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NETWORK WORKING GROUP N. Williams
Internet-Draft Sun
Expires: December 30, 2004 July 2004
A PRF API extension for the GSS-API
draft-ietf-kitten-gssapi-prf-01.txt
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on December 30, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines a Pseudo-Random Function (PRF) extension to the
Generic Security Service Applicatoin Programming Interface (GSS-API)
for keying application protocols given an established GSS-API
security context. The primary intended use of this function is to
key secure session layers that don't or cannot use GSS-API
per-message MIC (message integrity check) and wrap tokens for session
protection.
Williams Expires December 30, 2004 [Page 1]
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Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. GSS_Pseudo_random() . . . . . . . . . . . . . . . . . . . . . 5
3.1 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1 Normative References . . . . . . . . . . . . . . . . . . . . . 8
5.2 Informative References . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . 9
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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].
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2. Introduction
A need has arisen for users of the GSS-API to key applications'
cryptographic protocols using established GSS-API security contexts.
Such applications can use the GSS-API for authentication, but not for
transport security (for whatever reasons), and since the GSS-API does
not provide a method for obtaining keying material from established
security contexts such applications cannot make effective use of the
GSS-API.
To address this need we define a pseudo-random function (PRF)
extension to the GSS-API.
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3. GSS_Pseudo_random()
Inputs:
o context CONTEXT handle,
o prf_in OCTET STRING,
o desired_output_len INTEGER
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o prf_out OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_NO_CONTEXT indicates that a null context has been provided
as input.
o GSS_S_CONTEXT_EXPIRED indicates that an expired context has been
provided as input.
o GSS_S_UNAVAILABLE indicates that the mechanism lacks support for
this function.
o GSS_S_FAILURE indicates failure or lack of support; the minor
status code may provide additional information.
This function applies the established context's mechanism's keyed PRF
function to the input data (prf_in), keyed with key material
associated with the given security context and outputs the resulting
octet string (prf_out) of desired_output_len length.
The output string of this function MUST be a pseudo-random function
[GGM1][GGM2] of the input keyed with key material from the
established security context -- the chances of getting the same
output given different input parameters should be exponentially
small.
This function, applied to the same inputs by an initiator and
acceptor using the same established context, MUST produce the *same
results* for both, the initiator and acceptor, even if called
multiple times for the same context.
Mechanisms MAY limit the output of the PRF according, possibly in
ways related to the types of cryptographic keys available for the PRF
function, thus the prf_out output of GSS_Pseudo_random() MAY be
smaller than requested.
3.1 C-Bindings
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OM_uint32 gss_pseudo_random(
OM_uint32 *minor_status,
gss_ctx_id_t context,
const gss_buffer_t prf_in,
ssize_t desired_output_len,
gss_buffer_t prf_out
);
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4. Security Considerations
Care should be taken in properly designing a mechanism's PRF
function.
GSS mechanisms' PRF functions should use a key derived from contexts'
session keys and should preserve the forward security properties of
the mechanisms' key exchanges.
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5. References
5.1 Normative References
[GGM1] Goldreich, O., Goldwasser, S. and S. Micali, "How to
Construct Random Functions", October 1986.
[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.
5.2 Informative References
[GGM2] Goldreich, O., Goldwasser, S. and S. Micali, "On the
Cryptographic Applications of Random Functions", 1985.
[RFC1750] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
Author's Address
Nicolas Williams
Sun Microsystems
5300 Riata Trace Ct
Austin, TX 78727
US
EMail: Nicolas.Williams@sun.com
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Intellectual Property Statement
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.
Disclaimer of Validity
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 (2004). 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
Internet Society.
Williams Expires December 30, 2004 [Page 9]

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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-01.txt
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on December 30, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines the Pseudo-Random Function (PRF) for the
Kerberos V mechanism for the Generic Security Service Application
Programming 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.
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Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . . 3
2. Kerberos V GSS Mechanism PRF . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
4. Normative References . . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
Intellectual Property and Copyright Statements . . . . . . . . . 7
Williams Expires December 30, 2004 [Page 2]
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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].
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2. Kerberos V GSS Mechanism PRF
The GSS-API PRF [GSS-PRF] function for the Kerberos V mechanism [CFX]
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 and key usage X (TBD).
The security context MUST be fully established, else the mechanism
MUST fail with GSS_S_FAILURE as the major status code and
GSS_KRB5_S_KG_CTX_INCOMPLETE as the minor status code.
This PRF+ MUST be keyed with a key derived, with key usage (TBD),
from the session used by the initiator and acceptor, after the
security context is fully established, to derive keys for per-message
tokens. For the current Kerberos V mechanism [CFX] this means that
the PRF+ MUST be keyed with the acceptor-asserted subkey, if it did
assert such a key, or the initiator's sub-session key otherwise.
The PRF+ function is a simple counter-based extension of the Kerberos
V pseudo-random function [KRB5-CRYPTO] for the enctype of the
security context's keys:
PRF+(K, L, S) = truncate(L, T1 || T2 || .. || Tn)
Tn = pseudo-random-function(K, n || S)
where '||' is the concatenation operator, 'n' is encoded as a
network byte order 32-bit unsigned binary number, and where
truncate(L, S) truncates the input octet string S to length L.
The maximum output size of the Kerberos V mechanism's GSS-API PRF
then is, necessarily, 2^32 octets.
Implementations MUST support output size of up to 2^14 octets at
least.
If the implementation cannot produce the desired output then it MUST
output what it can.
The minimum input octet string length that implementations MUST
support is also 2^14 octets. If the input octet string is longer
than the maximum that an implementation can process then the
implementation MUST fail with GSS_S_FAILURE as the major status code
and GSS_KRB5_S_KG_INPUT_TOO_LONG as the minor status code.
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3. 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.
Legacy Kerberos V enctypes may be weak, particularly the single-DES
enctypes.
See also [GSS-PRF] for generic security considerations of
GSS_Pseudo_random().
The computational cost of computing this PRF+ may vary depending on
the Kerberos V enctypes 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 constitue 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.
4 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".
[KRB5-CRYPTO]
Raeburn, K., "Encryption and Checksum Specifications for
Kerberos 5".
[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
Williams Expires December 30, 2004 [Page 5]
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5300 Riata Trace Ct
Austin, TX 78727
US
EMail: Nicolas.Williams@sun.com
Williams Expires December 30, 2004 [Page 6]
Internet-Draft A PRF for the Kerberos V Mech July 2004
Intellectual Property Statement
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.
Disclaimer of Validity
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 (2004). 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
Internet Society.
Williams Expires December 30, 2004 [Page 7]