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Versions: 00

INTERNET-DRAFT                                     Kurt D. Zeilenga
Intended Category: Informational                   Isode Limited
Expires in six months                              20 November 2008
Obsoletes: 2195



                           CRAM-MD5 to Historic
               <draft-ietf-sasl-crammd5-to-historic-00.txt>



Status of this Memo

  This document is intended to be, after appropriate review and
  revision, submitted to the RFC Editor as a Informational document.
  Distribution of this memo is unlimited.  It is suggested that
  technical discussion regarding this document take place on the IETF
  SASL WG mailing list <ietf-sasl@imc.org>.  Please send editorial
  comments directly to the author <Kurt.Zeilenga@Isode.COM>.

  By submitting this Internet-Draft, each author represents that any
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  Copyright (C) The IETF Trust (2008).

  Please see the Full Copyright section near the end of this document
  for more information.





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INTERNET-DRAFT                  CRAM-MD5                20 November 2008


Abstract

  This document recommends the retirement of the CRAM-MD5 authentication
  mechanism, and discusses the reasons for doing so.  This document
  recommends RFC 2195 and its predecessor, RFC 2095, be moved to
  Historic status.


  [[Note to RFC Editor: please publish at same time that [SCRAM] is
  published.]]


1. CRAM-MD5

  CRAM-MD5 [RFC2195] is a authentication mechanism.  It was originally
  designed for use in Internet Messaging Access Protocol (IMAP)
  [RFC3501] and Post Office Protocol (POP) [RFC1939].  It is also
  registered as a Simple Authentication and Security Layer (SASL)
  [RFC4422] mechanism [IANA-SASL], though it has not been formally
  specified as SASL mechanism.

  CRAM-MD5 is a simple challenge/response protocol for establishing that
  both parties have knowledge of a shared secret derived from the user's
  password, presumedly a sequence of characters.

  While CRAM-MD5 is widely implemented and deployed on the Internet,
  interoperability is only possible where the client and server have an
  a priori agreement on the character set and encoding of the password,
  and any normalization to be applied before input to the cryptographic
  functions applied by both client and server.   Even where the client
  and server are implemented by the same developer, the client and
  server will not operate properly in absence of an a priori agreement
  (such as "passwords shall be a sequence of ASCII printable characters,
  encoded in a octet with zero parity, with no normalization").

  CRAM-MD5 does not provide adequate security services for use on the
  Internet.  CRAM-MD5 does not protect the user's authentication
  identifier from eavesdroppers.  CRAM-MD5 challenge/response exchange
  is subject to a number of passive and active attacks.

  CRAM-MD5 does not provide any data security services nor channel
  bindings [CBIND] to data security services (e.g., TLS [RFC5246])
  provided externally.

  RFC 2195 states no recommendation (or mandate) that implementors only
  offer CRAM-MD5 when external data security services are in place.  RFC
  2195 does not recommend (or mandate) that implementations supporting
  CRAM-MD5 implement any external data security service.



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  While it possible to revise RFC 2195 to address these and other
  deficiencies of the authentication mechanism, these changes would be
  disruptive to existing deployments.  For instance, if a revision were
  to specify that a particular character set, encoding, and
  normalization of the password is to be used, this mandate would
  disruptive to deployers who use an incompatible character set,
  encoding, and/or normalization.  Addition of additional security
  features, such as channel bindings, seems more appropriately done by
  introduced in a new mechanism.


2. Recommendations

  It is recommended RFC 2195 and its predecessor, RFC 2095, be moved to
  Historic status.

  It is recommended that application protocol designers and deployers
  consider the SASL PLAIN [RFC4616] mechanism protected by TLS [RFC5246]
  and/or the SASL Salted Challenge Response Authentication Mechanism
  (SCRAM) [SCRAM] as alternatives to CRAM-MD5.


3. Security Considerations

  The retirement of CRAM-MD5 may lead to use of stronger authentication
  mechanisms and, hence, may improve Internet security.


4. IANA Considerations

  It is requested that IANA update the SASL CRAM-MD5 registration upon
  publication approval of this document.

      Subject: Updated Registration of SASL CRAM-MD5 mechanism
      SASL mechanism (or prefix for the family): CRAM-MD5
      Security considerations: see RFC XXXX
      Published specification (recommended): RFC XXXX, RFC 2195
      Person & email address to contact for further information:
           Kurt Zeilenga <kurt.zeilenga@isode.com>
      Intended usage: LIMITED
      Owner/Change controller: IESG


7. Acknowledgments

  TBD





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8. Author's Address

  Kurt D. Zeilenga
  Isode Limited

  Email: Kurt.Zeilenga@Isode.COM


9. References

  [[Note to the RFC Editor: please replace the citation tags used in
  referencing Internet-Drafts with tags of the form RFCnnnn where
  possible.]]

9.1. Normative References

  [RFC2095]     Klensin, J., R. Catoe, and P. Krumviede, "IMAP/POP
                AUTHorize Extension for Simple Challenge/Response", RFC
                2095, January 1997.

  [RFC2195]     Klensin, J., R. Catoe, and P. Krumviede, "IMAP/POP
                AUTHorize Extension for Simple Challenge/Response", RFC
                2195, September 1997.

  [IANA-SASL]   IANA, "SIMPLE AUTHENTICATION AND SECURITY LAYER (SASL)
                MECHANISMS",
                <http://www.iana.org/assignments/sasl-mechanisms>.


9.2. Informative References


  [RFC1939]     Myers, J. and M. Rose, "Post Office Protocol - Version
                3", STD 53, RFC 1939, May 1996.

  [RFC3501]     Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
                4rev1", RFC 3501, March 2003.
  [RFC4422]     Melnikov, A. (Editor), K. Zeilenga (Editor), "Simple
                Authentication and Security Layer (SASL)", RFC 4422,
                June 2006.

  [RFC4616]     Zeilenga, K., "The PLAIN Simple Authentication and
                Security Layer (SASL) Mechanism", RFC 4616, August 2006.


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



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  [SCRAM]         Menon-Sen, Abhijit, C. Newman, "Salted Challenge
                Response Authentication Mechanism (SCRAM)", draft-
                newman-auth-scram-xx.txt, a work in progress.

  [CBIND]       Williams, N., "On the Use of Channel Bindings to Secure
                Channels", draft-williams-on-channel-binding-xx.txt, a
                work in progress.


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  Copyright (C) The IETF Trust (2008).

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