TLS Working Group                                         Mohamad Badra
Internet Draft                                         LIMOS Laboratory
Intended status: Informational                         February 1, 2008
Expires: July 2008



         ECDHE_PSK Ciphersuites for Transport Layer Security (TLS)
                     draft-badra-ecdhe-tls-psk-03.txt


Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on July 31, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This document extends RFC 4279 and RFC 4785 and specifies a set of
   ciphersuites that use an Elliptic Curve Diffie-Hellman exchange
   authenticated with a pre-shared key. These ciphersuites provide
   Perfect Forward Secrecy. It also specifies one authentication-only
   ciphersuites (with no encryption). This ciphersuite is useful when
   authentication and integrity protection is desired, but
   confidentiality is not needed or not permitted.



Badra                   Expires July 31, 2008                  [Page 1]


Internet-Draft      ECDHE_PSK Ciphersuites for TLS        February 2008


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

1. Introduction

   RFC 4279 specifies ciphersuites for supporting TLS using pre-shared
   symmetric keys and they (a) use only symmetric key operations for
   authentication, (b) use a Diffie-Hellman exchange authenticated with
   a pre-shared key, or (c) combines public key authentication of the
   server with pre-shared key authentication of the client.

   RFC 4785 specifies authentication-only ciphersuites (with no
   encryption).

   This document specifies a set of ciphersuites that use an Elliptic
   Curve Diffie-Hellman exchange authenticated with a pre-shared key.
   These ciphersuites provide Perfect Forward Secrecy. This document
   also specifies one authentication-only ciphersuites (with no
   encryption). This ciphersuite is useful when authentication and
   integrity protection is desired, but confidentiality is not needed or
   not permitted.

1.1. 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 ciphersuites in this section match the ciphersuites defined in
   [RFC4279], except that they use an Elliptic Curve Diffie-Hellman
   exchange [RFC4492] authenticated with a pre-shared key. They are
   defined as follow:

   CipherSuite                           Key Exchange  Cipher      Hash

   TLS_ECDHE_PSK_WITH_RC4_128_SHA        ECDHE_PSK     RC4_128      SHA
   TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA   ECDHE_PSK     3DES_EDE_CBC SHA
   TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA    ECDHE_PSK     AES_128_CBC  SHA
   TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA    ECDHE_PSK     AES_256_CBC  SHA

   When the ciphersuites defined in this document are used, the
   'ec_diffie_hellman_psk' case inside the ServerKeyExchange and
   ClientKeyExchange structure is used instead of the 'psk' case defined
   in [RFC4279] (i.e. The ServerKeyExchange and ClientKeyExchange
   messages include the Diffie-Hellman parameters). The PSK identity and


Badra                   Expires July 31, 2008                  [Page 2]


Internet-Draft      ECDHE_PSK Ciphersuites for TLS        February 2008


   identity hint fields MUST have the same meaning 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;

   The premaster secret is formed as follows. First, perform an ECDH
   operation (See section&nbsp;5.10 of [RFC4492]) to compute the shared
   secret. Next, concatenate a uint16 containing the length of the
   shared secret (in octets), the shared secret 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&nbsp;2 of [RFC4279]), with "other_secret"
   containing the shared secret:

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

3. 2. ECDHE_PSK Key Exchange Algorithm with NULL Encryption

   The ciphersuite in this section matches the ciphersuites defined in
   [RFC4785], except that it uses an Elliptic Curve Diffie-Hellman
   exchange authenticated with a pre-shared key.




Badra                   Expires July 31, 2008                  [Page 3]


Internet-Draft      ECDHE_PSK Ciphersuites for TLS        February 2008


   CipherSuite                     Key Exchange   Cipher      Hash

   TLS_ECDHE_PSK_WITH_NULL_SHA     ECDHE_PSK      NULL        SHA

4. Security Considerations

   The security considerations described throughout [RFC4346], [RFC4785]
   and [RFC4279] apply here as well.

5. IANA Considerations

   This document defines the following new ciphersuites, whose values
   are to be assigned from the TLS Cipher Suite registry defined in
   [RFC4346].

   CipherSuite TLS_ECDHE_PSK_WITH_RC4_128_SHA        = { 0xXX, 0xXX };
   CipherSuite TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA   = { 0xXX, 0xXX };
   CipherSuite TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA    = { 0xXX, 0xXX };
   CipherSuite TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA    = { 0xXX, 0xXX };
   CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA           = { 0xXX, 0xXX };

6. Acknowledgments

   The author would like to thank Bodo Moeller, Simon Josefsson, Uri
   Blumenthal, Pasi Eronen, and the TLS mailing list members for their
   comments on the document.

7. References

7.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4346] Dierks, T., Rescorla, E., "The TLS Protocol Version 1.1",
             RFC 4346, April 200P.

   [RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
             for Transport Layer Security (TLS)", RFC 4279, December
             2005.

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





Badra                   Expires July 31, 2008                  [Page 4]


Internet-Draft      ECDHE_PSK Ciphersuites for TLS        February 2008


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

Author's Addresses

   Mohamad Badra
   LIMOS Laboratory - UMR6158, CNRS
   France

   Email: badra@isima.fr


Intellectual Property Statement

   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 in BCP 78 and BCP 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 at
   http://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.

Disclaimer of Validity

   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.


Badra                   Expires July 31, 2008                  [Page 5]


Internet-Draft      ECDHE_PSK Ciphersuites for TLS        February 2008


Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.





































Badra                   Expires July 31, 2008                  [Page 6]