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


               A PRF for the Kerberos V GSS-API Mechanism
                draft-ietf-kitten-krb5-gssapi-prf-00.txt

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

Abstract

   This document defines the Pseudo-Random Function (PRF) for the
   Kerberos V GSS-API mechanism, based on the PRF defined for the
   Kerberos V cryptographic framework, for keying application protocols
   given an established Kerberos V GSS-API security context.









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Table of Contents

   1. Conventions used in this document  . . . . . . . . . . . . . . . 3
   2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3. Security Considerations  . . . . . . . . . . . . . . . . . . . . 5
   4. Normative  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
      Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
      Intellectual Property and Copyright Statements . . . . . . . . . 6











































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.  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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.  Introduction

   The GSS-API PRF [GSS-PRF] function for the Kerberos V mechanism shall
   be the output of a PRF+ function based on the enctype's PRF function
   keyed with the negotiated session key of the security context (e.g.,
   the acceptor's subkey) and key usage X (TBD).

   The PRF+ function is a simple counter-based extension of the
   enctype's prf using an 16-bit network byte order unsigned binary
   counter: PRF+(k, input) = random-to-key( k-truncate( prf(k, 0 ||
   input) || prf(k, 1 || input), ..  prf(k, n || input))).  The maximum
   output length for this PRF+ then is 65536 times the output length of
   the Kerberos V cryptographic framework PRF for the enctype of the
   input key.

   If the desired_output_len input parameter exceeds the maximum output
   of this function then the maximum will be output instead.


































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.  Security Considerations

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

   See also [GSS-PRF] for generic security considerations of
   GSS_Pseudo_random().

  Normative

   [GSS-PRF]  Williams, N., "A PRF API extension for the GSS-API".

   [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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Acknowledgment

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