draft-ietf-kitten-krb5-gssapi-prf-04.txt   rfc4402.txt 
NETWORK WORKING GROUP N. Williams Network Working Group N. Williams
Internet-Draft Sun Request for Comments: 4402 Sun
Expires: December 15, 2005 June 13, 2005 Category: Standards Track February 2006
A PRF for the Kerberos V GSS-API Mechanism
draft-ietf-kitten-krb5-gssapi-prf-04.txt
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http://www.ietf.org/ietf/1id-abstracts.txt. Service Application Program Interface (GSS-API) Mechanism
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document defines the Pseudo-Random Function (PRF) for the This document defines the Pseudo-Random Function (PRF) for the
Kerberos V mechanism for the Generic Security Service Application Kerberos V mechanism for the Generic Security Service Application
Programming Interface (GSS-API), based on the PRF defined for the Program Interface (GSS-API), based on the PRF defined for the
Kerberos V cryptographic framework, for keying application protocols Kerberos V cryptographic framework, for keying application protocols
given an established Kerberos V GSS-API security context. given an established Kerberos V GSS-API security context.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................2
1.1 Conventions used in this document . . . . . . . . . . . . . . 3 1.1. Conventions Used in This Document ..........................2
2. Kerberos V GSS Mechanism PRF . . . . . . . . . . . . . . . . . 3 2. Kerberos V GSS Mechanism PRF ....................................2
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 3. IANA Considerations .............................................3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations .........................................3
5. Normative References . . . . . . . . . . . . . . . . . . . . . 4 5. Normative References ............................................4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 5
Intellectual Property and Copyright Statements . . . . . . . . 6
1. Introduction 1. Introduction
This document specifies the Kerberos V GSS-API mechanism's pseudo- This document specifies the Kerberos V GSS-API mechanism's [RFC4121]
random function corresponding to [GSS-PRF]. The function is a "PRF+" pseudo-random function corresponding to [RFC4401]. The function is a
style construction. "PRF+" style construction. For more information see [RFC4401],
[RFC2743], [RFC2744], and [RFC4121].
1.1 Conventions used in this document 1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Kerberos V GSS Mechanism PRF 2. Kerberos V GSS Mechanism PRF
The GSS-API PRF [GSS-PRF] function for the Kerberos V mechanism The GSS-API PRF [RFC4401] function for the Kerberos V mechanism
[RFC1964] shall be the output of a PRF+ function based on the [RFC4121] shall be the output of a PRF+ function based on the
encryption type's PRF function keyed with the negotiated session key encryption type's PRF function keyed with the negotiated session key
of the security context corresponding to the 'prf_key' input of the security context corresponding to the 'prf_key' input
parameter of GSS_Pseudo_random(). parameter of GSS_Pseudo_random().
This PRF+ MUST be keyed with the key indicated by the 'prf_key' input This PRF+ MUST be keyed with the key indicated by the 'prf_key' input
parameter as follows: parameter as follows:
o GSS_C_PRF_KEY_FULL -- use the sub-session key asserted by the 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 acceptor, if any, or the sub-session asserted by the initiator, if
any, or the Ticket's session key any, or the Ticket's session key
skipping to change at page 3, line 52 skipping to change at page 3, line 5
where '||' is the concatenation operator, 'n' is encoded as a network where '||' is the concatenation operator, 'n' is encoded as a network
byte order 32-bit unsigned binary number, truncate(L, S) truncates byte order 32-bit unsigned binary number, truncate(L, S) truncates
the input octet string S to length L, and pseudo-random() is the the input octet string S to length L, and pseudo-random() is the
Kerberos V pseudo-random function [RFC3961]. Kerberos V pseudo-random function [RFC3961].
The maximum output size of the Kerberos V mechanism's GSS-API PRF 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- then is, necessarily, 2^32 times the output size of the pseudo-
random() function for the encryption type of the given key. random() function for the encryption type of the given key.
When the input size is longer than 2^14 octets as per [GSS-PRF] and When the input size is longer than 2^14 octets as per [RFC4401] and
exceeds an implementation's resources then the mechanism MUST return 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 GSS_S_FAILURE and GSS_KRB5_S_KG_INPUT_TOO_LONG as the minor status
code. code.
3. IANA Considerations 3. IANA Considerations
This document has no IANA considerations currently. If and when a This document has no IANA considerations currently. If and when a
relevant IANA registry of GSS-API symbols and constants is created 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 then the GSS_KRB5_S_KG_INPUT_TOO_LONG minor status code should be
added to such a registry. added to such a registry.
4. Security Considerations 4. Security Considerations
Kerberos V encryption types' PRF functions use a key derived from Kerberos V encryption types' PRF functions use a key derived from
contexts' session keys and should preserve the forward security contexts' session keys and should preserve the forward security
properties of the mechanisms' key exchanges. properties of the mechanisms' key exchanges.
Legacy Kerberos V encryption types may be weak, particularly the Legacy Kerberos V encryption types may be weak, particularly the
single-DES encryption types. single-DES encryption types.
See also [GSS-PRF] for generic security considerations of See also [RFC4401] for generic security considerations of
GSS_Pseudo_random(). GSS_Pseudo_random().
See also [RFC3961] for generic security considerations of the See also [RFC3961] for generic security considerations of the
Kerberos V cryptographic framework. Kerberos V cryptographic framework.
Use of Ticket session keys, rather than sub-session keys, when Use of Ticket session keys, rather than sub-session keys, when
initiators and acceptors fail to assert sub-session keys, is initiators and acceptors fail to assert sub-session keys, is
dangerous as ticket reuse can lead to key reuse, therefore initiators dangerous as ticket reuse can lead to key reuse; therefore,
should assert sub-session keys always, and acceptors should assert initiators should assert sub-session keys always, and acceptors
sub-session keys at least when initiators fail to do so.. 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 computational cost of computing this PRF+ may vary depending on
the Kerberos V encryption types being used, but generally the the Kerberos V encryption types being used, but generally the
computation of this PRF+ gets more expensive as the input and output 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+ octet string lengths grow (note that the use of a counter in the PRF+
construction allows for parallelization). This means that if an construction allows for parallelization). This means that if an
application can be tricked into providing very large input octet application can be tricked into providing very large input octet
strings and requesting very long output octet strings then that may strings and requesting very long output octet strings, then that may
constitute a denial of service attack on the application; therefore constitute a denial of service attack on the application; therefore,
applications SHOULD place appropriate limits on the size of any input applications SHOULD place appropriate limits on the size of any input
octet strings received from their peers without integrity protection. octet strings received from their peers without integrity protection.
5. Normative References 5. Normative References
[CFX] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
Version 5 GSS-API Mechanism: Version 2".
[GSS-PRF] Williams, N., "A PRF API extension for the GSS-API".
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
[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.
[RFC2743] Linn, J., "Generic Security Service Application Program [RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000. Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC2744] Wray, J., "Generic Security Service API Version 2 : [RFC2744] Wray, J., "Generic Security Service API Version 2 :
C-bindings", RFC 2744, January 2000. C-bindings", RFC 2744, January 2000.
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for [RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
Kerberos 5", RFC 3961, February 2005. 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 Author's Address
Nicolas Williams Nicolas Williams
Sun Microsystems Sun Microsystems
5300 Riata Trace Ct 5300 Riata Trace Ct
Austin, TX 78727 Austin, TX 78727
US US
Email: Nicolas.Williams@sun.com EMail: Nicolas.Williams@sun.com
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
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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.
Copyright Statement
Copyright (C) The Internet Society (2005). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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