GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools

Problem, Formatting or Query -  Send Feedback

Was this page helpful?-10+1


rfc:rfc4402

Network Working Group N. Williams Request for Comments: 4402 Sun Category: Standards Track February 2006

 A Pseudo-Random Function (PRF) for the Kerberos V Generic Security
     Service Application Program Interface (GSS-API) Mechanism

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

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

Table of Contents

 1. Introduction ....................................................2
    1.1. Conventions Used in This Document ..........................2
 2. Kerberos V GSS Mechanism PRF ....................................2
 3. IANA Considerations .............................................3
 4. Security Considerations .........................................3
 5. Normative References ............................................4

Williams Standards Track [Page 1] RFC 4402 A PRF for the Kerberos V Mechanism February 2006

1. Introduction

 This document specifies the Kerberos V GSS-API mechanism's [RFC4121]
 pseudo-random function corresponding to [RFC4401].  The function is a
 "PRF+" style construction.  For more information see [RFC4401],
 [RFC2743], [RFC2744], and [RFC4121].

1.1. 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].

2. Kerberos V GSS Mechanism PRF

 The GSS-API PRF [RFC4401] function for the Kerberos V mechanism
 [RFC4121] shall be the output of a PRF+ function based on the
 encryption type's PRF function keyed with the negotiated session key
 of the security context corresponding to the 'prf_key' input
 parameter of GSS_Pseudo_random().
 This PRF+ MUST be keyed with the key indicated by the 'prf_key' input
 parameter as follows:
 o  GSS_C_PRF_KEY_FULL -- use the sub-session key asserted by the
    acceptor, if any, or the sub-session asserted by the initiator, if
    any, or the Ticket's session key
 o  GSS_C_PRF_KEY_PARTIAL -- use the sub-session key asserted by the
    initiator, if any, or the Ticket's session key
 The PRF+ function is a simple counter-based extension of the Kerberos
 V pseudo-random function [RFC3961] for the encryption type of the
 security context's keys:
       PRF+(K, L, S) = truncate(L, T1 || T2 || .. || Tn)
       Tn = pseudo-random(K, n || S)
 where '||' is the concatenation operator, 'n' is encoded as a network
 byte order 32-bit unsigned binary number, truncate(L, S) truncates
 the input octet string S to length L, and pseudo-random() is the
 Kerberos V pseudo-random function [RFC3961].
 The maximum output size of the Kerberos V mechanism's GSS-API PRF
 then is, necessarily, 2^32 times the output size of the pseudo-
 random() function for the encryption type of the given key.

Williams Standards Track [Page 2] RFC 4402 A PRF for the Kerberos V Mechanism February 2006

 When the input size is longer than 2^14 octets as per [RFC4401] and
 exceeds an implementation's resources, then the mechanism MUST return
 GSS_S_FAILURE and GSS_KRB5_S_KG_INPUT_TOO_LONG as the minor status
 code.

3. IANA Considerations

 This document has no IANA considerations currently.  If and when a
 relevant IANA registry of GSS-API symbols and constants is created,
 then the GSS_KRB5_S_KG_INPUT_TOO_LONG minor status code should be
 added to such a registry.

4. Security Considerations

 Kerberos V encryption types' PRF functions use a key derived from
 contexts' session keys and should preserve the forward security
 properties of the mechanisms' key exchanges.
 Legacy Kerberos V encryption types may be weak, particularly the
 single-DES encryption types.
 See also [RFC4401] for generic security considerations of
 GSS_Pseudo_random().
 See also [RFC3961] for generic security considerations of the
 Kerberos V cryptographic framework.
 Use of Ticket session keys, rather than sub-session keys, when
 initiators and acceptors fail to assert sub-session keys, is
 dangerous as ticket reuse can lead to key reuse; therefore,
 initiators should assert sub-session keys always, and acceptors
 should assert sub-session keys at least when initiators fail to do
 so.
 The computational cost of computing this PRF+ may vary depending on
 the Kerberos V encryption types being used, but generally the
 computation of this PRF+ gets more expensive as the input and output
 octet string lengths grow (note that the use of a counter in the PRF+
 construction allows for parallelization).  This means that if an
 application can be tricked into providing very large input octet
 strings and requesting very long output octet strings, then that may
 constitute a denial of service attack on the application; therefore,
 applications SHOULD place appropriate limits on the size of any input
 octet strings received from their peers without integrity protection.

Williams Standards Track [Page 3] RFC 4402 A PRF for the Kerberos V Mechanism February 2006

5. Normative References

 [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.
 [RFC3961]  Raeburn, K., "Encryption and Checksum Specifications for
            Kerberos 5", RFC 3961, February 2005.
 [RFC4121]  Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
            Version 5 Generic Security Service Application Program
            Interface (GSS-API) Mechanism: Version 2", RFC 4121,
            July 2005.
 [RFC4401]  Williams, N., "A Pseudo-Random Function (PRF) API
            Extension for the Generic Security Service Application
            Program Interface (GSS-API)", RFC 4401, February 2006.

Author's Address

 Nicolas Williams
 Sun Microsystems
 5300 Riata Trace Ct
 Austin, TX  78727
 US
 EMail: Nicolas.Williams@sun.com

Williams Standards Track [Page 4] RFC 4402 A PRF for the Kerberos V Mechanism February 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 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.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Williams Standards Track [Page 5]

/data/webs/external/dokuwiki/data/pages/rfc/rfc4402.txt · Last modified: 2006/02/08 00:46 (external edit)