draft-ietf-ipsecme-rfc4307bis-04.txt   draft-ietf-ipsecme-rfc4307bis-05.txt 
Network Working Group Y. Nir Network Working Group Y. Nir
Internet-Draft Check Point Internet-Draft Check Point
Intended status: Standards Track T. Kivinen Intended status: Standards Track T. Kivinen
Expires: September 17, 2016 INSIDE Secure Expires: October 7, 2016 INSIDE Secure
P. Wouters P. Wouters
Red Hat Red Hat
D. Migault D. Migault
Ericsson Ericsson
March 16, 2016 April 5, 2016
Algorithm Implementation Requirements and Usage Guidance for IKEv2 Algorithm Implementation Requirements and Usage Guidance for IKEv2
draft-ietf-ipsecme-rfc4307bis-04 draft-ietf-ipsecme-rfc4307bis-05
Abstract Abstract
The IPsec series of protocols makes use of various cryptographic The IPsec series of protocols makes use of various cryptographic
algorithms in order to provide security services. The Internet Key algorithms in order to provide security services. The Internet Key
Exchange (IKE) protocol is used to negotiate the IPsec Security Exchange (IKE) protocol is used to negotiate the IPsec Security
Association (IPsec SA) parameters, such as which algorithms should be Association (IPsec SA) parameters, such as which algorithms should be
used. To ensure interoperability between different implementations, used. To ensure interoperability between different implementations,
it is necessary to specify a set of algorithm implementation it is necessary to specify a set of algorithm implementation
requirements and usage guidance to ensure that there is at least one requirements and usage guidance to ensure that there is at least one
algorithm that all implementations support. This document defines algorithm that all implementations support. This document defines
the current algorithm implementation requirements and usage guidance the current algorithm implementation requirements and usage guidance
for IKEv2. This document does not update the algorithms used for for IKEv2. This document does not update the algorithms used for
packet encryption using IPsec Encapsulated Security Payload (ESP) packet encryption using IPsec Encapsulated Security Payload (ESP).
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 17, 2016. This Internet-Draft will expire on October 7, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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2. Conventions Used in This Document . . . . . . . . . . . . . . 4 2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 5 3. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 5
3.1. Type 1 - IKEv2 Encryption Algorithm Transforms . . . . . 5 3.1. Type 1 - IKEv2 Encryption Algorithm Transforms . . . . . 5
3.2. Type 2 - IKEv2 Pseudo-random Function Transforms . . . . 6 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms . . . . 6
3.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 7 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 7
3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 8 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 8
4. IKEv2 Authentication . . . . . . . . . . . . . . . . . . . . 10 4. IKEv2 Authentication . . . . . . . . . . . . . . . . . . . . 10
4.1. IKEv2 Authentication Method . . . . . . . . . . . . . . . 10 4.1. IKEv2 Authentication Method . . . . . . . . . . . . . . . 10
4.1.1. Recommendations for RSA key length . . . . . . . . . 11 4.1.1. Recommendations for RSA key length . . . . . . . . . 11
4.2. Digital Signature Recommendations . . . . . . . . . . . . 11 4.2. Digital Signature Recommendations . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 5. Algorithms for Internet of Things . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
The Internet Key Exchange (IKE) protocol [RFC7296] is used to The Internet Key Exchange (IKE) protocol [RFC7296] is used to
negotiate the parameters of the IPsec SA, such as the encryption and negotiate the parameters of the IPsec SA, such as the encryption and
authentication algorithms and the keys for the protected authentication algorithms and the keys for the protected
communications between the two endpoints. The IKE protocol itself is communications between the two endpoints. The IKE protocol itself is
also protected by encryption which is negotiated between the two also protected by cryptographic algorithms which are negotiated
endpoints using IKE. Different implementations of IKE may negotiate between the two endpoints using IKE. Different implementations of
different algorithms based on their individual local policy. To IKE may negotiate different algorithms based on their individual
ensure interoperability, a set of "mandatory-to-implement" IKE local policy. To ensure interoperability, a set of "mandatory-to-
encryption algorithms is defined. implement" IKE cryptograhic algorithms is defined.
This document describes the parameters of the IKE protocol. It does This document describes the parameters of the IKE protocol. It does
not describe the cryptographic parameters of the AH or ESP protocols. not describe the cryptographic parameters of the AH or ESP protocols.
1.1. Updating Algorithm Implementation Requirements and Usage Guidance 1.1. Updating Algorithm Implementation Requirements and Usage Guidance
The field of cryptography evolves continuously. New stronger The field of cryptography evolves continuously. New stronger
algorithms appear and existing algorithms are found to be less secure algorithms appear and existing algorithms are found to be less secure
then originally thought. Therefore, algorithm implementation then originally thought. Therefore, algorithm implementation
requirements and usage guidance need to be updated from time to time requirements and usage guidance need to be updated from time to time
to reflect the new reality. The choices for algorithms must be to reflect the new reality. The choices for algorithms must be
conservative to minimize the risk of algorithm compromise. conservative to minimize the risk of algorithm compromise.
Algorithms need to be suitable for a wide variety of CPU Algorithms need to be suitable for a wide variety of CPU
architectures and device deployments ranging from high end bulk architectures and device deployments ranging from high end bulk
encryption devices to small low-power IoT devices. encryption devices to small low-power IoT devices.
The algorithm implementation requirements and usage guidance may need The algorithm implementation requirements and usage guidance may need
to change over time to adapt to the changing world. For this reason, to change over time to adapt to the changing world. For this reason,
the selection of mandatory-to-implement algorithms was removed from the selection of mandatory-to-implement algorithms was removed from
the main IKEv2 specification and placed in this document. the main IKEv2 specification and placed in a separate document.
1.2. Updating Algorithm Requirement Levels 1.2. Updating Algorithm Requirement Levels
The mandatory-to-implement algorithm of tomorrow should already be The mandatory-to-implement algorithm of tomorrow should already be
available in most implementations of IKE by the time it is made available in most implementations of IKE by the time it is made
mandatory. This document attempts to identify and introduce those mandatory. This document attempts to identify and introduce those
algorithms for future mandatory-to-implement status. There is no algorithms for future mandatory-to-implement status. There is no
guarantee that the algorithms in use today may become mandatory in guarantee that the algorithms in use today may become mandatory in
the future. Published algorithms are continuously subjected to the future. Published algorithms are continuously subjected to
cryptographic attack and may become too weak or could become cryptographic attack and may become too weak or could become
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2. Conventions Used in This Document 2. Conventions Used in This Document
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].
We define some additional terms here: We define some additional terms here:
SHOULD+ This term means the same as SHOULD. However, it is likely SHOULD+ This term means the same as SHOULD. However, it is likely
that an algorithm marked as SHOULD+ will be promoted at some that an algorithm marked as SHOULD+ will be promoted at
future time to be a MUST. some future time to be a MUST.
SHOULD- This term means the same as SHOULD. However, an algorithm SHOULD- This term means the same as SHOULD. However, an algorithm
marked as SHOULD- may be deprecated to a MAY in a future marked as SHOULD- may be deprecated to a MAY in a future
version of this document. version of this document.
MUST- This term means the same as MUST. However, we expect at some MUST- This term means the same as MUST. However, we expect at
point that this algorithm will no longer be a MUST in a some point that this algorithm will no longer be a MUST in
future document. Although its status will be determined at a a future document. Although its status will be determined
later time, it is reasonable to expect that if a future at a later time, it is reasonable to expect that if a
revision of a document alters the status of a MUST- future revision of a document alters the status of a MUST-
algorithm, it will remain at least a SHOULD or a SHOULD- algorithm, it will remain at least a SHOULD or a SHOULD-
level. level.
IoT stands for Internet of Things. IoT stands for Internet of Things.
Table 1
3. Algorithm Selection 3. Algorithm Selection
3.1. Type 1 - IKEv2 Encryption Algorithm Transforms 3.1. Type 1 - IKEv2 Encryption Algorithm Transforms
The algorithms in the below table are negotiated in the SA payload The algorithms in the below table are negotiated in the SA payload
and used for the Encrypted Payload. References to the specification and used for the Encrypted Payload. References to the specification
defining these algorithms and the ones in the following subsections defining these algorithms and the ones in the following subsections
are in the IANA registry [IKEV2-IANA]. Some of these algorithms are are in the IANA registry [IKEV2-IANA]. Some of these algorithms are
Authenticated Encryption with Associated Data (AEAD - [RFC5282]). Authenticated Encryption with Associated Data (AEAD - [RFC5282]).
Algorithms that are not AEAD MUST be used in conjunction with an Algorithms that are not AEAD MUST be used in conjunction with an
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| AES-GCM with a 16 octet ICV | SHOULD | Yes | [1] | | AES-GCM with a 16 octet ICV | SHOULD | Yes | [1] |
| ENCR_AES_CCM_8 | SHOULD | Yes | [1][IoT] | | ENCR_AES_CCM_8 | SHOULD | Yes | [1][IoT] |
| ENCR_3DES | MAY | No | | | ENCR_3DES | MAY | No | |
| ENCR_DES | MUST NOT | No | | | ENCR_DES | MUST NOT | No | |
+-----------------------------+----------+-------+----------+ +-----------------------------+----------+-------+----------+
[1] - This requirement level is for 128-bit keys. 256-bit keys are at [1] - This requirement level is for 128-bit keys. 256-bit keys are at
MAY. 192-bit keys can safely be ignored. [IoT] - This requirement is MAY. 192-bit keys can safely be ignored. [IoT] - This requirement is
for interoperability with IoT. for interoperability with IoT.
Table 2
ENCR_AES_CBC is raised from SHOULD+ in [RFC4307] to MUST. It is the ENCR_AES_CBC is raised from SHOULD+ in [RFC4307] to MUST. It is the
only shared mandatory-to-implement algorithm with RFC4307 and as a only shared mandatory-to-implement algorithm with RFC4307 and as a
result it is necessary for interoperability with IKEv2 implementation result it is necessary for interoperability with IKEv2 implementation
compatible with RFC4307. compatible with RFC4307.
ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of
RFC4307. It has been recommended by the CRFG and others as an RFC4307. It has been recommended by the CRFG and others as an
alternative to AES-CBC and AES-GCM. It is also being standardized alternative to AES-CBC and AES-GCM. It is also being standardized
for IPsec for the same reasons. At the time of writing, there were for IPsec for the same reasons. At the time of writing, there were
not enough IKEv2 implementations supporting ENCR_CHACHA20_POLY1305 to not enough IKEv2 implementations supporting ENCR_CHACHA20_POLY1305 to
be able to introduce it at the SHOULD+ level. be able to introduce it at the SHOULD+ level.
AES-GCM with a 16 octet ICV was not considered as in RFC4307. At the AES-GCM with a 16 octet ICV was not considered in RFC4307. At the
time RFC4307 was written, AES-GCM was not defined in an IETF time RFC4307 was written, AES-GCM was not defined in an IETF
document. AES-GCM was defined for ESP in [RFC4106] and later for document. AES-GCM was defined for ESP in [RFC4106] and later for
IKEv2 in [RFC5282]. The main motivation for adopting AES-GCM for ESP IKEv2 in [RFC5282]. The main motivation for adopting AES-GCM for ESP
is encryption performance and key longevity compared to AES-CBC. is encryption performance and key longevity compared to AES-CBC.
This resulted in AES-GCM being widely implemented for ESP. As the This resulted in AES-GCM being widely implemented for ESP. As the
computation load of IKEv2 is relatively small compared to ESP, many computation load of IKEv2 is relatively small compared to ESP, many
IKEv2 implementations have not implemented AES-GCM. For this reason, IKEv2 implementations have not implemented AES-GCM. For this reason,
AES-GCM is not promoted to a greater status than SHOULD. The reason AES-GCM is not promoted to a greater status than SHOULD. The reason
for promotion from MAY to SHOULD is to promote the slightly more for promotion from MAY to SHOULD is to promote the slightly more
secure AEAD method over the traditional encrypt+auth method. Its secure AEAD method over the traditional encrypt+auth method. Its
status is expected to be raised once widely implemented. As the status is expected to be raised once widely implemented. As the
advantage of the shorter (and weaker) ICVs is minimal, the 8 and 12 advantage of the shorter (and weaker) ICVs is minimal, the 8 and 12
octet ICV's remain at the MAY level. octet ICV's remain at the MAY level.
ENCR_AES_CCM_8 was not considered in RFC4307. This document ENCR_AES_CCM_8 was not considered in RFC4307. This document
considers it as SHOULD be implemented in order to be able to interact considers it as SHOULD be implemented in order to be able to interact
with Internet of Things devices. As this case is not a general use with Internet of Things devices. As this case is not a general use
case for non-IoT VPNs, its status is expected to remain as SHOULD. case for non-IoT VPNs, its status is expected to remain as SHOULD.
The 8 octet size of the ICV is expected to be sufficient for most use The 8 octet size of the ICV is expected to be sufficient for most use
cases of IKEv2, as far less packets are exchanged on the IKE SA cases of IKEv2, as far less packets are exchanged on those cases, and
compared to the IPsec SA. When implemented, ENCR_AES_CCM_8 MUST be IoT devices want to make packets as small as possible. When
implemented for key length 128 and MAY be implemented for key length implemented, ENCR_AES_CCM_8 MUST be implemented for key length 128
256. and MAY be implemented for key length 256.
ENCR_3DES has been downgraded from RFC4307 MUST- to SHOULD NOT. All ENCR_3DES has been downgraded from RFC4307 MUST- to SHOULD NOT. All
IKEv2 implementation already implement ENCR_AES_CBC, so there is no IKEv2 implementation already implement ENCR_AES_CBC, so there is no
need to keep support for the much slower ENCR_3DES. In addition, need to keep support for the much slower ENCR_3DES. In addition,
ENCR_CHACHA20_POLY1305 provides a more modern alternative to AES. ENCR_CHACHA20_POLY1305 provides a more modern alternative to AES.
ENCR_DES can be brute-forced using of-the-shelves hardware. It ENCR_DES can be brute-forced using of-the-shelves hardware. It
provides no meaningful security whatsoever and therefor MUST NOT be provides no meaningful security whatsoever and therefor MUST NOT be
implemented. implemented.
3.2. Type 2 - IKEv2 Pseudo-random Function Transforms 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms
Transform Type 2 Algorithms are pseudo-random functions used to Transform Type 2 algorithms are pseudo-random functions used to
generate random values when needed. generate pseudorandom values when needed.
If an algorithm is selected as the integrity algorithm, it SHOULD If an algorithm is selected as the integrity algorithm, it SHOULD
also be used as the PRF. When using an AEAD cipher, a choice of PRF also be used as the PRF. When using an AEAD cipher, a choice of PRF
needs to be made. The table below lists the recommended algorithms. needs to be made. The table below lists the recommended algorithms.
+-------------------+----------+---------+ +-------------------+----------+---------+
| Name | Status | Comment | | Name | Status | Comment |
+-------------------+----------+---------+ +-------------------+----------+---------+
| PRF_HMAC_SHA2_256 | MUST | | | PRF_HMAC_SHA2_256 | MUST | |
| PRF_HMAC_SHA2_512 | SHOULD+ | | | PRF_HMAC_SHA2_512 | SHOULD+ | |
| PRF_HMAC_SHA1 | MUST- | | | PRF_HMAC_SHA1 | MUST- | |
| PRF_AES128_CBC | SHOULD | [IoT] | | PRF_AES128_XCBC | SHOULD | [IoT] |
| PRF_HMAC_MD5 | MUST NOT | | | PRF_HMAC_MD5 | MUST NOT | |
+-------------------+----------+---------+ +-------------------+----------+---------+
[IoT] - This requirement is for interoperability with IoT [IoT] - This requirement is for interoperability with IoT
Table 3
PRF_HMAC_SHA2_256 was not mentioned in RFC4307, as no SHA2 based PRF_HMAC_SHA2_256 was not mentioned in RFC4307, as no SHA2 based
authentication was mentioned. PRF_HMAC_SHA2_256 MUST be implemented transforms were mentioned. PRF_HMAC_SHA2_256 MUST be implemented in
in order to replace SHA1 and PRF_HMAC_SHA1. order to replace SHA1 and PRF_HMAC_SHA1.
PRF_HMAC_SHA2_512 SHOULD be implemented as a future replacement for PRF_HMAC_SHA2_512 SHOULD be implemented as a future replacement for
PRF_HMAC_SHA2_256 or for when stronger security is required. PRF_HMAC_SHA2_256 or when stronger security is required.
PRF_HMAC_SHA2_512 is preferred over PRF_HMAC_SHA2_384, as the PRF_HMAC_SHA2_512 is preferred over PRF_HMAC_SHA2_384, as the
additional overhead of PRF_HMAC_SHA2_512 is negligible. additional overhead of PRF_HMAC_SHA2_512 is negligible.
PRF_HMAC_SHA1 has been downgraded from MUST in RFC4307 to MUST- as PRF_HMAC_SHA1 has been downgraded from MUST in RFC4307 to MUST- as
their is an industry-wide trend to deprecate its usage. their is an industry-wide trend to deprecate its usage.
PRF_AES128_CBC is only recommended in the scope of IoT, as Internet PRF_AES128_XCBC is only recommended in the scope of IoT, as Internet
of Things deployments tend to prefer AES based pseudo-random of Things deployments tend to prefer AES based pseudo-random
functions in order to avoid implementing SHA2. For the non-IoT VPN functions in order to avoid implementing SHA2. For the non-IoT VPN
deployment it has been downgraded from SHOULD in RFC4307 to MAY as it deployment it has been downgraded from SHOULD in RFC4307 to MAY as it
has not seen wide adoption. has not seen wide adoption.
PRF_HMAC_MD5 has been downgraded from MAY in RFC4307 to MUST NOT. PRF_HMAC_MD5 has been downgraded from MAY in RFC4307 to MUST NOT.
There is an industry-wide trend to deprecate its usage as MD5 support There is an industry-wide trend to deprecate its usage as MD5 support
is being removed from cryptographic libraries in general because its is being removed from cryptographic libraries in general because its
non-HMAC use is known to be subject to collision attacks, for example non-HMAC use is known to be subject to collision attacks, for example
as mentioned in [TRANSCRIPTION]. as mentioned in [TRANSCRIPTION].
skipping to change at page 8, line 11 skipping to change at page 8, line 19
| AUTH_HMAC_SHA2_512_256 | SHOULD | | | AUTH_HMAC_SHA2_512_256 | SHOULD | |
| AUTH_HMAC_SHA1_96 | MUST- | | | AUTH_HMAC_SHA1_96 | MUST- | |
| AUTH_AES_XCBC_96 | SHOULD | [IoT] | | AUTH_AES_XCBC_96 | SHOULD | [IoT] |
| AUTH_HMAC_MD5_96 | MUST NOT | | | AUTH_HMAC_MD5_96 | MUST NOT | |
| AUTH_DES_MAC | MUST NOT | | | AUTH_DES_MAC | MUST NOT | |
| AUTH_KPDK_MD5 | MUST NOT | | | AUTH_KPDK_MD5 | MUST NOT | |
+------------------------+----------+---------+ +------------------------+----------+---------+
[IoT] - This requirement is for interoperability with IoT [IoT] - This requirement is for interoperability with IoT
Table 4
AUTH_HMAC_SHA2_256_128 was not mentioned in RFC4307, as no SHA2 based AUTH_HMAC_SHA2_256_128 was not mentioned in RFC4307, as no SHA2 based
authentication was mentioned. AUTH_HMAC_SHA2_256_128 MUST be transforms were mentioned. AUTH_HMAC_SHA2_256_128 MUST be
implemented in order to replace AUTH_HMAC_SHA1_96. implemented in order to replace AUTH_HMAC_SHA1_96.
AUTH_HMAC_SHA2_512_256 SHOULD be implemented as a future replacement AUTH_HMAC_SHA2_512_256 SHOULD be implemented as a future replacement
of AUTH_HMAC_SHA2_256_128 or for when stronger security is required. of AUTH_HMAC_SHA2_256_128 or when stronger security is required.
This value has been preferred over AUTH_HMAC_SHA2_384, as the This value has been preferred over AUTH_HMAC_SHA2_384, as the
additional overhead of AUTH_HMAC_SHA2_512 is negligible. additional overhead of AUTH_HMAC_SHA2_512 is negligible.
AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC4307 to MUST- AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC4307 to MUST-
as there is an industry-wide trend to deprecate its usage. as there is an industry-wide trend to deprecate its usage.
AUTH_AES-XCBC is only recommended in the scope of IoT, as Internet of AUTH_AES-XCBC is only recommended in the scope of IoT, as Internet of
Things deployments tend to prefer AES based pseudo-random functions Things deployments tend to prefer AES based pseudo-random functions
in order to avoid implementing SHA2. For the non-IoT VPN deployment, in order to avoid implementing SHA2. For the non-IoT VPN deployment,
it has been downgraded from SHOULD in RFC4307 to MAY as it has not it has been downgraded from SHOULD in RFC4307 to MAY as it has not
skipping to change at page 9, line 4 skipping to change at page 8, line 45
been widely adopted. been widely adopted.
AUTH_HMAC_MD5_96, AUTH_DES_MAC and AUTH_KPDK_MD5 were not mentioned AUTH_HMAC_MD5_96, AUTH_DES_MAC and AUTH_KPDK_MD5 were not mentioned
in RFC4307 so its default status was MAY. It has been downgraded to in RFC4307 so its default status was MAY. It has been downgraded to
MUST NOT. There is an industry-wide trend to deprecate its usage. MUST NOT. There is an industry-wide trend to deprecate its usage.
MD5 support is being removed from cryptographic libraries in general MD5 support is being removed from cryptographic libraries in general
because its non-HMAC use is known to be subject to collision attacks, because its non-HMAC use is known to be subject to collision attacks,
for example as mentioned in [TRANSCRIPTION]. for example as mentioned in [TRANSCRIPTION].
3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms
There are several Modular Exponential (MODP) groups and several There are several Modular Exponential (MODP) groups and several
Elliptic Curve groups (ECC) that are defined for use in IKEv2. These Elliptic Curve groups (ECC) that are defined for use in IKEv2. These
groups are defined in both the [IKEv2] base document and in groups are defined in both the [IKEv2] base document and in
extensions documents and are identified by group number. Note that extensions documents and are identified by group number. Note that
it is critical to enforce a secure Diffie Hellman exchange as this it is critical to enforce a secure Diffie-Hellman exchange as this
exchange provides encryption for the session. If an attacker can exchange provides keys for the session. If an attacker can retrieve
retrieve the private numbers (for example a, b) (and? or?) the public the private numbers (a, or b) and the public values (g**a, and g**b),
values (for example g**a, g**b), then the attacker can compute the then the attacker can compute the secret and the keys used and
secret and the keys used and decrypt the exchange. Such an attack decrypt the exchange and IPsec SA created inside the IKEv2 SA. Such
can be performed off-line on a previously recorded communication, an attack can be performed off-line on a previously recorded
years after the communication happened. This differs from attacks communication, years after the communication happened. This differs
that need to be executed during the authentication which must be from attacks that need to be executed during the authentication which
performed online and in near real-time. must be performed online and in near real-time.
+------------+----------------------------------------+-------------+
| Number | Description | Status |
+------------+----------------------------------------+-------------+
| 14 | 2048-bit MODP Group | MUST |
| 19 | 256-bit random ECP group | SHOULD |
| 5 | 1536-bit MODP Group | SHOULD NOT |
| 2 | 1024-bit MODP Group | SHOULD NOT |
| 1 | 768-bit MODP Group | MUST NOT |
| 22 | 1024-bit MODP Group with 160-bit Prime | SHOULD NOT |
| | Order Subgroup | |
| 23 | 2048-bit MODP Group with 224-bit Prime | SHOULD NOT |
| | Order Subgroup | |
| 24 | 2048-bit MODP Group with 256-bit Prime | SHOULD NOT |
| | Order Subgroup | |
+------------+----------------------------------------+-------------+
Table 5 +--------+---------------------------------------------+------------+
| Number | Description | Status |
+--------+---------------------------------------------+------------+
| 14 | 2048-bit MODP Group | MUST |
| 19 | 256-bit random ECP group | SHOULD |
| 5 | 1536-bit MODP Group | SHOULD NOT |
| 2 | 1024-bit MODP Group | SHOULD NOT |
| 1 | 768-bit MODP Group | MUST NOT |
| 22 | 1024-bit MODP Group with 160-bit Prime | SHOULD NOT |
| | Order Subgroup | |
| 23 | 2048-bit MODP Group with 224-bit Prime | SHOULD NOT |
| | Order Subgroup | |
| 24 | 2048-bit MODP Group with 256-bit Prime | SHOULD NOT |
| | Order Subgroup | |
+--------+---------------------------------------------+------------+
Group 14 or 2048-bit MODP Group is raised from SHOULD+ in RFC4307 as Group 14 or 2048-bit MODP Group is raised from SHOULD+ in RFC4307 as
a replacement for 1024-bit MODP Group. Group 14 is widely a replacement for 1024-bit MODP Group. Group 14 is widely
implemented and considered secure. implemented and considered secure.
Group 19 or 256-bit random ECP group was not specified in RFC4307, as Group 19 or 256-bit random ECP group was not specified in RFC4307, as
this group were not specified at that time. Group 19 is widely this group were not specified at that time. Group 19 is widely
implemented and considered secure. implemented and considered secure.
Group 5 or 1536-bit MODP Group has been downgraded from MAY in Group 5 or 1536-bit MODP Group has been downgraded from MAY in
skipping to change at page 10, line 46 skipping to change at page 10, line 39
| Number | Description | Status | | Number | Description | Status |
+--------+---------------------------------------+------------+ +--------+---------------------------------------+------------+
| 1 | RSA Digital Signature | MUST | | 1 | RSA Digital Signature | MUST |
| 3 | DSS Digital Signature | SHOULD NOT | | 3 | DSS Digital Signature | SHOULD NOT |
| 9 | ECDSA with SHA-256 on the P-256 curve | SHOULD | | 9 | ECDSA with SHA-256 on the P-256 curve | SHOULD |
| 10 | ECDSA with SHA-384 on the P-384 curve | SHOULD | | 10 | ECDSA with SHA-384 on the P-384 curve | SHOULD |
| 11 | ECDSA with SHA-512 on the P-521 curve | SHOULD | | 11 | ECDSA with SHA-512 on the P-521 curve | SHOULD |
| 14 | Digital Signature | SHOULD | | 14 | Digital Signature | SHOULD |
+--------+---------------------------------------+------------+ +--------+---------------------------------------+------------+
Table 6 RSA Digital Signature is widely deployed and therefore kept for
RSA Digital Signature is widely deployed and therefor kept for
interoperability. It is expected to be downgraded in the future as interoperability. It is expected to be downgraded in the future as
its signatures are based on the older RSASSA-PKCS1-v1.5 which is no its signatures are based on the older RSASSA-PKCS1-v1.5 which is no
longer recommended. RSA authentication, as well as other specific longer recommended. RSA authentication, as well as other specific
Authentication Methods, are expected to be replaced with the generic Authentication Methods, are expected to be replaced with the generic
Digital Signature method of [RFC7427]. RSA Digital Signature is not Digital Signature method of [RFC7427]. RSA Digital Signature is not
recommended for keys smaller then 2048, but since these signatures recommended for keys smaller then 2048, but since these signatures
only have value in real-time, and need no future protection, smaller only have value in real-time, and need no future protection, smaller
keys was kept at SHOULD NOT instead of MUST NOT. keys was kept at SHOULD NOT instead of MUST NOT.
ECDSA based Authentication Methods are also expected to be downgraded ECDSA based Authentication Methods are also expected to be downgraded
skipping to change at page 11, line 33 skipping to change at page 11, line 23
+-------------------------------------------+------------+ +-------------------------------------------+------------+
| Description | Status | | Description | Status |
+-------------------------------------------+------------+ +-------------------------------------------+------------+
| RSA with key length 2048 | MUST | | RSA with key length 2048 | MUST |
| RSA with key length 3072 and 4096 | SHOULD | | RSA with key length 3072 and 4096 | SHOULD |
| RSA with key length between 2049 and 4095 | MAY | | RSA with key length between 2049 and 4095 | MAY |
| RSA with key length smaler than 2048 | SHOULD NOT | | RSA with key length smaler than 2048 | SHOULD NOT |
+-------------------------------------------+------------+ +-------------------------------------------+------------+
Table 7
4.2. Digital Signature Recommendations 4.2. Digital Signature Recommendations
Recommendations for when a hash function is involved in a signature: Recommendations for when a hash function is involved in a signature:
+--------+-------------+------------+---------+ +--------+-------------+------------+---------+
| Number | Description | Status | Comment | | Number | Description | Status | Comment |
+--------+-------------+------------+---------+ +--------+-------------+------------+---------+
| 1 | SHA1 | SHOULD NOT | | | 1 | SHA1 | SHOULD NOT | |
| 2 | SHA2-256 | MUST | | | 2 | SHA2-256 | MUST | |
| 3 | SHA2-384 | MAY | | | 3 | SHA2-384 | MAY | |
| 4 | SHA2-512 | SHOULD | | | 4 | SHA2-512 | SHOULD | |
+--------+-------------+------------+---------+ +--------+-------------+------------+---------+
Table 8
With the use of Digital Signature, RSASSA-PKCS1-v1.5 MAY be With the use of Digital Signature, RSASSA-PKCS1-v1.5 MAY be
implemented. RSASSA-PSS MUST be implemented. implemented. RSASSA-PSS MUST be implemented.
Recommendation of Authentication Method described in [RFC7427] Recommendation of Authentication Method described in [RFC7427]
notation: notation:
+------------------------------------+------------+---------+ +------------------------------------+------------+---------+
| Description | Status | Comment | | Description | Status | Comment |
+------------------------------------+------------+---------+ +------------------------------------+------------+---------+
| RSASSA-PSS with SHA-256 | SHOULD | | | RSASSA-PSS with SHA-256 | SHOULD | |
skipping to change at page 12, line 27 skipping to change at page 12, line 24
| RSASSA-PSS with Default Parameters | SHOULD NOT | | | RSASSA-PSS with Default Parameters | SHOULD NOT | |
| sha256WithRSAEncryption | MAY | | | sha256WithRSAEncryption | MAY | |
| sha384WithRSAEncryption | MAY | | | sha384WithRSAEncryption | MAY | |
| sha512WithRSAEncryption | MAY | | | sha512WithRSAEncryption | MAY | |
| sha512WithRSAEncryption | MAY | | | sha512WithRSAEncryption | MAY | |
| dsa-with-sha256 | MAY | | | dsa-with-sha256 | MAY | |
| ecdsa-with-sha384 | MAY | | | ecdsa-with-sha384 | MAY | |
| ecdsa-with-sha512 | MAY | ?SHOULD | | ecdsa-with-sha512 | MAY | ?SHOULD |
+------------------------------------+------------+---------+ +------------------------------------+------------+---------+
Table 9 5. Algorithms for Internet of Things
5. Security Considerations Some algorithms in this document are marked for the Internet of
Things (IoT). There are several reasons why the IoT devices want
have different set of algorithms than other users of IKEv2. Those
devices are usually very constrained, meaning the memory size and cpu
power is so limited, that they want to implement just minimal set of
algorithms. This means they quite often only implement one algorithm
and pick it so that the same algorithm is already implemented in
software or hardware for other users.
For example IEEE Std 802.15.4 [IEEE-802-15-4] devices has mandatory
to implement link level security using AES-CCM with 128 bit keys.
The IEEE Recommended Practice for Transport of Key Management
Protocol (KMP) Datagrams [IEEE-802-15-9] already provides a way to
use Minimal IKEv2 [RFC7815] over 802.15.4 to provide link keys for
the 802.15.4.
Those devices might want to use AES-CCM as their IKEv2 algorithm, so
they can reuse the hardware implementing it. They cannot use the
AES-CBC, as the hardware quite often do not include support for AES
decryption needed for it. So even when AES-CCM algorithm support
requires support for the AEAD [RFC5282] support for IKEv2, the
benefit of reusing crypto hardware makes it worthwhile.
Other important aspects of the IoT devices, that their transfer rates
are usually quite low (in order of tens of kbits/s), and each bit
they transmit costs a lot in energy consumption (shortening the
battery life). Because of this they usually want to use options
which support shorter packets. I.e., using 8 octet ICV instead of
16.
Also as each of those IoT devices have different constraints, we
cannot specify one exact profile for them. This document points out
some algorithms commonly used in the IoT devices, but there might be
devices using different set of algorithms, because of requirements
for the environment.
6. Security Considerations
The security of cryptographic-based systems depends on both the The security of cryptographic-based systems depends on both the
strength of the cryptographic algorithms chosen and the strength of strength of the cryptographic algorithms chosen and the strength of
the keys used with those algorithms. The security also depends on the keys used with those algorithms. The security also depends on
the engineering of the protocol used by the system to ensure that the engineering of the protocol used by the system to ensure that
there are no non-cryptographic ways to bypass the security of the there are no non-cryptographic ways to bypass the security of the
overall system. overall system.
The Diffie-Hellman Group parameter is the most important one to The Diffie-Hellman Group parameter is the most important one to
choose conservatively. Any party capturing all IKE and ESP traffic choose conservatively. Any party capturing all IKE and ESP traffic
skipping to change at page 13, line 8 skipping to change at page 13, line 41
This document concerns itself with the selection of cryptographic This document concerns itself with the selection of cryptographic
algorithms for the use of IKEv2, specifically with the selection of algorithms for the use of IKEv2, specifically with the selection of
"mandatory-to-implement" algorithms. The algorithms identified in "mandatory-to-implement" algorithms. The algorithms identified in
this document as "MUST implement" or "SHOULD implement" are not known this document as "MUST implement" or "SHOULD implement" are not known
to be broken at the current time, and cryptographic research so far to be broken at the current time, and cryptographic research so far
leads us to believe that they will likely remain secure into the leads us to believe that they will likely remain secure into the
foreseeable future. However, this isn't necessarily forever and it foreseeable future. However, this isn't necessarily forever and it
is expected that new revisions of this document will be issued from is expected that new revisions of this document will be issued from
time to time to reflect the current best practice in this area. time to time to reflect the current best practice in this area.
6. IANA Considerations 7. IANA Considerations
This document makes no requests of IANA. This document makes no requests of IANA.
7. Acknowledgements 8. Acknowledgements
The first version of this document was RFC 4307 by Jeffrey I. The first version of this document was RFC 4307 by Jeffrey I.
Schiller of the Massachusetts Institute of Technology (MIT). Much of Schiller of the Massachusetts Institute of Technology (MIT). Much of
the original text has been copied verbatim. the original text has been copied verbatim.
We would like to thank Paul Hoffman, Yaron Sheffer, John Mattsson and We would like to thank Paul Hoffman, Yaron Sheffer, John Mattsson and
Tommy Pauly for their valuable feedback. Tommy Pauly for their valuable feedback.
8. References 9. References
8.1. Normative References 9.1. 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, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode [RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
(GCM) in IPsec Encapsulating Security Payload (ESP)", RFC (GCM) in IPsec Encapsulating Security Payload (ESP)",
4106, DOI 10.17487/RFC4106, June 2005, RFC 4106, DOI 10.17487/RFC4106, June 2005,
<http://www.rfc-editor.org/info/rfc4106>. <http://www.rfc-editor.org/info/rfc4106>.
[RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the [RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the
Internet Key Exchange Version 2 (IKEv2)", RFC 4307, DOI Internet Key Exchange Version 2 (IKEv2)", RFC 4307,
10.17487/RFC4307, December 2005, DOI 10.17487/RFC4307, December 2005,
<http://www.rfc-editor.org/info/rfc4307>. <http://www.rfc-editor.org/info/rfc4307>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2 Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <http://www.rfc-editor.org/info/rfc7296>. 2014, <http://www.rfc-editor.org/info/rfc7296>.
[RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption [RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption
Algorithms with the Encrypted Payload of the Internet Key Algorithms with the Encrypted Payload of the Internet Key
Exchange version 2 (IKEv2) Protocol", RFC 5282, DOI Exchange version 2 (IKEv2) Protocol", RFC 5282,
10.17487/RFC5282, August 2008, DOI 10.17487/RFC5282, August 2008,
<http://www.rfc-editor.org/info/rfc5282>. <http://www.rfc-editor.org/info/rfc5282>.
8.2. Informative References 9.2. Informative References
[RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in [RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in
the Internet Key Exchange Version 2 (IKEv2)", RFC 7427, the Internet Key Exchange Version 2 (IKEv2)", RFC 7427,
DOI 10.17487/RFC7427, January 2015, DOI 10.17487/RFC7427, January 2015,
<http://www.rfc-editor.org/info/rfc7427>. <http://www.rfc-editor.org/info/rfc7427>.
[RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman [RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman
Tests for the Internet Key Exchange Protocol Version 2 Tests for the Internet Key Exchange Protocol Version 2
(IKEv2)", RFC 6989, DOI 10.17487/RFC6989, July 2013, (IKEv2)", RFC 6989, DOI 10.17487/RFC6989, July 2013,
<http://www.rfc-editor.org/info/rfc6989>. <http://www.rfc-editor.org/info/rfc6989>.
[RFC7815] Kivinen, T., "Minimal Internet Key Exchange Version 2
(IKEv2) Initiator Implementation", RFC 7815,
DOI 10.17487/RFC7815, March 2016,
<http://www.rfc-editor.org/info/rfc7815>.
[IKEV2-IANA] [IKEV2-IANA]
, "Internet Key Exchange Version 2 (IKEv2) Parameters", , "Internet Key Exchange Version 2 (IKEv2) Parameters",
<http://www.iana.org/assignments/ikev2-parameters>. <http://www.iana.org/assignments/ikev2-parameters>.
[TRANSCRIPTION] [TRANSCRIPTION]
Bhargavan, K. and G. Leurent, "Transcript Collision Bhargavan, K. and G. Leurent, "Transcript Collision
Attacks: Breaking Authentication in TLS, IKE, and SSH", Attacks: Breaking Authentication in TLS, IKE, and SSH",
NDSS , feb 2016. NDSS , feb 2016.
[IEEE-802-15-4]
"IEEE Standard for Low-Rate Wireless Personal Area
Networks (WPANs)", IEEE Standard 802.15.4, 2015.
[IEEE-802-15-9]
"IEEE Recommended Practice for Transport of Key Management
Protocol (KMP) Datagrams", IEEE Standard 802.15.9, 2016.
Authors' Addresses Authors' Addresses
Yoav Nir Yoav Nir
Check Point Software Technologies Ltd. Check Point Software Technologies Ltd.
5 Hasolelim st. 5 Hasolelim st.
Tel Aviv 6789735 Tel Aviv 6789735
Israel Israel
EMail: ynir.ietf@gmail.com EMail: ynir.ietf@gmail.com
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