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Versions: 00 01                                                         
INTERNET-DRAFT                              Stefan Santesson (Microsoft)
Intended Status: Informational                  Kevin Damour (Microsoft)
                                                 Phil Hallin (Microsoft)
Expires January 2009                                           July 2008

             Channel binding for HTTP Digest Authentication
                  <draft-santesson-digestbind-01.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
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   Internet-Drafts are working documents of the Internet Engineering
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Abstract

   This document specifies a method implemented by Microsoft to add
   channel binding capabilities to the http digest protocol defined in
   RFC 2617 [2617]














Santesson                                                       [Page 1]


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1.  Introduction

   This specification document Microsoft's existing implementation of
   TLS endpoint channel binding and service binding for http digest
   Authentication.

   The primary purpose of this feature is to safeguard resources against
   authentication forwarding attacks.

   Authentication forwarding is possible when http digest authentication
   takes place inside an outer secure channel (e.g. TLS).  In this case,
   there is no binding between the inner channel session key and the
   outer channel session key.  This specification defines a way to
   exchange necessary channel binding data for the outer channel within
   http digest authentication.

   This specification expands the defined set of authentication
   parameters defined in RFC 2617 [2617] for the Authorization request
   header, when used with digest authentication. The semantics of server
   and client nonce are expanded to facilitate negotiation of channel
   binding.


1.1  Terminology

   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 RFC 2119 [2119].


2. Protocol syntax

   Channel binding is provided through amendments to the WWW-
   Authenticate Response Header sent by the server and the Authorization
   Request Header returned by the client, both defined in RFC 2616
   [2616].

   Authentication parameters (directives) defined in this specification,
   are defined within the auth-param syntax defined in RFC 2617 [2617]:

      auth-param     = token "=" ( token | quoted-string )


2.1 WWW-Authenticate Response Header

   The WWW-Authenticate Response Header sent by the server MUST be
   formed according to RFC 2617 [2617] section 3.2.1, with the
   amendments specified in this section.



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INTERNET DRAFT      Channel binding for HTTP Digest            July 2008


   nonce
      A server signals that it supports channel binding according to
      this specification by invoking the following 12 characters in the
      server nonce:

      "+UpGrAdEd+v1"

   As the nonce directive is present, the qop-options directive MUST be
   present according to RFC 2617 [2617].

   This specification only supports channel binding when the outer
   channel is TLS.

2.2  Authorization Request Header

   The Authorization Request header sent by the client MUST be formed
   according to RFC 2617 [2617] section 3.2.2, with the amendments
   specified in this section.

   digest-response is expanded with the following directives:

      hashed-directives  = "hashed-dirs" "=" <"> 1#token <">
      service-name       = "service-name" "=" service-name-value
      charset            = "charset" "=" "utf-8"
      channel-binding    = <"> 32LHEX <">


   service-name-value is further defined as:

      service-name-value = serv-type "/" host [ "/" serv-name ]
      serv-type          = 1*ALPHA
      host               = 1*( ALPHA | DIGIT | "-" | "." )
      serv-name          = host

   Definition of directive values:

   cnonce
      On the client side, an upgraded client recognizes the leading
      "+UpGrAdEd+v1" string in the server nonce and interprets it to
      mean that the server understands channel bindings according to
      this specification. This extends the semantics from RFC 2617
      [2617] where the nonce is defined to be opaque to the client, but
      now conveys information from the server. If the client decides to
      send channel binding information, it includes the same
      "+UpGrAdEd+v1" prefix string at the beginning of the cnonce it
      generates. The MD5 ASCII hex of the unquoted service-name and
      channel-bindings directive values follows the upgraded prefix.




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      NOTE: Many existing client implementations ignores the "v1" part
      of the "+UpGrAdEd+v1" string and would not notice the difference
      if the string ended with "v2". This should be taken into
      consideration if a version 2 of this protocol is defined.


   hashed-directives
      The names of the directives, which values are hashed and included
      in the cnonce, provided as a quoted coma separated list. For
      version 1 (v1) of this specification, this directive MUST contain
      the following value:

      hashed-dirs = "service-name,channel-binding"


   service-name
      The service-name directive is defined identically as the digest-
      uri directive of RFC 2831 [2831]. All conventions defined for the
      digest-uri directive in RFC 2831 apply also to this directive.


   charset
      This directive, if present, specifies that the server supports
      UTF-8 encoding for the username and password. This directive and
      conventions for its use are defined in RFC 2831 [2831].


   channel-binding
      This directive carries the octets of a channel binding token as
      defined in the IANA registry for Channel Binding Types, defined
      under RFC 5056 [5056]. The selected channel binding type for
      implementations of this specification MUST be "tls-server-end-
      point"

3  IANA Considerations

   TBD

4 Security Considerations

   TBD










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INTERNET DRAFT      Channel binding for HTTP Digest            July 2008


5  References

5.1  Normative References

   [2119]   S. Bradner, "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.

   [2616]   R. Fielding, J. Gettys, J. Mogul, H. Frystyk,
            L. Masinter, P. Leach, T. Berners-Lee, "Hypertext
            Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [2617]   J. Franks, P. Hallam-Baker, J. Hostetler, S. Lawrence,
            P. Leach, A. Luotonen, L. Stewart, "HTTP Authentication:
            Basic and Digest Access Authentication", RFC 2617,
            June 1999.

   [2831]   P. Leach, C. Newman, "Using Digest Authentication as a
            SASL Mechanism", RFC 2831, May 2000.

   [5056]   N. Williams, "On the Use of Channel Bindings to Secure
            Channels", RFC 5056, November 2007.



5.2  Informative References

   No informative references are listed.
























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Appendix A - Example

   This is an example of a valid Authorization request header according
   to this specification:

      Authorization : Digest
      username="administrator",
      realm="jeremyv-dom2.nttest.example.com",
      nonce="+UpGrAdEd+v137576ac1877be8fe5993f505e48dc801d89a9e0a3e430
      9b4dd10177754546bf5db46ee3b77fcb6317f569396da0b53fa",
      uri="/dir/index.html",
      cnonce="+UpGrAdEd+v19f74f856d6b97542776f92fa6d6f3429eb5ffa78b385
      313f954e9f2226246bd9",
      nc=00000001,
      algorithm=MD5-sess,
      response="5da37a37d5b3867366f22133182f1ef4",
      qop="auth",
      charset=utf-8,
      hashed-dirs="service-name,channel-binding",
      service-name="TestServiceName/example.com",
      channel-binding="8674d6ce56be991be9c7549735f179f4"

   Editorial note: This example will be updated. It is syntactically
   correct, but some hash values are not reflecting the actual values in
   the example.


























Santesson                                                       [Page 6]


INTERNET DRAFT      Channel binding for HTTP Digest            July 2008


Authors' Addresses


   Stefan Santesson
   Microsoft
   One Microsoft Way
   Redmond, WA 98052
   USA

   EMail: stefans(at)microsoft.com

   Kevin Damour
   Microsoft
   One Microsoft Way
   Redmond, WA 98052
   USA

   EMail: kdamour(at)microsoft.com


   Phil Hallin
   Microsoft
   One Microsoft Way
   Redmond, WA 98052
   USA

   EMail: philh(at)microsoft.com
























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Expires January 2009








Santesson                                                       [Page 8]