Internet Engineering Task Force M. Badra INTERNET DRAFT LIMOS Laboratory Updates: 4785, 4279 Expires: November 2007 July 2007 ECDHE_PSK Ciphersuites for TLS Status 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 November 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document updates RFC 4785 and RFC 4279 and specifies a set of ciphersuites that use an Elliptic Curve Diffie-Hellman exchange authenticated with a pre-shared key. These ciphersuites provides Perfect Forward Secrecy. It specifies as well 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. The reader is expected to become familiar with RFC 4785 and RFC 4279 prior to studying this document. Badra Expires November 2007 [Page 1] Internet-Draft ECDHE_PSK Ciphersuites for TLS July 2007 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 provides Perfect Forward Secrecy. It specifies as well 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. 2. Updating RFC4279 The new ciphersuites proposed here 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 these ciphersuites are used, the ServerKeyExchange and ClientKeyExchange messages also include the Diffie-Hellman parameters. The PSK identity and identity hint fields have the same meaning as in the previous section (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; Badra Expires November 2007 [Page 2] Internet-Draft ECDHE_PSK Ciphersuites for TLS July 2007 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 Elliptic Curve Diffie-Hellman computation in the same way as for other Diffie-Hellman-based ciphersuites in [TLS1.0] or [TLS1.1]. Let Z be the value produced by this computation. 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 in RFC 4279) in [RFC4279], with "other_secret" containing Z: struct { opaque other_secret<0..2^16-1>; opaque psk<0..2^16-1>; }; Here "other_secret" comes from the Elliptic Curve Diffie-Hellman exchange (ECDHE_PSK). 3. Updating RFC4785 The new ciphersuite proposed here match the ciphersuites defined in [RFC4785], except that it uses an Elliptic Curve Diffie-Hellman exchange authenticated with a pre-shared key CipherSuite Key Exchange Cipher Hash TLS_ECDHE_PSK_WITH_NULL_SHA ECDHE_PSK NULL SHA 4. Security Considerations The security considerations described throughout [TLS1.0], [TLSv1.1], RFC 4785 and RFC 4279 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 [TLS1.1]. CipherSuite TLS_ECDHE_PSK_WITH_RC4_128_SHA = { 0xXX, 0xXX }; Badra Expires November 2007 [Page 3] Internet-Draft ECDHE_PSK Ciphersuites for TLS July 2007 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. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [TLS1.0] T., Dierks, C., Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [TLS1.1] 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. [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. Acknowledgements The authors would like to thank Bodo Moeller for comments on the document. Author's Addresses Mohamad Badra LIMOS Laboratory - UMR (6158), CNRS France Email: badra@isima.fr Full Copyright Statement Copyright (C) The IETF Trust (2007). 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. Badra Expires November 2007 [Page 4] Internet-Draft ECDHE_PSK Ciphersuites for TLS July 2007 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. Intellectual Property 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. Acknowledgement Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Badra Expires November 2007 [Page 5]