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KITTEN WORKING GROUP                                         N. Williams
Internet-Draft                                                       Sun
Intended status: Standards Track                            L. Johansson
Expires: September 8, 2010                                         SUNET
                                                           March 7, 2010


                       GSS-API Naming Extensions
              draft-ietf-kitten-gssapi-naming-exts-06.txt

Abstract

   The Generic Security Services API (GSS-API) provides a simple naming
   architecture that supports name-based authorization.  This document
   introduces new APIs that extend the GSS-API naming model to support
   name attribute transfer between GSS-API peers.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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
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   This Internet-Draft will expire on September 8, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.      Conventions used in this document  . . . . . . . . . . . .  3
   2.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  3
   3.      Name Attribute Authenticity  . . . . . . . . . . . . . . .  3
   4.      Name Attributes/Values as ACL Subjects . . . . . . . . . .  4
   5.      Attribute Name Syntax  . . . . . . . . . . . . . . . . . .  4
   6.      Mapping Mechanism Facilities to Name Attributes  . . . . .  4
   6.1.    Kerberos V and SPKM Authorization-Data . . . . . . . . . .  5
   6.2.    PKIX . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   6.2.1.  Standard PKIX Certificate Extensions . . . . . . . . . . .  5
   6.2.2.  Other PKIX Certificate Extensions and Attributes . . . . .  5
   6.3.    SAML attribute assertions  . . . . . . . . . . . . . . . .  6
   7.      API  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   7.1.    GSS_Display_name_ext() . . . . . . . . . . . . . . . . . .  6
   7.1.1.  C-Bindings . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.2.    GSS_Inquire_name() . . . . . . . . . . . . . . . . . . . .  7
   7.2.1.  C-Bindings . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.3.    GSS_Get_name_attribute() . . . . . . . . . . . . . . . . .  8
   7.3.1.  C-Bindings . . . . . . . . . . . . . . . . . . . . . . . .  9
   7.4.    GSS_Set_name_attribute() . . . . . . . . . . . . . . . . .  9
   7.4.1.  C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.5.    GSS_Delete_name_attribute()  . . . . . . . . . . . . . . . 11
   7.5.1.  C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 11
   7.6.    GSS_Export_name_composite()  . . . . . . . . . . . . . . . 11
   7.6.1.  C-Bindings . . . . . . . . . . . . . . . . . . . . . . . . 12
   8.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.      Security Considerations  . . . . . . . . . . . . . . . . . 12
   10.     References . . . . . . . . . . . . . . . . . . . . . . . . 13
   10.1.   Normative References . . . . . . . . . . . . . . . . . . . 13
   10.2.   Informative References . . . . . . . . . . . . . . . . . . 14
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 14











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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] .


2.  Introduction

   As described in [I-D.GSS-NAMING] the GSS-API's naming architecture
   suffers from certain limitations.  This document proposes concrete
   GSS-API extensions as outlined in [I-D.GSS-NAMING].

   A number of extensions to the GSS-API [RFC2743] and its C Bindings
   [RFC2744] are described herein.  The goal is to make information
   modeled as "name attributes" available to applications.  Such
   information MAY for instance be used by applications to make
   authorization-decisions.  For example, Kerberos V authorization data
   elements, both in their raw forms, as well as mapped to more useful
   value types, can be made available to GSS-API applications through
   these interfaces.

   The model is that GSS names have attributes.  The attributes of a
   name may be authenticated (eg an X509 attribute certificate or signed
   SAML attribute assertion), or may have been set on a GSS name for the
   purpose of locally "asserting" the attribute during credential
   acquisition or security context exchange.  Name attributes' values
   are network representations thereof (e.g., the actual value octets of
   the contents of an X.509 certificate extension, for example) and are
   intended to be useful for constructing portable access control
   facilities.  Applications may often require language- or platform-
   specific data types, rather than network representations of name
   attributes, so a function is provided to obtain objects of such types
   associated with names and name attributes.


3.  Name Attribute Authenticity

   An attribute is 'authenticated' iff there is a secure association
   between the attribute (and its values) and the trusted source of the
   peer credential.  Examples of authenticated attributes are (any part
   of) the signed portion of an X.509 certificate or AD-KDCIssued
   authorization-data elements in Kerberos V Tickets provided of course
   that the authenticity of the respective security associations (eg
   signatures) have been verified.

   Note that the fact that an attribute is authenticated does not imply
   anything about the semantics of the attribute nor that the trusted



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   credential source was authorized to assert the attribute.  Such
   interpretations SHOULD be the result of applying local policy to the
   attribute.

   An un-authentciated attribute is called _asserted_ in what
   follows.This is not to be confused with other uses of the word
   asserted or assertion eg "SAML attribute assertion", the attributes
   of which may be authenticated in the sense of this document for
   instance if the SAML attribute assertion was signed by a key trusted
   by the peer.


4.  Name Attributes/Values as ACL Subjects

   To facilitate the development of portable applications that make use
   of name attributes to construct and evaluate portable ACLs the GSS-
   API makes name attribute values available in canonical network
   encodings thereof.


5.  Attribute Name Syntax

   Attribute names are represented as opaque STRING elements in the API
   described below.  These attribute names have syntax and semantics
   that are understood by the application and by the lower-layer
   implementations (some of which are described below).  In order to
   present a consistent namespace to the application and at the same
   time impose as few transformation requirements as possible to lower-
   layer implementations attribute names SHOULD be URIs.

   Technologies used in lower-layer protocols may of course use
   attribute naming that are not based on URIs.  Notably X.509
   certificates will use OIDs for most naming purposes.  In this case
   OIDs MUST be mapped into URIs as described in [RFC3001] MUST be used.
   If for example the OID 1.2.3 denotes an Extended Key Usage (cf
   below), the corresponding GSS-API attribute name MUST be represented
   as urn:oid:1.2.3.


6.  Mapping Mechanism Facilities to Name Attributes

   In this section we describe two important examples of lower-layer
   implementations of this API.  These examples are not mandatory to
   implement and are only provided for reference.  The use of [RFC2119]-
   terms in this section is limited to those implementations of the GSS-
   API naming extensions that choose to implement these lower-layer
   technologies.  Future mappings SHOULD be documented as RFCs.




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   Kerberos V [RFC4120] and the Simple Public-Key GSS-API Mechanism,
   SPKM described in [RFC2025], both support the concept and encoding of
   containers of "authorization-data" as described in [RFC4120].

   PKIX [RFC5280] supports a number of attribute-like features, like
   Extended Key Usage values (EKUs) and certificate extensions.

6.1.  Kerberos V and SPKM Authorization-Data

   Authorization-data non-container elements asserted in Kerberos V AP-
   REQ Authenticators MUST be mapped into *asserted* GSS-API name
   attributes.

   Authorization-data included in Kerberos V Tickets that is not
   contained in AD-KDCIssued (with valid signature) MUST be mapped into
   *asserted* GSS-API name attributes.  Conversely, authorization-data
   elements in Kerberos V Tickets contained by AD-KDCIssued MUST be
   mapped into *authenticated* GSS-API name attributes.

6.2.  PKIX

6.2.1.  Standard PKIX Certificate Extensions

   PKIX certificate extensions MAY/SHOULD/MUST (see comment above) be
   represented as *authenticated* GSS-API name attributes named using
   the _same_ OID mapped to a URN.

   SubjectAltNames and Extended Key Usage OIDs, specifically, MUST be
   represented as *authenticated* GSS-API name attributes; see below.
   Certificate extensions MUST be represented as GSS-API name attributes
   named using the OIDs used for the extensions (represented as URNs).
   The value associated with Extended Key Usage attributes MUST have
   NULL value represented as a zero-length OCTET STRING.

   The standard PKIX certificate key usage (KUs, but not EKUs), MUST NOT
   be represented as GSS-API name attributes.

   PKIX certificate subjectAltNames MUST be mapped as *authenticated*
   GSS-API name attributes.  The values SHOULD be the values of the
   subjectAltName represented as OCTET STRINGs if the type of the
   subjectAltName supports a unique loss-less representation as string
   values.  Specifically dnsName, ipAddress, uniformResourceLocator and
   emailAddress MUST be returned using the corresponding string
   representation of those data types.

6.2.2.  Other PKIX Certificate Extensions and Attributes

   Any X.509 certificate extension not covered above SHOULD be



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   represented as GSS-API name attributes with the OID of the X.509
   extension and with OCTET STRING values containing the encoded value
   of the extension.

6.3.  SAML attribute assertions

   Attributes contained in SAML attribute assertions MUST be mapped to
   GSS-API name attributes with the same URIs as used in the SAML
   attribute name.

   SAML attributes found in SAML attribute assertions MUST NOT be mapped
   as authenticated unless the SAML attribute assertion was signed by a
   key trusted by the peer or otherwise protected from unauthorized
   modification.


7.  API

7.1.  GSS_Display_name_ext()

   Inputs:


   o  name NAME,

   o  display_as_name_type OBJECT IDENTIFIER

   Outputs:


   o  major_status INTEGER,

   o  minor_status INTEGER,

   o  display_name STRING

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_UNAVAILABLE indicates that the given name could not be
      displayed using the syntax of the given name type.

   o  GSS_S_FAILURE indicates a general error.

   This function displays a given name using the given name syntax, if
   possible.  This operation may require mapping MNs to generic name
   syntaxes or generic name syntaxes to mechanism-specific name



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   syntaxes; such mappings may not always be feasible and MAY be inexact
   or lossy, therefore this function may fail.

7.1.1.  C-Bindings

   OM_uint32 GSS_Display_name_ext(
     OM_uint32                     *minor_status,
     gss_name_t                    name,
     gss_OID                       display_as_name_type,
     gss_buffer_t                  display_name
   );

7.2.  GSS_Inquire_name()

   Inputs:


   o  name NAME

   Outputs:


   o  major_status INTEGER,

   o  minor_status INTEGER,

   o  name_is_MN BOOLEAN,

   o  mn_mech OBJECT IDENTIFIER,

   o  attrs SET OF OCTET STRING

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_FAILURE indicates a general error.

   This function outputs the set (represented as a NULL terminated array
   of gss_buffer_t) of attributes of a name.  It also indicates if a
   given NAME is an MN or not and, if it is, what mechanism it's an MN
   of.  The gss_buffer_set_t type and associated API is defined in
   [GFD.024]

7.2.1.  C-Bindings

   OM_uint32 gss_inquire_name(
     OM_uint32                     *minor_status,



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     gss_name_t                    name,
     int                           name_is_MN,
     gss_OID                       *MN_mech,
     gss_buffer_set_t              *attrs
   );

7.3.  GSS_Get_name_attribute()

   Inputs:


   o  name NAME,

   o  attr STRING

   Outputs:


   o  major_status INTEGER,

   o  minor_status INTEGER,

   o  authenticated BOOLEAN, -- TRUE iff authenticated by the trusted
      peer credential source.

   o  complete BOOLEAN -- TRUE iff this represents a complete set of
      values for the name.

   o  values SET OF OCTET STRING,

   o  display_values SET OF STRING

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_UNAVAILABLE indicates that the given attribute OID is not
      known or set.

   o  GSS_S_FAILURE indicates a general error.

   This function outputs the value(s) associated with a given GSS name
   object for a given name attribute.

   The complete flag denotes that (if TRUE) the set of values represents
   a complete set of values for this name.  The peer being an
   authoritative source of information for this attribute is a
   sufficient condition for the complete flag to be set by the peer.



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   In the federated case when several peers may hold some of the
   attributes about a name this flag may be highly dangerous and SHOULD
   NOT be used.

   NOTE: This function relies on the GSS-API notion of "SET OF" allowing
   for order preservation; this has been discussed on the KITTEN WG
   mailing list and the consensus seems to be that, indeed, that was
   always the intention.  It should be noted however that the order
   presented does not always reflect an underlying order of the
   mechanism specific source of the attribute values.

7.3.1.  C-Bindings

   The C-bindings of GSS_Get_name_attribute() requires one function call
   per-attribute value, for multi-valued name attributes.  This is done
   by using a single gss_buffer_t for each value and an input/output
   integer parameter to distinguish initial and subsequent calls and to
   indicate when all values have been obtained.

   The 'more' input/output parameter should point to an integer variable
   whose value, on first call to gss_name_attribute_get() MUST be -1,
   and whose value upon function call return will be non-zero to
   indicate that additional values remain, or zero to indicate that no
   values remain.  The caller should not modify this parameter after the
   initial call.  The status of the complete and authenticated flags
   MUST NOT change between multiple calls to iterate over values for an
   attribute.

   OM_uint32 gss_get_name_attribute(
     OM_uint32                     *minor_status,
     gss_name_t                    name,
     gss_buffer_t                  attr,
     int                           *authenticated,
     int                           *complete,
     gss_buffer_t                  value,
     gss_buffer_t                  display_value,
     int                           *more
   );

7.4.  GSS_Set_name_attribute()

   Inputs:


   o  name NAME,

   o  complete BOOLEAN, -- TRUE iff this represents a complete set of
      values for the name.



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   o  attr STRING,

   o  values SET OF OCTET STRING

   Outputs:


   o  major_status INTEGER,

   o  minor_status INTEGER

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_UNAVAILABLE indicates that the given attribute OID is not
      known or could not be set.

   o  GSS_S_FAILURE indicates a general error.

   The complete flag denotes that (if TRUE) the set of values represents
   a complete set of values for this name.  The peer being an
   authoritative source of information for this attribute is a
   sufficient condition for the complete flag to be set by the peer.

   In the federated case when several peers may hold some of the
   attributes about a name this flag may be highly dangerous and SHOULD
   NOT be used.

   NOTE: This function relies on the GSS-API notion of "SET OF" allowing
   for order preservation; this has been discussed on the KITTEN WG
   mailing list and the consensus seems to be that, indeed, that was
   always the intention.  It should be noted that underlying mechanisms
   may not respect the given order.

7.4.1.  C-Bindings

   The C-bindings of GSS_Set_name_attribute() requires one function call
   per-attribute value, for multi-valued name attributes -- each call
   adds one value.  To replace an attribute's every value delete the
   attribute's values first with GSS_Delete_name_attribute().

   OM_uint32 gss_set_name_attribute(
     OM_uint32                     *minor_status,
     gss_name_t                    name,
     int                           complete,
     gss_buffer_t                  attr,
     gss_buffer_t                  value



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   );

7.5.  GSS_Delete_name_attribute()

   Inputs:


   o  name NAME,

   o  attr STRING,

   Outputs:


   o  major_status INTEGER,

   o  minor_status INTEGER

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_UNAVAILABLE indicates that the given attribute OID is not
      known.

   o  GSS_S_UNAUTHORIZED indicates that a forbidden delete operation was
      attempted eg deleting a negative attribute.

   o  GSS_S_FAILURE indicates a general error.

   Deletion of negative authenticated attributes from NAME objects MUST
   NOT be allowed and must result in a GSS_S_UNAUTHORIZED.

7.5.1.  C-Bindings

   OM_uint32 gss_delete_name_attribute(
     OM_uint32                     *minor_status,
     gss_name_t                    name,
     gss_buffer_t                  attr
   );

7.6.  GSS_Export_name_composite()

   Inputs:


   o  name NAME




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   Outputs:


   o  major_status INTEGER,

   o  minor_status INTEGER,

   o  exp_composite_name OCTET STRING

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_FAILURE indicates a general error.

   This function outputs a token which can be imported with
   GSS_Import_name(), using GSS_C_NT_COMPOSITE_EXPORT as the name type
   and which preserves any name attribute information associated with
   the input name (which GSS_Export_name() may well not).  The token
   format is no specified here as this facility is intended for inter-
   process communication only; however, all such tokens MUST start with
   a two-octet token ID, hex 04 02, in network byte order.

   The OID for GSS_C_NT_COMPOSITE_EXPORT is <TBD>.

7.6.1.  C-Bindings

   OM_uint32 gss_export_name_composite(
     OM_uint32                     *minor_status,
     gss_name_t                    name,
     gss_buffer_t                  exp_composite_name
   );


8.  IANA Considerations

   This document creates a namespace of GSS-API name attributes.
   Attributes are named by URIs, so no single authority is technically
   needed for allocation.  However future deployment experience may
   indicate the need for an IANA registry for URIs used to reference
   names specified by IETF standards.  It is expected that this will be
   a registry of URNs but this document provides no further guidance on
   this registry.


9.  Security Considerations

   This document extends the GSS-API naming model to include support for



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   name attributes.  The intention is that name attributes are to be
   used as a basis for (among other things) authorization decisions or
   personalization for applications relying on GSS-API security
   contexts.

   The security of the application may be critically dependent on the
   security of the attributes.  This document classifies attributes as
   asserted or authenticated.  Asserted (non-authenticated) attributes
   MUST NOT be used if the attribute has security implications for the
   application (eg authorization decisions) since asserted attributes
   may easily be controlled by the peer directly.

   It is important to understand the meaning of 'authenticated' in this
   setting.  Authenticated does not imply that any semantic of the
   attribute is claimed to be true.  The only implication is that a
   trusted third party has asserted the attribute as opposed to the
   attribute being asserte by the peer itself.  Any additional semantics
   is always the result of applying policy.  For instance in a given
   deployment the mail attribute of the subject may be authenticated and
   sourced from an email system where 'authoritive' values are kept.  In
   another situations users may be allowed to modify their mail
   addresses freely.  In both cases the 'mail' attribute may be
   authenticated by virtue of being included in signed SAML attribute
   assertions or by other means authenticated by the underlying
   mechanism.

   When the underlying security mechanism does not provide a permanent
   unique identity (eg anonymous kerberos) the GSS-API naming extensions
   may be used to provide a replacement permanent unique identity
   attribute which in this case may be unique for each peer party.  This
   is analogous to the SAML permanentIdentifier attribute and has
   comparable security and privacy properties and implications.


10.  References

10.1.  Normative References

   [GFD.024]  Argonne National Laboratory, National Center for
              Supercomputing Applications, Argonne National Laboratory,
              and Argonne National Laboratory, "GSS-API Extensions",
              GFD GFD.024, June 2004.

   [RFC2025]  Adams, C., "The Simple Public-Key GSS-API Mechanism
              (SPKM)", RFC 2025, October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.



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   [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.

   [RFC3001]  Mealling, M., "A URN Namespace of Object Identifiers",
              RFC 3001, November 2000.

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,
              July 2005.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

10.2.  Informative References

   [I-D.GSS-NAMING]
              Hartman, S., "Desired Enhancements to GSSAPI Naming",
              draft-ietf-kitten-gss-naming-01.txt (work in progress),
              February 2005.


Authors' Addresses

   Nicolas      Williams
   Sun Microsystems
   5300 Riata Trace Ct
   Austin, TX  78727
   US

   Email: Nicolas.Williams@sun.com


   Leif Johansson
   Swedish University Network
   Thulegatan 11
   Stockholm
   Sweden

   Email: leifj@sunet.se
   URI:   http://www.sunet.se






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