draft-ietf-kitten-gssapi-prf-03.txt   draft-ietf-kitten-gssapi-prf-04.txt 
NETWORK WORKING GROUP N. Williams NETWORK WORKING GROUP N. Williams
Internet-Draft Sun Internet-Draft Sun
Expires: November 13, 2005 May 12, 2005 Expires: December 15, 2005 June 13, 2005
A PRF API extension for the GSS-API A PRF API extension for the GSS-API
draft-ietf-kitten-gssapi-prf-03.txt draft-ietf-kitten-gssapi-prf-04.txt
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This document defines a Pseudo-Random Function (PRF) extension to the This document defines a Pseudo-Random Function (PRF) extension to the
Generic Security Service Application Programming Interface (GSS-API) Generic Security Service Application Programming Interface (GSS-API)
for keying application protocols given an established GSS-API for keying application protocols given an established GSS-API
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Conventions used in this document . . . . . . . . . . . . . . 3 1.1 Conventions used in this document . . . . . . . . . . . . . . 3
2. GSS_Pseudo_random() . . . . . . . . . . . . . . . . . . . . . 3 2. GSS_Pseudo_random() . . . . . . . . . . . . . . . . . . . . . 3
2.1 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Java Bindings . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 Java Bindings . . . . . . . . . . . . . . . . . . . . . . . . 6
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1 Normative References . . . . . . . . . . . . . . . . . . . . . 7 5.1 Normative References . . . . . . . . . . . . . . . . . . . . . 7
5.2 Informative References . . . . . . . . . . . . . . . . . . . . 7 5.2 Informative References . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9
1. Introduction 1. Introduction
A need has arisen for users of the GSS-API to key applications' A need has arisen for users of the GSS-API to key applications'
cryptographic protocols using established GSS-API security contexts. cryptographic protocols using established GSS-API security contexts.
Such applications can use the GSS-API for authentication, but not for Such applications can use the GSS-API for authentication, but not for
transport security (for whatever reasons), and since the GSS-API does transport security (for whatever reasons), and since the GSS-API does
not provide a method for obtaining keying material from established not provide a method for obtaining keying material from established
security contexts such applications cannot make effective use of the security contexts such applications cannot make effective use of the
GSS-API. GSS-API.
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contexts that are not fully established, but applications MUST assume contexts that are not fully established, but applications MUST assume
that authentication, mutual or otherwise, has not completed until the that authentication, mutual or otherwise, has not completed until the
security context is fully established. security context is fully established.
Callers of GSS_Pseudo_random() should avoid accidentally calling it Callers of GSS_Pseudo_random() should avoid accidentally calling it
with the same inputs. One useful technique is to prepend to the with the same inputs. One useful technique is to prepend to the
prf_in input string, by convention, a string indicating the intended prf_in input string, by convention, a string indicating the intended
purpose of the PRF output in such a way that unique contexts in which purpose of the PRF output in such a way that unique contexts in which
the function is called yield unique inputs to it. the function is called yield unique inputs to it.
Pseudo-random functions are, by their nature, capable of producing
only limited amounts of cryptographically secure output. The exact
amount of output that one can safely use, unfortunately, varies from
one PRF to another (which prevents us from recommending specific
numbers). Because of this we recommend that unless you really know
what you are doing (i.e. you are a cryptographer and are qualified to
pass judgement on cryptographic functions in areas of period,
presence of short cycles, etc), you limit the amount of the PRF
output used to the necessary minimum.
5. References 5. References
5.1 Normative References 5.1 Normative References
[GGM1] Goldreich, O., Goldwasser, S., and S. Micali, "How to [GGM1] Goldreich, O., Goldwasser, S., and S. Micali, "How to
Construct Random Functions", October 1986. Construct Random Functions", October 1986.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
 End of changes. 

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