INTERNET-DRAFT S. Santesson (Microsoft) Intended Status: Informational Expires December 2008 June 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 May 2007 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 defined in this specification follow the auth-param syntax defined in [2617]: auth-param = token "=" ( token | quoted-string ) 2.1 WWW-Authenticate Response Header The WWW-Authenticate Response Header send 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 May 2007 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 [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. The following 3 directives are added to digest-response hashed-directives = "hashed-dirs" "=" <"> 1#token <"> service-name = "service-name" "=" service-name-value 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. 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. 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 Santesson [Page 3] INTERNET DRAFT Channel binding for HTTP Digest May 2007 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. channel-binding The hash of the TLS server's end entity certificate as it appears, octet for octet, in the server's Certificate message (note that the Certificate message contains a certificate_list, the first element of which is the server's end entity certificate. The hash function to be used is as follows: if the certificate's signature hash algorithm is either MD5 or SHA-1, then use SHA-256, otherwise use the certificate's signature hash algorithm. The reason for using a hash of the certificate is that some implementations need to track the channel binding of a TLS session in kernel-mode memory, which is often at a premium. 3 IANA Considerations TBD 4 Security Considerations TBD Santesson [Page 4] INTERNET DRAFT Channel binding for HTTP Digest May 2007 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 5.2 Informative References Santesson [Page 5] INTERNET DRAFT Channel binding for HTTP Digest May 2007 Authors' Addresses Stefan Santesson Microsoft One Microsoft Way Redmond, WA 98052 USA EMail: stefans@microsoft.com Santesson [Page 6] INTERNET DRAFT Channel binding for HTTP Digest May 2007 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 December 2008 Santesson [Page 7]