4 NETWORK WORKING GROUP N. Williams
6 Expires: December 15, 2005 June 13, 2005
9 A PRF API extension for the GSS-API
10 draft-ietf-kitten-gssapi-prf-04.txt
14 By submitting this Internet-Draft, each author represents that any
15 applicable patent or other IPR claims of which he or she is aware
16 have been or will be disclosed, and any of which he or she becomes
17 aware will be disclosed, in accordance with Section 6 of BCP 79.
19 Internet-Drafts are working documents of the Internet Engineering
20 Task Force (IETF), its areas, and its working groups. Note that
21 other groups may also distribute working documents as Internet-
24 Internet-Drafts are draft documents valid for a maximum of six months
25 and may be updated, replaced, or obsoleted by other documents at any
26 time. It is inappropriate to use Internet-Drafts as reference
27 material or to cite them other than as "work in progress."
29 The list of current Internet-Drafts can be accessed at
30 http://www.ietf.org/ietf/1id-abstracts.txt.
32 The list of Internet-Draft Shadow Directories can be accessed at
33 http://www.ietf.org/shadow.html.
35 This Internet-Draft will expire on December 15, 2005.
39 Copyright (C) The Internet Society (2005).
43 This document defines a Pseudo-Random Function (PRF) extension to the
44 Generic Security Service Application Programming Interface (GSS-API)
45 for keying application protocols given an established GSS-API
46 security context. The primary intended use of this function is to
47 key secure session layers that don't or cannot use GSS-API per-
48 message MIC (message integrity check) and wrap tokens for session
55 Williams Expires December 15, 2005 [Page 1]
57 Internet-Draft A PRF Extension for the GSS-API June 2005
62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
63 1.1 Conventions used in this document . . . . . . . . . . . . . . 3
64 2. GSS_Pseudo_random() . . . . . . . . . . . . . . . . . . . . . 3
65 2.1 C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 5
66 2.2 Java Bindings . . . . . . . . . . . . . . . . . . . . . . . . 6
67 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
68 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
69 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
70 5.1 Normative References . . . . . . . . . . . . . . . . . . . . . 7
71 5.2 Informative References . . . . . . . . . . . . . . . . . . . . 7
72 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8
73 Intellectual Property and Copyright Statements . . . . . . . . 9
111 Williams Expires December 15, 2005 [Page 2]
113 Internet-Draft A PRF Extension for the GSS-API June 2005
118 A need has arisen for users of the GSS-API to key applications'
119 cryptographic protocols using established GSS-API security contexts.
120 Such applications can use the GSS-API for authentication, but not for
121 transport security (for whatever reasons), and since the GSS-API does
122 not provide a method for obtaining keying material from established
123 security contexts such applications cannot make effective use of the
126 To address this need we define a pseudo-random function (PRF)
127 extension to the GSS-API.
129 1.1 Conventions used in this document
131 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
132 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
133 document are to be interpreted as described in [RFC2119].
135 2. GSS_Pseudo_random()
140 o context CONTEXT handle,
144 o prf_in OCTET STRING,
146 o desired_output_len INTEGER
151 o major_status INTEGER,
153 o minor_status INTEGER,
155 o prf_out OCTET STRING
157 Return major_status codes:
159 o GSS_S_COMPLETE indicates no error.
161 o GSS_S_NO_CONTEXT indicates that a null context has been provided
167 Williams Expires December 15, 2005 [Page 3]
169 Internet-Draft A PRF Extension for the GSS-API June 2005
172 o GSS_S_CONTEXT_EXPIRED indicates that an expired context has been
175 o GSS_S_UNAVAILABLE indicates that the mechanism lacks support for
176 this function or, if the security context is not fully
177 established, that the context is not ready to compute the PRF with
178 the given prf_key, or that the given prf_key is not available.
180 o GSS_S_FAILURE indicates general failure, possibly due to the given
181 input data being too large or of zero length, or due to the
182 desired_output_len being zero; the minor status code may provide
183 additional information.
185 This function applies the established context's mechanism's keyed
186 pseudo-random function (PRF) to the input data ('prf_in'), keyed with
187 key material associated with the given security context and
188 identified by 'prf_key', and outputs the resulting octet string
189 ('prf_out') of desired_output_len length.
191 The minimum input data length is one octet.
193 Mechanisms MUST be able to consume all the provided prf_in input data
194 that is 2^14 or fewer octets.
196 If a mechanism cannot consume as much input data as provided by the
197 caller, then GSS_Pseudo_random() MUST return GSS_S_FAILURE.
199 The minimum desired_output_len is one.
201 Mechanisms MUST be able to output at least up to 2^14 octets.
203 If the implementation cannot produce the desired output due to lack
204 of resources then it MUST output what it can and still return
207 The prf_key can take on the following values: GSS_C_PRF_KEY_FULL,
208 GSS_C_PRF_KEY_PARTIAL or mechanism-specific values, if any. This
209 parameter is intended to distinguish between the best cryptographic
210 keys that may be available only after full security context
211 establishment and keys that may be available prior to full security
212 context establishment. For some mechanisms, or contexts, those two
213 prf_key values MAY refer to the same cryptographic keys; for
214 mechanisms like the Kerberos V GSS-API mechanism [RFC1964] where one
215 peer may assert a key that may be considered better than the others
216 they MAY be different keys.
218 GSS_C_PRF_KEY_PARTIAL corresponds to a key that would be have been
219 used while the security context was partially established, even if it
223 Williams Expires December 15, 2005 [Page 4]
225 Internet-Draft A PRF Extension for the GSS-API June 2005
228 is fully established when GSS_Pseudo_random() is actually called.
229 Mechanism-specific prf_key values are intended to refer to any other
230 keys that may be available.
232 The GSS_C_PRF_KEY_FULL value corresponds to the best key available
233 for fully-established security contexts.
235 GSS_Pseudo_random() has the following properties:
237 o its output string MUST be a pseudo-random function [GGM1] [GGM2]
238 of the input keyed with key material from the given security
239 context -- the chances of getting the same output given different
240 input parameters should be exponentially small.
242 o when successfully applied to the same inputs by an initiator and
243 acceptor using the same security context, it MUST produce the
244 _same results_ for both, the initiator and acceptor, even if
245 called multiple times (as long as the security context is not
248 o upon full establishment of a security context all cryptographic
249 keys and/or negotiations used for computing the PRF with any
250 prf_key MUST be authenticated (mutually, if mutual authentication
251 is in effect for the given security context).
253 o the outputs of the mechanism's GSS_Pseudo_random() (for different
254 inputs) and its per-message tokens for the given security context
255 MUST be "cryptographically separate;" in other words, it must not
256 be feasible to recover key material for one mechanism operation or
257 transform its tokens and PRF outputs from one to the other given
258 only said tokens and PRF outputs. [This is a fancy way of saying
259 that key derivation and strong cryptographic operations and
260 constructions must be used.]
262 o as implied by the above requirement, it MUST NOT be possible to
263 access any raw keys of a security context through
264 GSS_Pseudo_random(), no matter what inputs are given.
266 Mechanisms MAY limit the output of the PRF, possibly in ways related
267 to the types of cryptographic keys available for the PRF function,
268 thus the prf_out output of GSS_Pseudo_random() MAY be smaller than
273 #define GSS_C_PRF_KEY_FULL 0
274 #define GSS_C_PRF_KEY_PARTIAL 1
279 Williams Expires December 15, 2005 [Page 5]
281 Internet-Draft A PRF Extension for the GSS-API June 2005
284 OM_uint32 gss_pseudo_random(
285 OM_uint32 *minor_status,
286 gss_ctx_id_t context,
288 const gss_buffer_t prf_in,
289 ssize_t desired_output_len,
293 Additional major status codes for the C-bindings:
295 o GSS_S_CALL_INACCESSIBLE_READ
297 o GSS_S_CALL_INACCESSIBLE_WRITE
303 For Java GSS_Pseudo_random() maps to a GSSContext method, 'prf':
305 public static final int GSS_C_PRF_KEY_FULL = 0
306 public static final int GSS_C_PRF_KEY_PARTIAL = 1
308 public byte[] prf(int prf_key, byte inBuf[], int outlen)
313 3. IANA Considerations
315 This document has no IANA considerations currently. If and when a
316 relevant IANA registry of GSS-API symbols is created then the generic
317 and language-specific function names, constant names and constant
318 values described above should be added to such a registry.
320 4. Security Considerations
322 Care should be taken in properly designing a mechanism's PRF
325 GSS mechanisms' PRF functions should use a key derived from contexts'
326 authenticated session keys and should preserve the forward security
327 properties of the mechanisms' key exchanges.
329 Some mechanisms may support the GSS PRF function with security
330 contexts that are not fully established, but applications MUST assume
331 that authentication, mutual or otherwise, has not completed until the
335 Williams Expires December 15, 2005 [Page 6]
337 Internet-Draft A PRF Extension for the GSS-API June 2005
340 security context is fully established.
342 Callers of GSS_Pseudo_random() should avoid accidentally calling it
343 with the same inputs. One useful technique is to prepend to the
344 prf_in input string, by convention, a string indicating the intended
345 purpose of the PRF output in such a way that unique contexts in which
346 the function is called yield unique inputs to it.
348 Pseudo-random functions are, by their nature, capable of producing
349 only limited amounts of cryptographically secure output. The exact
350 amount of output that one can safely use, unfortunately, varies from
351 one PRF to another (which prevents us from recommending specific
352 numbers). Because of this we recommend that unless you really know
353 what you are doing (i.e. you are a cryptographer and are qualified to
354 pass judgement on cryptographic functions in areas of period,
355 presence of short cycles, etc), you limit the amount of the PRF
356 output used to the necessary minimum.
360 5.1 Normative References
362 [GGM1] Goldreich, O., Goldwasser, S., and S. Micali, "How to
363 Construct Random Functions", October 1986.
365 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
366 Requirement Levels", BCP 14, RFC 2119, March 1997.
368 [RFC2743] Linn, J., "Generic Security Service Application Program
369 Interface Version 2, Update 1", RFC 2743, January 2000.
371 [RFC2744] Wray, J., "Generic Security Service API Version 2 :
372 C-bindings", RFC 2744, January 2000.
374 [RFC2853] Kabat, J. and M. Upadhyay, "Generic Security Service API
375 Version 2 : Java Bindings", RFC 2853, June 2000.
377 5.2 Informative References
379 [GGM2] Goldreich, O., Goldwasser, S., and S. Micali, "On the
380 Cryptographic Applications of Random Functions", 1985.
382 [RFC1750] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
383 Recommendations for Security", RFC 1750, December 1994.
385 [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
391 Williams Expires December 15, 2005 [Page 7]
393 Internet-Draft A PRF Extension for the GSS-API June 2005
404 Email: Nicolas.Williams@sun.com
447 Williams Expires December 15, 2005 [Page 8]
449 Internet-Draft A PRF Extension for the GSS-API June 2005
452 Intellectual Property Statement
454 The IETF takes no position regarding the validity or scope of any
455 Intellectual Property Rights or other rights that might be claimed to
456 pertain to the implementation or use of the technology described in
457 this document or the extent to which any license under such rights
458 might or might not be available; nor does it represent that it has
459 made any independent effort to identify any such rights. Information
460 on the procedures with respect to rights in RFC documents can be
461 found in BCP 78 and BCP 79.
463 Copies of IPR disclosures made to the IETF Secretariat and any
464 assurances of licenses to be made available, or the result of an
465 attempt made to obtain a general license or permission for the use of
466 such proprietary rights by implementers or users of this
467 specification can be obtained from the IETF on-line IPR repository at
468 http://www.ietf.org/ipr.
470 The IETF invites any interested party to bring to its attention any
471 copyrights, patents or patent applications, or other proprietary
472 rights that may cover technology that may be required to implement
473 this standard. Please address the information to the IETF at
477 Disclaimer of Validity
479 This document and the information contained herein are provided on an
480 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
481 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
482 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
483 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
484 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
485 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
490 Copyright (C) The Internet Society (2005). This document is subject
491 to the rights, licenses and restrictions contained in BCP 78, and
492 except as set forth therein, the authors retain all their rights.
497 Funding for the RFC Editor function is currently provided by the
503 Williams Expires December 15, 2005 [Page 9]