Cryptographic Suites for IPsec
RFC 4308

Network Working Group                                         P. Hoffman
Request for Comments: 4308                                VPN Consortium
Category: Standards Track                                  December 2005

                     Cryptographic Suites for IPsec

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 IPsec, Internet Key Exchange (IKE), and IKEv2 protocols rely on
   security algorithms to provide privacy and authentication between the
   initiator and responder.  There are many such algorithms available,
   and two IPsec systems cannot interoperate unless they are using the
   same algorithms.  This document specifies optional suites of
   algorithms and attributes that can be used to simplify the
   administration of IPsec when used in manual keying mode, with IKEv1
   or with IKEv2.

1.  Introduction

   This document is a companion to IPsec [RFC2401] and its two key
   exchange protocols, IKE [RFC2409] and IKEv2 [IKEv2].  Like most
   security protocols, IPsec, IKE, and IKEv2 allow users to chose which
   cryptographic algorithms they want to use to meet their security
   needs.

   Implementation experience with IPsec in manual key mode and with IKE
   has shown that there are so many choices for typical system
   administrators to make that it is difficult to achieve
   interoperability without careful pre-agreement.  Because of this, the
   IPsec Working Group agreed that there should be a small number of
   named suites that cover typical security policies.  These suites may
   be presented in the administrative interface of the IPsec system.
   These suites, often called "UI suites" ("user interface suites"), are
   optional and do not prevent implementers from allowing individual
   selection of the security algorithms.

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   Although the UI suites listed here are optional to implement, this
   document is on the standards track because implementers who call
   particular suites by the names used here have to conform to the
   suites listed in this document.  These suites should not be
   considered extensions to IPsec, IKE, and IKEv2, but instead
   administrative methods for describing sets of configurations.

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this document are to be interpreted as described in [RFC2119].

2.  UI Suites

   This section lists optional, non-mandatory suites that may be
   presented to system administrators to ease the burden of choosing
   among the many options in IPsec systems.  These suites cannot cover
   all of the options that an administrator needs to select.  Instead,
   they give values for a subset of the options.

   Note that these UI suites are simply collections of values for some
   options in IPsec.  Use of UI suites does not change the IPsec, IKE,
   or IKEv2 protocols in any way.  Specifically, the transform
   substructure in IKE and IKEv2 must be used to give the value for each
   specified option regardless of whether or not UI suites are used.

   Implementations that use UI suites SHOULD also provide a management
   interface for specifying values for individual cryptographic options.
   That is, it is unlikely that UI suites are a complete solution for
   matching the security policies of many IPsec users, and therefore an
   interface that gives a more complete set of options should be used as
   well.

   IPsec implementations that use these UI suites SHOULD use the suite
   names listed here.  IPsec implementations SHOULD NOT use names
   different than those listed here for the suites that are described,
   and MUST NOT use the names listed here for suites that do not match
   these values.  These requirements are necessary for interoperability.

   Note that the suites listed here are for use of IPsec in virtual
   private networks.  Other uses of IPsec will probably want to define
   their own suites and give them different names.

   Additional suites can be defined by RFCs.  The strings used to
   identify UI suites are registered by IANA.

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2.1.  Suite "VPN-A"

   This suite matches the commonly used corporate VPN security used in
   IKEv1 at the time of this document's publication.

   IPsec:
   Protocol               Encapsulating Security Payload (ESP) [RFC2406]
   ESP encryption         TripleDES in CBC mode [RFC2451]
   ESP integrity          HMAC-SHA1-96 [RFC2404]

   IKE and IKEv2:
   Encryption             TripleDES in CBC mode [RFC2451]
   Pseudo-random function HMAC-SHA1 [RFC2104]
   Integrity              HMAC-SHA1-96 [RFC2404]
   Diffie-Hellman group   1024-bit Modular Exponential (MODP) [RFC2409]

   Rekeying of Phase 2 (for IKE) or the CREATE_CHILD_SA (for IKEv2) MUST
   be supported by both parties in this suite.  The initiator of this
   exchange MAY include a new Diffie-Hellman key; if it is included, it
   MUST be of type 1024-bit MODP.  If the initiator of the exchange
   includes a Diffie-Hellman key, the responder MUST include a Diffie-
   Hellman key, and it MUST of type 1024-bit MODP.

2.2.  Suite "VPN-B"

   This suite is what many people expect the commonly used corporate VPN
   security that will be used within a few years of the time this
   document's publication.

   IPsec:
   Protocol                 ESP [RFC2406]
   ESP encryption           AES with 128-bit keys in CBC mode [AES-CBC]
   ESP integrity            AES-XCBC-MAC-96 [AES-XCBC-MAC]

   IKE and IKEv2:
   Encryption               AES with 128-bit keys in CBC mode [AES-CBC]
   Pseudo-random function   AES-XCBC-PRF-128 [AES-XCBC-PRF-128]
   Integrity                AES-XCBC-MAC-96 [AES-XCBC-MAC]
   Diffie-Hellman group     2048-bit MODP [RFC3526]

   Rekeying of Phase 2 (for IKE) or the CREATE_CHILD_SA (for IKEv2) MUST
   be supported by both parties in this suite.  The initiator of this
   exchange MAY include a new Diffie-Hellman key; if it is included, it
   MUST be of type 2048-bit MODP.  If the initiator of the exchange
   includes a Diffie-Hellman key, the responder MUST include a Diffie-
   Hellman key, and it MUST of type 2048-bit MODP.

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2.3.  Lifetimes for IKEv1

   IKEv1 has two security parameters that do not appear in IKEv2,
   namely, the lifetime of the Phase 1 and Phase 2 security associations
   (SAs).  Systems that use IKEv1 with either the VPN-A or VPN-B suites
   MUST use an SA lifetime of 86400 seconds (1 day) for Phase 1 and an
   SA lifetime of 28800 seconds (8 hours) for Phase 2.

3.  Acknowledgements

   Much of the text and ideas in this document came from earlier
   versions of the IKEv2 document edited by Charlie Kaufman.  Other text
   and ideas were contributed by other members of the IPsec Working
   Group.

4.  Security Considerations

   This document inherits all of the security considerations of the
   IPsec, IKE, and IKEv2 documents.

   Some of the security options specified in these suites may be found
   in the future to have properties significantly weaker than those that
   were believed at the time this document was produced.

5.  IANA Considerations

   IANA has created and will maintain a registry called, "Cryptographic
   Suites for IKEv1, IKEv2, and IPsec".  The registry consists of a text
   string and an RFC number that lists the associated transforms.  New
   entries can be added to the registry only after RFC publication and
   approval by an expert designated by the IESG.

   The initial values for the new registry are:

   Identifier    Defined in
   VPN-A         RFC 4308
   VPN-B         RFC 4308

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6.  Normative References

   [AES-CBC]          Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC
                      Cipher Algorithm and Its Use with IPsec", RFC
                      3602, September 2003.

   [AES-XCBC-MAC]     Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96
                      Algorithm and Its Use With IPsec", RFC 3566,
                      September 2003.

   [AES-XCBC-PRF-128] Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for
                      the Internet Key Exchange Protocol (IKE)", RFC
                      3664, January 2004.

   [IKEv2]            Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
                      Protocol", RFC 4306, December 2005.

   [RFC2104]          Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:
                      Keyed-Hashing for Message Authentication", RFC
                      2104, February 1997.

   [RFC2119]          Bradner, S., "Key words for use in RFCs to
                      Indicate Requirement Levels", BCP 14, RFC 2119,
                      March 1997.

   [RFC2401]          Kent, S. and R. Atkinson, "Security Architecture
                      for the Internet Protocol", RFC 2401, November
                      1998.

   [RFC2404]          Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96
                      within ESP and AH", RFC 2404, November 1998.

   [RFC2406]          Kent, S. and R. Atkinson, "IP Encapsulating
                      Security Payload (ESP)", RFC 2406, November 1998.

   [RFC2409]          Harkins, D. and D. Carrel, "The Internet Key
                      Exchange (IKE)", RFC 2409, November 1998.

   [RFC2451]          Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
                      Algorithms", RFC 2451, November 1998.

   [RFC3526]          Kivinen, T. and M. Kojo, "More Modular Exponential
                      (MODP) Diffie-Hellman groups for Internet Key
                      Exchange (IKE)", RFC 3526, May 2003.

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Author's Address

   Paul Hoffman
   VPN Consortium
   127 Segre Place
   Santa Cruz, CA  95060
   USA

   EMail: paul.hoffman@vpnc.org

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Full Copyright Statement

   Copyright (C) The Internet Society (2005).

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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