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Network Working Group                                      U. BlumenthalRequest for Comments: 4785                                       P. GoelCategory: Standards Track                              Intel Corporation                                                            January 2007Pre-Shared Key (PSK) Ciphersuites with NULL Encryption forTransport Layer Security (TLS)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) The IETF Trust (2007).Abstract   This document specifies authentication-only ciphersuites (with no   encryption) for the Pre-Shared Key (PSK) based Transport Layer   Security (TLS) protocol.  These ciphersuites are useful when   authentication and integrity protection is desired, but   confidentiality is not needed or not permitted.Table of Contents1. Introduction ....................................................21.1. Applicability Statement ....................................22. Conventions Used in This Document ...............................23. Cipher Usage ....................................................34. Security Considerations .........................................35. IANA Considerations .............................................36. Acknowledgments .................................................37. References ......................................................47.1. Normative References .......................................47.2. Informative References .....................................4Blumenthal & Goel           Standards Track                     [Page 1]

RFC 4785        PSK NULL Encryption Ciphersuites for TLS    January 20071.  Introduction   The RFC for Pre-Shared Key (PSK) based Transport Layer Security (TLS)   [TLS-PSK] specifies ciphersuites for supporting TLS using pre-shared   symmetric keys.  However, all the ciphersuites defined in [TLS-PSK]   require encryption.  However there are cases when only authentication   and integrity protection is required, and confidentiality is not   needed.  There are also cases when confidentiality is not permitted -   e.g., for implementations that must meet import restrictions in some   countries.  Even though no encryption is used, these ciphersuites   support authentication of the client and server to each other, and   message integrity.  This document augments [TLS-PSK] by adding three   more ciphersuites (PSK, DHE_PSK, RSA_PSK) with authentication and   integrity only - no encryption.  The reader is expected to become   familiar with [TLS-PSK] standards prior to studying this document.1.1.  Applicability Statement   The ciphersuites defined in this document are intended for a rather   limited set of applications, usually involving only a very small   number of clients and servers.  Even in such environments, other   alternatives may be more appropriate.   If the main goal is to avoid Public-key Infrastructures (PKIs),   another possibility worth considering is using self-signed   certificates with public key fingerprints.  Instead of manually   configuring a shared secret in, for instance, some configuration   file, a fingerprint (hash) of the other party's public key (or   certificate) could be placed there instead.   It is also possible to use the Secure Remote Password (SRP)   ciphersuites for shared secret authentication [SRP].  SRP was   designed to be used with passwords, and it incorporates protection   against dictionary attacks.  However, it is computationally more   expensive than the PSK ciphersuites in [TLS-PSK].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].Blumenthal & Goel           Standards Track                     [Page 2]

RFC 4785        PSK NULL Encryption Ciphersuites for TLS    January 20073.  Cipher Usage   The three new ciphersuites proposed here match the three cipher   suites defined in [TLS-PSK], except that we define suites with null   encryption.   The ciphersuites defined here use the following options for key   exchange and hash part of the protocol:   CipherSuite                     Key Exchange   Cipher      Hash   TLS_PSK_WITH_NULL_SHA           PSK            NULL        SHA   TLS_DHE_PSK_WITH_NULL_SHA       DHE_PSK        NULL        SHA   TLS_RSA_PSK_WITH_NULL_SHA       RSA_PSK        NULL        SHA   For the meaning of the terms PSK, please refer tosection 1 in [TLS-   PSK].  For the meaning of the terms DHE, RSA, and SHA, please refer   to appendixes A.5 and B in [TLS].4.  Security Considerations   As with all schemes involving shared keys, special care should be   taken to protect the shared values and to limit their exposure over   time.  As this document augments [TLS-PSK], everything stated in its   Security Consideration section applies here.  In addition, as cipher   suites 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 ciphersuites defined in this   document.5.  IANA Considerations   This document defines three new ciphersuites whose values are in the   TLS Cipher Suite registry defined in [TLS].   CipherSuite   TLS_PSK_WITH_NULL_SHA      = { 0x00, 0x2C };   CipherSuite   TLS_DHE_PSK_WITH_NULL_SHA  = { 0x00, 0x2D };   CipherSuite   TLS_RSA_PSK_WITH_NULL_SHA  = { 0x00, 0x2E };6.  Acknowledgments   The ciphersuites defined in this document are an augmentation to and   based on [TLS-PSK].Blumenthal & Goel           Standards Track                     [Page 3]

RFC 4785        PSK NULL Encryption Ciphersuites for TLS    January 20077.  References7.1.  Normative References   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate             Requirement Levels",BCP 14,RFC 2119, March 1997.   [TLS]     Dierks, T. and E. Rescorla, "The Transport Layer Security             (TLS) Protocol Version 1.1",RFC 4346, April 2006.   [TLS-PSK] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites             for Transport Layer Security (TLS)",RFC 4279, December             2005.7.2.  Informative References   [SRP]     Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin,             "Using SRP for TLS Authentication", Work in Progress,             December 2006.Authors' Addresses   Uri Blumenthal   Intel Corporation   1515 State Route 10,   PY2-1 10-4   Parsippany, NJ 07054   USA   EMail: urimobile@optonline.net   Purushottam Goel   Intel Corporation   2111 N.E. 25 Ave.   JF3-414   Hillsboro, OR 97124   USA   EMail: Purushottam.Goel@intel.comBlumenthal & Goel           Standards Track                     [Page 4]

RFC 4785        PSK NULL Encryption Ciphersuites for TLS    January 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   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 inBCP 78 andBCP 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 athttp://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 currently provided by the   Internet Society.Blumenthal & Goel           Standards Track                     [Page 5]