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heimdal/doc/standardisation/draft-ietf-kitten-gssapi-store-cred-01.txt
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NETWORK WORKING GROUP N. Williams
Internet-Draft Sun
Expires: April 19, 2006 October 16, 2005
GSS-API Extension for Storing Delegated Credentials
draft-ietf-kitten-gssapi-store-cred-01.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on April 19, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document defines a new function for the GSS-API which allows
applications to store delegated (and other) credentials in the
implicit GSS-API credential store. This is needed for GSS-API
applications to use delegated credentials as they would use other
credentials.
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Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. GSS_Store_cred() . . . . . . . . . . . . . . . . . . . . . . . 5
4. C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security considerations . . . . . . . . . . . . . . . . . . . 9
7. Normative . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . 11
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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
The GSS-API [RFC2743] clearly assumes that credentials exist in an
implicit store whence they can be acquired using GSS_Acquire_cred()
and GSS_Add_cred() or through use of the default credential.
Multiple credential stores may exist on a given host, but only one
store may be accessed by GSS_Acquire_cred() and GSS_Add_cred() at any
given time.
This assumption can be seen in sections 1.1.1.2 and 1.1.1.3 of
[RFC2743] as well as in section 3.5 of [RFC2744].
Note to the RFC editor: please remove this note before publication.]
Applications may be able to change the credential store from which
credentials can be acquired, either by changing user contexts (where
the applications have the privilege to do so) or by other means
(where a user may have multiple credential stores).
Some GSS-API acceptor applications always change user contexts, after
accepting a GSS-API security context and making appropriate
authorization checks, to the user context corresponding to the
initiator principal name or to a context requested by the initiator.
The means by which credential stores are managed are generally beyond
the scope of the GSS-API.
In the case of delegated credential handles however, such credentials
do not exist in the acceptor's credential store or in the credential
stores of the user contexts to which the acceptor application might
change - which is precisely the raison d'etre of credential
delegation. But the GSS-API provides no mechanism by which delegated
credential handles can be made available for acquisition through
GSS_Acquire_cred()/GSS_Add_cred(). The GSS-API also does not provide
any credential import/export interfaces like the GSS-API context
import/export interfaces.
Thus acceptors are limited to making only direct use of delegated
credential handles and only with GSS_Init_sec_context(),
GSS_Inquire_cred*() and GSS_Release_cred(). This limitation is
particularly onerous on Unix systems where a call to exec() to
replace the process image obliterates the delegated credentials
handle.
In order to make delegated credentials generally as useful as
credentials that can be acquired with GSS_Acquire_cred() and
GSS_Add_cred() a primitive is needed which allows storing of
credentials in the implicit credential store. This primitive we call
"GSS_Store_cred()."
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3. GSS_Store_cred()
Inputs:
o input_cred_handle CREDENTIAL HANDLE, -- credential to store; MUST
NOT be GSS_C_NO_CREDENTIAL
o cred_usage INTEGER -- 0=INITIATE-AND-ACCEPT, 1=INITIATE-ONLY,
2=ACCEPT-ONLY
o desired_mech_element OBJECT IDENTIFIER, -- if GSS_C_NULL_OID then
store all the elements of the input_cred_handle, otherwise store
only the element of the corresponding mechanism
o overwrite_cred BOOLEAN, -- if TRUE replace any credential for the
same principal in the credential store
o default_cred BOOLEAN -- if TRUE make the stored credential
available as the default credential (for acquisition with
GSS_C_NO_NAME as the desired name or for use as
GSS_C_NO_CREDENTIAL)
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o mech_elements_stored SET OF OBJECT IDENTIFIER, -- the set of
mechanism OIDs for which credential elements were successfully
stored
o cred_usage_stored INTEGER -- like cred_usage, but indicates what
kind of credential was stored (useful when the cred_usage input
parameter is set to INITIATE-AND-ACCEPT)
Return major_status codes:
o GSS_S_COMPLETE indicates that the credentials were successfully
stored.
o GSS_S_CREDENTIALS_EXPIRED indicates that the input credentials had
expired or expired before they could be stored.
o GSS_S_NO_CRED indicates that no input credentials were given.
o GSS_S_UNAVAILABLE indicates that the credential store is not
available.
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o GSS_S_DUPLICATE_ELEMENT indicates that an element of the input
credential could not be stored because a credential for the same
principal exists in the current credential store and the
overwrite_cred input argument was FALSE.
o GSS_S_FAILURE indicates that the credential could not be stored
for some other reason. The minor status code may provide more
information if a non-GSS_C_NULL_OID desired_mech_element was
given.
GSS_Store_cred() is used to store, in the current credential store, a
given credential that has either been acquired from a different
credential store or been accepted as a delegated credential.
Specific mechanism elements of a credential can be stored one at a
time by specifying a non-GSS_C_NULL_OID mechanism OID as the
desired_mech_element input argument, in which case the minor status
output SHOULD have a mechanism-specific value when the major status
is not GSS_S_COMPLETE.
The initiator, acceptor or both usages of the input credential may be
stored as per the cred_usage input argument.
The credential elements that were actually stored, when the major
status is GSS_S_COMPLETE, are indicated through the cred_usage_stored
and mech_elements_stored function outputs.
If credentials already exist in the current store for the principal
of the input_cred_handle, then those credentials are not replaced
with the input credentials unless the overwrite_cred input argument
is TRUE.
Finally, if the current credential store has no default credential
(that is, no credential that could be acquired for GSS_C_NO_NAME) or
if the default_cred input argument is TRUE, and the input credential
can be successfully stored, then the input credential will be
available for acquisition with GSS_C_NO_NAME as the desired name
input to GSS_Acquire_cred() or GSS_Add_cred() as well as for use as
GSS_C_NO_CREDENTIAL for the cred_handle inputs to GSS_Inquire_cred(),
GSS_Inquire_cred_by_mech(), GSS_Init_sec_context() and
GSS_Accept_sec_context().
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4. C-Bindings
The C-bindings for GSS_Store_cred() make use of types from and are
designed based on the style of the GSS-APIv2 C-Bindings [RFC2744].
OM_uint32 gss_store_cred(
OM_uint32 *minor_status,
gss_cred_id_t input_cred,
gss_cred_usage_t cred_usage,
const gss_OID desired_mech,
OM_uint32 overwrite_cred,
OM_uint32 default_cred,
gss_OID_set *elements_stored,
gss_cred_usage_t *cred_usage_stored)
Figure 1
The two boolean arguments, 'overwrite_cred' and 'default_cred' are
typed as OM_uint32; 0 corresponds to FALSE, non-zero values
correspond to TRUE.
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5. Examples
The intended usage of GSS_Store_cred() is to make delegated
credentials available to child processes of GSS-API acceptor
applications. Example pseudo-code:
/*
* <GSS_Accept_sec_context() loop resulting in GSS_S_COMPLETE,
* an initiator name (hereafter, "src_name") and a delegated
* credential handle (hereafter "deleg_cred").>
*
* <"requested_username" is a username derived from the
* initiator name or explicitly requested by the initiator
* application.>
*/
...
if (authorize_gss_client(src_name, requested_username)) {
/*
* For Unix-type platforms this may mean calling setuid() and
* it may or may not also mean setting/unsetting such
* environment variables as KRB5CCNAME and what not.
*/
if (change_user_context(requested_username))
(void) gss_store_creds(&minor_status, deleg_cred,
GSS_C_INITIATE, actual_mech,
0, 1, NULL, NULL);
}
else ...
}
else ...
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6. Security considerations
Acceptor applications MUST only store delegated credentials into
appropriate credential stores and only after proper authorization of
the authenticated initiator principal to the requested service(s).
Acceptor applications that have no use for delegated credentials MUST
release them (such acceptor applications that use the GSS-API
C-Bindings may simply provide a NULL value for the
delegated_cred_handle argument to gss_accept_sec_context()).
7. Normative
[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.
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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
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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
Internet Society.
Williams Expires April 19, 2006 [Page 11]
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