TLS Working Group                                         Mohamad Badra
Internet Draft                                         LIMOS Laboratory
Intended status: Informational                       September 29, 2008
Expires: March 2009



         ECDHE_PSK Ciphersuites for Transport Layer Security (TLS)
                      draft-ietf-tls-ecdhe-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 March 29, 2009.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

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





Badra                   Expires March 29, 2009                 [Page 1]


Internet-Draft     ECDHE_PSK Cipher Suites for TLS       September 2008


   Table of Contents

   1. Introduction...................................................3
      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..................................5
      3.1. ECDHE_PSK Cipher Suites Using the SHA-1 Hash..............5
      3.2. ECDHE_PSK Cipher Suites Using SHA-2 Hashes................5
   4. ECDHE_PSK Based Cipher Suites with NULL Encryption.............5
      4.1. ECDHE_PSK Cipher Suites 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........................................6
   6. IANA Considerations............................................6
   7. Acknowledgments................................................6
   8. References.....................................................6
      8.1. Normative References......................................6
   Author's Addresses................................................7
   Intellectual Property Statement...................................7
   Disclaimer of Validity............................................8



























Badra                   Expires March 29, 2009                 [Page 2]


Internet-Draft     ECDHE_PSK Cipher Suites for TLS       September 2008


1. Introduction

   RFC 4279 specifies cipher suites for supporting TLS using pre-shared
   symmetric keys which (a) use only symmetric key operations for
   authentication, (b) use a Diffie-Hellman exchange authenticated with
   a pre-shared key, 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 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 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.  One of these ciphersuites provides authentication-
   only.

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

1.1. Applicability Statement

   The ciphersuites defined in Sections 3.1 and 4.1 can be negotiated,
   whatever the negotiated TLS version is.

   The ciphersuites defined in Sections 3.2 and 4.2 can be negotiated in
   TLS version 1.2 or higher.

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 ciphersuites described in this document make use of the EC
   parameter negotiation mechanism defined in RFC 4492.  When the
   ciphersuites defined in this document are used, the


Badra                   Expires March 29, 2009                 [Page 3]


Internet-Draft     ECDHE_PSK Cipher Suites for TLS       September 2008


   '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 Diffie-Hellman parameters).
   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;

   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>;
         };






Badra                   Expires March 29, 2009                 [Page 4]


Internet-Draft     ECDHE_PSK Cipher Suites for TLS       September 2008


3. ECDHE_PSK Based Cipher Suites

3.1. ECDHE_PSK Cipher Suites Using the SHA-1 Hash

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

      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};

   For all four cipher suites, the PRF is the TLS PRF [RFC5246] with
   SHA-1 as the hash function, and the MAC is HMAC [RFC2104] with SHA-1
   as the hash function.

3.2. ECDHE_PSK Cipher Suites Using SHA-2 Hashes

      CipherSuite TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256   = {0xXX,0xXX};
      CipherSuite TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384   = {0xXX,0xXX};

   The above two cipher suites are the same as the corresponding AES
   cipher suites in section 3.1 above, except for the hash and PRF
   algorithms, which SHALL be as follows:

       For TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256, the PRF is the TLS PRF
       [RFC5246] with SHA-256 as the hash function, and the MAC is HMAC
       [RFC2104] with SHA-256 as the hash function.

       For TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384, the PRF is the TLS PRF
       [RFC5246] with SHA-384 as the hash function, and the MAC is HMAC
       [RFC2104] with SHA-384 as the hash function.

4. ECDHE_PSK Based Cipher Suites with NULL Encryption

4.1. ECDHE_PSK Cipher Suites 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             = {0xXX,0xXX};

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

      CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA256          = {0xXX,0xXX};
      CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA384          = {0xXX,0xXX};


Badra                   Expires March 29, 2009                 [Page 5]


Internet-Draft     ECDHE_PSK Cipher Suites for TLS       September 2008


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

5. Security Considerations

   The security considerations described throughout [RFC5246],
   [RFC4785], [RFC4492], and [RFC4279] apply here 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.

6. IANA Considerations

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

      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_AES_128_CBC_SHA256   = {0xXX,0xXX};
      CipherSuite TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384   = {0xXX,0xXX};
      CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA             = {0xXX,0xXX};
      CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA256          = {0xXX,0xXX};
      CipherSuite TLS_ECDHE_PSK_WITH_NULL_SHA384          = {0xXX,0xXX};

7. Acknowledgments

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

8. References

8.1. Normative References

   [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.


Badra                   Expires March 29, 2009                 [Page 6]


Internet-Draft     ECDHE_PSK Cipher Suites for TLS       September 2008


   [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.

   [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.

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.






Badra                   Expires March 29, 2009                 [Page 7]


Internet-Draft     ECDHE_PSK Cipher Suites for TLS       September 2008


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.

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 March 29, 2009                 [Page 8]