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Versions: 00 01 02 03 05 06 07 08 RFC 4476

Internet Draft                                               C. Francis
PKIX Working Group                                             Raytheon
February 2006                                                 D. Pinkas
Expires: August 2006                                               Bull




                   Attribute Certificate Policies extension
                   <draft-ietf-pkix-acpolicies-extn-08.txt>




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Copyright Notice

   Copyright (C) The Internet Society (2006).  All Rights Reserved.

Abstract

   This document describes one certificate extension to explicitly
   state the Attribute Certificate Policies (ACPs) that apply to a
   given Attribute Certificate (AC).  The goal of this document is to
   allow relying parties to perform an additional test when validating
   an AC, i.e. to assess whether a given AC carrying some attributes
   can be accepted on the basis of references to one or more specific
   ACPs.

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 [RFC 2119].

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1. Introduction

   When issuing a Public Key Certificate (PKC), a Certificate
   Authority (CA) can perform various levels of verification with
   regard to the subject identity (see [RFC 3280]).  A CA makes its
   verification procedures, as well as other operational rules it
   abides by, "visible" through a certificate policy, which may be
   referenced by a certificate policies extension in the PKC.

   The purpose of this document is to define an AC policies extension
   able to explicitly state the AC policies that apply to a given AC,
   but not the AC policies themselves. Attribute Certificates are
   defined in [RFC 3281].

2. AC Policies Extension Semantics

   An Attribute Certificate Policy is a named set of rules that
   indicates the applicability of an AC to a particular community
   and/or class of application with common security requirements and
   which defines rules for the generation, issuance and revocation of
   ACs.  It may also include additional rules for attributes
   registration.

   It should thus be noticed that an Attribute Authority (AA) does not
   necessarily support one single ACP. However, for each AC that is
   delivered the AA SHALL make sure that the policy applies to all
   the attributes that are contained in it.

   An ACP may be used by an AC user to decide whether or not to trust
   the attributes contained in an AC for a particular purpose.

   When an AC contains an AC policies extension, the extension MAY,
   at the option of the AA, be either critical or non-critical.

   The AC Policies extension MAY be included in an AC.  Like all
   X.509 certificate extensions [X.509], the AC policies extension is
   defined using ASN.1 [ASN1]. See Annex A.

   The definitions are presented in the 1988 Abstract Syntax Notation
   One (ASN.1) rather than the 1997 ASN.1 syntax used in the most
   recent ISO/IEC/ITU-T standards.

   The AC policies extension is identified by id-pe-acPolicies.

      id-pe-acPolicies OBJECT IDENTIFIER ::= { iso(1)
        identified-organization(3) dod(6) internet(1) security(5)
        mechanisms(5) id-pkix(7) id-pe(1) 15 }

   The AC policies extension includes a list of AC policies recognized
   by the AA that apply to the attributes included in the AC.




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   AC Policies may be defined by any organization with a need.  Object
   identifiers used to identify AC Policies are assigned in accordance
   with [ITU-T Rec. X.660 | ISO/IEC 9834-1].

   The AC policies extension in an AC indicates the AC policies for
   which the AC is valid.

   An application that recognizes this extension and its content SHALL
   process the extension regardless of the value of the criticality
   flag.

   If the extension is both flagged non-critical and is not recognized
   by the AC using application, then the application MAY ignore it.

   If the extension is marked critical or is recognized by the AC
   using application, it indicates that the attributes contained in
   the attribute certificate SHALL only be used for the purpose, and
   in accordance with the rules associated with one of the indicated
   AC policies. If none of the ACP identifiers is adequate for the
   application, then the AC MUST be rejected.

   If the extension is marked critical or is recognized by the AC
   using application, AC using applications MUST use the list of AC
   policies to determine whether it is appropriate to use the
   attributes contained in that AC for a particular transaction. When
   the appropriate policy is not found, the AC SHALL be rejected.

2.1 AC Policy Extension Syntax

   The syntax for the AC Policy extension is:

   AcPoliciesSyntax ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

   PolicyInformation ::= SEQUENCE {
       policyIdentifier      AcPolicyId,
       policyQualifiers      SEQUENCE SIZE (1..MAX) OF
                                      PolicyQualifierInfo OPTIONAL}

   AcPolicyId ::= OBJECT IDENTIFIER

    PolicyQualifierInfo ::= SEQUENCE {
         policyQualifierId  PolicyQualifierId,
         qualifier          ANY DEFINED BY policyQualifierId }

   -- policyQualifierIds for Internet policy qualifiers

    id-qt            OBJECT IDENTIFIER ::=  { id-pkix 2 }
    id-qt-acps       OBJECT IDENTIFIER ::=  { id-qt 4 }
    id-qt-acunotice  OBJECT IDENTIFIER ::=  { id-qt 5 }

    id-qt-acps OBJECT IDENTIFIER ::= { iso(1)
      identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) id-pkix(7) id-qt(2) 4 }

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    id-qt-acunotice OBJECT IDENTIFIER ::= { iso(1)
      identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) id-pkix(7) id-qt(2) 5 }

    PolicyQualifierId ::=
         OBJECT IDENTIFIER ( id-qt-acps | id-qt-acunotice )

   -- ACPS pointer qualifier

   ACPSuri ::= IA5String
   -- ACP statement user notice qualifier

   ACUserNotice ::= UserNotice
   -- UserNotice is defined in [RFC3280]

   To promote interoperability, this document RECOMMENDS that policy
   information terms consist of only an OID.  When more than one policy
   is used, the policy requirements have to be non-conflicting, e.g.
   one policy may refine the general requirements mandated by another
   policy.

   The extension defined in this specification supports two policy
   qualifier types for use by ACP writers and AAs.  The qualifier
   types are the ACPS Pointer and the AC User.

   Notice qualifiers.

   The ACPS Pointer qualifier contains a pointer to an Attribute
   Certification Practice Statement (ACPS) published by the AA.
   The pointer is in the form of a URI.  Processing requirements for
   this qualifier are a local matter.

   The AC User Notice is intended for display to a relying party when
   an attribute certificate is used.  The application software SHOULD
   display the AC User Notice of the AC. The AC User Notice is defined
   in [RFC3280]. It has two optional fields: the noticeRef field and
   the explicitText field.

      The noticeRef field, if used, names an organization and
      identifies, by number, a particular textual statement prepared by
      that organization.  For example, it might identify the
      organization's name and notice number 1.  In a typical
      implementation, the application software will have a notice file
      containing the current set of notices for the AA; the
      application will extract the notice text from the file and
      display it.  Messages MAY be multilingual, allowing the software
      to select the particular language message for its own
      environment.

      An explicitText field includes the textual statement directly in
      the certificate.  The explicitText field is a string with a
      maximum size of 200 characters.


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   If both the noticeRef and explicitText options are included in the
   one qualifier and if the application software can locate the notice
   text indicated by the noticeRef option, then that text SHOULD be
   displayed; otherwise, the explicitText string SHOULD be displayed.

2.2 Attribute Certificate Policies

   The scope of this document is not the definition of the detailed
   content of ACPs themselves, therefore specific policies are not
   defined in this document.

3. Security Considerations

   The ACP defined in this document applies for all the attributes
   that are included in one AC.  AAs SHALL ensure that the ACP applies
   to all the attributes which are included in the ACs they issue.

   Attributes may be dynamically grouped in several ACs.  It should
   be observed that since an AC may be issued under more than one ACP,
   the attributes included in a given AC MUST be compliant with all
   the ACPs from that AC.

   When verifying an AC, a relying party MUST determine that the AC
   was issued by a trusted AA and then has the appropriate policy.

   Failure of AAs to protect their private keys will permit an
   attacker to masquerade as them, potentially generating false ACs
   or revocation status.  Existence of bogus ACs and revocation status
   will undermine confidence in the system.  If the compromise is
   detected, all ACs issued by the AA MUST be revoked.

   Rebuilding after such a compromise will be problematic, so AAs are
   advised to implement a combination of strong technical measures
   (e.g., tamper-resistant cryptographic modules) and appropriate
   management procedures (e.g., separation of duties) to avoid such
   an incident.

   Loss of an AA's private signing key may also be problematic.
   The AA would not be able to produce revocation status or
   perform AC renewal (i.e. the issue of a new AC with the same set
   of attributes with the same values, for the same holder, from the
   same AA but with a different validity period).  AC issuers are
   advised to maintain secure backup for signing keys.  The security
   of the key backup procedures is a critical factor in avoiding key
   compromise.

   The availability and freshness of revocation status will affect the
   degree of assurance that should be placed in a long-lived AC.  While
   long-lived ACs expire naturally, events may occur during its natural
   lifetime which negate the binding between the AC holder and the
   attributes.  If revocation status is untimely or unavailable, the
   assurance associated with the binding is clearly reduced.


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   The binding between an AC holder and attributes cannot be stronger
   than the cryptographic module implementation and algorithms used to
   generate the signature.  Short key lengths or weak hash algorithms
   will limit the utility of an AC.  AAs are encouraged to note
   advances in cryptology so they can employ strong cryptographic
   techniques.

   If an AC is tied to the holder's PKC using the baseCertificateID
   component of the Holder field and the PKI in use includes a rogue
   CA with the same issuer name specified in the baseCertificateID
   component, this rogue CA could issue a PKC to a malicious party,
   using the same issuer name and serial number as the proper
   holder's PKC.  Then the malicious party could use this PKC in
   conjunction with the AC.  This scenario SHOULD be avoided by
   properly managing and configuring the PKI so that there cannot be
   two CAs with the same name.  Another alternative is to tie ACs to
   PKCs using the publicKeyCert type in the ObjectDigestInfo field.
   Failing this, AC verifiers have to establish (using other means)
   that the potential collisions cannot actually occur, for example,
   the Certificate Policy Statements (CPSs) of the CAs involved may
   make it clear that no such name collisions can occur.

   Implementers MUST ensure that following validation of an AC, only
   attributes that the issuer is trusted to issue are used in
   authorization decisions.  Other attributes, which MAY be present
   MUST be ignored. AC verifiers SHALL support means of being provided
   with this information.  The AA controls PKC extension (see
   [RFC 3281]) is one possibility, but is optional to implement.
   Configuration information is a likely alternative means, while
   out-of-bands means is also another means.  This becomes very
   important if an AC verification application trusts more than one
   AC issuer.

4.  IANA Considerations

   The AC policies extension is identified by an object identifier
   (OID).  The OID for the AC policies extension defined in this
   document was assigned from an arc delegated by the IANA to the PKIX
   Working Group.

   No further action by the IANA is necessary for this document.

5. References

5.1 Normative references

   [ITU-T Rec. X.660 | ITU-T Recommendation Rec X.660 (1992)
   ISO/IEC 9834-1]   | ISO/IEC 9834-1: 1993, Information
                    technology - Open Systems Interconnection
                    Procedures for the operation of OSI
                    Registration Authorities: General procedures.

   [RFC3280]  Certificate and Certificate Revocation List (CRL) Profile.
              R. Housley, W.Polk, W.Ford, and D. Solo. April 2002.

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   [RFC3281]  An Internet Attribute Certificate Profile for
              Authorization. S. Farrell S. and R. Housley. April 2002.

   [ASN1]     X.680 - X.693 | ISO/IEC 8824: 1-4 Abstract Syntax
              Notation One (ASN.1).

5.2 Informative reference

   [X.509]    ITU-T Recommendation X.509 (2000): Information Technology
              Open Systems Interconnections - The Directory:
              Public-key and Attribute Frameworks, March 2000

Author's Addresses

    Christopher S. Francis
    Raytheon
    1501 72nd Street North, MS 25
    St. Petersburg, Florida  33764
    Email: Chris_S_Francis@Raytheon.com

    Denis Pinkas
    Bull
    Rue Jean Jaures
    78340 Les Clayes-sous-Bois
    FRANCE
    Email: Denis.Pinkas@bull.net

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.





































Francis, Pinkas                                                  Page 8
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Annex A (normative): ASN.1 Definitions

ASN.1 Module

AcPolicies { iso(1) identified-organization(3) dod(6)
     internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
     id-mod-ac-policies(26) }

DEFINITIONS IMPLICIT TAGS ::=

BEGIN

-- EXPORTS ALL --

IMPORTS

-- Imports from RFC 3280 [RFC3280], Appendix A

       UserNotice
          FROM PKIX1Implicit88 { iso(1) identified-organization(3)
          dod(6) internet(1) security(5) mechanisms(5) pkix(7)
          id-mod(0) 19 }

       id-pkix, id-pe
          FROM PKIX1Explicit88 { iso(1) identified-organization(3)
          dod(6) internet(1) security(5) mechanisms(5) pkix(7)
          id-mod(0) 18 };

-- Locally defined OIDs

    -- policyQualifierIds for Internet policy qualifiers

   id-qt                    OBJECT IDENTIFIER ::=  { id-pkix 2 }
   id-qt-acps               OBJECT IDENTIFIER ::=  { id-qt 4 }
   id-qt-acunotice          OBJECT IDENTIFIER ::=  { id-qt 5 }

-- Attributes

   id-pe-acPolicies         OBJECT IDENTIFIER ::= { id-pe 15 }

   AcPoliciesSyntax ::=     SEQUENCE SIZE (1..MAX) OF PolicyInformation

   PolicyInformation ::=    SEQUENCE {
      policyIdentifier         AcPolicyId,
      policyQualifiers         SEQUENCE SIZE (1..MAX) OF
                               PolicyQualifierInfo OPTIONAL }

   AcPolicyId ::=           OBJECT IDENTIFIER

   PolicyQualifierInfo ::=  SEQUENCE {
      policyQualifierId        PolicyQualifierId,
      qualifier                ANY DEFINED BY policyQualifierId }



Francis, Pinkas                                                  Page 9
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   PolicyQualifierId ::=
      OBJECT IDENTIFIER               ( id-qt-acps | id-qt-acunotice )
   -- ACPS pointer qualifier

   ACPSuri ::=         IA5String
   -- ACP statement user notice qualifier

   ACUserNotice ::=    UserNotice
   -- UserNotice is defined in [RFC3280]

END











































Francis, Pinkas                                                 Page 10


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