[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 RFC 4305

INTERNET-DRAFT                                    Donald E. Eastlake 3rd
                                                   Motorola Laboratories
Expires: July 2004                                          January 2004



   Cryptographic Algorithm Implementation Requirements For ESP And AH
   ------------- --------- -------------- ------------ --- --- --- --
              <draft-ietf-ipsec-esp-ah-algorithms-01.txt>


Status of This Document

   Distribution of this draft is unlimited. Comments should be sent to
   the authors.

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.  Internet-Drafts are
   working documents of the Internet Engineering Task Force (IETF), its
   areas, and its working groups.  Note that other groups may also
   distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."  The list
   of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft
   Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.



Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.


Abstract

   The IPSEC series of protocols makes use of various cryptographic
   algorithms in order to provide security services. The Encapsulating
   Security Payload (ESP) and the Authentication Header (AH) provide two
   mechanisms for protecting data being sent over an IPSEC Security
   Association (SA).  To ensure interoperability between disparate
   implementations it is necessary to specify a set of mandatory to
   implement algorithms to ensure at least one algorithm that all
   implementations will have available. This document defines the
   current set of mandatory to implement algorithms for ESP and AH as
   well as specifying algorithms that should be implemented because they
   may be promoted to mandatory at some future time.




D. Eastlake 3rd                                                 [Page 1]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


Acknowledgement

   Much of the wording herein was adapted from "Cryptographic Algorithms
   for use in the Internet Key Exchange Version 2" <draft-ietf-ipsec-
   ikev2-algorithms-*.txt> by Jeffrey I. Schiller.


Table of Contents

      Status of This Document....................................1
      Copyright Notice...........................................1
      Abstract...................................................1

      Acknowledgement............................................2
      Table of Contents..........................................2

      1. Introduction............................................3
      2. Requirements Terminology................................3
      3. Algorithm Selection.....................................4
      3.1 Encapsulating Security Payload.........................4
      3.1.1 ESP Encryption and Authentication Algorithms.........4
      3.1.2 ESP Combined Mode Algorithms.........................5
      3.2 Authentication Header..................................5
      4. Security Considerations.................................6
      5. IANA Considerations.....................................6

      Normative References.......................................7
      Informative References.....................................7

      Author's Address...........................................9

      Full Copyright Statement..................................10
      Expiration and File Name..................................10



















D. Eastlake 3rd                                                 [Page 2]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


1. Introduction

   The Encapsulating Security Payload (ESP) and the Authentication
   Header (AH) provide two mechanisms for protecting data being sent
   over an IPSEC Security Association (SA) [IPSEC, ESP, AH].  To ensure
   interoperability between disparate implementations it is necessary to
   specify a set of mandatory to implement algorithms to ensure at least
   one algorithm that all implementations will have available. This
   document defines the current set of mandatory to implement algorithms
   for ESP and AH as well as specifying algorithms that should be
   implemented because they may be promoted to mandatory at some future
   time.

   The nature of cryptography is that new algorithms surface
   continuously and existing algorithms are continuously attacked. An
   algorithm believed to be strong today may be demonstrated to be weak
   tomorrow.  Given this, the choice of mandatory to implement algorithm
   should be conservative so as to minimize the likelihood of it being
   compromised quickly. Thought should also be given to performance
   considerations as many uses of IPSEC will be in environments where
   performance is a concern.

   Finally we need to recognize that the mandatory to implement
   algorithm(s) may need to change over time to adapt to the changing
   world. For this reason the selection of mandatory to implement
   algorithms is not included the main IPSEC, ESP, or AH specifications.
   It is instead placed in this document. As the choice of algorithm
   changes, only this document should need to be updated.

   Ideally the mandatory to implement algorithm of tomorrow should
   already be available in most implementations of IPSEC by the time it
   is made mandatory. To facilitate this we will attempt to identify
   such algorithms as they are known today in this document. There is no
   guarantee that the algorithms we believe today may be mandatory in
   the future will in fact become so. All algorithms known today are
   subject to cryptographic attack, and may be broken in the future.



2. Requirements Terminology

   Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and
   "MAY" that appear in this document are to be interpreted as described
   in [RFC 2119].

   In addition we will 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.


D. Eastlake 3rd                                                 [Page 3]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


   SHOULD-     This terms means the same as SHOULD. However it is likely
               that an algorithm marked as SHOULD- will be deprecated to
               a MAY or worse in a future version of this document.
   MUST-       This term means the same as MUST. However we expect at
               some point in the future this algorithm will no longer be
               a MUST.



3. Algorithm Selection

   For IPSEC implementations to interoperate, they must support one or
   more security algorithms in common.  This section specifies the
   security algorithm implementation requirements for standards
   comformant ESP and AH implementations. The security algorithms
   actually used for any particular ESP or AH security association is
   determined by a negotiation mechahism, such as the Internet Key
   Exchange (IKE [RFC 2409, IKEv2]), or pre-establishment.

   Of course, additional standard and proprietary algorithms beyond
   those listed below can be implemented.



3.1 Encapsulating Security Payload

   The implementation conformance requirements for security algorithms
   for ESP are given in the tables below.  See section 2 for definitions
   of the values in the "Requirement" column.



3.1.1 ESP Encryption and Authentication Algorithms

   These tables list encryption and authentication algorithms for the
   IPSEC Encapsulating Security Payload protocol.

      Requirement    Encryption Algorithm
      -----------    --------------------
      MUST           NULL (1)
      MUST-          TripleDES-CBC [RFC 2451]
      SHOULD+        AES-CBC with 128-bit keys [RFC 3602]
      SHOULD         AES-CTR [AES-CTR]
      SHOULD NOT     DES-CBC [RFC 2405] (3)

      Requirement    Authentication Algorithm
      -----------    ------------------------
      MUST           HMAC-SHA1-96 [RFC 2404]
      MUST           NULL (1)
      SHOULD+        AES-XCBC-MAC-96 [RFC 3566]


D. Eastlake 3rd                                                 [Page 4]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


      MAY            HMAC-MD5-96 [RFC 2403] (2)

   Notes:

   1. Since ESP encryption and authentication are optional, support for
      the two "NULL" algorithms is required to maintain consistency with
      the way these services are negotiated. NOTE that while
      authentication and encryption can each be "NULL", they MUST NOT
      both be "NULL".
   2. Weaknesses have become apparent in MD5, however these should not
      effect the use of MD5 with HMAC.
   3. DES, with its small key size and publicly demonstrated special
      purpose cracking hardware, is of questionable security for general
      use.




3.1.2 ESP Combined Mode Algorithms

   As specified in [ESP], combined mode algorithms are supported which
   provide both confidentiality and authentication services.  Support of
   such algorithms will require proper structuring of ESP
   implementations. Under many circumstances, combined mode algorithms
   provide significant efficiency and throughput advantages.  Although
   there are no suggested or required combined algorithms at this time,
   AES-CCM [CCM], which is in the process of being adopted as the
   prefered mode for security in IEEE 802.11 [802.11i], is expected to
   be of interest in the near future.



3.2 Authentication Header

   The implementation conformance requirements for security algorithms
   for AH are given below. See section 2 for definitions of the values
   in the "Requirement" column. As you would suspect, all of these
   algorithms are authentication algorithms.

      Requirement    Algorithm
      -----------    ---------
      MUST           HMAC-SHA1-96 [RFC 2404]
      SHOULD+        AES-XCBC-MAC-96 [RFC 3566]
      MAY            HMAC-MD5-96 [RFC 2403] (1)

   Notes:

   1. Weaknesses have become apparent in MD5, however these should not
      effect the use of MD5 with HMAC.



D. Eastlake 3rd                                                 [Page 5]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


4. Security Considerations

   The security of cryptographic based systems depends on both the
   strength of the cryptographic algorithms chosen, the strength of the
   keys used with those algorithms and the engineering and
   administration of the protocol used by the system to ensure that
   there are no non-cryptographic ways to bypass the security of the
   overall system.

   This document concerns itself with the selection of cryptographic
   algorithms for the use of ESP and AH, specifically with the selection
   of "Mandatory to Implement" algorithms. The algorithms identified in
   this document as MUST implement or SHOULD implement are not known to
   be broken at the current time and cryptographic research so far leads
   us to believe that they will likely remain secure into the
   foreseeable future. However, this isn't necessarily forever. We would
   therefore expect that new revisions of this document will be issued
   from time to time that reflect the current best practice in this
   area.



5. IANA Considerations

   This document does not define any new registries nor elements in
   existing registries.


























D. Eastlake 3rd                                                 [Page 6]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


Normative References

   [AES CTR] - "Using AES Counter Mode With IPSec ESP", draft-ietf-
   ipsec-ciph-aes-ctr-*.txt, R. Housley, July 2003.

   [AH] - "IP Authentication Header", draft-ietf-ipsec-rfc2402bis-*.txt,
   S. Kent, September 2003.

   [ESP] - "IP Encapsulating Security Payload (ESP)", draft-ietf-ipsec-
   esp-v3-*.txt, S. Kent, January 2004.

   [IPSEC] - "Security Architecture for the Internet Protocol", draft-
   ietf-ipsec-rfc2401bis-*.txt, S. Kent, October 2003.

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

   [RFC 2403] - "The Use of HMAC-MD5-96 within ESP and AH", C. Madson,
   and R. Glenn, November 1998.

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

   [RFC 2405] - "The ESP DES-CBC Cipher Algorithm With Explicit IV", C.
   Madson, and N. Doraswamy, November 1998.

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

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

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



Informative References

   [802.11i] - LAN/MAN Specific Requirements - Part 11: Wireless Medium
   Access Control (MAC) and physical layer (PHY) specifications: Medium
   Access Control (MAC) Security Enhancements, IEEE Std 802.11i/D7.0,
   October 2003.

   [AES CCM] - "Using AES CCM Mode With IPsec ESP", draft-ietf-ipsec-
   ciph-aes-ccm-05.txt which is in the RFC Editor Queue, R. Housley,
   November 2003.

   [IKEv2] - "Internet Key Exchange (IKEv2) Protocol", draft-ietf-ipsec-
   ikev2-*.txt, C. Kaufman, October 2003.


D. Eastlake 3rd                                                 [Page 7]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


   [RFC 791] - "Internet Protocol", J. Postel, September 1981.

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
















































D. Eastlake 3rd                                                 [Page 8]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


Author's Address

   Donald E. Eastlake 3rd
   Motorola Laboratories
   155 Beaver Street
   Milford, MA 01757 USA

   Telephone:   +1-508-786-7554 (w)
                +1-508-634-2066 (h)
   EMail:       Donald.Eastlake@Motorola.com










































D. Eastlake 3rd                                                 [Page 9]

INTERNET-DRAFT    Cryptographic Algorithms For ESP & AH     January 2004


Full Copyright Statement

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS 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.



Expiration and File Name

   This draft expires July 2004.

   Its file name is draft-ietf-ipsec-esp-ah-algorithms-01.txt.

















D. Eastlake 3rd                                                [Page 10]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/