< draft-ietf-ipsecme-rfc4307bis-16.txt   draft-ietf-ipsecme-rfc4307bis-17.txt >
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Internet-Draft Check Point Internet-Draft Check Point
Obsoletes: 4307 (if approved) T. Kivinen Obsoletes: 4307 (if approved) T. Kivinen
Updates: 7296 (if approved) INSIDE Secure Updates: 7296 (if approved) INSIDE Secure
Intended status: Standards Track P. Wouters Intended status: Standards Track P. Wouters
Expires: August 20, 2017 Red Hat Expires: August 20, 2017 Red Hat
D. Migault D. Migault
Ericsson Ericsson
February 16, 2017 February 16, 2017
Algorithm Implementation Requirements and Usage Guidance for IKEv2 Algorithm Implementation Requirements and Usage Guidance for IKEv2
draft-ietf-ipsecme-rfc4307bis-16 draft-ietf-ipsecme-rfc4307bis-17
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
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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
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Updating Algorithm Implementation Requirements and Usage 1.1. Conventions Used in This Document . . . . . . . . . . . . 3
1.2. Updating Algorithm Implementation Requirements and Usage
Guidance . . . . . . . . . . . . . . . . . . . . . . . . 3 Guidance . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Updating Algorithm Requirement Levels . . . . . . . . . . 3 1.3. Updating Algorithm Requirement Levels . . . . . . . . . . 4
1.3. Document Audience . . . . . . . . . . . . . . . . . . . . 4 1.4. Document Audience . . . . . . . . . . . . . . . . . . . . 5
2. Conventions Used in This Document . . . . . . . . . . . . . . 5 2. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 5
3. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 5 2.1. Type 1 - IKEv2 Encryption Algorithm Transforms . . . . . 5
3.1. Type 1 - IKEv2 Encryption Algorithm Transforms . . . . . 5 2.2. Type 2 - IKEv2 Pseudo-random Function Transforms . . . . 7
3.2. Type 2 - IKEv2 Pseudo-random Function Transforms . . . . 7 2.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 8
3.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 8 2.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 9
3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 9 2.5. Summary of Changes from RFC 4307 . . . . . . . . . . . . 10
3.5. Summary of Changes from RFC 4307 . . . . . . . . . . . . 10 3. IKEv2 Authentication . . . . . . . . . . . . . . . . . . . . 11
4. IKEv2 Authentication . . . . . . . . . . . . . . . . . . . . 11 3.1. IKEv2 Authentication Method . . . . . . . . . . . . . . . 11
4.1. IKEv2 Authentication Method . . . . . . . . . . . . . . . 11 3.1.1. Recommendations for RSA key length . . . . . . . . . 12
4.1.1. Recommendations for RSA key length . . . . . . . . . 12 3.2. Digital Signature Recommendations . . . . . . . . . . . . 12
4.2. Digital Signature Recommendations . . . . . . . . . . . . 12 4. Algorithms for Internet of Things . . . . . . . . . . . . . . 13
5. Algorithms for Internet of Things . . . . . . . . . . . . . . 13 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . 16 8.2. Informative References . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
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 cryptographic algorithms which are negotiated also protected by cryptographic algorithms which are negotiated
between the two endpoints using IKE. Different implementations of between the two endpoints using IKE. Different implementations of
IKE may negotiate different algorithms based on their individual IKE may negotiate different algorithms based on their individual
local policy. To ensure interoperability, a set of "mandatory-to- local policy. To ensure interoperability, a set of "mandatory-to-
implement" IKE cryptographic algorithms is defined. implement" IKE cryptographic algorithms is defined.
This document describes the parameters of the IKE protocol and This document describes the parameters of the IKE protocol and
updates the IKEv2 specification because it changes the mandatory to updates the IKEv2 specification. It changes the mandatory to
implement authentication algorithms of the section 4 of the RFC7296 implement authentication algorithms of Section 4 of [RFC7296] by
by saying RSA key lengths of less than 2048 are SHOULD NOT. It does saying RSA key lengths of less than 2048 SHOULD NOT be used. 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. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
When used in the tables in this document, these terms indicate that
the listed algorithm MUST, MUST NOT, SHOULD, SHOULD NOT or MAY be
implemented as part of an IKEv2 implementation. Additional terms
used in this document are:
SHOULD+ This term means the same as SHOULD. However, it is likely
that an algorithm marked as SHOULD+ will be promoted at
some future time to be a MUST.
SHOULD- This term means the same as SHOULD. However, an algorithm
marked as SHOULD- may be deprecated to a MAY in a future
version of this document.
MUST- This term means the same as MUST. However, it is expected
at some point that this algorithm will no longer be a MUST
in a future document. Although its status will be
determined at a later time, it is reasonable to expect that
if a future revision of a document alters the status of a
MUST- algorithm, it will remain at least a SHOULD or a
SHOULD- level.
IoT stands for Internet of Things.
1.2. 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 realityI 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 a separate document. the main IKEv2 specification and placed in this separate document.
1.2. Updating Algorithm Requirement Levels 1.3. 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
completely broken before this document is updated. completely broken before this document is updated.
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requires this specific use case to be taken into account as well. requires this specific use case to be taken into account as well.
IoT devices are resource constrained devices and their choice of IoT devices are resource constrained devices and their choice of
algorithms are motivated by minimizing the footprint of the code, the algorithms are motivated by minimizing the footprint of the code, the
computation effort and the size of the messages to send. This computation effort and the size of the messages to send. This
document indicates "(IoT)" when a specified algorithm is specifically document indicates "(IoT)" when a specified algorithm is specifically
listed for IoT devices. Requirement levels that are marked as "IoT" listed for IoT devices. Requirement levels that are marked as "IoT"
apply to IoT devices and to server-side implementations that might apply to IoT devices and to server-side implementations that might
presumably need to interoperate with them, including any general- presumably need to interoperate with them, including any general-
purpose VPN gateways. purpose VPN gateways.
1.3. Document Audience 1.4. Document Audience
The recommendations of this document mostly target IKEv2 implementers The recommendations of this document mostly target IKEv2 implementers
as implementations need to meet both high security expectations as as implementations need to meet both high security expectations as
well as high interoperability between various vendors and with well as high interoperability between various vendors and with
different versions. Interoperability requires a smooth move to more different versions. Interoperability requires a smooth move to more
secure cipher suites. This may differ from a user point of view that secure cipher suites. This may differ from a user point of view that
may deploy and configure IKEv2 with only the safest cipher suite. may deploy and configure IKEv2 with only the safest cipher suite.
This document does not give any recommendations for the use of This document does not give any recommendations for the use of
algorithms, it only gives implementation recommendations for algorithms, it only gives implementation recommendations for
implementations. The use of algorithms by users is dictated by the implementations. The use of algorithms by users is dictated by the
security policy requirements for that specific user, and are outside security policy requirements for that specific user, and are outside
the scope of this document. the scope of this document.
IKEv1 is out of scope of this document. IKEv1 is deprecated and the IKEv1 is out of scope of this document. IKEv1 is deprecated and the
recommendations of this document must not be considered for IKEv1, as recommendations of this document must not be considered for IKEv1, as
most IKEv1 implementations have been "frozen" and will not be able to most IKEv1 implementations have been "frozen" and will not be able to
update the list of mandatory-to-implement algorithms. update the list of mandatory-to-implement algorithms.
2. Conventions Used in This Document 2. Algorithm Selection
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
We define some additional terms here:
SHOULD+ This term means the same as SHOULD. However, it is likely
that an algorithm marked as SHOULD+ will be promoted at
some future time to be a MUST.
SHOULD- This term means the same as SHOULD. However, an algorithm
marked as SHOULD- may be deprecated to a MAY in a future
version of this document.
MUST- This term means the same as MUST. However, we expect at
some point that this algorithm will no longer be a MUST in
a future document. Although its status will be determined
at a later time, it is reasonable to expect that if a
future revision of a document alters the status of a MUST-
algorithm, it will remain at least a SHOULD or a SHOULD-
level.
IoT stands for Internet of Things.
3. Algorithm Selection
3.1. Type 1 - IKEv2 Encryption Algorithm Transforms 2.1. 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 one of
integrity algorithms in Section 3.3. the integrity algorithms in Section 2.3.
+------------------------+----------+-------+---------+ +------------------------+----------+-------+---------+
| Name | Status | AEAD? | Comment | | Name | Status | AEAD? | Comment |
+------------------------+----------+-------+---------+ +------------------------+----------+-------+---------+
| ENCR_AES_CBC | MUST | No | (1) | | ENCR_AES_CBC | MUST | No | (1) |
| ENCR_CHACHA20_POLY1305 | SHOULD | Yes | | | ENCR_CHACHA20_POLY1305 | SHOULD | Yes | |
| ENCR_AES_GCM_16 | SHOULD | Yes | (1) | | ENCR_AES_GCM_16 | SHOULD | Yes | (1) |
| ENCR_AES_CCM_8 | SHOULD | Yes | (IoT) | | ENCR_AES_CCM_8 | SHOULD | Yes | (IoT) |
| ENCR_3DES | MAY | No | | | ENCR_3DES | MAY | No | |
| ENCR_DES | MUST NOT | No | | | ENCR_DES | MUST NOT | No | |
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interoperability with IoT. Only 128-bit keys are at SHOULD level. interoperability with IoT. Only 128-bit keys are at SHOULD level.
192-bit and 256-bit remain at the MAY level. 192-bit and 256-bit remain at the MAY level.
ENCR_AES_CBC is raised from SHOULD+ for 128-bit keys and MAY for ENCR_AES_CBC is raised from SHOULD+ for 128-bit keys and MAY for
256-bit keys in [RFC4307] to MUST. 192-bit keys remain at the MAY 256-bit keys in [RFC4307] to MUST. 192-bit keys remain at the MAY
level. ENCR_AES_CBC is the only shared mandatory-to-implement level. ENCR_AES_CBC is the only shared mandatory-to-implement
algorithm with RFC4307 and as a result it is necessary for algorithm with RFC4307 and as a result it is necessary for
interoperability with IKEv2 implementation compatible with RFC4307. interoperability with IKEv2 implementation 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 as an alternative to RFC4307. It has been recommended by the Crypto Forum Research Group
AES-CBC and AES-GCM. It is also being standardized for IPsec for the (CFRG) of the IRTF as an alternative to AES-CBC and AES-GCM. It is
same reasons. At the time of writing, there were not enough IKEv2 also being standardized for IPsec for the same reasons. At the time
implementations supporting ENCR_CHACHA20_POLY1305 to be able to of writing, there were not enough IKEv2 implementations supporting
introduce it at the SHOULD+ level. ENCR_CHACHA20_POLY1305 to be able to introduce it at the SHOULD+
level.
ENCR_AES_GCM_16 was not considered in RFC4307. At the time RFC4307 ENCR_AES_GCM_16 was not considered in RFC4307. At the time RFC4307
was written, AES-GCM was not defined in an IETF document. AES-GCM was written, AES-GCM was not defined in an IETF document. AES-GCM
was defined for ESP in [RFC4106] and later for IKEv2 in [RFC5282]. was defined for ESP in [RFC4106] and later for IKEv2 in [RFC5282].
The main motivation for adopting AES-GCM for ESP is encryption The main motivation for adopting AES-GCM for ESP is encryption
performance compared to AES-CBC. This resulted in AES-GCM being performance compared to AES-CBC. This resulted in AES-GCM being
widely implemented for ESP. As the computation load of IKEv2 is widely implemented for ESP. As the computation load of IKEv2 is
relatively small compared to ESP, many IKEv2 implementations have not relatively small compared to ESP, many IKEv2 implementations have not
implemented AES-GCM. For this reason, AES-GCM is not promoted to a implemented AES-GCM. For this reason, AES-GCM is not promoted to a
greater status than SHOULD. The reason for promotion from MAY to greater status than SHOULD. The reason for promotion from MAY to
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SHOULD is to promote the slightly more secure AEAD method over the SHOULD is to promote the slightly more secure AEAD method over the
traditional encrypt+auth method. Its status is expected to be raised traditional encrypt+auth method. Its status is expected to be raised
once widely implemented. As the advantage of the shorter (and once widely implemented. As the advantage of the shorter (and
weaker) ICVs is minimal, the 8 and 12 octet ICV's remain at the MAY weaker) ICVs is minimal, the 8 and 12 octet ICV's remain at the MAY
level. 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 those cases, and cases of IKEv2, as far less packets are exchanged in those cases, and
IoT devices want to make packets as small as possible. The SHOULD IoT devices want to make packets as small as possible. The SHOULD
level is for 128-bit keys, 256-bit keys remains at MAY level. level is for 128-bit keys, 256-bit keys remains at MAY level.
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 implementations 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 off-the-shelf hardware. It
provides no meaningful security whatsoever and therefor MUST NOT be provides no meaningful security whatsoever and therefore MUST NOT be
implemented. implemented.
3.2. Type 2 - IKEv2 Pseudo-random Function Transforms 2.2. 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 pseudo-random values when needed. generate pseudo-random values when needed.
+-------------------+----------+---------+ +-------------------+----------+---------+
| 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- | |
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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.
Cryptographic attacks against MD5, such as collision attacks Cryptographic attacks against MD5, such as collision attacks
mentioned in [TRANSCRIPTION], are resulting in an industry-wide trend mentioned in [TRANSCRIPTION], are resulting in an industry-wide trend
to deprecate and remove MD5 (and thus HMAC-MD5) from cryptographic to deprecate and remove MD5 (and thus HMAC-MD5) from cryptographic
libraries. libraries.
3.3. Type 3 - IKEv2 Integrity Algorithm Transforms 2.3. Type 3 - IKEv2 Integrity 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 are in the IANA registry. When an AEAD defining these algorithms are in the IANA registry. When an AEAD
algorithm (see Section 3.1) is proposed, this algorithm transform algorithm (see Section 2.1) is proposed, this algorithm transform
type is not in use. type is not in use.
+------------------------+----------+---------+ +------------------------+----------+---------+
| Name | Status | Comment | | Name | Status | Comment |
+------------------------+----------+---------+ +------------------------+----------+---------+
| AUTH_HMAC_SHA2_256_128 | MUST | | | AUTH_HMAC_SHA2_256_128 | MUST | |
| 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 | |
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as cryptographic attacks against SHA1 are increasing, resulting in an as cryptographic attacks against SHA1 are increasing, resulting in an
industry-wide trend to deprecate its usage industry-wide trend to deprecate its usage
AUTH_AES_XCBC_96 is only recommended in the scope of IoT, as Internet AUTH_AES_XCBC_96 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 deployment, it has been downgraded from SHOULD in RFC4307 to MAY as
it has not been widely adopted. it has not been widely adopted.
AUTH_DES_MAC, AUTH_HMAC_MD5_96, and AUTH_KPDK_MD5 were not mentioned AUTH_DES_MAC, AUTH_HMAC_MD5_96, and AUTH_KPDK_MD5 were not mentioned
in RFC4307 so their default status ware MAY. They have been in RFC4307 so their default statuses were MAY. They have been
downgraded to MUST NOT. There is an industry-wide trend to deprecate downgraded to MUST NOT. There is an industry-wide trend to deprecate
DES and MD5. MD5 support is being removed from cryptographic DES and MD5. MD5 support is being removed from cryptographic
libraries in general because its non-HMAC use is known to be subject libraries in general because its non-HMAC use is known to be subject
to collision attacks, for example as mentioned in [TRANSCRIPTION]. to collision attacks, for example as mentioned in [TRANSCRIPTION].
3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms 2.4. 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 [RFC7296] base document and in groups are defined in both the [RFC7296] 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 keys for the session. If an attacker can retrieve exchange provides keys for the session. If an attacker can retrieve
one of the private numbers (a or b) and the complementary public one of the private numbers (a or b) and the complementary public
value (g**a or g**b), then the attacker can compute the secret and value (g**b or g**a), then the attacker can compute the secret and
the keys used and decrypt the exchange and IPsec SA created inside the keys used and decrypt the exchange and IPsec SA created inside
the IKEv2 SA. Such an attack can be performed off-line on a the IKEv2 SA. Such an attack can be performed off-line on a
previously recorded communication, years after the communication previously recorded communication, years after the communication
happened. This differs from attacks that need to be executed during happened. This differs from attacks that need to be executed during
the authentication which must be performed online and in near real- the authentication which must be performed online and in near real-
time. time.
+--------+---------------------------------------------+------------+ +--------+---------------------------------------------+------------+
| Number | Description | Status | | Number | Description | Status |
+--------+---------------------------------------------+------------+ +--------+---------------------------------------------+------------+
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| | Order Subgroup | | | | Order Subgroup | |
| 24 | 2048-bit MODP Group with 256-bit Prime | SHOULD NOT | | 24 | 2048-bit MODP Group with 256-bit Prime | SHOULD NOT |
| | Order Subgroup | | | | 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 defined at that time. Group 19 is widely this group was not defined 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
RFC4307 to SHOULD NOT. It was specified earlier, but is now RFC4307 to SHOULD NOT. It was specified earlier, but is now
considered to be vulnerable to be broken within the next few years by considered to be vulnerable to being broken within the next few years
a nation state level attack, so its security margin is considered too by a nation state level attack, so its security margin is considered
narrow. too narrow.
Group 2 or 1024-bit MODP Group has been downgraded from MUST- in Group 2 or 1024-bit MODP Group has been downgraded from MUST- in
RFC4307 to SHOULD NOT. It is known to be weak against sufficiently RFC4307 to SHOULD NOT. It is known to be weak against sufficiently
funded attackers using commercially available mass-computing funded attackers using commercially available mass-computing
resources, so its security margin is considered too narrow. It is resources, so its security margin is considered too narrow. It is
expected in the near future to be downgraded to MUST NOT. expected in the near future to be downgraded to MUST NOT.
Group 1 or 768-bit MODP Group was not mentioned in RFC4307 and so its Group 1 or 768-bit MODP Group was not mentioned in RFC4307 and so its
status was MAY. It can be broken within hours using cheap of-the- status was MAY. It can be broken within hours using cheap of-the-
shelves hardware. It provides no security whatsoever. shelves hardware. It provides no security whatsoever.
Group 22, 23 and 24 are MODP Groups with Prime Order Subgroups thater Group 22, 23 and 24 are MODP Groups with Prime Order Subgroups that
are not safe-primes. The seeds for these groups have not been are not safe-primes. The seeds for these groups have not been
publicly released, resulting in reduced trust in these groups. These publicly released, resulting in reduced trust in these groups. These
groups were proposed as alternatives for group 2 and 14 but never saw groups were proposed as alternatives for group 2 and 14 but never saw
wide deployment. It has been shown that Group 22 with 1024-bit MODP wide deployment. It has been shown that Group 22 with 1024-bit MODP
is too weak and academia have the resources to generate malicious is too weak and academia have the resources to generate malicious
values at this size. This has resulted in Group 22 to be demoted to values at this size. This has resulted in Group 22 to be demoted to
MUST NOT. Group 23 and 24 have been demoted to SHOULD NOT and are MUST NOT. Group 23 and 24 have been demoted to SHOULD NOT and are
expected to be further downgraded in the near future to MUST NOT. expected to be further downgraded in the near future to MUST NOT.
Since Group 23 and 24 have small subgroups, the checks specified in Since Group 23 and 24 have small subgroups, the checks specified in
"Additional Diffie-Hellman Test for the IKEv2" [RFC6989] section 2.2 "Additional Diffie-Hellman Test for the IKEv2" [RFC6989] section 2.2
first bullet point MUST be done when these groups are used. first bullet point MUST be done when these groups are used.
3.5. Summary of Changes from RFC 4307 2.5. Summary of Changes from RFC 4307
The following table summarizes the changes from RFC 4307. The following table summarizes the changes from RFC 4307.
RFC EDITOR: PLEASE REMOVE THIS PARAGRAPH AND REPLACE XXXX IN THE RFC EDITOR: PLEASE REMOVE THIS PARAGRAPH AND REPLACE XXXX IN THE
TABLE BELOW WITH THE NUMBER OF THIS RFC TABLE BELOW WITH THE NUMBER OF THIS RFC
+---------------------+------------------+------------+ +---------------------+------------------+------------+
| Algorithm | RFC 4307 | RFC XXXX | | Algorithm | RFC 4307 | RFC XXXX |
+---------------------+------------------+------------+ +---------------------+------------------+------------+
| ENCR_3DES | MUST- | MAY | | ENCR_3DES | MUST- | MAY |
| ENCR_NULL | MUST NOT[errata] | MUST NOT | | ENCR_NULL | MUST NOT[errata] | MUST NOT |
skipping to change at page 11, line 24 skipping to change at page 11, line 24
| AUTH_HMAC_MD5_96 | MAY | MUST NOT | | AUTH_HMAC_MD5_96 | MAY | MUST NOT |
| AUTH_HMAC_SHA1_96 | MUST | MUST- | | AUTH_HMAC_SHA1_96 | MUST | MUST- |
| AUTH_AES_XCBC_96 | SHOULD+ | SHOULD | | AUTH_AES_XCBC_96 | SHOULD+ | SHOULD |
| Group 2 (1024-bit) | MUST- | SHOULD NOT | | Group 2 (1024-bit) | MUST- | SHOULD NOT |
| Group 14 (2048-bit) | SHOULD+ | MUST | | Group 14 (2048-bit) | SHOULD+ | MUST |
+---------------------+------------------+------------+ +---------------------+------------------+------------+
(*) This algorithm is not mentioned in the above sections, so it (*) This algorithm is not mentioned in the above sections, so it
defaults to MAY. defaults to MAY.
4. IKEv2 Authentication 3. IKEv2 Authentication
IKEv2 authentication may involve a signatures verification. IKEv2 authentication may involve a signatures verification.
Signatures may be used to validate a certificate or to check the Signatures may be used to validate a certificate or to check the
signature of the AUTH value. Cryptographic recommendations regarding signature of the AUTH value. Cryptographic recommendations regarding
certificate validation are out of scope of this document. What is certificate validation are out of scope of this document. What is
mandatory to implement is provided by the PKIX Community. This mandatory to implement is provided by the PKIX Community. This
document is mostly concerned on signature verification and generation document is mostly concerned with signature verification and
for the authentication. generation for the authentication.
4.1. IKEv2 Authentication Method 3.1. IKEv2 Authentication Method
+--------+---------------------------------------+------------+ +--------+---------------------------------------+------------+
| Number | Description | Status | | Number | Description | Status |
+--------+---------------------------------------+------------+ +--------+---------------------------------------+------------+
| 1 | RSA Digital Signature | MUST | | 1 | RSA Digital Signature | MUST |
| 2 | Shared Key Message Integrity Code | MUST | | 2 | Shared Key Message Integrity Code | 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 |
+--------+---------------------------------------+------------+ +--------+---------------------------------------+------------+
RSA Digital Signature is widely deployed and therefore kept for RSA Digital Signature is widely deployed and therefore 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].
recommended for keys smaller then 2048, but since these signatures
only have value in real-time, and need no future protection, smaller
keys was kept at SHOULD NOT instead of MUST NOT.
Shared Key Message Integrity Code is widely deployed and mandatory to Shared Key Message Integrity Code is widely deployed and mandatory to
implement in the IKEv2 in the RFC7296. implement in the IKEv2 in the RFC7296.
ECDSA based Authentication Methods are also expected to be downgraded ECDSA based Authentication Methods are also expected to be downgraded
as it does not provide hash function agility. Instead, ECDSA (like as these do not provide hash function agility. Instead, ECDSA (like
RSA) is expected to be performed using the generic Digital Signature RSA) is expected to be performed using the generic Digital Signature
method. method.
DSS Digital Signature is bound to SHA-1 and has the same level of DSS Digital Signature is bound to SHA-1 and has the same level of
security as 1024-bit RSA. It is expected to be downgraded to MUST security as 1024-bit RSA. It is expected to be downgraded to MUST
NOT in the future. NOT in the future.
Digital Signature [RFC7427] is expected to be promoted as it provides Digital Signature [RFC7427] is expected to be promoted as it provides
hash function, signature format and algorithm agility. hash function, signature format and algorithm agility.
4.1.1. Recommendations for RSA key length 3.1.1. Recommendations for RSA key length
+-------------------------------------------+------------+ +-------------------------------------------+------------+
| 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 smaller than 2048 | SHOULD NOT | | RSA with key length smaller than 2048 | SHOULD NOT |
+-------------------------------------------+------------+ +-------------------------------------------+------------+
The IKEv2 RFC7296 mandates support for the RSA keys of size 1024 or The IKEv2 RFC7296 mandates support for the RSA keys of size 1024 or
2048 bits, but here we make key sizes less than 2048 SHOULD NOT as 2048 bits, but key sizes less than 2048 are updated to SHOULD NOT as
there is industry-wide trend to deprecate key lengths less than 2048 there is industry-wide trend to deprecate key lengths less than 2048
bits. bits. Since these signatures only have value in real-time, and need
no future protection, smaller keys were kept at SHOULD NOT instead of
MUST NOT.
4.2. Digital Signature Recommendations 3.2. Digital Signature Recommendations
When Digital Signature authentication method is implemented, then the When a Digital Signature authentication method is implemented, the
following recommendations are applied for hash functions: following recommendations are applied for hash functions:
+--------+-------------+----------+---------+ +--------+-------------+----------+---------+
| Number | Description | Status | Comment | | Number | Description | Status | Comment |
+--------+-------------+----------+---------+ +--------+-------------+----------+---------+
| 1 | SHA1 | MUST NOT | | | 1 | SHA1 | MUST 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 | |
+--------+-------------+----------+---------+ +--------+-------------+----------+---------+
When Digital Signature authentication method is used with RSA When Digital Signature authentication method is used with RSA
signature algorithm, then RSASSA-PSS MUST be supported and RSASSA- signature algorithm, RSASSA-PSS MUST be supported and RSASSA-
PKCS1-v1.5 MAY be supported. PKCS1-v1.5 MAY be supported.
The following table lists recommendations for authentication methods The following table lists recommendations for authentication methods
in RFC7427 [RFC7427] notation. These recommendations are applied in RFC7427 [RFC7427] notation. These recommendations are applied
only if Digital Signature authentication method is implemented. only if Digital Signature authentication method is implemented.
+------------------------------------+----------+---------+ +------------------------------------+----------+---------+
| Description | Status | Comment | | Description | Status | Comment |
+------------------------------------+----------+---------+ +------------------------------------+----------+---------+
| RSASSA-PSS with SHA-256 | MUST | | | RSASSA-PSS with SHA-256 | MUST | |
skipping to change at page 13, line 37 skipping to change at page 13, line 37
| sha1WithRSAEncryption | MUST NOT | | | sha1WithRSAEncryption | MUST NOT | |
| dsa-with-sha1 | MUST NOT | | | dsa-with-sha1 | MUST NOT | |
| ecdsa-with-sha1 | MUST NOT | | | ecdsa-with-sha1 | MUST NOT | |
| RSASSA-PSS with Empty Parameters | MUST NOT | (*) | | RSASSA-PSS with Empty Parameters | MUST NOT | (*) |
| RSASSA-PSS with Default Parameters | MUST NOT | (*) | | RSASSA-PSS with Default Parameters | MUST NOT | (*) |
+------------------------------------+----------+---------+ +------------------------------------+----------+---------+
(*) Empty or Default parameters means it is using SHA1, which is at (*) Empty or Default parameters means it is using SHA1, which is at
level MUST NOT. level MUST NOT.
5. Algorithms for Internet of Things 4. Algorithms for Internet of Things
Some algorithms in this document are marked for use with the Internet Some algorithms in this document are marked for use with the Internet
of Things (IoT). There are several reasons why IoT devices prefer a of Things (IoT). There are several reasons why IoT devices prefer a
different set of algorithms from regular IKEv2 clients. IoT devices different set of algorithms from regular IKEv2 clients. IoT devices
are usually very constrained, meaning the memory size and CPU power are usually very constrained, meaning the memory size and CPU power
is so limited, that these clients only have resources to implement is so limited, that these clients only have resources to implement
and run one set of algorithms. For example, instead of implementing and run one set of algorithms. For example, instead of implementing
AES and SHA, these devices typically use AES_XCBC as integrity AES and SHA, these devices typically use AES_XCBC as integrity
algorithm so SHA does not need to be implemented. algorithm so SHA does not need to be implemented.
skipping to change at page 14, line 25 skipping to change at page 14, line 25
are usually quite low (in order of tens of kbits/s), and each bit are usually quite low (in order of tens of kbits/s), and each bit
they transmit has an energy consumption cost associated with it and they transmit has an energy consumption cost associated with it and
shortens their battery life. Therefore, shorter packets are shortens their battery life. Therefore, shorter packets are
preferred. This is the reason for recommending the 8 octet ICV over preferred. This is the reason for recommending the 8 octet ICV over
the 16 octet ICV. the 16 octet ICV.
Because different IoT devices will have different constraints, this Because different IoT devices will have different constraints, this
document cannot specify the one mandatory profile for IoT. Instead, document cannot specify the one mandatory profile for IoT. Instead,
this document points out commonly used algorithms with IoT devices. this document points out commonly used algorithms with IoT devices.
6. Security Considerations 5. 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 15, line 5 skipping to change at page 15, line 5
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.
7. IANA Considerations 6. IANA Considerations
This document renames some of the names in the "Transform Type 1 - This document renames some of the names in the "Transform Type 1 -
Encryption Algorithm Transform IDs" registry of the "Internet Key Encryption Algorithm Transform IDs" registry of the "Internet Key
Exchange Version 2 (IKEv2) Parameters". All the other names have Exchange Version 2 (IKEv2) Parameters". All the other names have
ENCR_ prefix except 3, and all other entries use names in format of ENCR_ prefix except 3, and all other entries use names in format of
uppercase words separated with underscores except 6. This document uppercase words separated with underscores except 6. This document
changes those names to match others. changes those names to match others.
This document requests IANA to rename following entries for the AES- This document requests IANA to rename following entries for the AES-
GCM cipher [RFC4106] and the Camellia cipher [RFC5529]: GCM cipher [RFC4106] and the Camellia cipher [RFC5529]:
skipping to change at page 15, line 46 skipping to change at page 15, line 46
Number Name ESP Reference IKEv2 Reference Number Name ESP Reference IKEv2 Reference
... ...
18 ENCR_AES_GCM_8 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX] 18 ENCR_AES_GCM_8 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX]
19 ENCR_AES_GCM_12 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX] 19 ENCR_AES_GCM_12 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX]
20 ENCR_AES_GCM_16 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX] 20 ENCR_AES_GCM_16 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX]
... ...
25 ENCR_CAMELLIA_CCM_8 [RFC5529][RFCXXXX] - 25 ENCR_CAMELLIA_CCM_8 [RFC5529][RFCXXXX] -
26 ENCR_CAMELLIA_CCM_12 [RFC5529][RFCXXXX] - 26 ENCR_CAMELLIA_CCM_12 [RFC5529][RFCXXXX] -
27 ENCR_CAMELLIA_CCM_16 [RFC5529][RFCXXXX] - 27 ENCR_CAMELLIA_CCM_16 [RFC5529][RFCXXXX] -
8. Acknowledgements 7. 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,
Tommy Pauly for their valuable feedback. Tommy Pauly, Eric Rescorla and Pete Resnick for their valuable
feedback and reviews.
9. References 8. References
9.1. Normative References 8.1. 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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/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)", (GCM) in IPsec Encapsulating Security Payload (ESP)",
RFC 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>.
skipping to change at page 16, line 38 skipping to change at page 16, line 39
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, Exchange version 2 (IKEv2) Protocol", RFC 5282,
DOI 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>.
9.2. Informative References 8.2. 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>.
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