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 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 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html 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] INTERNET DRAFT Channel binding for HTTP Digest July 2008 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. Santesson [Page 2] 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. Santesson [Page 3] INTERNET DRAFT Channel binding for HTTP Digest July 2008 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 Santesson [Page 4] 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. Santesson [Page 5] INTERNET DRAFT Channel binding for HTTP Digest July 2008 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 Santesson [Page 7] INTERNET DRAFT Channel binding for HTTP Digest July 2008 Copyright (C) The IETF Trust (2008). 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. 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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. Expires January 2009 Santesson [Page 8]