PKIX Working Group D. Pinkas (Bull)
INTERNET-DRAFT T. Gindin (IBM)
Expires: December 2002 June 2002
Target category: Standard Track
Internet X.509 Public Key Infrastructure
Permanent Identifier
<draft-ietf-pkix-pi-05.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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Abstract
This document define a new form of name, called permanent
identifier, that may be included in the subjectAltName extension
of a public key certificate issued to an entity.
The permanent identifier is an optional feature that may be used
by a CA to indicate that the certificate relates to the same
entity even if the name or the affiliation of that entity stored
in the subject or another name form in the subjectAltName extension
has changed.
The subject name, carried in the subject field, is only unique
for each subject entity certified by the one CA as defined by the
issuer name field. Also, the new name form can carry a
name that is unique for each subject entity certified by a CA.
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1 Introduction
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.
This specification is one part of a family of standards for the
X.509 Public Key Infrastructure (PKI) for the Internet. It is based
on RFC 3280, which defines underlying certificate formats and
semantics needed for a full implementation of this standard.
The subject field of a public key certificate identifies the entity
associated with the public key stored in the subject public key
field. Names and identities of a subject may be carried in the
subject field and/or the subjectAltName extension. Where subject
field is non-empty, it MUST contain an X.500 distinguished
name (DN). The DN MUST be unique for each subject entity certified
by a single CA as defined by the issuer name field.
The subject name changes whenever any of the components of that
name gets changed. There are several reasons for such a change to
happen.
For employees of a company or organization, the person may get
a different position within the same company and thus will
move from one organization unit to another one. Including the
organization unit in the name may however be very useful to
allow the relying parties (RP's) using that certificate to
identify the right individual.
For citizens, an individual may change their name by legal
processes, especially women as a result of marriage.
Any certificate subject identified by geographical location may
relocate and change at least some of the location attributes
(e.g. country name, state or province, locality, or street).
A permanent identifier may be useful in three contexts: access
control, non-repudiation and audit records.
For access control, the permanent identifier may be used in
an ACL (Access Control List) instead of the DN or any other
form of name and would not need to be changed, even if the
subject name of the entity changes.
For non-repudiation, the permanent identifier may be used to
link different transactions to the same entity, even when
the subject name of the entity changes.
For audit records, the permanent identifier may be used to
link different audit records to the same entity, even when
the subject name of the entity changes.
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When two certificates from different CA's contain both the same
permanent identifier value and the same type of permanent
identifier from a given Assigner Authority, then these
certificates relate to the same entity, whatever the content of
the DN or other subjectAltName components may be.
2. Definition of a Permanent Identifier
A CA which includes a permanent identifier in a certificate is
certifying that any public key certificate containing that
identifier refers to the same entity, whatever the content of
the DN or other subjectAltName components may be.
The use of a permanent identifier is OPTIONAL. This name is
defined as a form of otherName from the GeneralName structure in
SubjectAltName. The permanent identifier is defined as follows:
id-on-permanentIdentifier OBJECT IDENTIFIER ::= { id-on 3 }
PermanentIdentifier ::= SEQUENCE {
identifierValue IdentifierValue,
identifierType IdentifierType OPTIONAL,
matchingRule [0] IMPLICIT OBJECT IDENTIFIER OPTIONAL
}
IdentifierValue ::= CHOICE {
iA5String IA5String,
uTF8String UTF8String
}
IdentifierType ::= CHOICE {
registeredOID OBJECT IDENTIFIER,
uri IA5String
}
The IdentifierValue supports two syntaxes: IA5String or UTF8String.
IA5String is variable length data of ASCII octets. UTF8String is
variable length data of octets. UTF-8 is an ASCII-preserving
encoding method for Unicode (ISO 10646), the Universal Character Set
(UCS). The UCS allows to support most of the world's writing systems
using a single character set.
The IdentifierType field, when present, identifies both the
organization responsible for assigning the content of the identifier
field and the type of that field.
When the IdentifierType field is missing, then it is assumed that
the organization responsible for assigning the content of the
identifier field is the CA itself and that there is only one type
of such identifier for the CA.
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The IdentifierType field may contain either:
a) an Object Identifier (i.e. an OID), or
b) a permanent URI using IA5String.
Characteristically, when an OID is used, the prefix of the OID
identifies the organization, and a suffix is used to identify the
type of permanent identifier being identified. Essentially the
same thing is true of URI's.
Note: the full arc of the object identifier used to identify the
permanent identifier name form is derived using:
id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) }
id-on OBJECT IDENTIFIER ::= { id-pkix 8 } -- other name forms
If identifierType is missing, then the permanent identifier is
locally unique to the CA.
If identifierType is present, then the permanent identifier is
globally unique among all CAs.
The matchingRule is an OID. When the OID is missing the
following matching rule SHALL be used:
The Alphanumeric Identifier Match rule compares for equality a
presented value with an attribute value of type UTF8String
or IA5String, which is interpreted as a series of alphanumeric
characters. The rules for matching are that a working comparison
value is constructed from each of the two values by including
only the digits and alphabetic characters appearing in the value;
and then the two comparison values are compared using
CaseIgnoreMatch. This rule is intended for use only with
identifiers in variants of the Latin, Greek, and Cyrillic scripts.
Note: other matching rules can be used (see in chapter 6 of X.520).
Two such examples are:
caseIgnoreMatch {2 5 13 2} defined in section 6.1.1 of X.520, and
caseExactMatch {2 5 13 5} defined in section 6.1.4 of X.520.
3. Security considerations
A given entity may have at an instant of time or at different
instants of time multiple forms of identities.
If the permanent identifier is locally unique to the CA (i.e.
identifierType is not present), then two certificates from the
same CA can be compared. When they contain two identical permanent
identifiers, then a relying party may determine that they refer to
the same entity.
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If the permanent identifier is globally unique among all CAs (i.e.
identifierType is present), then two certificates from different
CAs can be compared. When they contain two identical permanent
identifiers, then a relying party may determine that they refer to
the same entity.
The permanent identifier identifies the entity, irrespective of any
attribute extension. When a public key certificate contains
attribute extensions, the permanent identifier, if present, should
not be used for access control purposes but only for audit purposes.
The reason is that since these attributes may change, access could
be granted on attributes that were originally present in a
certificate issued to that entity but are no more present in the
current certificate.
The content and the format of the IdentifierValue is defined by the
Assigner Authority. An Assigner Authority who wishes to permit
IdentifierValues to be matched using a matching rule different from
the one specified in this document would be required to specify a
matching rule. Many such matching rules are specified in ITU-T X.520.
Subject names in certificates are chosen by the issuing CA and are
mandated to be unique for each CA; so there can be no name collision
between subject names from the same CA. These names may be an
end-entity name, when the certificate is a leaf certificate or a
CA name, when it is a CA certificate.
Since a name is only unique towards its superior CA, unless some
naming constraints are being used, a name would only be guaranteed
to be globally unique when considered to include a sequence of all
the names of the superior CAs. Thus, two certificates which contain
a permanent identifier extension without a identifierType may have
their permanent identifier extensions compared for equality either
by comparing the public key values of the two CAs which have issued
these two certificates or by comparing the sequence of CA names in
the certification path from the trust anchor to the CA, inclusive.
The certification of different CAs with the same DN by different
CAs has other negative consequences in various parts of the PKI,
notably rendering the IssuerAndSerialNumber structure in RFC 2630
section 5.3 ambiguous.
4. References
4.1. Normative
[RFC 2026] S. Bradner, "The Internet Standards Process - Revision 3"
November 1996.
[RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
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[RFC 3280] R. Housley, W. Ford, W. Polk, and D. Solo, "Internet X.509
Public Key Infrastructure: Certificate and CRL Profile", April 2002.
4.2. Informative
[X.501] ITU-T Recommendation X.501 (1997 E): Information Technology
- Open Systems Interconnection - The Directory: Models, June 1997.
[X.509] ITU-T Recommendation X.509 (1997 E): Information Technology
- Open Systems Interconnection - The Directory: Authentication
Framework, June 1997.
[X.520] ITU-T Recommendation X.520: Information Technology - Open
Systems Interconnection - The Directory: Selected Attribute Types,
June 1997.
[X.660] ITU-T Recommendation X.660: Information Technology -
Open Systems Interconnection - Procedures for the Operation of
OSI Registration Authorities: General Procedures, 1992.
[X.680] ITU-T Recommendation X.680: Information Technology -
Abstract Syntax Notation One, 1997.
5. Author's Addresses
Denis Pinkas
Bull
68, Route de Versailles
78434 Louveciennes Cedex
FRANCE
Email: Denis.Pinkas@bull.net
Thomas Gindin
IBM Corporation
6710 Rockledge Drive
Bethesda, MD 20817
USA
Email: tgindin@us.ibm.com
6. Intellectual Property Rights
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification
can be obtained from the IETF Secretariat.
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The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
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APPENDIX
ASN.1 definitions
A.1. 1988 ASN.1 Module
PKIXpermanentidentifier88 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-permanent-identifier-88(14) }
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
id-pkix, AttributeType,
FROM PKIX1Explicit88 {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-pkix1-explicit-88(1)}
-- Object Identifiers
-- Externally defined OIDs
-- Arc for other name forms
id-on OBJECT IDENTIFIER ::= { id-pkix 8 }
-- permanent identifier
id-on-permanentIdentifier OBJECT IDENTIFIER ::= { id-on 3 }
PermanentIdentifier ::= SEQUENCE {
identifierValue IdentifierValue,
identifierType IdentifierType OPTIONAL,
matchingRule [0] IMPLICIT OBJECT IDENTIFIER OPTIONAL
}
IdentifierValue ::= CHOICE {
iA5String IA5String,
uTF8String UTF8String
}
IdentifierType ::= CHOICE {
registeredOID OBJECT IDENTIFIER,
uri IA5String
}
END
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A.2. 1993 ASN.1 Module
PKIXpermanentidentifier93 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-permanent-identifier-93(15) }
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
id-pkix, ATTRIBUTE
FROM PKIX1Explicit93 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit-93(3)};
-- Object Identifiers
-- Externally defined OIDs
-- Arc for other name forms
id-on OBJECT IDENTIFIER ::= { id-pkix 8 }
-- Locally defined OIDs
id-on-permanentIdentifier OBJECT IDENTIFIER ::= { id-on 3 }
-- permanent identifier
permanentIdentifier ATTRIBUTE ::= {
WITH SYNTAX PermanentIdentifier
ID id-on-permanentIdentifier }
PermanentIdentifier ::= SEQUENCE {
identifierValue IdentifierValue,
identifierType IdentifierType OPTIONAL,
matchingRule [0] IMPLICIT OBJECT IDENTIFIER OPTIONAL
}
IdentifierValue ::= CHOICE {
iA5String IA5String,
uTF8String UTF8String
}
IdentifierType ::= CHOICE {
registeredOID OBJECT IDENTIFIER,
uri IA5String,
}
END
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B. OID's for organizations
In order to obtain an OID for an identifier type, organizations need
first to have a registered OID for themselves (or must use a permanent
URI). In some cases, OID's are provided for free. In other cases a
one-time fee is required. The main difference lies in the nature of
the information that is collected at the time of registration and how
this information is verified for its accuracy.
B.1. Using IANA (Internet Assigned Numbers Authority)
The application form for a Private Enterprise Number in the IANA's
OID list is: http://www.iana.org/cgi-bin/enterprise.pl.
Currently IANA assigns numbers for free. The IANA-registered Private
Enterprises prefix is: iso.org.dod.internet.private.enterprise
(1.3.6.1.4.1)
These numbers are used, among other things, for defining private
SNMP MIBs.
The official assignments under this OID are stored in the IANA file
"enterprise-numbers" available at:
ftp://ftp.isi.edu/in-notes/iana/assignments/enterprise-numbers
B.2. Using an ISO member body
ISO has defined the OID structure in a such a way so that every ISO
member-body has its own unique OID. Then every ISO member-body is free
to allocate its own arc space below.
Organizations and enterprises may contact the ISO member-body where
their organization or enterprise is established to obtain an
organization/enterprise OID.
Currently, ISO members do not assign organization/enterprise OID's for
free.
Most of them do not publish registries of such OID's which they have
assigned, sometimes restricting the access to registered organizations
or preferring to charge inquirers for the assignee of an OID on a
per-inquiry basis. The use of OID's from an ISO member organization
which does not publish such a registry may impose extra costs on the
CA that needs to make sure that the OID corresponds to the registered
organization.
As an example, AFNOR (Association Francaise de Normalisation - the
French organization that is a member of ISO) has defined an arc to
allocate OID's for companies:
{iso (1) member-body (2) fr (250) type-org (1) organisation (n)}
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C. Full Copyright Statement
Copyright (C) The Internet Society (2002). 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. In addition, the
ASN.1 modules presented in Appendices A and B may be used in whole or
in part without inclusion of the copyright notice. 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
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