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>
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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]
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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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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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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.
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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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INTERNET DRAFT Channel binding for HTTP Digest July 2008
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Expires January 2009
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