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-
-INTERNET-DRAFT Nicolas Williams
- Sun Microsystems
- September 2003
-
-
-
- GSS-APIv2 Extension for Storing Delegated Credentials
- <draft-williams-gssapi-store-deleg-creds-01.txt>
-
-
-
-
-Status of this Memo
-
- This document is an Internet-Draft and is in full conformance with
- all provisions of Section 10 of RFC2026 [RFC2026].
-
- 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 draft expires on January 30th, 2004. Please send comments to
- the authors.
-
-
-Copyright Notice
-
- Copyright (C) The Internet Society (2003). All Rights Reserved.
-
-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.
-
-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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-
-Table of Contents
-
- 1 Introduction
- 2 GSS_Store_cred()
- 2.1 C-Bindings for GSS_Store_cred()
- 3 Examples
- 4 Security Considerations
- 5 References
- 5.1 Normative References
- 6 Author's Address
-
-1 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.
-
- [NOTE: 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
-
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- replace the process image obliterates the delegated credentials
- handle.
-
- [NOTE: Delegated credentials are practically unusable on Unix
- implementations of Secure Shell (SSHv2) servers, except where
- there are extended interfaces for dealing with delegated
- credentials, which to date have always been
- mechanism-specific interfaces.
-
- Note to the RFC editor: please remove this note before
- publication.]
-
- 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()."
-
- [NOTE: Simon Wilkinson's patches to OpenSSH for GSS-API sport a
- simple internal interface for storing delegated credentials
- in users' credential store - this internal interface wraps
- around two mechanism specific internal interfaces for storing
- GSI and Kerberos V credentials.
-
- Simon's code shows that:
-
- a) a generic method is needed for making delegated
- credentials available for indirect use through acquisition
- (as opposed to just using the actual delegated cred
- handle)
-
- b) it is possible to design and implement such a generic
- method for storing delegated credentials.
-
- No new concepts are added to the GSS-API by this document,
- but the implicit existence of a credential store in the
- background is made explicit, and a deficiency of the GSS-API
- is corrected.
-
- Compare this to the GGF proposal which includes a credential
- import/export facility (like the existing context import/
- export facility), but with an option to export as
- "environment variables," meaning something like "store these
- input creds in some new credential store and then tell me the
- name of that credential store through some output environment
- variable"[*]. Thus, the GGF export-cred-to-environment-
- variable proposal adds knowledge of environment variables to
- the GSS-API, which this proposal does not. Note that a
- credential import/export facility along the lines of the
- existing context import/export facility may be useful and
- complements the GSS_Store_cred() interface; in fact, with
- GSS_Store_cred() it should be possible to remove the
- 'option_req' input parameter and export-to-env-var features
-
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- of the GGF's GSS_Export_cred() credential export proposal.
-
- [*] For the exact semantics see section 1.2, paragraph 6 of
- draft-engert-ggf-gss-extensions-00.txt
-
- One side effect of GSS_Store_cred(), however, is that it
- allows applications that can switch their current credential
- store to move credentials from one store to the other; this
- is a direct result of making it possible to store a
- credential given a GSS-API credential handle. Perhaps there
- should be some text allowing, or recommending, that
- implementations of GSS_Store_cred() allow only the storage of
- credentials acquired through credential delegation.
-
- Note to the RFC editor: please remove this note before
- publication.]
-
-2 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)
-
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- 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.
-
- 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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-
-2.1 C-Bindings for GSS_Store_cred()
-
- 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)
-
- The two boolean arguments, 'overwrite_cred' and 'default_cred' are
- typed as OM_uint32; 0 corresponds to FALSE, non-zero values
- correspond to TRUE.
-
-3 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 ...
-
-4 Security Considerations
-
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- 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()).
-
-5 References
-
-5.1 Normative References
-
- [RFC2026]
- S. Bradner, RFC2026: "The Internet Standard Process - Revision
- 3," October 1996, Obsoletes - RFC 1602, Status: Best Current
- Practice.
-
- [RFC2119]
- S. Bradner, RFC2119 (BCP14): "Key words for use in RFCs to
- Indicate Requirement Levels," March 1997, Status: Best Current
- Practice.
-
- [RFC2743]
- J. Linn, RFC2743: "Generic Security Service Application Program
- Interface Version 2, Update 1," January 2000, Status: Proposed
- Standard.
-
- [RFC2744]
- J. Wray, RFC2744: "Generic Security Service API Version 2 :
- C-bindings," January 2000, Status: Proposed Standard.
-
-6 Author's Address
-
- Nicolas Williams
- Sun Microsystems
- 5300 Riata Trace Ct
- Austin, TX 78727
- Email: Nicolas.Williams@sun.com
-
-Full Copyright Statement
-
- Copyright (C) The Internet Society (2003). All Rights Reserved.
-
- This document and translations of it may be copied and furnished to
- others, and derivative works that comment on or otherwise explain it
- or assist in its implementation may be prepared, copied, published
- and distributed, in whole or in part, without restriction of any
- kind, provided that the above copyright notice and this paragraph are
- included on all such copies and derivative works. However, this
- document itself may not be modified in any way, such as by removing
- the copyright notice or references to the Internet Society or other
- Internet organizations, except as needed for the purpose of
-
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- developing Internet standards in which case the procedures for
- copyrights defined in the Internet Standards process must be
- followed, or as required to translate it into languages other than
- English.
-
- The limited permissions granted above are perpetual and will not be
- revoked by the Internet Society or its successors or assigns.
-
- This document and the information contained herein is provided on an
- "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
- TASK FORCE DISCLAIMS 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.
-
-Acknowledgement
-
- Funding for the RFC Editor function is currently provided by the
- Internet Society.
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