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



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


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Copyright Notice


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


Abstract


   This document defines a Pseudo-Random Function (PRF) extension to the
   GSS-API for keying application protocols given an established GSS-API
   security context.









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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 . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   5.  Normative  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  6
       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.


   At this point EAP may be the primary consumer of this extension.







































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3.  GSS_Pseudo_random()


   Inputs:


   o  context CONTEXT handle,
   o  prf_in OCTET STRING


   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_FAILURE indicates failure or lack of support; the minor
      status code may provide additional information.


   This function applies the 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 result (prf_out).


3.1  C-Bindings


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


















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4.  Security Considerations


   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.


   Care should be taken in properly designing a mechanism's PRF
   function.  Cryptographic hash functions which do not provide strong
   collision resistance should not be used, except through HMAC.


   GSS mechanisms' PRF functions may output fewer octets than the
   application may need, therefore GSS-API applications that use
   GSS_Pseudo_random() may require a "PRF+" construction based on
   GSS_Pseudo_random().


   [Question:  Should GSS_Pseudo_random() have an input roughly
   corresponding to the "key usage" used for key derivation in Kerberos
   V?]


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.



Authors' Addresses


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


   EMail: Nicolas.Williams@sun.com



   Sam Hartman
   Massachussets Institute of Technology
   ...
   ..., MA  ...
   US





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   EMail: hartmans@mit.edu



















































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Intellectual Property Statement


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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
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Acknowledgment


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   Internet Society.




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