Movatterモバイル変換

Network Working Group                                        A. KeromytisRequest for Comments: 2857                     University of PennsylvaniaCategory: Standards Track                                       N. Provos                            Center for Information Technology Integration                                                                June 2000The Use of HMAC-RIPEMD-160-96 within ESP and AHStatus 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 (2000).  All Rights Reserved.Abstract   This memo describes the use of the HMAC algorithm [RFC 2104] in   conjunction with the RIPEMD-160 algorithm [RIPEMD-160] as an   authentication mechanism within the revised IPSEC Encapsulating   Security Payload [ESP] and the revised IPSEC Authentication Header   [AH].  HMAC with RIPEMD-160 provides data origin authentication and   integrity protection.   Further information on the other components necessary for ESP and AH   implementations is provided by [Thayer97a].1.  Introduction   This memo specifies the use of RIPEMD-160 [RIPEMD-160] combined with   HMAC [RFC 2104] as a keyed authentication mechanism within the   context of the Encapsulating Security Payload and the Authentication   Header.  The goal of HMAC-RIPEMD-160-96 is to ensure that the packet   is authentic and cannot be modified in transit.   HMAC is a secret key authentication algorithm.  Data integrity and   data origin authentication as provided by HMAC are dependent upon the   scope of the distribution of the secret key.  If only the source and   destination know the HMAC key, this provides both data origin   authentication and data integrity for packets sent between the two   parties; if the HMAC is correct, this proves that it must have been   added by the source.Keromytis & Provos          Standards Track                     [Page 1]

RFC 2857          HMAC-RIPEMD-160-96 within ESP and AH         June 2000   In this memo, HMAC-RIPEMD-160-96 is used within the context of ESP   and AH.  For further information on how the various pieces of ESP -   including the confidentiality mechanism -- fit together to provide   security services, refer to [ESP] and [Thayer97a].  For further   information on AH, refer to [AH] and [Thayer97a].   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC 2119].2. Algorithm and Mode   [RIPEMD-160] describes the underlying RIPEMD-160 algorithm, while   [RFC 2104] describes the HMAC algorithm.  The HMAC algorithm provides   a framework for inserting various hashing algorithms such as RIPEMD-   160.   HMAC-RIPEMD-160-96 operates on 64-byte blocks of data.  Padding   requirements are specified in [RIPEMD-160] and are part of the   RIPEMD-160 algorithm.  Padding bits are only necessary in computing   the HMAC-RIPEMD-160 authenticator value and MUST NOT be included in   the packet.   HMAC-RIPEMD-160-96 produces a 160-bit authenticator value.  This   160-bit value can be truncated as described inRFC2104.  For use with   either ESP or AH, a truncated value using the first 96 bits MUST be   supported.  Upon sending, the truncated value is stored within the   authenticator field.  Upon receipt, the entire 160-bit value is   computed and the first 96 bits are compared to the value stored in   the authenticator field.  No other authenticator value lengths are   supported by HMAC-RIPEMD-160-96.   The length of 96 bits was selected because it is the default   authenticator length as specified in [AH] and meets the security   requirements described in [RFC 2104].2.1  Performance   [Bellare96a] states that "(HMAC) performance is essentially that of   the underlying hash function".  [RIPEMD-160] provides some   performance analysis.  As of this writing no detailed performance   analysis has been done of HMAC or HMAC combined with RIPEMD-160.   [RFC 2104] outlines an implementation modification which can improve   per-packet performance without affecting interoperability.Keromytis & Provos          Standards Track                     [Page 2]

RFC 2857          HMAC-RIPEMD-160-96 within ESP and AH         June 20003. Keying Material   HMAC-RIPEMD-160-96 is a secret key algorithm.  While no fixed key   length is specified in [RFC 2104], for use with either ESP or AH a   fixed key length of 160-bits MUST be supported.  Key lengths other   than 160-bits SHALL NOT be supported.  A key length of 160-bits was   chosen based on the recommendations in [RFC 2104] (i.e. key lengths   less than the authenticator length decrease security strength and   keys longer than the authenticator length do not significantly   increase security strength).   [RFC 2104] discusses requirements for key material, which includes a   discussion on requirements for strong randomness.  A strong pseudo-   random function MUST be used to generate the required 160-bit key.   Implementors should refer toRFC 1750 for guidance on the   requirements for such functions.   At the time of this writing there are no specified weak keys for use   with HMAC.  This does not mean to imply that weak keys do not exist.   If, at some point, a set of weak keys for HMAC are identified, the   use of these weak keys must be rejected followed by a request for   replacement keys or a newly negotiated Security Association.   [ESP] describes the general mechanism to obtain keying material for   the ESP transform.  The derivation of the key from some amount of   keying material does not differ between the manual and automatic key   management mechanisms.   In order to provide data origin authentication, the key distribution   mechanism must ensure that unique keys are allocated and that they   are distributed only to the parties participating in the   communication.   [RFC 2104] states that for "minimally reasonable hash functions" the   "birthday attack" is impractical.  For a 64-byte block hash such as   HMAC-RIPEMD-160-96, an attack involving the successful processing of   2**64 blocks would be infeasible unless it were discovered that the   underlying hash had collisions after processing 2**30 blocks.  (A   hash with such weak collision-resistance characteristics would   generally be considered to be unusable.) No time-based attacks are   discussed in the document.   While it it still cryptographically prudent to perform frequent   rekeying, current literature does not include any recommended key   lifetimes for HMAC-RIPEMD.  When recommendations for HMAC-RIPEMD key   lifetimes become available they will be included in a revised version   of this document.Keromytis & Provos          Standards Track                     [Page 3]

RFC 2857          HMAC-RIPEMD-160-96 within ESP and AH         June 20004.  Interaction with the ESP Cipher Mechanism   As of this writing, there are no known issues which preclude the use   of the HMAC-RIPEMD-160-96 algorithm with any specific cipher   algorithm.5.  Security Considerations   The security provided by HMAC-RIPEMD-160-96 is based upon the   strength of HMAC, and to a lesser degree, the strength of RIPEMD-160.   At the time of this writing there are no known practical   cryptographic attacks against RIPEMD-160.   It is also important to consider that while RIPEMD-160 was never   developed to be used as a keyed hash algorithm, HMAC had that   criteria from the onset.   [RFC 2104] also discusses the potential additional security which is   provided by the truncation of the resulting hash.  Specifications   which include HMAC are strongly encouraged to perform this hash   truncation.   As [RFC 2104] provides a framework for incorporating various hash   algorithms with HMAC, it is possible to replace RIPEMD-160 with other   algorithms such as SHA-1.  [RFC 2104] contains a detailed discussion   on the strengths and weaknesses of HMAC algorithms.   As is true with any cryptographic algorithm, part of its strength   lies in the correctness of the algorithm implementation, the security   of the key management mechanism and its implementation, the strength   of the associated secret key, and upon the correctness of the   implementation in all of the participating systems.  [Kapp97]   contains test vectors and example code to assist in verifying the   correctness of HMAC-RIPEMD-160-96 code.6.  Acknowledgements   This document is derived from work by C. Madson and R. Glenn and from   previous works by Jim Hughes, those people that worked with Jim on   the combined DES/CBC+HMAC-MD5 ESP transforms, the ANX bakeoff   participants, and the members of the IPsec working group.7.  References   [RIPEMD-160]  3.ISO/IEC 10118-3:1998, "Information technology -                 Security techniques - Hash-functions - Part 3:                 Dedicated hash-functions," International Organization                 for Standardization, Geneva, Switzerland, 1998.Keromytis & Provos          Standards Track                     [Page 4]

RFC 2857          HMAC-RIPEMD-160-96 within ESP and AH         June 2000   [RFC 2104]    Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:                 Keyed-Hashing for Message Authentication",RFC 2104,                 September, 1997.   [Bellare96a]  Bellare, M., Canetti, R., Krawczyk, H., "Keying Hash                 Functions for Message Authentication", Advances in                 Cryptography, Crypto96 Proceeding, June 1996.   [ESP]         Kent, S. and R. Atkinson, "IP Encapsulating Security                 Payload (ESP)",RFC 2406, November 1998.   [AH]          Kent, S. and R. Atkinson, "IP Authentication Header",RFC 2402, November 1998.   [Thayer97a]   Thayer, R., Doraswamy, N. and R. Glenn, "IP Security                 Document Roadmap",RFC 2411, November 1998.   [Kapp97]      Kapp, J., "Test Cases for HMAC-RIPEMD160 and HMAC-                 RIPEMD128",RFC 2286, March 1998.   [RFC 1750]    Eastlake 3rd, D., Crocker, S. and J. Schiller,                 "Randomness Recommendations for Security",RFC 1750,                 December 1994.   [RFC 2119]    Bradner, S., "Key words for use in RFCs to Indicate                 Requirement Levels",BCP 14,RFC 2119, March 1997.8.  Authors' Addresses      Angelos D. Keromytis      Distributed Systems Lab      Computer and Information Science Department      University of Pennsylvania      200 S. 33rd Street      Philadelphia, PA 19104 - 6389      EMail: angelos@dsl.cis.upenn.edu      Niels Provos      Center for Information Technology Integration      University of Michigan      519 W. William      Ann Arbor, Michigan 48103 USA      EMail: provos@citi.umich.eduKeromytis & Provos          Standards Track                     [Page 5]

RFC 2857          HMAC-RIPEMD-160-96 within ESP and AH         June 2000   The IPsec working group can be contacted through the chairs:      Robert Moskowitz      International Computer Security Association      EMail: rgm@icsa.net      Ted T'so      VA Linux Systems      EMail: tytso@valinux.comKeromytis & Provos          Standards Track                     [Page 6]

RFC 2857          HMAC-RIPEMD-160-96 within ESP and AH         June 20009.  Full Copyright Statement   Copyright (C) The Internet Society (2000).  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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Keromytis & Provos          Standards Track                     [Page 7]