< draft-ietf-ipsecme-rfc4307bis-01.txt   draft-ietf-ipsecme-rfc4307bis-02.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: May 12, 2016 INSIDE Secure Expires: July 07, 2016 INSIDE Secure
P. Wouters P. Wouters
Red Hat Red Hat
D. Migault D. Migault
Ericsson Ericsson
November 9, 2015 January 04, 2016
Cryptographic Algorithms for Use in the Internet Key Exchange Version 2 Algorithm Implementation Requirements and Usage Guidance for IKEv2
(IKEv2) draft-ietf-ipsecme-rfc4307bis-02
draft-ietf-ipsecme-rfc4307bis-01
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 protocol provides a mechanism to negotiate which algorithms Exchange protocol provides a mechanism to negotiate which algorithms
should be used in any given association. However, to ensure should be used in any given Security Association. To ensure
interoperability between disparate implementations, it is necessary interoperability between different implementations, it is necessary
to specify a set of mandatory-to-implement algorithms to ensure that to specify a set of algorithm implementation requirements and Usage
there is at least one algorithm that all implementations will have guidance to ensure that there is at least one algorithm that all
available. This document defines the current set of algorithms that implementations will have available. This document defines the
are mandatory to implement as part of IKEv2, as well as algorithms current algorithm implementation requirements and usage guidance of
that should be implemented because they may be promoted to mandatory IKEv2. This document does not update the algorithms used for packet
at some future time. 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 May 12, 2016. This Internet-Draft will expire on July 07, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3 1.1. Updating Algorithm Implementation Requirements and Usage
3. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 3 Guidance . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. IKEv2 Transform Type 1 Algorithms . . . . . . . . . . . . 3 1.2. Updating Algorithm Requirement Levels . . . . . . . . . . 3
3.2. IKEv2 Transform Type 3 Algorithms . . . . . . . . . . . . 4 1.3. Document Audience . . . . . . . . . . . . . . . . . . . . 4
3.3. IKEv2 Transform Type 2 Algorithms . . . . . . . . . . . . 5 2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3.4. Diffie-Hellman Groups . . . . . . . . . . . . . . . . . . 5 3. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 3.1. Type 1 - IKEv2 Encryption Algorithm Transforms . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 6 4. IKEv2 Authentication . . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 7 4.1. IKEv2 Authentication Method . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Digital Signature Recommendation . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
The Internet Key Exchange protocol [RFC7296] is used to negotiate the
IPsec parameters, such as encryption algorithms and keys, for
protected communications between two endpoints. The IKEv2 protocol
itself is also protected by encryption, which is also negotiated
between the two endpoints. Negotiation is performed by IKEv2 itself.
This document describes the encryption parameters of the IKE
protocol, not the encryption parameters of the ESP (IPsec) protocol.
Different implementations of IKEv2 may negotiate different encryption
algorithms based on their individual local policy. To ensure
interoperability, a set of "mandatory-to-implement" IKEv2 encryption
algorithms is defined.
The Internet Key Exchange protocol [RFC7296] provides for the 1.1. Updating Algorithm Implementation Requirements and Usage Guidance
negotiation of cryptographic algorithms between both endpoints of a
cryptographic association. Different implementations of IPsec and
IKE may provide different algorithms. However, the IETF desires that
all implementations should have some way to interoperate. In
particular, this requires that IKE define a set of mandatory-to-
implement algorithms because IKE itself uses such algorithms as part
of its own negotiations. This requires that some set of algorithms
be specified as "mandatory-to-implement" for IKE.
The nature of cryptography is that new algorithms surface The field of cryptography evolves continiously. New stronger
continuously and existing algorithms are continuously attacked. An algorithms appear and existing algorithms are found to be less secure
algorithm believed to be strong today may be demonstrated to be weak then originally thought. Therefore, algorithm implementation
tomorrow. Given this, the choice of mandatory-to-implement algorithm requirements and usage guidance need to be updated from time to time
should be conservative so as to minimize the likelihood of it being to reflect the new reality. The choices for algorithms must be
compromised quickly. Thought should also be given to performance conservative to minimize the risk of algorithm compromised.
considerations as many uses of IPsec will be in environments where Algorithms need to be suitable for a wide variety of CPU
performance is a concern. architectures and device deployments ranging from high end bulk
encryption devices to small low-power IoT devices.
Finally, we need to recognize that the mandatory-to-implement The algorithm implementation requirements and usage guidance may need
algorithm(s) may need to change over time to adapt to the changing to change over time to adapt to the changing world. For this reason,
world. For this reason, the selection of mandatory-to-implement the selection of mandatory-to-implement algorithms was removed from
algorithms was removed from the main IKEv2 specification and placed the main IKEv2 specification and placed in this document.
in this document. As the choice of algorithm changes, only this
document should need to be updated. 1.2. Updating Algorithm Requirement Levels
Ideally, the mandatory-to-implement algorithm of tomorrow should Ideally, the mandatory-to-implement algorithm of tomorrow should
already be available in most implementations of IPsec by the time it already be available in most implementations of IKE by the time it is
is made mandatory. To facilitate this, we will attempt to identify made mandatory. To facilitate this, this document attempts to
those algorithms (that are known today) in this document. There is identify those algorithms for future mandatory-to-implement. There
no guarantee that the algorithms we believe today may be mandatory in is no guarantee that the algorithms in use today may become mandatory
the future will in fact become so. All algorithms known today are in the future. Published algorithms are continiously subjected to
subject to cryptographic attack and may be broken in the future. cryptographic attack and may become too weak or could become
completely broken before this document is updated.
This document only provides recommendations for the mandatory-to-
implement algorithms or algorithms too weak that are recommended not
to be implemented. As a result, any algorithm not mentioned in this
document MAY be implemented. For clarification and consistency with
[RFC4307] an algorithm will be set to MAY only when it has been
downgraded.
Although this document updates the algorithms in order to keep the
IKEv2 communication secure over time, it also aims at providing
recommendations so that IKEv2 implementations remain interoperable.
IKEv2 interoperability is addressed by an incremental introduction or
deprecation of algorithms. In addition, this document also considers
the new use cases for IKEv2 deployment, such as Internet of Things
(IoT).
It is expected that deprecation of an algorithm is performed
gradually. This provides time for various implementations to update
their implemented algorithms while remaining interoperable. Unless
there are strong security reasons, an algorithm is expected to be
downgraded from MUST to MUST- or SHOULD, instead of MUST NOT.
Similarly, an algorithm that has not been mentioned as mandatory-to-
implement is expected to be introduced with a SHOULD instead of a
MUST.
The current trend toward Internet of Things and its adoption of IKEv2
requires this specific use case to be taken into account as well.
IoT devices are resource constrainted devices and their choice of
algorithms are motivated by minimizing the fooprint of the code, the
computation effort and the size of the messages to send. This
document indicates IoT when a specified algorithm is specifically
listed for IoT devices.
1.3. Document Audience
The recommendations of this document target IKEv2 implementers. In
other words, the recommendations should not be considered for IKEv2
configuration, as a preference for some algorithms. [PAUL: I don't
understand this. Clearly MTI are good default choices?]
IKEv1 is out of scope of this document. IKEv1 is deprecated and the
recommendations of this document must not be considered for IKEv1.
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 that an algorithm marked as SHOULD+ will be promoted at some
some future time to be a MUST. 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 MUST- This term means the same as MUST. However, we expect at
some point that this algorithm will no longer be a MUST in some point that this algorithm will no longer be a MUST in a
a future document. Although its status will be determined future document. Although its status will be determined at
at a later time, it is reasonable to expect that if a a later time, it is reasonable to expect that if a future
future revision of a document alters the status of a MUST- 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-.
IoT stands for Internet of Things.
Table 1
3. Algorithm Selection 3. Algorithm Selection
3.1. IKEv2 Transform Type 1 Algorithms 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 in the ENCR payload. References to the specifications and used in the ENCR payload. References to the specifications
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 the Algorithms that are not AEAD MUST be used in conjunction with an
integrity algorithms in Section 3.2. integrity algorithms in Section 3.3.
+-----------------------------+----------+-------+---------+ +-----------------------------+----------+-------+----------+
| 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 | |
| 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] | | 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. MAY. 192-bit keys can safely be ignored. [IoT] - This requirement is
for interoperability with IoT.
Explanation about AES-CBC is TBD. Table 2
Explanation about ChaCha20 is TBD. ENCR_AES_CBC is raised from SHOULD+ in RFC4307. It is the only
shared mandatory-to-implement algorithm with RFC4307 and as a result
is necessary for interoperability with IKEv2 implementation
compatible with RFC4307.
Explanation about AES-GCM is TBD. 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
alternative to AES and AES-GCM. It is also being standarized for
IPsec for the same reasons. At the time of writing, there were not
enough IKEv2 implementations of ENCR_CHACHA20_POLY1305 to be able to
introduce it at the SHOULD+ level.
Explanation about AES-CCM is TBD. AES-GCM with a 16 octet ICV was not considered as in RFC4307. At the
time RFC4307 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]. The main motivation for adopting AES-GCM for ESP
is encryption performance as well as key longevity - compared to AES-
CBC for example. This resulted in AES-GCM widely implemented for
ESP. As the load of IKEv2 is expected to remain relatively small,
many IKEv2 implementations do not include AES-GCM. In addition to
its former MAY, this document does not promote AES-GCM to a greater
status than SHOULD so to preserve interoperability between IKEv2
implementations. [PAUL: I dont follow the reasoning, as we could
have AES and AES-GCM at MUST level] This document considers AES-GCM
as mandatory to implement to promote the slightly more secure AEAD
method over the traditional encrypt+auth method. Its status is
expected to be raised once widely deployed.
Explanation about 3DES is TBD. ENCR_AES_CCM_8 was not considered in RFC4307. This document
considers it SHOULD be implemented in order to be able to interact
with Internet of Things devices. As this case is not a general use
case for VPNs, its status is expected to remain to SHOULD. The 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 compared to the IPsec
SA. When implemented, ENCR_AES_CCM_8 MUST be implemented for key
length 128 and MAY be implemented for key length 256.
Explanation about DES is TBD. ENCR_3DES has been downgraded from RFC4307 MUST-. All IKEv2
implementation already implement ENCR_AES_CBC, so there is no need to
keep ENCR_3DES. In addition, ENCR_CHACHA20_POLY1305 provides a more
modern alternative to AES. [PAUL: removed 'efficient' as we said
above encryption efficiency at the IKE level hardly matters]
3.2. IKEv2 Transform Type 3 Algorithms ENCR_DES can be brute-forced using of-the-shelves hardware. It
provides no meaningful security whatsoever and therefor MUST NOT be
implemented.
The algorithms in the below table are negotiated in the SA payload 3.2. Type 2 - IKEv2 Pseudo-random Function Transforms
and used in the ENCR payload. References to the specifications
defining these algorithms are in the IANA registry. When an AEAD
algorithm (see Section 3.1) is used, no algorithm from this table
needs to be used.
+------------------------+---------+ Transform Type 2 Algorithms are pseudo-random functions used to
| Name | Status | generate random values when needed.
+------------------------+---------+
| AUTH_HMAC_SHA2_256_128 | MUST |
| AUTH_HMAC_SHA2_512_256 | SHOULD+ |
| AUTH_HMAC_SHA1_96 | MUST- |
| AUTH_AES_XCBC_96 | MAY |
+------------------------+---------+
Explanation about SHA-256 is TBD. In general, if you can trust an algorithm as INTEG algorithm, you can
and should also use it as the PRF. When using an AEAD cipher, the
choice is PRF is open, and picking one of the SHA2 variants is
recommended.
Explanation about SHA-512 is TBD. +-------------------+---------+---------+
| Name | Status | Comment |
+-------------------+---------+---------+
| PRF_HMAC_SHA2_256 | MUST | |
| PRF_HMAC_SHA2_512 | SHOULD+ | |
| PRF_HMAC_SHA1 | MUST- | [1] |
| PRF_AES128_CBC | SHOULD | [IoT] |
+-------------------+---------+---------+
Explanation about SHA-1 is TBD. [IoT] - This requirement is for interoperability with IoT
Explanation about AES-XCBC is TBD. Table 3
3.3. IKEv2 Transform Type 2 Algorithms PRF_HMAC_SHA2_256 was not mentioned in RFC4307, as no SHA2 based
authentication was mentioned. PRF_HMAC_SHA2_256 MUST be implemented
in order to replace SHA1 and PRF_HMAC_SHA1.
Transform Type 2 Algorithms are pseudo-random functions used to PRF_HMAC_SHA2_512 SHOULD be implemented as as a future replacement of
generate random values when needed. SHA2_256 or when stronger security is required. PRF_HMAC_SHA2_512 is
preferred over PRF_HMAC_SHA2_384, as the overhead of
PRF_HMAC_SHA2_512 is negligible.
+-------------------+---------+ PRF_HMAC_SHA1_96 has been downgraded from MUST in RFC4307. There is
| Name | Status | an industry-wide trend to deprecate its usage.
+-------------------+---------+
| PRF_HMAC_SHA2_256 | MUST |
| PRF_HMAC_SHA2_512 | SHOULD+ |
| PRF_HMAC_SHA1 | MUST- |
| PRF_AES128_CBC | MAY |
+-------------------+---------+
Explanation about SHA-256 is TBD. PRF_AES128_CBC is only recommended in the scope of IoT, as Internet
of Things deployments tend to prefer AES based pseudo-random
functions in order to avoid implementing SHA2. For the wide VPN
deployment, as it has not been widely adopted, it has been downgraded
from SHOULD in RFC4307 to MAY.
Explanation about SHA-512 is TBD. 3.3. Type 3 - IKEv2 Integrity Algorithm Transforms
Explanation about SHA-1 is TBD. The algorithms in the below table are negotiated in the SA payload
and used in the ENCR payload. References to the specifications
defining these algorithms are in the IANA registry. When an AEAD
algorithm (see Section 3.1) is proposed, this algorithm transform
type is not in use.
Explanation about AES-XCBC is TBD. +------------------------+--------+---------+
| Name | Status | Comment |
+------------------------+--------+---------+
| AUTH_HMAC_SHA2_256_128 | MUST | |
| AUTH_HMAC_SHA2_512_256 | SHOULD | |
| AUTH_HMAC_SHA1_96 | SHOULD | |
| AUTH_AES_XCBC_96 | SHOULD | [IoT] |
+------------------------+--------+---------+
3.4. Diffie-Hellman Groups [IoT] - This requirement is for interoperability with IoT
Table 4
AUTH_HMAC_SHA2_256_128 was not mentioned in RFC4307, as no SHA2 based
authentication was mentioned. AUTH_HMAC_SHA2_256_128 MUST be
implemented in order to replace AUTH_HMAC_SHA1_96.
AUTH_HMAC_SHA2_512_256 SHOULD be implemented as as a future
replacement of AUTH_HMAC_SHA2_256_128 or when stronger security is
required. This value has been preferred to AUTH_HMAC_SHA2_384, as
the overhead of AUTH_HMAC_SHA2_512 is negligible.
AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC4307. There is
an industry-wide trend to deprecate its usage.
AUTH_AES-XCBC is only recommended in the scope of IoT, as Internet of
Things deployments tend to prefer AES based pseudo-random functions
in order to avoid implementing SHA2. For the wide VPN deployment, as
it has not been widely adopted, it has been downgraded from SHOULD in
RFC4307 to MAY.
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. They Elliptic Curve groups (ECC) that are defined for use in IKEv2. They
are defined in both the [IKEv2] base document and in extensions are defined in both the [IKEv2] base document and in extensions
documents. They are identified by group number. documents. They are identified by group number.
+--------+--------------------------+------------+ +--------+--------------------------+------------+
| Number | Description | Status | | Number | Description | Status |
+--------+--------------------------+------------+ +--------+--------------------------+------------+
| 14 | 2048-bit MODP Group | MUST | | 14 | 2048-bit MODP Group | MUST |
| 19 | 256-bit random ECP group | SHOULD | | 19 | 256-bit random ECP group | SHOULD |
| 5 | 1536-bit MODP Group | SHOULD NOT |
| 2 | 1024-bit MODP Group | SHOULD NOT | | 2 | 1024-bit MODP Group | SHOULD NOT |
| 1 | 768-bit MODP Group | MUST NOT | | 1 | 768-bit MODP Group | MUST NOT |
| TBD | Curve25519 | MAY |
+--------+--------------------------+------------+ +--------+--------------------------+------------+
Explanation about Group 14 is TBD. Table 5
Explanation about Group 19 is TBD. 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
implemented and considered secure
Explanation about Group 2 is TBD. Group 19 or 256-bit random ECP group was not specified in RFC4307.
Group 19 is widely implemented and considered secure
Group 5 or 1536-bit MODP Group is downgrade from MUST- to SHOULD NOT.
It was specified earlier, but now considered to be vulnerable to be
broken within the next few years by a nation state level attack, so
its security margin is considered too narrow.
Explanation about Group 1 is TBD. Group 2 or 1024-bit MODP Group is downgrade from MUST- to SHOULD NOT.
It was specified earlier, but now it is known to be weak against
sufficiently funded attackers using commercially available mass-
computing resources, so its security margin is considered too narrow.
It is expected in the near future to be downgraded to MUST NOT.
4. Security Considerations Group 1 or 768-bit MODP Group can be broken within hours using cheap
of-the-shelves hardware. It provides no security whatsoever.
Curve25519 has been designed with performance and security in mind
and have been recommended by CFRG. At the time of writing, the IKEv2
specification is still at the draft status. This document specifies
it as to encourage its implementation and deployment. If it gets
widely implemented then it most likely will be upgraded to SHOULD or
even MUST in the future.
4. IKEv2 Authentication
IKEv2 authentication may involve a signatures verification.
Signatures may be used to validate a certificate or to check the
signature of the AUTH value. Cryptographic recommendations regarding
certificate validation are out of scope of this document as what
mandatory implementations are provided by the PKIX WG. This document
is mostly concerned on signature verification and generation for the
authentication.
4.1. IKEv2 Authentication Method
+----------+-----------------------+----------+---------------------+
| Number | Description | Status | Comment |
+----------+-----------------------+----------+---------------------+
| 1 | RSA Digital Signature | MUST | With keys length |
| | | | 2048 |
| 1 | RSA Digital Signature | SHOULD | With keys length |
| | | | 3072/4096 |
| 1 | RSA Digital Signature | MUST NOT | With keys length |
| | | | lower than 2048 |
| 3 | DSS Digital Signature | MAY | |
| 9 | ECDSA with SHA-256 on | SHOULD | |
| | the P-256 curve | | |
| 10 | ECDSA with SHA-384 on | SHOULD | |
| | the P-384 curve | | |
| 11 | ECDSA with SHA-512 on | SHOULD | |
| | the P-521 curve | | |
| 14 | Digital Signature | SHOULD | |
+----------+-----------------------+----------+---------------------+
Table 6
RSA Digital Signature is mostly kept for interoperability. It is
expected to be downgraded in the future as signatures are based on
RSASSA-PKCS1-v1.5, not any more recommemded. Instead, more robust
use of RSA is expected to be performed via the Digital Signature
method.
ECDSA family are also expected to be downgraded as it does not
provide hash function agility. Instead ECDSA is expected to be
performed using the generic Digital Signature method.
DSS Digital Signature is bound to SHA-1 and thus is expected to be
downgraded to MUST NOT in the future.
Digital Signature is expected to be promoted as it provides hash
function, signature format and algorithm agility.
[MGLT: Do we have any recommendation for the authentication based on
PSK?]
4.2. Digital Signature Recommendation
Recommended methods: RSA (MUST), ECDSA (SHOULD), Ed25519 (MAY),
Ed25519ph(MAY), Ed448(MAY), Ed448ph(MAY)?
Here are the recommendations when a hash function is involved in a
signature.
+--------+----------------------+----------+---------+
| Number | Description | Status | Comment |
+--------+----------------------+----------+---------+
| 1 | SHA1 | MUST | |
| 2 | SHA2-256 | MUST | |
| 3 | SHA2-384 | MAY | |
| 4 | SHA2-512 | SHOULD | |
| | Other hash functions | MUST NOT | |
+--------+----------------------+----------+---------+
Table 7
With the use of Digital Signature, RSASSA-PKCS1-v1.5 MAY be
implemented, and RSASSA-PSS MUST be implemented.
RSA keys MUST be greater or equal than 20148 bits.
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 Groups parameter is the most important one to
choose conservatively. Any party capturing all traffic that can
break the selected DH group can retroactively gain access to the
symmetric keys used to encrypt all the IPsec data. However,
specifying extremely large DH group also puts a considerable load on
the device, especially when this is a large VPN gateway or an IoT
constrained device.
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. We foreseeable future. However, this isn't necessarily forever and it
would therefore expect that new revisions of this document will be is expected that new revisions of this document will be issued from
issued from time to time that reflect the current best practice in time to time to reflect the current best practice in this area.
this area.
5. IANA Considerations 6. IANA Considerations
This document makes no requests of IANA. This document makes no requests of IANA.
6. 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.
7. References We would like to thanks Paul Hoffman, Yaron Sheffer and Tommy Pauly
for their valuable feed backs.
7.1. Normative References 8. 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/
DOI 10.17487/RFC2119, March 1997, 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
(GCM) in IPsec Encapsulating Security Payload (ESP)", RFC
4106, DOI 10.17487/RFC4106, June 2005,
<http://www.rfc-editor.org/info/rfc4106>.
[RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the
Internet Key Exchange Version 2 (IKEv2)", RFC 4307, DOI
10.17487/RFC4307, December 2005,
<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, Exchange version 2 (IKEv2) Protocol", RFC 5282, DOI
DOI 10.17487/RFC5282, August 2008, 10.17487/RFC5282, August 2008,
<http://www.rfc-editor.org/info/rfc5282>. <http://www.rfc-editor.org/info/rfc5282>.
7.2. Informative References 8.2. Informative References
[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>.
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
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