Movatterモバイル変換

Network Working Group                                           P. ChownRequest for Comments: 3268                            Skygate TechnologyCategory: Standards Track                                      June 2002Advanced Encryption Standard (AES) Ciphersuites for Transport LayerSecurity (TLS)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 (2002).  All Rights Reserved.Abstract   This document proposes several new ciphersuites.  At present, the   symmetric ciphers supported by Transport Layer Security (TLS) are   RC2, RC4, International Data Encryption Algorithm (IDEA), Data   Encryption Standard (DES), and triple DES.  The protocol would be   enhanced by the addition of Advanced Encryption Standard (AES)   ciphersuites.Overview   At present, the symmetric ciphers supported by TLS are RC2, RC4,   IDEA, DES, and triple DES.  The protocol would be enhanced by the   addition of AES [AES] ciphersuites, for the following reasons:   1. RC2, RC4, and IDEA are all subject to intellectual property      claims.  RSA Security Inc. has trademark rights in the names RC2      and RC4, and claims that the RC4 algorithm itself is a trade      secret.  Ascom Systec Ltd. owns a patent on the IDEA algorithm.   2. Triple DES is much less efficient than more modern ciphers.   3. Now that the AES process is completed there will be commercial      pressure to use the selected cipher.  The AES is efficient and has      withstood extensive cryptanalytic efforts.  The AES is therefore a      desirable choice.Chown                       Standards Track                     [Page 1]

RFC 3268                AES Ciphersuites for TLS               June 2002   4. Currently the DHE ciphersuites only allow triple DES (along with      some "export" variants which do not use a satisfactory key      length).  At the same time the DHE ciphersuites are the only ones      to offer forward secrecy.   This document proposes several new ciphersuites, with the aim of   overcoming these problems.Cipher Usage   The new ciphersuites proposed here are very similar to the following,   defined in [TLS]:   TLS_RSA_WITH_3DES_EDE_CBC_SHA   TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA   TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA   TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA   TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA   TLS_DH_anon_WITH_3DES_EDE_CBC_SHA   All the ciphersuites described here use the AES in cipher block   chaining (CBC) mode.  Furthermore, they use SHA-1 [SHA-1] in an HMAC   construction as described in section 5 of [TLS].  (Although the TLS   ciphersuite names include the text "SHA", this actually refers to the   modified SHA-1 version of the algorithm.)   The ciphersuites differ in the type of certificate and key exchange   method.  The ciphersuites defined here use the following options for   this part of the protocol:   CipherSuite                        Certificate type (if applicable)                                      and key exchange algorithm   TLS_RSA_WITH_AES_128_CBC_SHA       RSA   TLS_DH_DSS_WITH_AES_128_CBC_SHA    DH_DSS   TLS_DH_RSA_WITH_AES_128_CBC_SHA    DH_RSA   TLS_DHE_DSS_WITH_AES_128_CBC_SHA   DHE_DSS   TLS_DHE_RSA_WITH_AES_128_CBC_SHA   DHE_RSA   TLS_DH_anon_WITH_AES_128_CBC_SHA   DH_anon   TLS_RSA_WITH_AES_256_CBC_SHA       RSA   TLS_DH_DSS_WITH_AES_256_CBC_SHA    DH_DSS   TLS_DH_RSA_WITH_AES_256_CBC_SHA    DH_RSA   TLS_DHE_DSS_WITH_AES_256_CBC_SHA   DHE_DSS   TLS_DHE_RSA_WITH_AES_256_CBC_SHA   DHE_RSA   TLS_DH_anon_WITH_AES_256_CBC_SHA   DH_anonChown                       Standards Track                     [Page 2]

RFC 3268                AES Ciphersuites for TLS               June 2002   For the meanings of the terms RSA, DH_DSS, DH_RSA, DHE_DSS, DHE_RSA   and DH_anon, please refer to sections7.4.2 and7.4.3 of [TLS].   The AES supports key lengths of 128, 192 and 256 bits.  However, this   document only defines ciphersuites for 128- and 256-bit keys.  This   is to avoid unnecessary proliferation of ciphersuites.  Rijndael   actually allows for 192- and 256-bit block sizes as well as the 128-   bit blocks mandated by the AES process.  The ciphersuites defined   here all use 128-bit blocks.   The new ciphersuites will have the following definitions:   CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA      = { 0x00, 0x2F };   CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA   = { 0x00, 0x30 };   CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA   = { 0x00, 0x31 };   CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA  = { 0x00, 0x32 };   CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA  = { 0x00, 0x33 };   CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA  = { 0x00, 0x34 };   CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA      = { 0x00, 0x35 };   CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA   = { 0x00, 0x36 };   CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA   = { 0x00, 0x37 };   CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA  = { 0x00, 0x38 };   CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA  = { 0x00, 0x39 };   CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA  = { 0x00, 0x3A };Security Considerations   It is not believed that the new ciphersuites are ever less secure   than the corresponding older ones.  The AES is believed to be secure,   and it has withstood extensive cryptanalytic attack.   The ephemeral Diffie-Hellman ciphersuites provide forward secrecy   without any known reduction in security in other areas.  To obtain   the maximum benefit from these ciphersuites:   1. The ephemeral keys should only be used once.  With the TLS      protocol as currently defined there is no significant efficiency      gain from reusing ephemeral keys.   2. Ephemeral keys should be destroyed securely when they are no      longer required.   3. The random number generator used to create ephemeral keys must not      reveal past output even when its internal state is compromised.Chown                       Standards Track                     [Page 3]

RFC 3268                AES Ciphersuites for TLS               June 2002   [TLS] describes the anonymous Diffie-Hellman (ADH) ciphersuites as   deprecated.  The ADH ciphersuites defined here are not deprecated.   However, when they are used, particular care must be taken:   1. ADH provides confidentiality but not authentication.  This means      that (if authentication is required) the communicating parties      must authenticate to each other by some means other than TLS.   2. ADH is vulnerable to man-in-the-middle attacks, as a consequence      of the lack of authentication.  The parties must have a way of      determining whether they are participating in the same TLS      connection.  If they are not, they can deduce that they are under      attack, and presumably abort the connection.      For example, if the parties share a secret, it is possible to      compute a MAC of the TLS Finished message.  An attacker would have      to negotiate two different TLS connections; one with each      communicating party.  The Finished messages would be different in      each case, because they depend on the parties' public keys (among      other things).  For this reason, the MACs computed by each party      would be different.      It is important to note that authentication techniques which do      not use the Finished message do not usually provide protection      from this attack.  For example, the client could authenticate to      the server with a password, but it would still be vulnerable to      man-in-the-middle attacks.      Recent research has identified a chosen plaintext attack which      applies to all ciphersuites defined in [TLS] which use CBC mode.      This weakness does not affect the common use of TLS on the World      Wide Web, but may affect the use of TLS in other applications.      When TLS is used in an application where this attack is possible,      attackers can determine the truth or otherwise of a hypothesis      that particular plaintext data was sent earlier in the session.      No key material is compromised.      It is likely that the CBC construction will be changed in a future      revision of the TLS protocol.Intellectual Property   The IETF takes no position regarding the validity or scope of any   intellectual property or other rights that might be claimed to   pertain to the implementation or use other technology described in   this document or the extent to which any license under such rights   might or might not be available; neither does it represent that it   has made any effort to identify any such rights.  Information on theChown                       Standards Track                     [Page 4]

RFC 3268                AES Ciphersuites for TLS               June 2002   IETF's procedures with respect to rights in standards-track and   standards-related documentation can be found inBCP-11.  Copies of   claims of rights made available for publication 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 implementors or users of this specification can   be obtained from the IETF Secretariat.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights which may cover technology that may be required to practice   this standard.  Please address the information to the IETF Executive   Director.   During the development of the AES, NIST published the following   statement on intellectual property:      SPECIAL NOTE - Intellectual Property      NIST reminds all interested parties that the adoption of AES is      being conducted as an open standards-setting activity.      Specifically, NIST has requested that all interested parties      identify to NIST any patents or inventions that may be required      for the use of AES.  NIST hereby gives public notice that it may      seek redress under the antitrust laws of the United States against      any party in the future who might seek to exercise patent rights      against any user of AES that have not been disclosed to NIST in      response to this request for information.Acknowledgements   I would like to thank the ietf-tls mailing list contributors who have   made helpful suggestions for this document.References   [TLS]    Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",RFC2246, January 1999.   [AES]    National Institute of Standards and Technology,            "Specification for the Advanced Encryption Standard (AES)"            FIPS 197.  November 26, 2001.   [SHA-1]  FIPS PUB 180-1, "Secure Hash Standard," National Institute            of Standards and Technology, U.S. Department of Commerce,            April 17, 1995.Chown                       Standards Track                     [Page 5]

RFC 3268                AES Ciphersuites for TLS               June 2002Author's Address   Pete Chown   Skygate Technology Ltd   8 Lombard Road   London   SW19 3TZ   United Kingdom   Phone: +44 20 8542 7856   EMail: pc@skygate.co.ukChown                       Standards Track                     [Page 6]

RFC 3268                AES Ciphersuites for TLS               June 2002Full Copyright Statement   Copyright (C) The Internet Society (2002).  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.Chown                       Standards Track                     [Page 7]