Network Working Group P. Hoffman
Request for Comments: 4109 VPN Consortium
Updates: 2409 May 2005
Category: Standards Track
Algorithms for Internet Key Exchange version 1 (IKEv1)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The required and suggested algorithms in the original Internet Key
Exchange version 1 (IKEv1) specification do not reflect the current
reality of the IPsec market requirements. The original specification
allows weak security and suggests algorithms that are thinly
implemented. This document updates RFC 2409, the original
specification, and is intended for all IKEv1 implementations deployed
today.
Hoffman Standards Track [Page 1]RFC 4109 Algorithms for IKEv1 May 2005
1. Introduction
The original IKEv1 definition, [RFC2409], has a set of MUST-level and
SHOULD-level requirements that do not match the needs of IPsec users.
This document updates RFC 2409 by changing the algorithm requirements
defined there.
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC2119].
2. Old Algorithm Requirements
RFC 2409 has the following MUST-level and SHOULD-level requirements:
o DES for encryption MUST be supported.
o MD5 and SHA-1 for hashing and HMAC functions MUST be supported.
o Pre-shared secrets for authentication MUST be supported.
o Diffie-Hellman MODP group 1 (discrete log 768 bits) MUST be
supported.
o TripleDES for encryption SHOULD be supported.
o Tiger for hashing SHOULD be supported.
o DSA and RSA for authentication with signatures SHOULD be
supported.
o RSA for authentication with encryption SHOULD be supported.
o Diffie-Hellman MODP group 2 (discrete log 1024 bits) SHOULD be
supported.
RFC 2409 gives two conflicting requirement levels for Diffie-Hellman
MODP groups with elliptic curves. Section 4 of that specification
says that "IKE implementations ... MAY support ECP and EC2N groups",
but Sections 6.3 and 6.4 say that MODP groups 3 and 4 for EC2N groups
SHOULD be supported.
3. New Algorithm Requirements
The new requirements for IKEv1 are listed here. Note that some of
the requirements are the same as those in RFC 2409, whereas others
are changed.
o TripleDES for encryption MUST be supported.
o AES-128 in CBC mode [RFC3602] for encryption SHOULD be supported.
o SHA-1 for hashing and HMAC functions MUST be supported.
o Pre-shared secrets for authentication MUST be supported.
o AES-128 in XCBC mode for PRF functions ([RFC3566] and [RFC3664])
SHOULD be supported.
o Diffie-Hellman MODP group 2 (discrete log 1024 bits) MUST be
supported.
Hoffman Standards Track [Page 2]RFC 4109 Algorithms for IKEv1 May 2005
o Diffie-Hellman MODP group 14 (discrete log 2048 bits) [RFC3526]
SHOULD be supported.
o RSA for authentication with signatures SHOULD be supported.
If additional updates are made to IKEv1 in the future, then it is
very likely that implementation of AES-128 in CBC mode for encryption
will become mandatory.
The other algorithms that were listed at MUST-level and SHOULD-level
in RFC 2409 are now MAY-level. This includes DES for encryption, MD5
and Tiger for hashing, Diffie-Hellman MODP group 1, Diffie-Hellman
MODP groups with elliptic curves, DSA for authentication with
signatures, and RSA for authentication with encryption.
DES for encryption, MD5 for hashing, and Diffie-Hellman MODP group 1
are dropped to MAY due to cryptographic weakness.
Tiger for hashing, Diffie-Hellman MODP groups with elliptic curves,
DSA for authentication with signatures, and RSA for authentication
with encryption are dropped due to lack of any significant deployment
and interoperability.
4. Summary
Algorithm RFC 2409 This document
------------------------------------------------------------------
DES for encryption MUST MAY (crypto weakness)
TripleDES for encryption SHOULD MUST
AES-128 for encryption N/A SHOULD
MD5 for hashing and HMAC MUST MAY (crypto weakness)
SHA1 for hashing and HMAC MUST MUST
Tiger for hashing SHOULD MAY (lack of deployment)
AES-XCBC-MAC-96 for PRF N/A SHOULD
Pre-shared secrets MUST MUST
RSA with signatures SHOULD SHOULD
DSA with signatures SHOULD MAY (lack of deployment)
RSA with encryption SHOULD MAY (lack of deployment)
D-H Group 1 (768) MUST MAY (crypto weakness)
D-H Group 2 (1024) SHOULD MUST
D-H Group 14 (2048) N/A SHOULD
D-H elliptic curves SHOULD MAY (lack of deployment)
5. Security Considerations
This document is all about security. All the algorithms that are
either MUST-level or SHOULD-level in the "new algorithm requirements"
section of this document are believed to be robust and secure at the
time of this writing.
Hoffman Standards Track [Page 3]RFC 4109 Algorithms for IKEv1 May 2005
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
Diffie-Hellman groups for Internet Key Exchange (IKE)",
RFC 3526, May 2003.
[RFC3566] Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96 Algorithm
and Its Use With IPsec", RFC 3566, September 2003.
[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602, September
2003.
[RFC3664] Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the
Internet Key Exchange Protocol (IKE)", RFC 3664, January
2004.
Author's Address
Paul Hoffman
VPN Consortium
127 Segre Place
Santa Cruz, CA 95060
US
EMail: paul.hoffman@vpnc.org
Hoffman Standards Track [Page 4]RFC 4109 Algorithms for IKEv1 May 2005
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Hoffman Standards Track [Page 5]
