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NETWORK WORKING GROUP                                        N. Williams
Internet-Draft                                                       Sun
Expires: December 30, 2004                                     July 2004


                  A PRF API extension for the GSS-API
                  draft-ietf-kitten-gssapi-prf-00.txt

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   This Internet-Draft will expire on December 30, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   This document defines a Pseudo-Random Function (PRF) extension to the
   Generic Security Service Applicatoin Programming Interface (GSS-API)
   for keying application protocols given an established GSS-API
   security context.  The primary intended use of this function is to
   key secure session layers that don't or cannot use GSS-API
   per-message MIC (message integrity check) and wrap tokens for session
   protection.






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Table of Contents

   1.  Conventions used in this document  . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  GSS_Pseudo_random()  . . . . . . . . . . . . . . . . . . . . .  5
   3.1 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   5.  Normative  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  7
       Intellectual Property and Copyright Statements . . . . . . . .  8









































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1.  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].














































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2.  Introduction

   A need has arisen for users of the GSS-API to key applications'
   cryptographic protocols using established GSS-API security contexts.
   Such applications can use the GSS-API for authentication, but not for
   transport security (for whatever reasons), and since the GSS-API does
   not provide a method for obtaining keying material from established
   security contexts such applications cannot make effective use of the
   GSS-API.

   To address this need we define a PRF extension to the GSS-API.








































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3.  GSS_Pseudo_random()

   Inputs:

   o  context CONTEXT handle,
   o  prf_in OCTET STRING,
   o  desired_output_len INTEGER

   Outputs:

   o  major_status INTEGER,
   o  minor_status INTEGER,
   o  prf_out OCTET STRING

   Return major_status codes:
   o  GSS_S_COMPLETE indicates no error.
   o  GSS_S_NO_CONTEXT indicates that a null context has been provided
      as input.
   o  GSS_S_CONTEXT_EXPIRED indicates that an expired context has been
      provided as input.
   o  GSS_S_UNAVAILABLE indicates that the mechanism lacks support for
      this functions.
   o  GSS_S_FAILURE indicates failure or lack of support; the minor
      status code may provide additional information.

   This function applies the established context's mechanism's keyed PRF
   function to the input data (prf_in), keyed with key material
   associated with the given security context and outputs the resulting
   octet string (prf_out) of desired_output_len length.

   Mechanisms MAY limit the output of the PRF according, possibly in
   ways related to the types of cryptographic keys available for the PRF
   function, thus the prf_out output of GSS_Pseudo_random() MAY be
   smaller than requested.

   This function, applied to the same inputs by an initiator and
   acceptor using the same established context, produces the *same
   results* for both, the initiator and acceptor.

   Applications SHOULD NOT make more than one GSS PRF call
   per-established security context.

   If an application makes multiple calls, per established security
   context, to the GSS PRF, then it is up to the application to ensure
   synchronization of order of function calls between initiator and
   acceptor; such applications SHOULD provide different input octet
   strings to each such GSS PRF call.  The result of making multiple
   calls to the GSS PRF in different order on the initiator and acceptor



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   sides is undefined.

3.1  C-Bindings

   OM_uint32 gss_pseudo_random(
     OM_uint32                  *minor_status,
     gss_ctx_id_t                       context,
     const gss_buffer_t         prf_in,
     ssize_t            desired_output_len,
     gss_buffer_t               prf_out
   );








































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4.  Security Considerations

   Care should be taken in properly designing a mechanism's PRF
   function.

   GSS mechanisms' PRF functions should use a key derived from contexts'
   session keys and should preserve the forward security properties of
   the mechanisms' key exchanges.

5  Normative

   [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.


Author's Address

   Nicolas Williams
   Sun Microsystems
   5300 Riata Trace Ct
   Austin, TX  78727
   US

   EMail: Nicolas.Williams@sun.com





















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Intellectual Property Statement

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   pertain to the implementation or use of the technology described in
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Copyright Statement

   Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




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