draft-ietf-kitten-gssapi-prf-02.txt   draft-ietf-kitten-gssapi-prf-03.txt 
NETWORK WORKING GROUP N. Williams NETWORK WORKING GROUP N. Williams
Internet-Draft Sun Internet-Draft Sun
Expires: December 30, 2004 July 2004 Expires: November 13, 2005 May 12, 2005
A PRF API extension for the GSS-API A PRF API extension for the GSS-API
draft-ietf-kitten-gssapi-prf-02.txt draft-ietf-kitten-gssapi-prf-03.txt
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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 Applicatoin 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
security context. The primary intended use of this function is to security context. The primary intended use of this function is to
key secure session layers that don't or cannot use GSS-API key secure session layers that don't or cannot use GSS-API per-
per-message MIC (message integrity check) and wrap tokens for session message MIC (message integrity check) and wrap tokens for session
protection. protection.
Table of Contents Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Conventions used in this document . . . . . . . . . . . . . . 3
3. GSS_Pseudo_random() . . . . . . . . . . . . . . . . . . . . . 5 2. GSS_Pseudo_random() . . . . . . . . . . . . . . . . . . . . . 3
3.1 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 2.2 Java Bindings . . . . . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1 Normative References . . . . . . . . . . . . . . . . . . . . . 8 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5.2 Informative References . . . . . . . . . . . . . . . . . . . . 8 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8 5.1 Normative References . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 9 5.2 Informative References . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7
1. Conventions used in this document Intellectual Property and Copyright Statements . . . . . . . . 8
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. 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.
To address this need we define a pseudo-random function (PRF) To address this need we define a pseudo-random function (PRF)
extension to the GSS-API. extension to the GSS-API.
3. GSS_Pseudo_random() 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. GSS_Pseudo_random()
Inputs: Inputs:
o context CONTEXT handle, o context CONTEXT handle,
o prf_key INTEGER,
o prf_in OCTET STRING, o prf_in OCTET STRING,
o desired_output_len INTEGER o desired_output_len INTEGER
Outputs: Outputs:
o major_status INTEGER, o major_status INTEGER,
o minor_status INTEGER, o minor_status INTEGER,
o prf_out OCTET STRING o prf_out OCTET STRING
Return major_status codes: Return major_status codes:
o GSS_S_COMPLETE indicates no error. o GSS_S_COMPLETE indicates no error.
o GSS_S_NO_CONTEXT indicates that a null context has been provided o GSS_S_NO_CONTEXT indicates that a null context has been provided
as input. as input.
o GSS_S_CONTEXT_EXPIRED indicates that an expired context has been o GSS_S_CONTEXT_EXPIRED indicates that an expired context has been
provided as input. provided as input.
o GSS_S_UNAVAILABLE indicates that the mechanism lacks support for o GSS_S_UNAVAILABLE indicates that the mechanism lacks support for
this function or, if the security context is not fully this function or, if the security context is not fully
established, that the context is not ready to compute the PRF. established, that the context is not ready to compute the PRF with
o GSS_S_FAILURE indicates failure or lack of support; the minor the given prf_key, or that the given prf_key is not available.
status code may provide additional information.
This function applies the established context's mechanism's keyed PRF o GSS_S_FAILURE indicates general failure, possibly due to the given
function to the input data (prf_in), keyed with key material input data being too large or of zero length, or due to the
associated with the given security context and outputs the resulting desired_output_len being zero; the minor status code may provide
octet string (prf_out) of desired_output_len length. additional information.
The output string of this function MUST be a pseudo-random function This function applies the established context's mechanism's keyed
[GGM1][GGM2] of the input keyed with key material from the pseudo-random function (PRF) to the input data ('prf_in'), keyed with
established security context -- the chances of getting the same key material associated with the given security context and
output given different input parameters should be exponentially identified by 'prf_key', and outputs the resulting octet string
small. ('prf_out') of desired_output_len length.
This function, applied to the same inputs by an initiator and The minimum input data length is one octet.
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 Mechanisms MUST be able to consume all the provided prf_in input data
ways related to the types of cryptographic keys available for the PRF that is 2^14 or fewer octets.
function, thus the prf_out output of GSS_Pseudo_random() MAY be
smaller than requested.
Mechanisms may be able to compute PRFs with security contexts that If a mechanism cannot consume as much input data as provided by the
are not fully established, therefore applications MAY call caller, then GSS_Pseudo_random() MUST return GSS_S_FAILURE.
GSS_Pseudo_random() with such security contexts. Such mechanisms
MUST return GSS_S_UNAVAILABLE when called on to compute a PRF given a
security context that is not fully established and also not ready for
PRF computation. Mechanisms that allow for PRF computation prior to
full security context establishment MUST use the same PRF and key
material, for any given security context, both, before and after full
context establishment, and the PRF and key material negotiation MUT
be authenticated when the security context is fully established.
3.1 C-Bindings The minimum desired_output_len is one.
Mechanisms MUST be able to output at least up to 2^14 octets.
If the implementation cannot produce the desired output due to lack
of resources then it MUST output what it can and still return
GSS_S_COMPLETE.
The prf_key can take on the following values: GSS_C_PRF_KEY_FULL,
GSS_C_PRF_KEY_PARTIAL or mechanism-specific values, if any. This
parameter is intended to distinguish between the best cryptographic
keys that may be available only after full security context
establishment and keys that may be available prior to full security
context establishment. For some mechanisms, or contexts, those two
prf_key values MAY refer to the same cryptographic keys; for
mechanisms like the Kerberos V GSS-API mechanism [RFC1964] where one
peer may assert a key that may be considered better than the others
they MAY be different keys.
GSS_C_PRF_KEY_PARTIAL corresponds to a key that would be have been
used while the security context was partially established, even if it
is fully established when GSS_Pseudo_random() is actually called.
Mechanism-specific prf_key values are intended to refer to any other
keys that may be available.
The GSS_C_PRF_KEY_FULL value corresponds to the best key available
for fully-established security contexts.
GSS_Pseudo_random() has the following properties:
o its output string MUST be a pseudo-random function [GGM1] [GGM2]
of the input keyed with key material from the given security
context -- the chances of getting the same output given different
input parameters should be exponentially small.
o when successfully applied to the same inputs by an initiator and
acceptor using the same security context, it MUST produce the
_same results_ for both, the initiator and acceptor, even if
called multiple times (as long as the security context is not
expired).
o upon full establishment of a security context all cryptographic
keys and/or negotiations used for computing the PRF with any
prf_key MUST be authenticated (mutually, if mutual authentication
is in effect for the given security context).
o the outputs of the mechanism's GSS_Pseudo_random() (for different
inputs) and its per-message tokens for the given security context
MUST be "cryptographically separate;" in other words, it must not
be feasible to recover key material for one mechanism operation or
transform its tokens and PRF outputs from one to the other given
only said tokens and PRF outputs. [This is a fancy way of saying
that key derivation and strong cryptographic operations and
constructions must be used.]
o as implied by the above requirement, it MUST NOT be possible to
access any raw keys of a security context through
GSS_Pseudo_random(), no matter what inputs are given.
Mechanisms MAY limit the output of the PRF, 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.
2.1 C-Bindings
#define GSS_C_PRF_KEY_FULL 0
#define GSS_C_PRF_KEY_PARTIAL 1
OM_uint32 gss_pseudo_random( OM_uint32 gss_pseudo_random(
OM_uint32 *minor_status, OM_uint32 *minor_status,
gss_ctx_id_t context, gss_ctx_id_t context,
int prf_key,
const gss_buffer_t prf_in, const gss_buffer_t prf_in,
ssize_t desired_output_len, ssize_t desired_output_len,
gss_buffer_t prf_out gss_buffer_t prf_out
); );
Additional major status codes for the C-bindings:
o GSS_S_CALL_INACCESSIBLE_READ
o GSS_S_CALL_INACCESSIBLE_WRITE
See [RFC2744].
2.2 Java Bindings
For Java GSS_Pseudo_random() maps to a GSSContext method, 'prf':
public static final int GSS_C_PRF_KEY_FULL = 0
public static final int GSS_C_PRF_KEY_PARTIAL = 1
public byte[] prf(int prf_key, byte inBuf[], int outlen)
throws GSSException
See [RFC2853].
3. IANA Considerations
This document has no IANA considerations currently. If and when a
relevant IANA registry of GSS-API symbols is created then the generic
and language-specific function names, constant names and constant
values described above should be added to such a registry.
4. Security Considerations 4. Security Considerations
Care should be taken in properly designing a mechanism's PRF Care should be taken in properly designing a mechanism's PRF
function. function.
GSS mechanisms' PRF functions should use a key derived from contexts' GSS mechanisms' PRF functions should use a key derived from contexts'
session keys and should preserve the forward security properties of authenticated session keys and should preserve the forward security
the mechanisms' key exchanges. properties of the mechanisms' key exchanges.
Some mechanisms may support the GSS PRF function with security Some mechanisms may support the GSS PRF function with security
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
with the same inputs. One useful technique is to prepend to the
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
the function is called yield unique inputs to it.
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.
[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.
[RFC2853] Kabat, J. and M. Upadhyay, "Generic Security Service API
Version 2 : Java Bindings", RFC 2853, June 2000.
5.2 Informative References 5.2 Informative References
[GGM2] Goldreich, O., Goldwasser, S. and S. Micali, "On the [GGM2] Goldreich, O., Goldwasser, S., and S. Micali, "On the
Cryptographic Applications of Random Functions", 1985. Cryptographic Applications of Random Functions", 1985.
[RFC1750] Eastlake, D., Crocker, S. and J. Schiller, "Randomness [RFC1750] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994. Recommendations for Security", RFC 1750, December 1994.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
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
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WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
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Internet Society. Internet Society.
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