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Network Working Group                                         P. HoffmanRequest for Comments: 4109                                VPN ConsortiumUpdates:2409                                                   May 2005Category: Standards TrackAlgorithms 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 updatesRFC 2409, the original   specification, and is intended for all IKEv1 implementations deployed   today.Hoffman                     Standards Track                     [Page 1]

RFC 4109                  Algorithms for IKEv1                  May 20051.  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 updatesRFC 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 RequirementsRFC 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 Sections6.3 and6.4 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 inRFC 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   inRFC 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      AlgorithmRFC 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 20056.  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.orgHoffman                     Standards Track                     [Page 4]

RFC 4109                  Algorithms for IKEv1                  May 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Hoffman                     Standards Track                     [Page 5]