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rfc:rfc5288

Network Working Group J. Salowey Request for Comments: 5288 A. Choudhury Category: Standards Track D. McGrew

                                                   Cisco Systems, Inc.
                                                           August 2008
        AES Galois Counter Mode (GCM) Cipher Suites for 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.

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 Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Conventions Used in This Document . . . . . . . . . . . . . . . 2
 3.  AES-GCM Cipher Suites . . . . . . . . . . . . . . . . . . . . . 2
 4.  TLS Versions  . . . . . . . . . . . . . . . . . . . . . . . . . 3
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
 6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   6.1.  Counter Reuse . . . . . . . . . . . . . . . . . . . . . . . 4
   6.2.  Recommendations for Multiple Encryption Processors  . . . . 4
 7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
 8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
   8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6

Salowey, et al. Standards Track [Page 1] RFC 5288 AES-GCM Cipher suites August 2008

1. 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 in Section 3.5 of [RFC4366], the

Salowey, 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; see Section 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 it

Salowey, 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 in Section 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 || Variable

Salowey, 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 2008

8. References

8.1. 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 2008

Authors' 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.com

Salowey, et al. Standards Track [Page 7] RFC 5288 AES-GCM Cipher suites August 2008

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 contained in BCP 78, and except as set forth therein, the authors
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Salowey, et al. Standards Track [Page 8]

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