Internet Engineering Task Force (IETF) S. Josefsson

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.

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RFC 6339 GSS-API Capsulate and OID Comparison August 2011

Table of Contents

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.

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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.

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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.

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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.

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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.

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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.

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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: [email protected]
URI: http://josefsson.org/

Love Hornquist Astrand
Apple, Inc.

EMail: [email protected]

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