Internet Engineering Task Force (IETF)                      S. Josefsson
Request for Comments: 6339                                        SJD AB
Category: Standards Track                           L. Hornquist Astrand
ISSN: 2070-1721                                              Apple, Inc.
                                                             August 2011

Context Token Encapsulate/Decapsulate and OID Comparison Functions for
the Generic Security Service Application Program Interface (GSS-API)

Abstract

   This document describes three abstract Generic Security Service
   Application Program Interface (GSS-API) interfaces used to
   encapsulate/decapsulate context tokens and compare OIDs.  This
   document also specifies C bindings for the abstract interfaces.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6339.

Copyright Notice

   Copyright (c) 2011 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Conventions Used in This Document . . . . . . . . . . . . . . . 2
   3.  GSS_Encapsulate_token Call  . . . . . . . . . . . . . . . . . . 3
     3.1.  gss_encapsulate_token . . . . . . . . . . . . . . . . . . . 3
   4.  GSS_Decapsulate_token Call  . . . . . . . . . . . . . . . . . . 4
     4.1.  gss_decapsulate_token . . . . . . . . . . . . . . . . . . . 5
   5.  GSS_OID_equal Call  . . . . . . . . . . . . . . . . . . . . . . 6
     5.1.  gss_oid_equal . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Test Vector . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     9.2.  Informative Reference . . . . . . . . . . . . . . . . . . . 8

1. Introduction

   The Generic Security Service Application Program Interface (GSS-API)
   [RFC2743] is a framework that provides security services to
   applications using a variety of authentication mechanisms.  There are
   widely implemented C bindings [RFC2744] for the abstract interface.

   For initial context tokens, a mechanism-independent token format may
   be used (see Section 3.1 of [RFC2743]).  Some protocols, e.g., Simple
   Authentication and Security Layer (SASL) GS2 [RFC5801], need the
   ability to add and remove this token header, which contains some
   ASN.1 tags, a length, and the mechanism OID to and from context
   tokens.  This document adds two GSS-API interfaces
   (GSS_Encapsulate_token and GSS_Decapsulate_token) so that GSS-API
   libraries can provide this functionality.

   Being able to compare OIDs is useful, for example, when validating
   that a negotiated mechanism matches the requested one.  This document
   adds one GSS-API interface (GSS_OID_equal) for this purpose.

   Text from this specification can be used as implementation
   documentation, and for this reason, Sections 3, 4, 5, 6, and 8 should
   be considered code components.

2. Conventions Used in This Document

   The document uses terms from, and is structured in a similar way as,
   [RFC2743] and [RFC2744].  The normative reference to [RFC5587] is for
   the C types "gss_const_buffer_t" and "gss_const_OID"; nothing else
   from that document is required to implement this document.

3. GSS_Encapsulate_token Call

   Inputs:

   o  input_token OCTET STRING -- buffer with token data to encapsulate

   o  token_oid OBJECT IDENTIFIER -- object identifier of mechanism for
      the token

   Outputs:

   o  major_status INTEGER

   o  output_token OCTET STRING -- Encapsulated token data; caller must
      release with GSS_Release_buffer()

   Return major_status codes:

   o  GSS_S_COMPLETE indicates that completion was successful and that
      output parameters hold correct information.

   o  GSS_S_FAILURE indicates that encapsulation failed for reasons
      unspecified at the GSS-API level.

   GSS_Encapsulate_token() is used to add the mechanism-independent
   token header to GSS-API context token data.

3.1. gss_encapsulate_token

   OM_uint32 gss_encapsulate_token (
     gss_const_buffer_t input_token,
     gss_const_OID token_oid,
     gss_buffer_t output_token)

   Purpose:

   Add the mechanism-independent token header to GSS-API context token
   data.

   Parameters:

   input_token            buffer, opaque, read
                          Buffer with GSS-API context token data.

   token_oid              Object ID, read
                          Object identifier of token.

   output_token           buffer, opaque, modify
                          Encapsulated token data; caller must release
                          with gss_release_buffer().

   Function values:       GSS status codes

   GSS_S_COMPLETE         Indicates that completion was successful and
                          that output parameters hold correct
                          information.

   GSS_S_FAILURE          Indicates that encapsulation failed for
                          reasons unspecified at the GSS-API level.

4. GSS_Decapsulate_token Call

   Inputs:

   o  input_token OCTET STRING -- buffer with token to decapsulate

   o  token_oid OBJECT IDENTIFIER -- expected object identifier of token

   Outputs:

   o  major_status INTEGER

   o  output_token OCTET STRING -- Decapsulated token data; caller must
      release with GSS_Release_buffer()

   Return major_status codes:

   o  GSS_S_COMPLETE indicates that completion was successful and that
      output parameters hold correct information.

   o  GSS_S_DEFECTIVE_TOKEN means that the token failed consistency
      checks (e.g., OID mismatch or ASN.1 DER length errors).

   o  GSS_S_FAILURE indicates that decapsulation failed for reasons
      unspecified at the GSS-API level.

   GSS_Decapsulate_token() is used to remove the mechanism-independent
   token header from an initial GSS-API context token.

4.1. gss_decapsulate_token

   OM_uint32
   gss_decapsulate_token (
     gss_const_buffer_t input_token,
     gss_const_OID token_oid,
     gss_buffer_t output_token)

   Purpose:

   Remove the mechanism-independent token header from an initial GSS-API
   context token.

   Parameters:

   input_token            buffer, opaque, read
                          Buffer with GSS-API context token.

   token_oid              Object ID, read
                          Expected object identifier of token.

   output_token           buffer, opaque, modify
                          Decapsulated token data; caller must release
                          with gss_release_buffer().

   Function values:       GSS status codes

   GSS_S_COMPLETE         Indicates that completion was successful and
                          that output parameters hold correct
                          information.

   GSS_S_DEFECTIVE_TOKEN  Means that the token failed consistency checks
                          (e.g., OID mismatch or ASN.1 DER length
                          errors).

   GSS_S_FAILURE          Indicates that decapsulation failed for
                          reasons unspecified at the GSS-API level.

5. GSS_OID_equal Call

   Inputs:

   o  first_oid OBJECT IDENTIFIER -- first object identifier to compare

   o  second_oid OBJECT IDENTIFIER -- second object identifier to
      compare

   Return codes:

   o  non-0 when neither OID is GSS_C_NO_OID and the two OIDs are equal.

   o  0 when the two OIDs are not identical or either OID is equal to
      GSS_C_NO_OID.

   GSS_OID_equal() is used to add compare two OIDs for equality.  The
   value GSS_C_NO_OID will not match any OID, including GSS_C_NO_OID
   itself.

5.1. gss_oid_equal

   extern int
   gss_oid_equal (
     gss_const_OID first_oid,
     gss_const_OID second_oid
   )

   Purpose:

   Compare two OIDs for equality.  The value GSS_C_NO_OID will not match
   any OID, including GSS_C_NO_OID itself.

   Parameters:

   first_oid              Object ID, read
                          First object identifier to compare.

   second_oid             Object ID, read
                          Second object identifier to compare.

   Function values:       GSS status codes

   non-0                  Neither OID is GSS_C_NO_OID, and the two OIDs
                          are equal.

0 The two OIDs are not identical, or either OID
is equal to GSS_C_NO_OID.

6. Test Vector

   For the GSS_Encapsulate_token function, if the "input_token" buffer
   is the 3-byte octet sequence "foo" and the "token_oid" OID is
   1.2.840.113554.1.2.2, which encoded corresponds to the 9-byte-long
   octet sequence (using C notation)
   "\x2a\x86\x48\x86\xf7\x12\x01\x02\x02", the output should be the
   16-byte-long octet sequence (again in C notation)
   "\x60\x0e\x06\x09\x2a\x86\x48\x86\xf7\x12\x01\x02\x02\x66\x6f\x6f".
   These values may also be used to test the GSS_Decapsulate_token
   interface.

7. Acknowledgements

   Greg Hudson pointed out the 'const' problem with the C bindings in
   earlier versions of this document, and Luke Howard suggested to
   resolve it by using the [RFC5587] types.  Stephen Farrell suggested
   several editorial improvements and the security consideration
   regarding absent security features of the encapsulation function.
   Chris Lonvick suggested some improvements.

8. Security Considerations

   The security considerations of the base GSS-API specification
   ([RFC2743]) and the base C bindings ([RFC2744]) are inherited.

   Encapsulation of data does not provide any kind of integrity or
   confidentiality.

   Implementations need to treat input as potentially untrustworthy for
   purposes of dereferencing memory objects to avoid security
   vulnerabilities.  In particular, ASN.1 DER length fields are a common
   source of mistakes.

9. References

9.1. Normative References

   [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.

   [RFC5587]  Williams, N., "Extended Generic Security Service Mechanism
              Inquiry APIs", RFC 5587, July 2009.

9.2. Informative Reference

   [RFC5801]  Josefsson, S. and N. Williams, "Using Generic Security
              Service Application Program Interface (GSS-API) Mechanisms
              in Simple Authentication and Security Layer (SASL): The
              GS2 Mechanism Family", RFC 5801, July 2010.

Authors' Addresses

   Simon Josefsson
   SJD AB
   Hagagatan 24
   Stockholm  113 47
   SE

   EMail: simon@josefsson.org
   URI:   http://josefsson.org/

   Love Hornquist Astrand
   Apple, Inc.

   EMail: lha@apple.com