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<pre>Network Working Group N. Williams
Request for Comments: 5554 Sun
Updates: <a href="./rfc2743">2743</a> May 2009
Category: Standards Track
<span class="h1">Clarifications and Extensions to</span>
<span class="h1">the Generic Security Service Application Program Interface (GSS-API)</span>
<span class="h1">for the Use of Channel Bindings</span>
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 <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>).
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
<a href="#section-1">1</a>. Introduction ....................................................<a href="#page-2">2</a>
<a href="#section-2">2</a>. Conventions Used in This Document ...............................<a href="#page-2">2</a>
<a href="#section-3">3</a>. New Requirements for GSS-API Mechanisms .........................<a href="#page-2">2</a>
<a href="#section-4">4</a>. Generic Structure for GSS-API Channel Bindings ..................<a href="#page-2">2</a>
<a href="#section-5">5</a>. Security Considerations .........................................<a href="#page-3">3</a>
<a href="#section-6">6</a>. References ......................................................<a href="#page-4">4</a>
<a href="#section-6.1">6.1</a>. Normative References .......................................<a href="#page-4">4</a>
<a href="#section-6.2">6.2</a>. Informative References .....................................<a href="#page-4">4</a>
<span class="grey">Williams Standards Track [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc5554">RFC 5554</a> GSS-API Channel Bindings May 2009</span>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
The base GSS-API version 2, update 1 specification [<a href="./rfc2743" title=""Generic Security Service Application Program Interface Version 2, Update 1"">RFC2743</a>] provides
a facility for channel binding (see also [<a href="./rfc5056" title=""On the Use of Channel Bindings to Secure Channels"">RFC5056</a>]), but its
treatment is incomplete. The GSS-API C-bindings specification
[<a href="./rfc2744" title=""Generic Security Service API Version 2 : C-bindings"">RFC2744</a>] 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.
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Conventions Used in This Document</span>
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 [<a href="./rfc2119" title=""Key words for use in RFCs to Indicate Requirement Levels"">RFC2119</a>].
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. New Requirements for GSS-API Mechanisms</span>
Given the publication of <a href="./rfc5056">RFC 5056</a>, we now assert that all new GSS-API
mechanisms that support channel binding MUST conform to [<a href="./rfc5056" title=""On the Use of Channel Bindings to Secure Channels"">RFC5056</a>].
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Generic Structure for GSS-API Channel Bindings</span>
The base GSS-API version 2, update 1 specification [<a href="./rfc2743" title=""Generic Security Service Application Program Interface Version 2, Update 1"">RFC2743</a>] 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
[<a href="./rfc2744" title=""Generic Security Service API Version 2 : C-bindings"">RFC2744</a>] then defines, in terms of C, what should have been a
generic structure for channel bindings. The Kerberos V GSS mechanism
[<a href="./rfc4121" title=""The Kerberos Version 5 Generic Security Service Application Program Interface (GSS-API) Mechanism: Version 2"">RFC4121</a>] 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
[<a href="./rfc2744" title=""Generic Security Service API Version 2 : C-bindings"">RFC2744</a>] 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 <a href="./rfc2743">RFC 2743</a>. Although the figure below is, indeed, a valid
ASN.1 [<a href="#ref-CCITT.X680" title=""Abstract Syntax Notation One (ASN.1): Specification of basic notation"">CCITT.X680</a>] 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
<span class="grey">Williams Standards Track [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc5554">RFC 5554</a> GSS-API Channel Bindings May 2009</span>
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 <a href="./rfc2744">RFC2744</a>
initiator-address OCTET STRING, -- See <a href="./rfc2744">RFC2744</a>
acceptor-address-type INTEGER, -- See <a href="./rfc2744">RFC2744</a>
acceptor-address OCTET STRING, -- See <a href="./rfc2744">RFC2744</a>
application-data OCTET STRING -- See <a href="./rfc5056">RFC5056</a>
}
Abstract GSS-API Channel Bindings Structure
The values for the address fields are described in [<a href="./rfc2744" title=""Generic Security Service API Version 2 : C-bindings"">RFC2744</a>].
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, [<a href="./rfc4121" title=""The Kerberos Version 5 Generic Security Service Application Program Interface (GSS-API) Mechanism: Version 2"">RFC4121</a>] 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.
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. Security Considerations</span>
For general security considerations relating to channel bindings, see
[<a href="./rfc5056" title=""On the Use of Channel Bindings to Secure Channels"">RFC5056</a>].
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.
<span class="grey">Williams Standards Track [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc5554">RFC 5554</a> GSS-API Channel Bindings May 2009</span>
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. References</span>
<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>. Normative References</span>
[<a id="ref-RFC2119">RFC2119</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.
[<a id="ref-RFC2743">RFC2743</a>] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", <a href="./rfc2743">RFC 2743</a>, January 2000.
[<a id="ref-RFC2744">RFC2744</a>] Wray, J., "Generic Security Service API Version 2 :
C-bindings", <a href="./rfc2744">RFC 2744</a>, January 2000.
[<a id="ref-RFC4121">RFC4121</a>] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
Version 5 Generic Security Service Application Program
Interface (GSS-API) Mechanism: Version 2", <a href="./rfc4121">RFC 4121</a>,
July 2005.
[<a id="ref-RFC5056">RFC5056</a>] Williams, N., "On the Use of Channel Bindings to Secure
Channels", <a href="./rfc5056">RFC 5056</a>, November 2007.
<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>. Informative References</span>
[<a id="ref-CCITT.X680">CCITT.X680</a>] 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]
</pre>
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