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rfc: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.

Copyright Notice

 Copyright (c) 2009 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents in effect on the date of
 publication of this document (http://trustee.ietf.org/license-info).
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.

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.

Table of Contents

 1. Introduction ....................................................2
 2. Conventions Used in This Document ...............................2
 3. New Requirements for GSS-API Mechanisms .........................2
 4. Generic Structure for GSS-API Channel Bindings ..................2
 5. Security Considerations .........................................3
 6. References ......................................................4
    6.1. Normative References .......................................4
    6.2. Informative References .....................................4

Williams Standards Track [Page 1] RFC 5554 GSS-API Channel Bindings May 2009

1. 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.

2. 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].

3. 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].

4. 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

Williams Standards Track [Page 2] RFC 5554 GSS-API Channel Bindings May 2009

 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.

5. 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.

Williams Standards Track [Page 3] RFC 5554 GSS-API Channel Bindings May 2009

6. References

6.1. 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.

6.2. 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: Nicolas.Williams@sun.com

Williams Standards Track [Page 4]

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