Network Working Group                                           M. Badra
Request for Comments: 5489                         CNRS/LIMOS Laboratory
Category: Informational                                        I. Hajjeh
                                                             INEOVATION
                                                             March 2009


      ECDHE_PSK Cipher Suites for Transport Layer Security (TLS)

Status of This Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard of any kind.  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

  This document extends RFC 4279, RFC 4492, and RFC 4785 and specifies
  a set of cipher suites that use a pre-shared key (PSK) to
  authenticate an Elliptic Curve Diffie-Hellman exchange with Ephemeral
  keys (ECDHE).  These cipher suites provide Perfect Forward Secrecy
  (PFS).






Badra & Hajjeh               Informational                      [Page 1]

RFC 5489            ECDHE_PSK Cipher Suites for TLS           March 2009


Table of Contents

  1. Introduction ....................................................2
     1.1. Applicability Statement ....................................3
     1.2. Conventions Used in This Document ..........................3
  2. ECDHE_PSK Key Exchange Algorithm ................................3
  3. ECDHE_PSK-Based Cipher Suites ...................................4
     3.1. ECDHE_PSK Cipher Suites Using the SHA-1 Hash ...............4
     3.2. ECDHE_PSK Cipher Suites Using SHA-2 Hashes .................4
  4. ECDHE_PSK-Based Cipher Suites with NULL Encryption ..............5
     4.1. ECDHE_PSK Cipher Suite Using the SHA-1 Hash with
          NULL Encryption ............................................5
     4.2. ECDHE_PSK Cipher Suites Using SHA-2 Hashes with
          NULL Encryption ............................................5
  5. Security Considerations .........................................5
  6. IANA Considerations .............................................6
  7. Acknowledgments .................................................6
  8. Normative References ............................................6

1.  Introduction

  RFC 4279 specifies cipher suites for supporting TLS using pre-shared
  symmetric keys that (a) use only symmetric key operations for
  authentication, (b) use a Diffie-Hellman exchange authenticated with
  a pre-shared key (PSK), or (c) combine public key authentication of
  the server with pre-shared key authentication of the client.

  RFC 4785 specifies authentication-only cipher suites (with no
  encryption).  These cipher suites are useful when authentication and
  integrity protection is desired, but confidentiality is not needed or
  not permitted.

  RFC 4492 defines a set of Elliptic Curve Cryptography (ECC)-based
  cipher suites for TLS and describes the use of ECC certificates for
  client authentication.  In particular, it specifies the use of
  Elliptic Curve Diffie-Hellman (ECDH) key agreement in a TLS handshake
  and the use of the Elliptic Curve Digital Signature Algorithm (ECDSA)
  as a new authentication mechanism.

  This document specifies a set of cipher suites that use a PSK to
  authenticate an ECDH exchange.  These cipher suites provide Perfect
  Forward Secrecy.  Some of these cipher suites provide authentication
  only.

  The reader is expected to become familiar with RFC 4279, RFC 4492,
  and RFC 4785 prior to studying this document.





Badra & Hajjeh               Informational                      [Page 2]

RFC 5489            ECDHE_PSK Cipher Suites for TLS           March 2009


1.1.  Applicability Statement

  The cipher suites defined in this document can be negotiated,
  whatever the negotiated TLS version is.

  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.  ECDHE_PSK Key Exchange Algorithm

  The cipher suites described in this document make use of the elliptic
  curve (EC) parameter negotiation mechanism defined in RFC 4492.  When
  the cipher suites defined in this document are used, the
  'ec_diffie_hellman_psk' case inside the ServerKeyExchange and
  ClientKeyExchange structure MUST be used instead of the 'psk' case
  defined in [RFC4279] (i.e., the ServerKeyExchange and
  ClientKeyExchange messages include the EC Diffie-Hellman parameters
  in the form specified in Sections 5.4 and 5.7 of [RFC4492]).  The PSK
  identity and identity hint fields have the same meaning and encoding
  as specified in [RFC4279] (note that the ServerKeyExchange message is
  always sent, even if no PSK identity hint is provided).

  The format of the ServerKeyExchange and ClientKeyExchange messages is
  shown below.

     struct {
         select (KeyExchangeAlgorithm) {
             /* other cases for rsa, diffie_hellman, etc. */
             case ec_diffie_hellman_psk:  /* NEW */
                 opaque psk_identity_hint<0..2^16-1>;
                 ServerECDHParams params;
         };
     } ServerKeyExchange;

     struct {
         select (KeyExchangeAlgorithm) {
             /* other cases for rsa, diffie_hellman, etc. */
             case ec_diffie_hellman_psk:   /* NEW */
                 opaque psk_identity<0..2^16-1>;
                 ClientECDiffieHellmanPublic public;
         } exchange_keys;
     } ClientKeyExchange;



Badra & Hajjeh               Informational                      [Page 3]

RFC 5489            ECDHE_PSK Cipher Suites for TLS           March 2009


  The premaster secret is formed as follows.  First, perform the ECDH
  computation as described in Section 5.10 of [RFC4492].  Let Z be the
  octet string produced by this computation.  Next, concatenate a
  uint16 containing the length of Z (in octets), Z itself, a uint16
  containing the length of the PSK (in octets), and the PSK itself.

  This corresponds to the general structure for the premaster secrets
  (see Note 1 in Section 2 of [RFC4279]), with "other_secret"
  containing Z.

     struct {
         opaque other_secret<0..2^16-1>;
         opaque psk<0..2^16-1>;
     };

3.  ECDHE_PSK-Based Cipher Suites

3.1.  ECDHE_PSK Cipher Suites Using the SHA-1 Hash

     CipherSuite TLS_ECDHE_PSK_WITH_RC4_128_SHA          = {0xC0,0x33};
     CipherSuite TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA     = {0xC0,0x34};
     CipherSuite TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA      = {0xC0,0x35};
     CipherSuite TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA      = {0xC0,0x36};

  The above four cipher suites match the cipher suites defined in
  [RFC4279], except that they use an Elliptic Curve Diffie-Hellman
  exchange [RFC4492] authenticated with a PSK, and:

  o  The Message Authentication Code (MAC) is the Hashed Message
     Authentication Code (HMAC) [RFC2104] with SHA-1 as the hash
     function.

  o  When negotiated in a version of TLS prior to 1.2, the Pseudo-
     Random Function (PRF) from that version is used; otherwise, the
     PRF is the TLS PRF [RFC5246] with SHA-256 as the hash function.

3.2.  ECDHE_PSK Cipher Suites Using SHA-2 Hashes

     CipherSuite TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256   = {0xC0,0x37};
     CipherSuite TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384   = {0xC0,0x38};

  The above two cipher suites are the same as the corresponding
  Advanced Encryption Standard (AES) cipher suites in Section 3.1
  above, except for the hash and PRF algorithms, which SHALL be as
  follows:






Badra & Hajjeh               Informational                      [Page 4]

RFC 5489            ECDHE_PSK Cipher Suites for TLS           March 2009


  o  For the cipher suite TLS_ECDHE_PSK_WITH_AES_128_CBC_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 the cipher suite TLS_ECDHE_PSK_WITH_AES_256_CBC_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.

4.  ECDHE_PSK-Based Cipher Suites with NULL Encryption

4.1.  ECDHE_PSK Cipher Suite Using the SHA-1 Hash with NULL Encryption

  The following cipher suite matches the cipher suites defined in
  Section 3.1, except that we define a suite with NULL encryption.

     CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA             = {0xC0,0x39};

4.2.  ECDHE_PSK Cipher Suites Using SHA-2 Hashes with NULL Encryption

  The following two cipher suites are the same as the corresponding
  cipher suites in Section 3.2, but with NULL encryption (instead of
  AES).

     CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA256          = {0xC0,0x3A};
     CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA384          = {0xC0,0x3B};

5.  Security Considerations

  The security considerations described throughout [RFC5246],
  [RFC4785], [RFC4492], and [RFC4279] apply here as well.  In
  particular, as the 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 Section 4 of this document.








Badra & Hajjeh               Informational                      [Page 5]

RFC 5489            ECDHE_PSK Cipher Suites for TLS           March 2009


  Implementers and administrators should monitor the general statements
  on recommended cryptographic algorithms (e.g., SHA-1 hash function)
  that are published from time to time by various forums, including the
  IETF, as a base for the portfolio they support and the policies for
  strength of function acceptable for the cipher suites they set.

6.  IANA Considerations

  This document defines the following new cipher suites, whose values
  have been assigned from the TLS Cipher Suite registry defined in
  [RFC5246].

     CipherSuite TLS_ECDHE_PSK_WITH_RC4_128_SHA          = {0xC0,0x33};
     CipherSuite TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA     = {0xC0,0x34};
     CipherSuite TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA      = {0xC0,0x35};
     CipherSuite TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA      = {0xC0,0x36};
     CipherSuite TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256   = {0xC0,0x37};
     CipherSuite TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384   = {0xC0,0x38};
     CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA             = {0xC0,0x39};
     CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA256          = {0xC0,0x3A};
     CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA384          = {0xC0,0x3B};

7.  Acknowledgments

  The author appreciates Alfred Hoenes for his detailed review and
  effort on resolving issues in discussion.  The author would like to
  acknowledge Bodo Moeller, Simon Josefsson, Uri Blumenthal, Pasi
  Eronen, Paul Hoffman, Joseph Salowey, Mark Tillinghast, and the TLS
  mailing list members for their comments on the document.

8.  Normative References

  [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.

  [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
             Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
             for Transport Layer Security (TLS)", RFC 4492, May 2006.





Badra & Hajjeh               Informational                      [Page 6]

RFC 5489            ECDHE_PSK Cipher Suites for TLS           March 2009


  [RFC4785]  Blumenthal, U. and P. Goel, "Pre-Shared Key (PSK)
             Ciphersuites with NULL Encryption for Transport Layer
             Security (TLS)", RFC 4785, January 2007.

  [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
             (TLS) Protocol Version 1.2", RFC 5246, August 2008.

Authors' Addresses

  Mohamad Badra
  CNRS/LIMOS Laboratory
  Campus de cezeaux, Bat. ISIMA
  Aubiere  63170
  France

  EMail: [email protected]


  Ibrahim Hajjeh
  INEOVATION
  France

  EMail: [email protected]




























Badra & Hajjeh               Informational                      [Page 7]


You are viewing proxied material from gopher.fnord.one. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.