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Network Working Group                                         J. SaloweyRequest for Comments: 5288                                  A. ChoudhuryCategory: Standards Track                                      D. McGrew                                                     Cisco Systems, Inc.                                                             August 2008AES Galois Counter Mode (GCM) Cipher Suites for TLSStatus 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.Abstract   This memo describes the use of the Advanced Encryption Standard (AES)   in Galois/Counter Mode (GCM) as a Transport Layer Security (TLS)   authenticated encryption operation.  GCM provides both   confidentiality and data origin authentication, can be efficiently   implemented in hardware for speeds of 10 gigabits per second and   above, and is also well-suited to software implementations.  This   memo defines TLS cipher suites that use AES-GCM with RSA, DSA, and   Diffie-Hellman-based key exchange mechanisms.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions Used in This Document . . . . . . . . . . . . . . .23.  AES-GCM Cipher Suites . . . . . . . . . . . . . . . . . . . . .24.  TLS Versions  . . . . . . . . . . . . . . . . . . . . . . . . .35.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .46.  Security Considerations . . . . . . . . . . . . . . . . . . . .46.1.  Counter Reuse . . . . . . . . . . . . . . . . . . . . . . .46.2.  Recommendations for Multiple Encryption Processors  . . . .47.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .58.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .68.1.  Normative References  . . . . . . . . . . . . . . . . . . .68.2.  Informative References  . . . . . . . . . . . . . . . . . .6Salowey, et al.             Standards Track                     [Page 1]

RFC 5288                 AES-GCM Cipher suites               August 20081.  Introduction   This document describes the use of AES [AES] in Galois Counter Mode   (GCM) [GCM] (AES-GCM) with various key exchange mechanisms as a   cipher suite for TLS.  AES-GCM is an authenticated encryption with   associated data (AEAD) cipher (as defined in TLS 1.2 [RFC5246])   providing both confidentiality and data origin authentication.  The   following sections define cipher suites based on RSA, DSA, and   Diffie-Hellman key exchanges; ECC-based (Elliptic Curve Cryptography)   cipher suites are defined in a separate document [RFC5289].   AES-GCM is not only efficient and secure, but hardware   implementations can achieve high speeds with low cost and low   latency, because the mode can be pipelined.  Applications that   require high data throughput can benefit from these high-speed   implementations.  AES-GCM has been specified as a mode that can be   used with IPsec ESP [RFC4106] and 802.1AE Media Access Control (MAC)   Security [IEEE8021AE].2.  Conventions Used in This Document   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 [RFC2119].3.  AES-GCM Cipher Suites   The following cipher suites use the new authenticated encryption   modes defined in TLS 1.2 with AES in Galois Counter Mode (GCM) [GCM]:      CipherSuite TLS_RSA_WITH_AES_128_GCM_SHA256 = {0x00,0x9C}      CipherSuite TLS_RSA_WITH_AES_256_GCM_SHA384 = {0x00,0x9D}      CipherSuite TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 = {0x00,0x9E}      CipherSuite TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 = {0x00,0x9F}      CipherSuite TLS_DH_RSA_WITH_AES_128_GCM_SHA256 = {0x00,0xA0}      CipherSuite TLS_DH_RSA_WITH_AES_256_GCM_SHA384 = {0x00,0xA1}      CipherSuite TLS_DHE_DSS_WITH_AES_128_GCM_SHA256 = {0x00,0xA2}      CipherSuite TLS_DHE_DSS_WITH_AES_256_GCM_SHA384 = {0x00,0xA3}      CipherSuite TLS_DH_DSS_WITH_AES_128_GCM_SHA256 = {0x00,0xA4}      CipherSuite TLS_DH_DSS_WITH_AES_256_GCM_SHA384 = {0x00,0xA5}      CipherSuite TLS_DH_anon_WITH_AES_128_GCM_SHA256 = {0x00,0xA6}      CipherSuite TLS_DH_anon_WITH_AES_256_GCM_SHA384 = {0x00,0xA7}   These cipher suites use the AES-GCM authenticated encryption with   associated data (AEAD) algorithms AEAD_AES_128_GCM and   AEAD_AES_256_GCM described in [RFC5116].  Note that each of these   AEAD algorithms uses a 128-bit authentication tag with GCM (in   particular, as described inSection 3.5 of [RFC4366], theSalowey, et al.             Standards Track                     [Page 2]

RFC 5288                 AES-GCM Cipher suites               August 2008   "truncated_hmac" extension does not have an effect on cipher suites   that do not use HMAC).  The "nonce" SHALL be 12 bytes long consisting   of two parts as follows: (this is an example of a "partially   explicit" nonce; seeSection 3.2.1 in [RFC5116]).             struct {                opaque salt[4];                opaque nonce_explicit[8];             } GCMNonce;   The salt is the "implicit" part of the nonce and is not sent in the   packet.  Instead, the salt is generated as part of the handshake   process: it is either the client_write_IV (when the client is   sending) or the server_write_IV (when the server is sending).  The   salt length (SecurityParameters.fixed_iv_length) is 4 octets.   The nonce_explicit is the "explicit" part of the nonce.  It is chosen   by the sender and is carried in each TLS record in the   GenericAEADCipher.nonce_explicit field.  The nonce_explicit length   (SecurityParameters.record_iv_length) is 8 octets.   Each value of the nonce_explicit MUST be distinct for each distinct   invocation of the GCM encrypt function for any fixed key.  Failure to   meet this uniqueness requirement can significantly degrade security.   The nonce_explicit MAY be the 64-bit sequence number.   The RSA, DHE_RSA, DH_RSA, DHE_DSS, DH_DSS, and DH_anon key exchanges   are performed as defined in [RFC5246].   The Pseudo Random Function (PRF) algorithms SHALL be as follows:      For cipher suites ending with _SHA256, the PRF is the TLS PRF      [RFC5246] with SHA-256 as the hash function.      For cipher suites ending with _SHA384, the PRF is the TLS PRF      [RFC5246] with SHA-384 as the hash function.   Implementations MUST send TLS Alert bad_record_mac for all types of   failures encountered in processing the AES-GCM algorithm.4.  TLS Versions   These cipher suites make use of the authenticated encryption with   additional data defined in TLS 1.2 [RFC5246].  They MUST NOT be   negotiated in older versions of TLS.  Clients MUST NOT offer these   cipher suites if they do not offer TLS 1.2 or later.  Servers that   select an earlier version of TLS MUST NOT select one of these cipher   suites.  Because TLS has no way for the client to indicate that itSalowey, et al.             Standards Track                     [Page 3]

RFC 5288                 AES-GCM Cipher suites               August 2008   supports TLS 1.2 but not earlier, a non-compliant server might   potentially negotiate TLS 1.1 or earlier and select one of the cipher   suites in this document.  Clients MUST check the TLS version and   generate a fatal "illegal_parameter" alert if they detect an   incorrect version.5.  IANA Considerations   IANA has assigned the following values for the cipher suites defined   in this document:      CipherSuite TLS_RSA_WITH_AES_128_GCM_SHA256 = {0x00,0x9C}      CipherSuite TLS_RSA_WITH_AES_256_GCM_SHA384 = {0x00,0x9D}      CipherSuite TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 = {0x00,0x9E}      CipherSuite TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 = {0x00,0x9F}      CipherSuite TLS_DH_RSA_WITH_AES_128_GCM_SHA256 = {0x00,0xA0}      CipherSuite TLS_DH_RSA_WITH_AES_256_GCM_SHA384 = {0x00,0xA1}      CipherSuite TLS_DHE_DSS_WITH_AES_128_GCM_SHA256 = {0x00,0xA2}      CipherSuite TLS_DHE_DSS_WITH_AES_256_GCM_SHA384 = {0x00,0xA3}      CipherSuite TLS_DH_DSS_WITH_AES_128_GCM_SHA256 = {0x00,0xA4}      CipherSuite TLS_DH_DSS_WITH_AES_256_GCM_SHA384 = {0x00,0xA5}      CipherSuite TLS_DH_anon_WITH_AES_128_GCM_SHA256 = {0x00,0xA6}      CipherSuite TLS_DH_anon_WITH_AES_256_GCM_SHA384 = {0x00,0xA7}6.  Security Considerations   The security considerations in [RFC5246] apply to this document as   well.  The remainder of this section describes security   considerations specific to the cipher suites described in this   document.6.1.  Counter Reuse   AES-GCM security requires that the counter is never reused.  The IV   construction inSection 3 is designed to prevent counter reuse.   Implementers should also understand the practical considerations of   IV handling outlined in Section 9 of [GCM].6.2.  Recommendations for Multiple Encryption Processors   If multiple cryptographic processors are in use by the sender, then   the sender MUST ensure that, for a particular key, each value of the   nonce_explicit used with that key is distinct.  In this case, each   encryption processor SHOULD include, in the nonce_explicit, a fixed   value that is distinct for each processor.  The recommended format is        nonce_explicit = FixedDistinct || VariableSalowey, et al.             Standards Track                     [Page 4]

RFC 5288                 AES-GCM Cipher suites               August 2008   where the FixedDistinct field is distinct for each encryption   processor, but is fixed for a given processor, and the Variable field   is distinct for each distinct nonce used by a particular encryption   processor.  When this method is used, the FixedDistinct fields used   by the different processors MUST have the same length.   In the terms of Figure 2 in [RFC5116], the Salt is the Fixed-Common   part of the nonce (it is fixed, and it is common across all   encryption processors), the FixedDistinct field exactly corresponds   to the Fixed-Distinct field, the Variable field corresponds to the   Counter field, and the explicit part exactly corresponds to the   nonce_explicit.   For clarity, we provide an example for TLS in which there are two   distinct encryption processors, each of which uses a one-byte   FixedDistinct field:          Salt          = eedc68dc          FixedDistinct = 01       (for the first encryption processor)          FixedDistinct = 02       (for the second encryption processor)   The GCMnonces generated by the first encryption processor, and their   corresponding nonce_explicit, are:          GCMNonce                    nonce_explicit          ------------------------    ----------------------------          eedc68dc0100000000000000    0100000000000000          eedc68dc0100000000000001    0100000000000001          eedc68dc0100000000000002    0100000000000002          ...   The GCMnonces generated by the second encryption processor, and their   corresponding nonce_explicit, are          GCMNonce                    nonce_explicit          ------------------------    ----------------------------          eedc68dc0200000000000000    0200000000000000          eedc68dc0200000000000001    0200000000000001          eedc68dc0200000000000002    0200000000000002          ...7.  Acknowledgements   This document borrows heavily from [RFC5289].  The authors would like   to thank Alex Lam, Simon Josefsson, and Pasi Eronen for providing   useful comments during the review of this document.Salowey, et al.             Standards Track                     [Page 5]

RFC 5288                 AES-GCM Cipher suites               August 20088.  References8.1.  Normative References   [AES]         National Institute of Standards and Technology,                 "Advanced Encryption Standard (AES)", FIPS 197,                 November 2001.   [GCM]         Dworkin, M., "Recommendation for Block Cipher Modes of                 Operation: Galois/Counter Mode (GCM) and GMAC",                 National Institute of Standards and Technology SP 800-                 38D, November 2007.   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate                 Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC5116]     McGrew, D., "An Interface and Algorithms for                 Authenticated Encryption",RFC 5116, January 2008.   [RFC5246]     Dierks, T. and E. Rescorla, "The Transport Layer                 Security (TLS) Protocol Version 1.2",RFC 5246,                 August 2008.8.2.  Informative References   [IEEE8021AE]  Institute of Electrical and Electronics Engineers,                 "Media Access Control Security", IEEE Standard 802.1AE,                 August 2006.   [RFC4106]     Viega, J. and D. McGrew, "The Use of Galois/Counter                 Mode (GCM) in IPsec Encapsulating Security Payload                 (ESP)",RFC 4106, June 2005.   [RFC4366]     Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen,                 J., and T. Wright, "Transport Layer Security (TLS)                 Extensions",RFC 4366, April 2006.   [RFC5289]     Rescorla, E., "TLS Elliptic Curve Cipher Suites with                 SHA-256/384 and AES Galois Counter Mode",RFC 5289,                 August 2008.Salowey, et al.             Standards Track                     [Page 6]

RFC 5288                 AES-GCM Cipher suites               August 2008Authors' Addresses   Joseph Salowey   Cisco Systems, Inc.   2901 3rd. Ave   Seattle, WA  98121   USA   EMail: jsalowey@cisco.com   Abhijit Choudhury   Cisco Systems, Inc.   3625 Cisco Way   San Jose, CA  95134   USA   EMail: abhijitc@cisco.com   David McGrew   Cisco Systems, Inc.   170 W Tasman Drive   San Jose, CA  95134   USA   EMail: mcgrew@cisco.comSalowey, et al.             Standards Track                     [Page 7]

RFC 5288                 AES-GCM Cipher suites               August 2008Full Copyright Statement   Copyright (C) The IETF Trust (2008).   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, THE IETF TRUST 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.Salowey, et al.             Standards Track                     [Page 8]