Movatterモバイル変換

Network Working Group                                        N. WilliamsRequest for Comments: 4402                                           SunCategory: Standards Track                                  February 2006A Pseudo-Random Function (PRF) for the Kerberos V Generic SecurityService Application Program Interface (GSS-API) MechanismStatus 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 Contents1. Introduction ....................................................21.1. Conventions Used in This Document ..........................22. Kerberos V GSS Mechanism PRF ....................................23. IANA Considerations .............................................34. Security Considerations .........................................35. Normative References ............................................4Williams                    Standards Track                     [Page 1]

RFC 4402           A PRF for the Kerberos V Mechanism      February 20061.  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 20065.  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.comWilliams                    Standards Track                     [Page 4]

RFC 4402           A PRF for the Kerberos V Mechanism      February 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 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 inBCP 78 andBCP 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 athttp://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]