RFC5554
Network Working Group N. Williams Request for Comments: 5554 Sun Updates: 2743 May 2009 Category: Standards Track
Clarifications and Extensions to
the Generic Security Service Application Program Interface (GSS-API)
for the Use of Channel Bindings
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
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Abstract
This document clarifies and generalizes the Generic Security Service Application Programming Interface (GSS-API) "channel bindings" facility, and imposes requirements on future GSS-API mechanisms and programming language bindings of the GSS-API.
Contents
Introduction
The base GSS-API version 2, update 1 specification RFC2743 provides a facility for channel binding (see also RFC5056), but its treatment is incomplete. The GSS-API C-bindings specification RFC2744 expands somewhat on this facility in what should be a generic way, but is instead a C-specific way, thus leaving the treatment of this facility incomplete.
This document clarifies the GSS-API's channel binding facility and generalizes the parts of it that are specified in the C-bindings document but that should have been generic from the start.
Conventions Used in This Document
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 RFC2119.
New Requirements for GSS-API Mechanisms
Given the publication of RFC 5056, we now assert that all new GSS-API mechanisms that support channel binding MUST conform to RFC5056.
Generic Structure for GSS-API Channel Bindings
The base GSS-API version 2, update 1 specification RFC2743 provides a facility for channel binding. It models channel bindings as an OCTET STRING and leaves it to the GSS-API version 2, update 1 C-bindings specification to specify the structure of the contents of the channel bindings OCTET STRINGs. The C-bindings specification RFC2744 then defines, in terms of C, what should have been a generic structure for channel bindings. The Kerberos V GSS mechanism RFC4121 also defines a method for encoding GSS channel bindings in a way that is independent of the C-bindings -- otherwise, the mechanism's channel binding facility would not be useable with other language bindings.
In other words, the structure of GSS channel bindings given in RFC2744 is actually generic in spite of being specified in terms of C concepts and syntax.
We generalize it as shown below, using the same pseudo-ASN.1 as is used in RFC 2743. Although the figure below is, indeed, a valid ASN.1 [CCITT.X680] type, we do not provide a full ASN.1 module as none is needed because no standard encoding of this structure is needed -- the definition below is part of an abstract API, not part
of a protocol defining bits on the wire. GSS-API mechanisms do need to encode the contents of this structure, but that encoding will be mechanism specific (see below).
GSS-CHANNEL-BINDINGS ::= SEQUENCE {
initiator-address-type INTEGER, -- See RFC2744
initiator-address OCTET STRING, -- See RFC2744
acceptor-address-type INTEGER, -- See RFC2744
acceptor-address OCTET STRING, -- See RFC2744
application-data OCTET STRING -- See RFC5056
}
Abstract GSS-API Channel Bindings Structure
The values for the address fields are described in RFC2744.
New language-specific bindings of the GSS-API SHOULD specify a language-specific formulation of this structure.
Where a language binding of the GSS-API models channel bindings as OCTET STRINGs (or the language's equivalent), then the implementation MUST assume that the given bindings correspond only to the application-data field of GSS-CHANNEL-BINDINGS as shown above, rather than some encoding of GSS-CHANNEL-BINDINGS.
As mentioned above, RFC4121 describes an encoding of the above GSS- CHANNEL-BINDINGS structure and then hashes that encoding. Other GSS- API mechanisms are free to use that encoding.
Security Considerations
For general security considerations relating to channel bindings, see RFC5056.
Language bindings that use OCTET STRING (or equivalent) for channel bindings will not support the use of network addresses as channel bindings. This should not cause any security problems, as the use of network addresses as channel bindings is not generally secure. However, it is important that "end-point channel bindings" not be modeled as network addresses; otherwise, such channel bindings may not be useable with all language bindings of the GSS-API.
References
Normative References
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
RFC2743 Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
RFC2744 Wray, J., "Generic Security Service API Version 2 :
C-bindings", RFC 2744, January 2000.
RFC4121 Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
Version 5 Generic Security Service Application Program
Interface (GSS-API) Mechanism: Version 2", RFC 4121,
July 2005.
RFC5056 Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, November 2007.
Informative References
[CCITT.X680] International Telephone and Telegraph Consultative
Committee, "Abstract Syntax Notation One (ASN.1):
Specification of basic notation", CCITT Recommendation
X.680, July 2002.
Author's Address
Nicolas Williams Sun Microsystems 5300 Riata Trace Ct Austin, TX 78727 US
EMail: [email protected]
