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Moving DIGEST-MD5 to Historic
RFC 6331

Internet Engineering Task Force (IETF)                       A. Melnikov
Request for Comments: 6331                                 Isode Limited
Obsoletes: 2831                                                July 2011
Category: Informational
ISSN: 2070-1721

                     Moving DIGEST-MD5 to Historic

Abstract

   This memo describes problems with the DIGEST-MD5 Simple
   Authentication and Security Layer (SASL) mechanism as specified in
   RFC 2831.  It marks DIGEST-MD5 as OBSOLETE in the IANA Registry of
   SASL mechanisms and moves RFC 2831 to Historic status.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6331.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Melnikov                      Informational                     [Page 1]
RFC 6331              Moving DIGEST-MD5 to Historic            July 2011

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.    Introduction and Overview . . . . . . . . . . . . . . . . . . 2
   2.    Security Considerations . . . . . . . . . . . . . . . . . . . 5
   3.    IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
   4.    Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 5
   5.    References  . . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.1.  Normative References  . . . . . . . . . . . . . . . . . . . . 5
   5.2.  Informative References  . . . . . . . . . . . . . . . . . . . 5

1.  Introduction and Overview

   [RFC2831] defines how HTTP Digest Authentication [RFC2617] can be
   used as a Simple Authentication and Security Layer (SASL) [RFC4422]
   mechanism for any protocol that has a SASL profile.  It was intended
   both as an improvement over CRAM-MD5 [RFC2195] and as a convenient
   way to support a single authentication mechanism for web, email, the
   Lightweight Directory Access Protocol (LDAP), and other protocols.
   While it can be argued that it is an improvement over CRAM-MD5, many
   implementors commented that the additional complexity of DIGEST-MD5
   makes it difficult to implement fully and securely.

   Below is an incomplete list of problems with the DIGEST-MD5 mechanism
   as specified in [RFC2831]:

   1.  The mechanism has too many options and modes.  Some of them are
       not well described and are not widely implemented.  For example,
       DIGEST-MD5 allows the "qop" directive to contain multiple values,
       but it also allows for multiple qop directives to be specified.
       The handling of multiple options is not specified, which results
       in minor interoperability problems.  Some implementations
       amalgamate multiple qop values into one, while others treat
       multiple qops as an error.  Another example is the use of an
       empty authorization identity.  In SASL, an empty authorization
       identity means that the client is willing to authorize as the

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