4 NETWORK WORKING GROUP N. Williams
6 Expires: April 19, 2006 October 16, 2005
9 GSS-API Extension for Storing Delegated Credentials
10 draft-ietf-kitten-gssapi-store-cred-01.txt
14 By submitting this Internet-Draft, each author represents that any
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35 This Internet-Draft will expire on April 19, 2006.
39 Copyright (C) The Internet Society (2005).
43 This document defines a new function for the GSS-API which allows
44 applications to store delegated (and other) credentials in the
45 implicit GSS-API credential store. This is needed for GSS-API
46 applications to use delegated credentials as they would use other
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62 1. Conventions used in this document . . . . . . . . . . . . . . 3
63 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
64 3. GSS_Store_cred() . . . . . . . . . . . . . . . . . . . . . . . 5
65 4. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 7
66 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
67 6. Security considerations . . . . . . . . . . . . . . . . . . . 9
68 7. Normative . . . . . . . . . . . . . . . . . . . . . . . . . . 9
69 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10
70 Intellectual Property and Copyright Statements . . . . . . . . 11
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116 1. Conventions used in this document
118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
120 document are to be interpreted as described in [RFC2119].
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174 The GSS-API [RFC2743] clearly assumes that credentials exist in an
175 implicit store whence they can be acquired using GSS_Acquire_cred()
176 and GSS_Add_cred() or through use of the default credential.
177 Multiple credential stores may exist on a given host, but only one
178 store may be accessed by GSS_Acquire_cred() and GSS_Add_cred() at any
181 This assumption can be seen in sections 1.1.1.2 and 1.1.1.3 of
182 [RFC2743] as well as in section 3.5 of [RFC2744].
184 Note to the RFC editor: please remove this note before publication.]
186 Applications may be able to change the credential store from which
187 credentials can be acquired, either by changing user contexts (where
188 the applications have the privilege to do so) or by other means
189 (where a user may have multiple credential stores).
191 Some GSS-API acceptor applications always change user contexts, after
192 accepting a GSS-API security context and making appropriate
193 authorization checks, to the user context corresponding to the
194 initiator principal name or to a context requested by the initiator.
195 The means by which credential stores are managed are generally beyond
196 the scope of the GSS-API.
198 In the case of delegated credential handles however, such credentials
199 do not exist in the acceptor's credential store or in the credential
200 stores of the user contexts to which the acceptor application might
201 change - which is precisely the raison d'etre of credential
202 delegation. But the GSS-API provides no mechanism by which delegated
203 credential handles can be made available for acquisition through
204 GSS_Acquire_cred()/GSS_Add_cred(). The GSS-API also does not provide
205 any credential import/export interfaces like the GSS-API context
206 import/export interfaces.
208 Thus acceptors are limited to making only direct use of delegated
209 credential handles and only with GSS_Init_sec_context(),
210 GSS_Inquire_cred*() and GSS_Release_cred(). This limitation is
211 particularly onerous on Unix systems where a call to exec() to
212 replace the process image obliterates the delegated credentials
215 In order to make delegated credentials generally as useful as
216 credentials that can be acquired with GSS_Acquire_cred() and
217 GSS_Add_cred() a primitive is needed which allows storing of
218 credentials in the implicit credential store. This primitive we call
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232 o input_cred_handle CREDENTIAL HANDLE, -- credential to store; MUST
233 NOT be GSS_C_NO_CREDENTIAL
235 o cred_usage INTEGER -- 0=INITIATE-AND-ACCEPT, 1=INITIATE-ONLY,
238 o desired_mech_element OBJECT IDENTIFIER, -- if GSS_C_NULL_OID then
239 store all the elements of the input_cred_handle, otherwise store
240 only the element of the corresponding mechanism
242 o overwrite_cred BOOLEAN, -- if TRUE replace any credential for the
243 same principal in the credential store
245 o default_cred BOOLEAN -- if TRUE make the stored credential
246 available as the default credential (for acquisition with
247 GSS_C_NO_NAME as the desired name or for use as
252 o major_status INTEGER,
254 o minor_status INTEGER,
256 o mech_elements_stored SET OF OBJECT IDENTIFIER, -- the set of
257 mechanism OIDs for which credential elements were successfully
260 o cred_usage_stored INTEGER -- like cred_usage, but indicates what
261 kind of credential was stored (useful when the cred_usage input
262 parameter is set to INITIATE-AND-ACCEPT)
264 Return major_status codes:
266 o GSS_S_COMPLETE indicates that the credentials were successfully
269 o GSS_S_CREDENTIALS_EXPIRED indicates that the input credentials had
270 expired or expired before they could be stored.
272 o GSS_S_NO_CRED indicates that no input credentials were given.
274 o GSS_S_UNAVAILABLE indicates that the credential store is not
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284 o GSS_S_DUPLICATE_ELEMENT indicates that an element of the input
285 credential could not be stored because a credential for the same
286 principal exists in the current credential store and the
287 overwrite_cred input argument was FALSE.
289 o GSS_S_FAILURE indicates that the credential could not be stored
290 for some other reason. The minor status code may provide more
291 information if a non-GSS_C_NULL_OID desired_mech_element was
294 GSS_Store_cred() is used to store, in the current credential store, a
295 given credential that has either been acquired from a different
296 credential store or been accepted as a delegated credential.
298 Specific mechanism elements of a credential can be stored one at a
299 time by specifying a non-GSS_C_NULL_OID mechanism OID as the
300 desired_mech_element input argument, in which case the minor status
301 output SHOULD have a mechanism-specific value when the major status
302 is not GSS_S_COMPLETE.
304 The initiator, acceptor or both usages of the input credential may be
305 stored as per the cred_usage input argument.
307 The credential elements that were actually stored, when the major
308 status is GSS_S_COMPLETE, are indicated through the cred_usage_stored
309 and mech_elements_stored function outputs.
311 If credentials already exist in the current store for the principal
312 of the input_cred_handle, then those credentials are not replaced
313 with the input credentials unless the overwrite_cred input argument
316 Finally, if the current credential store has no default credential
317 (that is, no credential that could be acquired for GSS_C_NO_NAME) or
318 if the default_cred input argument is TRUE, and the input credential
319 can be successfully stored, then the input credential will be
320 available for acquisition with GSS_C_NO_NAME as the desired name
321 input to GSS_Acquire_cred() or GSS_Add_cred() as well as for use as
322 GSS_C_NO_CREDENTIAL for the cred_handle inputs to GSS_Inquire_cred(),
323 GSS_Inquire_cred_by_mech(), GSS_Init_sec_context() and
324 GSS_Accept_sec_context().
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342 The C-bindings for GSS_Store_cred() make use of types from and are
343 designed based on the style of the GSS-APIv2 C-Bindings [RFC2744].
346 OM_uint32 gss_store_cred(
347 OM_uint32 *minor_status,
348 gss_cred_id_t input_cred,
349 gss_cred_usage_t cred_usage,
350 const gss_OID desired_mech,
351 OM_uint32 overwrite_cred,
352 OM_uint32 default_cred,
353 gss_OID_set *elements_stored,
354 gss_cred_usage_t *cred_usage_stored)
359 The two boolean arguments, 'overwrite_cred' and 'default_cred' are
360 typed as OM_uint32; 0 corresponds to FALSE, non-zero values
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398 The intended usage of GSS_Store_cred() is to make delegated
399 credentials available to child processes of GSS-API acceptor
400 applications. Example pseudo-code:
404 * <GSS_Accept_sec_context() loop resulting in GSS_S_COMPLETE,
405 * an initiator name (hereafter, "src_name") and a delegated
406 * credential handle (hereafter "deleg_cred").>
408 * <"requested_username" is a username derived from the
409 * initiator name or explicitly requested by the initiator
414 if (authorize_gss_client(src_name, requested_username)) {
416 * For Unix-type platforms this may mean calling setuid() and
417 * it may or may not also mean setting/unsetting such
418 * environment variables as KRB5CCNAME and what not.
420 if (change_user_context(requested_username))
421 (void) gss_store_creds(&minor_status, deleg_cred,
422 GSS_C_INITIATE, actual_mech,
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452 6. Security considerations
454 Acceptor applications MUST only store delegated credentials into
455 appropriate credential stores and only after proper authorization of
456 the authenticated initiator principal to the requested service(s).
458 Acceptor applications that have no use for delegated credentials MUST
459 release them (such acceptor applications that use the GSS-API
460 C-Bindings may simply provide a NULL value for the
461 delegated_cred_handle argument to gss_accept_sec_context()).
465 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
466 Requirement Levels", BCP 14, RFC 2119, March 1997.
468 [RFC2743] Linn, J., "Generic Security Service Application Program
469 Interface Version 2, Update 1", RFC 2743, January 2000.
471 [RFC2744] Wray, J., "Generic Security Service API Version 2 :
472 C-bindings", RFC 2744, January 2000.
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516 Email: Nicolas.Williams@sun.com
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