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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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 }
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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
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