RFC 5554

Clarifications and Extensions to the Generic Security Service Application Program Interface (GSS-API) for the Use of Channel Bindings

📅 published May 2009, from ietf

Clarifications and Extensions to the Generic Security Service Application Program Interface (GSS-API) for the Use of Channel Bindings 🎀

  • RFC: 5554
  • Authors: N. Williams (Nicolas Williams, Sun) 💜
  • Category: Standards Track ✨
  • Date: May 2009 🌸
  • Updates: 2743 (RFC 2743) 🦋

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 (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. It's giving "tidying up the group chat" energy 🫶

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

1. Introduction ✨

Okay so the base GSS-API version 2, update 1 spec [RFC2743] has a channel binding facility (see also [RFC5056]), but honestly? Its treatment is incomplete 🙈 The GSS-API C-bindings spec [RFC2744] adds some more detail to that facility in what should be a generic way, but it's instead a C-specific way, so the treatment is still incomplete. Not ideal, bestie.

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. Main character glow-up arc 💅

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]. These are the rules-of-the-road words, so read them carefully 👑

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]. No exceptions, periodt 💅

4. Generic Structure for GSS-API Channel Bindings 🧚

Okay so the base GSS-API version 2, update 1 spec [RFC2743] has a channel binding facility. It models channel bindings as an OCTET STRING and leaves it to the GSS-API version 2, update 1 C-bindings spec to define the structure of what goes inside those OCTET STRINGs. The C-bindings spec [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 way to encode GSS channel bindings that doesn't depend on the C-bindings. Otherwise, the mechanism's channel binding facility wouldn't be usable with other language bindings, and nobody wants that 😭

In other words, the structure of GSS channel bindings given in [RFC2744] is actually generic, even though it's written in C concepts and syntax. Lowkey iconic 🌈

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, 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. Be intentional about it, bestie ✨

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. This one is a MUST, so no vibes-based implementing 🙅‍♀️

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]. Read that one too, it's the real tea 🍓

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. Big warning energy here, so don't skip this part 💀

Heads up: if your binding uses OCTET STRINGs, network addresses won't work as channel bindings, and "end-point channel bindings" must not be modeled as network addresses, or they might not work with every GSS-API language binding. Protect your channel bindings, babe 🛡️

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
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