryptographic primitive, AES-128. Within the protected data frames,
AES-128 is used in CBC mode of operation (see [CBC]). The CBC mode AES-128 is used in CBC mode of operation (see [CBC]). This mode
is well-defined and well-understood. This mode requires an requires an Initialization Vector (IV) that has the same size as the
Initialization Vector (IV) that has the same size as the block size. block size. For security reasons, the IV should be randomly
For security reasons, the IV should be randomly generated. generated.
In a nutshell, the CBC mode proceeds as follows. The IV is XORed In a nutshell, the CBC mode proceeds as follows. The IV is XORed
with the first plaintext block before it is encrypted. Then for with the first plaintext block before it is encrypted. Then for
successive blocks, the previous ciphertext block is XORed with the successive blocks, the previous ciphertext block is XORed with the
current plaintext, before it is encrypted. current plaintext, before it is encrypted.
Note that in order to provide integrity protection, the CBC-encrypted
ciphertext MUST be accompanied by a MAC.
[Editor's Note: Description about the computation of the IV is
missing]
6.1.2. Integrity 6.1.2. Integrity
Ciphersuite 1 uses CMAC as Message Authentication Code. CMAC is Ciphersuite 1 uses CMAC as Message Authentication Code. CMAC is
recommended by NIST. Among its advantages, CMAC is capable to work recommended by NIST. Among its advantages, CMAC is capable to work
with messages of arbitrary length. A detailed description of CMAC with messages of arbitrary length. A detailed description of CMAC
can be found in [CMAC]. can be found in [CMAC].
The following instantiation is used: AES-128-CMAC(SK, Input) denotes The following instantiation is used: AES-128-CMAC(SK, Input) denotes
the MAC of Input under the key SK. the MAC of Input under the key SK.
where Input refers to the following content: where Input refers to the following content:
o Value of SEC_SK in message GPSK-2 o Value of SEC_SK(Value) in message GPSK-2
o Value of SEC_SK in message GPSK-3 o Value of SEC_SK(Value) in message GPSK-3
o Value of SEC_SK in message GPSK-4 o Value of SEC_SK(Value) in message GPSK-4
6.1.3. Key Derivation 6.1.3. Key Derivation
This ciphersuite instantiates the KDF in the following way: This ciphersuite instantiates the KDF in the following way:
inputString = RAND_Client || ID_Client || RAND_Server || ID_Server inputString = RAND_Client || ID_Client || RAND_Server || ID_Server
MK = GKDF-16 (Zero-String, PL || PSK || CSuite_SEL || inputString) MK = GKDF-16 (Zero-String, PL || PSK || CSuite_SEL || inputString)
KDF_out = GKDF-160 (MK, inputString) MSK = GKDF-160 (MK, inputString)[0..63]
MSK = KDF_out[0..63]
EMSK = KDF_out[64..127] EMSK = GKDF-160 (MK, inputString)[64..127]
SK = KDF_out[128..143] SK = GKDF-160 (MK, inputString)[128..143]
PK = KDF_out[144..159] PK = GKDF-160 (MK, inputString)[144..159]
MID = GKDF-16 (Zero-String, "Method ID" || EAP_Method_Type || MID = GKDF-16 (Zero-String, "Method ID" || EAP_Method_Type ||
CSuite_Sel || inputString) CSuite_Sel || inputString)
6.2. Ciphersuite #2 6.2. Ciphersuite #2
6.2.1. Encryption 6.2.1. Encryption
Ciphersuite 2 does not include an algorithm for encryption. With a Ciphersuite 2 does not include an algorithm for encryption. With a
NULL encryption algorithm, encryption is defined as: NULL encryption algorithm, encryption is defined as:
skipping to change at page 14, line 49 skipping to change at page 14, line 5
6.2.2. Integrity 6.2.2. Integrity
Ciphersuite 2 uses the keyed MAC function HMAC, with the SHA256 hash Ciphersuite 2 uses the keyed MAC function HMAC, with the SHA256 hash
algorithm. algorithm.
For integrity protection the following instantiation is used: For integrity protection the following instantiation is used:
HMAC-SHA256(SK, Input) denotes the MAC of Input under the key SK HMAC-SHA256(SK, Input) denotes the MAC of Input under the key SK
where Input refers to the following content: where Input refers to the following content:
o Value of SEC_SK in message GPSK-2 o Value of SEC_SK(Value) in message GPSK-2
o Value of SEC_SK in message GPSK-3 o Value of SEC_SK(Value) in message GPSK-3
o Value of SEC_SK in message GPSK-4 o Value of SEC_SK(Value) in message GPSK-4
6.2.3. Key Derivation 6.2.3. Key Derivation
This ciphersuite instantiates the KDF in the following way: This ciphersuite instantiates the KDF in the following way:
inputString = RAND_Client || ID_Client || RAND_Server || ID_Server inputString = RAND_Client || ID_Client || RAND_Server || ID_Server
MK = GKDF-32 (Zero-String, PL || PSK || CSuite_SEL || inputString) MK = GKDF-32 (Zero-String, PL || PSK || CSuite_SEL || inputString)
KDF_out = GKDF-192 (MK, inputString) MSK = GKDF-192 (MK, inputString)[0..63]
MSK = KDF_out[0..63]
EMSK = KDF_out[64..127] EMSK = GKDF-192 (MK, inputString)[64..127]
SK = KDF_out[128..159] SK = GKDF-192 (MK, inputString)[128..159]
PK = KDF_out[160..191] PK = GKDF-192 (MK, inputString)[160..191]
MID = GKDF-16 (Zero-String, "Method ID" || EAP_Method_Type || MID = GKDF-16 (Zero-String, "Method ID" || EAP_Method_Type ||
CSuite_Sel || inputString) CSuite_Sel || inputString)
7. Packet Formats 7. Packet Formats
This section defines the packet format of the EAP-GPSK messages. This section defines the packet format of the EAP-GPSK messages.
7.1. Header Format 7.1. Header Format
skipping to change at page 16, line 13 skipping to change at page 15, line 13
The Code, Identifier, Length, and Type fields are all part of the EAP The Code, Identifier, Length, and Type fields are all part of the EAP
header, and defined in [RFC3748]. IANA has allocated EAP Method Type header, and defined in [RFC3748]. IANA has allocated EAP Method Type
XX for EAP-GPSK, thus the Type field in the EAP header MUST be XX. XX for EAP-GPSK, thus the Type field in the EAP header MUST be XX.
The OP-Code field is one of four values: The OP-Code field is one of four values:
o 0x01 : GPSK-1 o 0x01 : GPSK-1
o 0x02 : GPSK-2 o 0x02 : GPSK-2
o 0x03 : GPSK-3 o 0x03 : GPSK-3
o 0x04 : GPSK-4 o 0x04 : GPSK-4
o 0x05 : GPSK-Fail
o 0x06 : GPSK-Protected-Fail
7.2. Ciphersuite Formatting 7.2. Ciphersuite Formatting
Ciphersuites are encoded as 6-octet arrays. The first three octets Ciphersuites are encoded as 6-octet arrays. The first three octets
indicate the CSuite/Vendor field. For vendor-specific ciphersuites, indicate the CSuite/Vendor field. For vendor-specific ciphersuites,
this represents the vendor OID. The last three octets indicate the this represents the vendor OID. The last three octets indicate the
CSuite/Specifier field, which identifies the particular ciphersuite. CSuite/Specifier field, which identifies the particular ciphersuite.
The 3-byte CSuite/Vendor value 0x000000 indicates ciphersuites The 3-octet CSuite/Vendor value 0x000000 indicates ciphersuites
allocated by the IETF. allocated by the IETF.
Graphically, they are represented as Graphically, they are represented as
--- bit offset ---> --- bit offset --->
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CSuite/Vendor = 0x000000 or OID | | CSuite/Vendor = 0x000000 or OID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 20, line 26 skipping to change at page 19, line 26
... KS-octet payload MAC ... ... KS-octet payload MAC ...
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: GPSK-4 Payload Figure 10: GPSK-4 Payload
If the optional protected data payload is not included, then If the optional protected data payload is not included, then
length(PD_Payload)=0 and the PD payload is excluded. The MAC MUST length(PD_Payload)=0 and the PD payload is excluded. The MAC MUST
always be included, regardless of the presence of PD_Payload_3. always be included, regardless of the presence of PD_Payload_3.
The GPSK-Fail payload format is defined as follows:
--- bit offset --->
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Failure-Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: GPSK-Fail Payload
The GPSK-Protected-Fail payload format is defined as follows:
--- bit offset --->
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Failure-Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
... KS-octet payload MAC ...
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: GPSK-Protected-Fail Payload
The Failure-Code field is one of three values, but can be extended:
o 0x00000001: PSK Not Found
o 0x00000002: Authentication Failure
o 0x00000003: Authorization Failure
o 0x00000004 through 0xFFFFFFFF : Unallocated
"PSK Not Found" indicates a key for a particular user could not be
located, making authentication impossible. "Authentication Failure"
indicates a MAC failure due to a PSK mismatch. "Authorization
Failure" indicates that while the PSK being used is correct, the user
is not authorized to connect.
7.4. Protected Data 7.4. Protected Data
The protected data blocks are a generic mechanism for the client and The protected data blocks are a generic mechanism for the client and
server to securely exchange data. If the specified ciphersuite has a server to securely exchange data. If the specified ciphersuite has a
NULL encryption primitive, then this channel only offers NULL encryption primitive, then this channel only offers
authenticity, and not confidentiality. authenticity, and not confidentiality.
These payloads are encoded as the concatenation of type-length-value These payloads are encoded as the concatenation of type-length-value
(TLV) tripples. (TLV) tripples.
skipping to change at page 21, line 24 skipping to change at page 21, line 24
... PD_Payload Value ... ... PD_Payload Value ...
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For PData/Vendor field 0x000000, the following PData/Specifier fields For PData/Vendor field 0x000000, the following PData/Specifier fields
are defined: are defined:
o 0x000000 : Reserved o 0x000000 : Reserved
o 0x000001 : Protected Results Indication o 0x000001 : Protected Results Indication
o 0x000002 through 0xFFFFFF : Unallocated o 0x000002 through 0xFFFFFF : Unallocated
[Editor's Note: Text for protected results indication needs to be 8. Packet Processing Rules
added here.]
8. Security Considerations This section defines how the EAP client and EAP server MUST behave
when received packet is deemed invalid.
Any packet that cannot be parsed by the EAP client or the EAP server
MUST be silently discarded. An EAP client or EAP server receiving
any unexpected packet (i.e. an EAP client receiving GPSK-3 before
receving GPSK-1 or before transmitting GPSK-2) MUST silently discard
the packet.
GPSK-1 contains no MAC protection, so provided it properly parses, it
MUST be accepted by the client. If the EAP client decides the
ID_Server is that of a AAA server to which it does not wish to
authenticate, the EAP client should respond with an EAP-NACK.
For GPSK-2, if ID_Client is for an unknown user, the EAP server MUST
send either a "PSK Not Found" GPSK-Fail message, or an
"Authentication Failure" GPSK-Fail, depending on its policy, and
discard the received packet. If the MAC validation fails, the server
MUST transmit a GPSK-Fail message specifying "Authentication
Failure". and discard the received packet. If the RAND_Server or
CSuite_List field in GPSK-2 does not match the values in GPSK-1, the
server MUST silently discard the packet. If server policy determines
the client is not authorized and the MAC is correct, the server MUST
transmit a GPSK-Protected-Fail message indicating "Authorization
Failure" and discard the received packet.
A client receiving a GPSK-Fail or GPSK-Protected-Fail message in
response to a GPSK-2 message MUST either transmit an EAP-Failure
message and end the session, or retry transmission of GPSK-2,
attempting to correct whatever failure occured. If MAC validation on
a GPSK-Protected-Fail packet fails, then the received packet MUST be
silently discarded.
For GPSK-3, a client MUST silently discard any packet containing
whose RAND_Client, RAND_Server, or CSuite_Sel fields do match those
transmitted in GPSK-2. An EAP client MUST silently discard any
packet whose MAC fails.
For GPSK-4, a server MUST silently discard any packet whose MAC fails
validation.
If a decryption failure of a protected payload is detected, the
recipient MUST silently discard the GPSK packet.
9. Security Considerations
[RFC3748] highlights several attacks that are possible against EAP [RFC3748] highlights several attacks that are possible against EAP
since EAP itself does not provide any security. since EAP itself does not provide any security.
This section discusses the claimed security properties of EAP-GPSK as This section discusses the claimed security properties of EAP-GPSK as
well as vulnerabilities and security recommendations in the threat well as vulnerabilities and security recommendations in the threat
model of [RFC3748]. model of [RFC3748].
8.1. Mutual Authentication 9.1. Mutual Authentication
EAP-GPSK provides mutual authentication. EAP-GPSK provides mutual authentication.
The server believes that the peer is authentic because it can The server believes that the peer is authentic because it can
calculate a valid MAC and the peer believes that the server is calculate a valid MAC and the peer believes that the server is
authentic because it can calculate another valid MAC. authentic because it can calculate another valid MAC.
The key used for mutual authentication is computed again based on the The key used for mutual authentication is computed again based on the
long-term secret PSK that has to provide sufficient entropy and long-term secret PSK that has to provide sufficient entropy and
therefore sufficient strength. In this way EAP-GPSK is no different therefore sufficient strength. In this way EAP-GPSK is no different
than other authentication protocols based on pre-shared keys. than other authentication protocols based on pre-shared keys.
8.2. Protected Result Indications 9.2. Protected Result Indications
EAP-GPSK offers the capability to exchange protected result EAP-GPSK offers the capability to exchange protected result
indications using the protected data payloads. indications using the protected data payloads.
8.3. Integrity Protection 9.3. Integrity Protection
EAP-GPSK provides integrity protection based on the ciphersuites EAP-GPSK provides integrity protection based on the ciphersuites
suggested in this document. suggested in this document.
8.4. Replay Protection 9.4. Replay Protection
EAP-GPSK provides replay protection of its mutual authentication part EAP-GPSK provides replay protection of its mutual authentication part
thanks to the use of random numbers RAND_Server and RAND_P. Since thanks to the use of random numbers RAND_Server and RAND_P. Since
RAND_Server is 128 bit long, one expects to have to record 2**64 RAND_Server is 16 octets long, one expects to have to record 2**64
(i.e., approximately 1.84*10**19) EAP-GPSK successful authentication (i.e., approximately 1.84*10**19) EAP-GPSK successful authentication
before an protocol run can be replayed. Hence, EAP-GPSK provides before an protocol run can be replayed. Hence, EAP-GPSK provides
replay protection of its mutual authentication part as long as replay protection of its mutual authentication part as long as
RAND_Server and RAND_Client are chosen at random, randomness is RAND_Server and RAND_Client are chosen at random, randomness is
critical for security. critical for replay protection.
8.5. Reflection attacks 9.5. Reflection attacks
EAP-GPSK provides protection against reflection attacks in case of an EAP-GPSK provides protection against reflection attacks in case of an
extended authentication because of the messages are constructed in a extended authentication because the messages are constructed in a
different fashion. different fashion.
8.6. Dictionary Attacks 9.6. Dictionary Attacks
EAP-GPSK relies on a long-term shared secret (PSK) that MUST be based EAP-GPSK relies on a long-term shared secret (PSK) that MUST be based
on at least 128 bits of entropy to guarantee security against on at least 16 octets of entropy to guarantee security against
dictionary attacks. Users who use passwords or weak keys are not dictionary attacks. Users who use passwords are not guaranteed
guaranteed security against dictionary attacks. Derivation of the security against dictionary attacks. Derivation of the long-term
long-term shared secret from a password is highly discouraged. shared secret from a password is strongly discouraged.
8.7. Key Derivation 9.7. Key Derivation
EAP-GPSK supports key derivation as shown in Section 4. EAP-GPSK supports key derivation as shown in Section 4.
8.8. Denial of Service Resistance 9.8. Denial of Service Resistance
Denial of Service resistance (DoS) has not been a design goal for Denial of Service (DoS) resistance has not been a design goal for
EAP-GPSK. EAP-GPSK.
It is however believed that EAP-GPSK does not provide any obvious and It is however believed that EAP-GPSK does not provide any obvious and
avoidable venue for such attacks. avoidable venue for such attacks.
It is worth noting that the server has to maintain some state when it It is worth noting that the server has to maintain some state when it
engages in an EAP-GPSK conversation, namely to generate and to engages in an EAP-GPSK conversation, namely to generate and to
remember the 16-byte RAND_S. This should however not lead to resource remember the 16-octet RAND_S. This should however not lead to
exhaustion as this state and the associated computation are fairly resource exhaustion as this state and the associated computation are
lightweight. fairly lightweight.
It is recommended that EAP-GPSK does not allow EAP notifications to It is recommended that EAP-GPSK does not allow EAP notifications to
be interleaved in its dialog to prevent potential DoS attacks. be interleaved in its dialog to prevent potential DoS attacks.
Indeed, since EAP Notifications are not integrity protected, they can Indeed, since EAP Notifications are not integrity protected, they can
easily be spoofed by an attacker. Such an attacker could force a easily be spoofed by an attacker. Such an attacker could force a
peer that allows EAP Notifications to engage in a discussion which peer that allows EAP Notifications to engage in a discussion which
would delay his authentication or result in the peer taking would delay his authentication or result in the peer taking
unexpected actions (e.g., in case a notification is used to prompt unexpected actions (e.g., in case a notification is used to prompt
the peer to do some "bad" action). the peer to do some "bad" action).
It is up to the implementation of EAP-GPSK or to the peer and the It is up to the implementation of EAP-GPSK or to the peer and the
server to specify the maximum number of failed cryptographic checks server to specify the maximum number of failed cryptographic checks
that are allowed. that are allowed.
8.9. Session Independence 9.9. Session Independence
Thanks to its key derivation mechanisms, EAP-GPSK provides session Thanks to its key derivation mechanisms, EAP-GPSK provides session
independence: passive attacks (such as capture of the EAP independence: passive attacks (such as capture of the EAP
conversation) or active attacks (including compromise of the MSK or conversation) or active attacks (including compromise of the MSK or
EMSK) do not enable compromise of subsequent or prior MSKs or EMSKs. EMSK) do not enable compromise of subsequent or prior MSKs or EMSKs.
The assumption that RAND_Client and RAND_Server are random is central The assumption that RAND_Client and RAND_Server are random is central
for the security of EAP-GPSK in general and session independance in for the security of EAP-GPSK in general and session independance in
particular. particular.
8.10. Exposition of the PSK 9.10. Exposition of the PSK
EAP-GPSK does not provide perfect forward secrecy. Compromise of the EAP-GPSK does not provide perfect forward secrecy. Compromise of the
PSK leads to compromise of recorded past sessions. PSK leads to compromise of recorded past sessions.
Compromise of the PSK enables the attacker to impersonate the peer Compromise of the PSK enables the attacker to impersonate the peer
and the server and it allows the adversary to compromise future and the server and it allows the adversary to compromise future
sessions. sessions.
EAP-GPSK provides no protection against a legitimate peer sharing its EAP-GPSK provides no protection against a legitimate peer sharing its
PSK with a third party. Such protection may be provided by PSK with a third party. Such protection may be provided by
appropriate repositories for the PSK, which choice is outside the appropriate repositories for the PSK, which choice is outside the
scope of this document. The PSK used by EAP-GPSK must only be shared scope of this document. The PSK used by EAP-GPSK must only be shared
between two parties: the peer and the server. In particular, this between two parties: the peer and the server. In particular, this
PSK must not be shared by a group of peers communicating with the PSK must not be shared by a group of peers communicating with the
same server. same server.
The PSK used by EAP-GPSK must be cryptographically separated from The PSK used by EAP-GPSK must be cryptographically separated from
keys used by other protocols, otherwise the security of EAP-GPSK may keys used by other protocols, otherwise the security of EAP-GPSK may
be compromised. be compromised.
8.11. Fragmentation 9.11. Fragmentation
EAP-GPSK does not support fragmentation and reassembly since the EAP-GPSK does not support fragmentation and reassembly since the
message size is kept small. message size is small.
8.12. Channel Binding 9.12. Channel Binding
This document enables the ability to exchange channel binding This document enables the ability to exchange channel binding
information. It does not, however, define the encoding of channel information. It does not, however, define the encoding of channel
binding information in the document. binding information in the document.
8.13. Fast Reconnect 9.13. Fast Reconnect
EAP-GPSK does not provide the fast reconnect capability since this EAP-GPSK does not provide the fast reconnect capability since this
method is already at the lower limit of the number of roundtrips and method is already at (or close to) the lower limit of the number of
the cryptographic operations. roundtrips and the cryptographic operations.
8.14. Identity Protection 9.14. Identity Protection
Identity protection is not specified in this document. Extensions Identity protection is not specified in this document. Extensions
can be defined that enhanced this protocol to provide this feature. can be defined that enhance this protocol to provide this feature.
8.15. Protected Ciphersuite Negotiation 9.15. Protected Ciphersuite Negotiation
EAP-GPSK provides protected ciphersuite negotiation via the EAP-GPSK provides protected ciphersuite negotiation via the
indication of available ciphersuites by the server in the first indication of available ciphersuites by the server in the first
message and a confirmation by the client in the subsequent message. message and a confirmation by the client in the subsequent message.
8.16. Confidentiality 9.16. Confidentiality
Although EAP-GPSK provides confidentiality in its protected data Although EAP-GPSK provides confidentiality in its protected data
payloads, it cannot claim to do so as per Section 7.2.1 of [RFC3748]. payloads, it cannot claim to do so as per Section 7.2.1 of [RFC3748].
8.17. Cryptographic Binding 9.17. Cryptographic Binding
Since EAP-GPSK does not tunnel another EAP method, it does not Since EAP-GPSK does not tunnel another EAP method, it does not
implement cryptographic binding. implement cryptographic binding.
9. IANA Considerations 10. IANA Considerations
This document requires IANA to allocate a new EAP Type for EAP-GPSK. This document requires IANA to allocate a new EAP Type for EAP-GPSK.
This document requires IANA to create a new registry for ciphersuites This document requires IANA to create a new registry for
and protected data types. IANA is furthermore instructed to add the ciphersuites, protected data types, and failure codes. IANA is
specified ciphersuites and protected data types to this registry as furthermore instructed to add the specified ciphersuites, protected
defined in this document. Values can be added or modified with data types, and failure codes to this registry as defined in this
informational RFCs defining either block-based or hash-based document. Values can be added or modified with informational RFCs
ciphersuites. Each ciphersuite needs to provide processing rules and defining either block-based or hash-based ciphersuites, protected
needs to specify how the following algorithms are instantiated: data payloads, or failure codes. Each ciphersuite needs to provide
Encryption, Integrity and Key Derivation. Additionally, the processing rules and needs to specify how the following algorithms
preferred key size needs to be specified. are instantiated: Encryption, Integrity and Key Derivation.
Additionally, the preferred key size needs to be specified.
The following layout represents the initial ciphersuite CSuite/ The following layout represents the initial ciphersuite CSuite/
Specifier registry setup: Specifier registry setup:
o 0x000000 : Reserved o 0x000000 : Reserved
o 0x000001 : AES-CBC-128, AES-CMAC-128, GKDF-128 o 0x000001 : AES-CBC-128, AES-CMAC-128, GKDF-128
o 0x000002 : NULL, HMAC-SHA256, GKDF-256 o 0x000002 : NULL, HMAC-SHA256, GKDF-256
o 0x000003 through 0xFFFFFF : Unallocated o 0x000003 through 0xFFFFFF : Unallocated
The following is the initial protected data PData/Specifier registry The following is the initial protected data PData/Specifier registry
setup: setup:
o 0x000000 : Reserved o 0x000000 : Reserved
o 0x000001 : Protected Results Indication o 0x000001 : Protected Results Indication
o 0x000002 through 0xFFFFFF : Unallocated o 0x000002 through 0xFFFFFF : Unallocated
10. Contributors The following layout represents the initial Failure-Code registry
setup:
o 0x00000001: PSK Not Found
o 0x00000002: Authentication Failure
o 0x00000003: Authorization Failure
o 0x00000004 through 0xFFFFFFFF : Unallocated
11. Contributors
This work is a joint effort of the EAP Method Update (EMU) design This work is a joint effort of the EAP Method Update (EMU) design
team of the EMU Working Group that was created to develop a mechanism team of the EMU Working Group that was created to develop a mechanism
based on strong shared secrets that meets RFC 3748 [RFC3748] and RFC based on strong shared secrets that meets RFC 3748 [RFC3748] and RFC
4017 [RFC4017] requirements. The contributors (in alphabetical 4017 [RFC4017] requirements. The design team members (in
order) include: alphabetical order) were:
o Jari Arkko o Jari Arkko
o Mohamad Badra o Mohamad Badra
o Uri Blumenthal o Uri Blumenthal
o Charles Clancy o Charles Clancy
o Lakshminath Dondeti o Lakshminath Dondeti
o David McGrew o David McGrew
o Joe Salowey o Joe Salowey
o Sharma Suman o Sharma Suman
o Hannes Tschofenig o Hannes Tschofenig
o Jesse Walker o Jesse Walker
Finally, we would like to thank Thomas Otto for his draft reviews, Finally, we would like to thank Thomas Otto for his draft reviews,
feedback and text contributions. feedback and text contributions.
11. Acknowledgment 12. Acknowledgment
We would like to thank We would like to thank
o Jouni Malinen and Bernard Aboba for their early draft comments in o Jouni Malinen and Bernard Aboba for their early draft comments in
June 2006. June 2006. Jouni Malinen developed the first prototype
implementation. It can be found at:
http://hostap.epitest.fi/releases/snapshots/
o Lakshminath Dondeti, David McGrew, Bernard Aboba, Michaela o Lakshminath Dondeti, David McGrew, Bernard Aboba, Michaela
Vanderveen and Ray Bell for their input to the ciphersuite Vanderveen and Ray Bell for their input to the ciphersuite
discussions between July and August 2006. discussions between July and August 2006.
o Lakshminath for his detailed draft review (sent to the EMU ML on o Lakshminath Dondeti for his detailed draft review (sent to the EMU
the 12th July 2006). ML on the 12th July 2006).
o Based on a review requested from NIST Quynh Dang suggested changes
to the GKDF function (December 2006).
12. Open Issues 13. Open Issues
The list of open issues can be found at: The list of open issues can be found at:
http://www.tschofenig.com:8080/eap-gpsk/ http://www.tschofenig.com:8080/eap-gpsk/
A first prototype implementation by Jouni Malinen can be found at: 14. References
http://hostap.epitest.fi/releases/snapshots/
13. References
13.1. Normative References 14.1. 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", March 1997. Requirement Levels", March 1997.
[RFC2486bis] [RFC2486bis]
Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", Network Access Identifier",
draft-ietf-radext-rfc2486bis-06 (work in progress), draft-ietf-radext-rfc2486bis-06 (work in progress),
July 2005. July 2005.
[RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 [RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, September 2001. (SHA1)", RFC 3174, September 2001.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004. RFC 3748, June 2004.
13.2. Informative References 14.2. Informative References
[I-D.clancy-eap-pax] [I-D.clancy-eap-pax]
Clancy, C. and W. Arbaugh, "EAP Password Authenticated Clancy, C. and W. Arbaugh, "EAP Password Authenticated
Exchange", draft-clancy-eap-pax-11 (work in progress), Exchange", draft-clancy-eap-pax-11 (work in progress),
September 2006. September 2006.
[I-D.bersani-eap-psk] [I-D.bersani-eap-psk]
Tschofenig, H. and F. Bersani, "The EAP-PSK Protocol: a Tschofenig, H. and F. Bersani, "The EAP-PSK Protocol: a
Pre-Shared Key EAP Method", draft-bersani-eap-psk-11 (work Pre-Shared Key EAP Method", draft-bersani-eap-psk-11 (work
in progress), June 2006. in progress), June 2006.
skipping to change at page 27, line 19 skipping to change at page 28, line 24
(work in progress), October 2006. (work in progress), October 2006.
[I-D.vanderveen-eap-sake] [I-D.vanderveen-eap-sake]
Vanderveen, M. and H. Soliman, "Extensible Authentication 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)", draft-vanderveen-eap-sake-02 Establishment (EAP-SAKE)", draft-vanderveen-eap-sake-02
(work in progress), May 2006. (work in progress), May 2006.
[I-D.ietf-eap-keying] [I-D.ietf-eap-keying]
Aboba, B., "Extensible Authentication Protocol (EAP) Key Aboba, B., "Extensible Authentication Protocol (EAP) Key
Management Framework", draft-ietf-eap-keying-15 (work in Management Framework", draft-ietf-eap-keying-16 (work in
progress), October 2006. progress), January 2007.
[RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible [RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible
Authentication Protocol (EAP) Method Requirements for Authentication Protocol (EAP) Method Requirements for
Wireless LANs", RFC 4017, March 2005. Wireless LANs", RFC 4017, March 2005.
[CMAC] National Institute of Standards and Technology, [CMAC] National Institute of Standards and Technology,
"Recommendation for Block Cipher Modes of Operation: The "Recommendation for Block Cipher Modes of Operation: The
CMAC Mode for Authentication", Special Publication CMAC Mode for Authentication", Special Publication
(SP) 800-38B, May 2005. (SP) 800-38B, May 2005.
[CBC] National Institute of Standards and Technology, [CBC] National Institute of Standards and Technology,
"Recommendation for Block Cipher Modes of Encryption. "Recommendation for Block Cipher Modes of Encryption.
Methods and Techniques.", Special Publication (SP) 800- Methods and Techniques.", Special Publication (SP) 800-
38A, December 2001. 38A, December 2001.
Authors' Addresses Authors' Addresses
T. Charles Clancy T. Charles Clancy
DoD Laboratory for Telecommunication Sciences DoD Laboratory for Telecommunications Sciences
8080 Greenmeade Drive 8080 Greenmead Drive
College Park, MD 20740 College Park, MD 20740
USA USA
Email: clancy@ltsnet.net Email: clancy@ltsnet.net
Hannes Tschofenig Hannes Tschofenig
Siemens Siemens Networks GmbH & Co KG
Otto-Hahn-Ring 6 Otto-Hahn-Ring 6
Munich, Bavaria 81739 Munich, Bavaria 81739
Germany Germany
Email: Hannes.Tschofenig@siemens.com Email: Hannes.Tschofenig@siemens.com
URI: http://www.tschofenig.com URI: http://www.tschofenig.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
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