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rfc:rfc5487

Network Working Group M. Badra Request for Comments: 5487 CNRS/LIMOS Laboratory Category: Standards Track March 2009

             Pre-Shared Key Cipher Suites for TLS with
              SHA-256/384 and AES Galois Counter Mode

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) 2009 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents in effect on the date of
 publication of this document (http://trustee.ietf.org/license-info).
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Abstract

 RFC 4279 and RFC 4785 describe pre-shared key cipher suites for
 Transport Layer Security (TLS).  However, all those cipher suites use
 SHA-1 in their Message Authentication Code (MAC) algorithm.  This
 document describes a set of pre-shared key cipher suites for TLS that
 uses stronger digest algorithms (i.e., SHA-256 or SHA-384) and
 another set that uses the Advanced Encryption Standard (AES) in
 Galois Counter Mode (GCM).

Badra Standards Track [Page 1] RFC 5487 TLS PSK New MAC and AES-GCM March 2009

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   1.1.  Applicability Statement . . . . . . . . . . . . . . . . . . 3
   1.2.  Conventions Used in This Document . . . . . . . . . . . . . 3
 2.  PSK, DHE_PSK, and RSA_PSK Key Exchange Algorithms with
     AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
 3.  PSK, DHE_PSK, and RSA_PSK Key Exchange with SHA-256/384 . . . . 4
   3.1.  PSK Key Exchange Algorithm with SHA-256/384 . . . . . . . . 4
   3.2.  DHE_PSK Key Exchange Algorithm with SHA-256/384 . . . . . . 5
   3.3.  RSA_PSK Key Exchange Algorithm with SHA-256/384 . . . . . . 5
 4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
 6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
   7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7

1. Introduction

 The benefits of pre-shared symmetric-key vs. public-/private-key pair
 based authentication for the key exchange in TLS have been explained
 in the Introduction of [RFC4279].  This document leverages the
 already defined algorithms for the application of newer, generally
 regarded stronger, cryptographic primitives and building blocks.
 TLS 1.2 [RFC5246] adds support for authenticated encryption with
 additional data (AEAD) cipher modes [RFC5116].  This document
 describes the use of Advanced Encryption Standard [AES] in Galois
 Counter Mode [GCM] (AES-GCM) with various pre-shared key (PSK)
 authenticated key exchange mechanisms ([RFC4279] and [RFC4785]) in
 cipher suites for TLS.
 This document also specifies PSK cipher suites for TLS that replace
 SHA-1 by SHA-256 or SHA-384 [SHS].  RFC 4279 [RFC4279] and RFC 4785
 [RFC4785] describe PSK cipher suites for TLS.  However, all of the
 RFC 4279 and the RFC 4785 cipher suites use HMAC-SHA1 as their MAC
 algorithm.  Due to recent analytic work on SHA-1 [Wang05], the IETF
 is gradually moving away from SHA-1 and towards stronger hash
 algorithms.
 Related TLS cipher suites with key exchange algorithms that are
 authenticated using public/private key pairs have recently been
 specified:
 o  RSA-, DSS-, and Diffie-Hellman-based cipher suites in [RFC5288],
    and

Badra Standards Track [Page 2] RFC 5487 TLS PSK New MAC and AES-GCM March 2009

 o  ECC-based cipher suites with SHA-256/384 and AES-GCM in [RFC5289].
 The reader is expected to become familiar with these two memos prior
 to studying this document.

1.1. Applicability Statement

 The cipher suites defined in Section 3 can be negotiated, whatever
 the negotiated TLS version is.
 The cipher suites defined in Section 2 can be negotiated in TLS
 version 1.2 or higher.
 The applicability statement in [RFC4279] applies to this document as
 well.

1.2. 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].

2. PSK, DHE_PSK, and RSA_PSK Key Exchange Algorithms with AES-GCM

 The following six cipher suites use the new authenticated encryption
 modes defined in TLS 1.2 with AES in Galois Counter Mode [GCM].  The
 cipher suites with the DHE_PSK key exchange algorithm
 (TLS_DHE_PSK_WITH_AES_128_GCM_SHA256 and
 TLS_DHE_PSK_WITH_AES_256_GCM_SHA348) provide Perfect Forward Secrecy
 (PFS).
    CipherSuite TLS_PSK_WITH_AES_128_GCM_SHA256        = {0x00,0xA8};
    CipherSuite TLS_PSK_WITH_AES_256_GCM_SHA384        = {0x00,0xA9};
    CipherSuite TLS_DHE_PSK_WITH_AES_128_GCM_SHA256    = {0x00,0xAA};
    CipherSuite TLS_DHE_PSK_WITH_AES_256_GCM_SHA384    = {0x00,0xAB};
    CipherSuite TLS_RSA_PSK_WITH_AES_128_GCM_SHA256    = {0x00,0xAC};
    CipherSuite TLS_RSA_PSK_WITH_AES_256_GCM_SHA384    = {0x00,0xAD};
 These cipher suites use authenticated encryption with additional data
 (AEAD) algorithms, AEAD_AES_128_GCM and AEAD_AES_256_GCM, as
 described in RFC 5116.  GCM is used as described in [RFC5288].
 The PSK, DHE_PSK, and RSA_PSK key exchanges are performed as defined
 in [RFC4279].

Badra Standards Track [Page 3] RFC 5487 TLS PSK New MAC and AES-GCM March 2009

 The Pseudo-Random Function (PRF) algorithms SHALL be as follows:
 o  For cipher suites ending with _SHA256, the PRF is the TLS PRF
    [RFC5246] with SHA-256 as the hash function.
 o  For cipher suites ending with _SHA384, the PRF is the TLS PRF
    [RFC5246] with SHA-384 as the hash function.
 Implementations MUST send a TLS Alert 'bad_record_mac' for all types
 of failures encountered in processing the AES-GCM algorithm.

3. PSK, DHE_PSK, and RSA_PSK Key Exchange with SHA-256/384

 The first two cipher suites described in each of the following three
 sections use AES [AES] in Cipher Block Chaining (CBC) mode [MODES]
 for data confidentiality, whereas the other two cipher suites do not
 provide data confidentiality; all cipher suites provide integrity
 protection and authentication using HMAC-based MACs.

3.1. PSK Key Exchange Algorithm with SHA-256/384

    CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA256        = {0x00,0xAE};
    CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA384        = {0x00,0xAF};
    CipherSuite TLS_PSK_WITH_NULL_SHA256               = {0x00,0xB0};
    CipherSuite TLS_PSK_WITH_NULL_SHA384               = {0x00,0xB1};
 The above four cipher suites are the same as the corresponding cipher
 suites in RFC 4279 and RFC 4785 (with names ending in "_SHA" in place
 of "_SHA256" or "_SHA384"), except for the hash and PRF algorithms,
 as explained below.
 o  For cipher suites with names ending in "_SHA256":
  • The MAC is HMAC [RFC2104] with SHA-256 as the hash function.
  • When negotiated in a version of TLS prior to 1.2, the PRF from

that version is used; otherwise, the PRF is the TLS PRF

       [RFC5246] with SHA-256 as the hash function.
 o  For cipher suites with names ending in "_SHA384":
  • The MAC is HMAC [RFC2104] with SHA-384 as the hash function.
  • When negotiated in a version of TLS prior to 1.2, the PRF from

that version is used; otherwise, the PRF is the TLS PRF

       [RFC5246] with SHA-384 as the hash function.

Badra Standards Track [Page 4] RFC 5487 TLS PSK New MAC and AES-GCM March 2009

3.2. DHE_PSK Key Exchange Algorithm with SHA-256/384

    CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA256    = {0x00,0xB2};
    CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA384    = {0x00,0xB3};
    CipherSuite TLS_DHE_PSK_WITH_NULL_SHA256           = {0x00,0xB4};
    CipherSuite TLS_DHE_PSK_WITH_NULL_SHA384           = {0x00,0xB5};
 The above four cipher suites are the same as the corresponding cipher
 suites in RFC 4279 and RFC 4785 (with names ending in "_SHA" in place
 of "_SHA256" or "_SHA384"), except for the hash and PRF algorithms,
 as explained in Section 3.1.

3.3. RSA_PSK Key Exchange Algorithm with SHA-256/384

    CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA256    = {0x00,0xB6};
    CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA384    = {0x00,0xB7};
    CipherSuite TLS_RSA_PSK_WITH_NULL_SHA256           = {0x00,0xB8};
    CipherSuite TLS_RSA_PSK_WITH_NULL_SHA384           = {0x00,0xB9};
 The above four cipher suites are the same as the corresponding cipher
 suites in RFC 4279 and RFC 4785 (with names ending in "_SHA" in place
 of "_SHA256" or "_SHA384"), except for the hash and PRF algorithms,
 as explained in Section 3.1.

4. Security Considerations

 The security considerations in [RFC4279], [RFC4785], and [RFC5288]
 apply to this document as well.  In particular, as authentication-
 only cipher suites (with no encryption) defined here do not support
 confidentiality, care should be taken not to send sensitive
 information (such as passwords) over connections protected with one
 of the cipher suites with NULL encryption defined in this document.

5. IANA Considerations

 IANA has assigned the following values for the cipher suites defined
 in this document:
    CipherSuite TLS_PSK_WITH_AES_128_GCM_SHA256        = {0x00,0xA8};
    CipherSuite TLS_PSK_WITH_AES_256_GCM_SHA384        = {0x00,0xA9};
    CipherSuite TLS_DHE_PSK_WITH_AES_128_GCM_SHA256    = {0x00,0xAA};
    CipherSuite TLS_DHE_PSK_WITH_AES_256_GCM_SHA384    = {0x00,0xAB};
    CipherSuite TLS_RSA_PSK_WITH_AES_128_GCM_SHA256    = {0x00,0xAC};
    CipherSuite TLS_RSA_PSK_WITH_AES_256_GCM_SHA384    = {0x00,0xAD};
    CipherSuite TLS_PSK_WITH_AES_128_CBC_SHA256        = {0x00,0xAE};
    CipherSuite TLS_PSK_WITH_AES_256_CBC_SHA384        = {0x00,0xAF};
    CipherSuite TLS_PSK_WITH_NULL_SHA256               = {0x00,0xB0};
    CipherSuite TLS_PSK_WITH_NULL_SHA384               = {0x00,0xB1};

Badra Standards Track [Page 5] RFC 5487 TLS PSK New MAC and AES-GCM March 2009

    CipherSuite TLS_DHE_PSK_WITH_AES_128_CBC_SHA256    = {0x00,0xB2};
    CipherSuite TLS_DHE_PSK_WITH_AES_256_CBC_SHA384    = {0x00,0xB3};
    CipherSuite TLS_DHE_PSK_WITH_NULL_SHA256           = {0x00,0xB4};
    CipherSuite TLS_DHE_PSK_WITH_NULL_SHA384           = {0x00,0xB5};
    CipherSuite TLS_RSA_PSK_WITH_AES_128_CBC_SHA256    = {0x00,0xB6};
    CipherSuite TLS_RSA_PSK_WITH_AES_256_CBC_SHA384    = {0x00,0xB7};
    CipherSuite TLS_RSA_PSK_WITH_NULL_SHA256           = {0x00,0xB8};
    CipherSuite TLS_RSA_PSK_WITH_NULL_SHA384           = {0x00,0xB9};

6. Acknowledgments

 This document borrows from [RFC5289].  The author appreciates Alfred
 Hoenes for his detailed review and effort on resolving issues in
 discussion.  The author would like also to acknowledge Ibrahim
 Hajjeh, Simon Josefsson, Hassnaa Moustafa, Joseph Salowey, and Pascal
 Urien for their reviews of the content of the document.

7. References

7.1. Normative References

 [AES]      National Institute of Standards and Technology,
            "Specification for the Advanced Encryption Standard
            (AES)", FIPS 197, November 2001.
 [GCM]      National Institute of Standards and Technology,
            "Recommendation for Block Cipher Modes of Operation:
            Galois/Counter Mode (GCM) for Confidentiality and
            Authentication", SP 800-38D, November 2007.
 [MODES]    National Institute of Standards and Technology,
            "Recommendation for Block Cipher Modes of Operation -
            Methods and Techniques", SP 800-38A, December 2001.
 [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
            Hashing for Message Authentication", RFC 2104,
            February 1997.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4279]  Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
            for Transport Layer Security (TLS)", RFC 4279,
            December 2005.
 [RFC4785]  Blumenthal, U. and P. Goel, "Pre-Shared Key (PSK)
            Ciphersuites with NULL Encryption for Transport Layer
            Security (TLS)", RFC 4785, January 2007.

Badra Standards Track [Page 6] RFC 5487 TLS PSK New MAC and AES-GCM March 2009

 [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.
 [RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
            Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
            August 2008.
 [SHS]      National Institute of Standards and Technology, "Secure
            Hash Standard", FIPS 180-2, August 2002.

7.2. Informative References

 [RFC5289]  Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
            256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
            August 2008.
 [Wang05]   Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the
            Full SHA-1", CRYPTO 2005, August 2005.

Author's Address

 Mohamad Badra
 CNRS/LIMOS Laboratory
 Campus de cezeaux, Bat. ISIMA
 Aubiere  63170
 France
 EMail: badra@isima.fr

Badra Standards Track [Page 7]

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