PKIX Working Group D. Pinkas (Bull)
INTERNET-DRAFT T. Gindin (IBM)
Expires: January 2005 July 2004
Target category: Standard Track
Internet X.509 Public Key Infrastructure
Permanent Identifier
<draft-ietf-pkix-pi-10.txt>
Status of this Memo
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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 two or more certificates relate to the
same entity, even if they contain different subject name (DNs) or
different names in the subjectAltName extension, or 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. However, 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 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 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 consists of an identifier value assigned
within a given naming space by the organization which is
authoritative for that naming space. The organization assigning
the identifier value may be the CA that has issued the certificate
or a different organization called an Assigner Authority.
An Assigner Authority may be a government, a government agency, a
corporation, or any other sort of organization. It MUST have a
unique identifier to distinguish it from any other such authority.
In this standard, that identifier MUST be an object identifier.
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.
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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.
For two certificates which have been both verified to be valid
according to a given validation policy and which contain a permanent
identifier, those certificates relate to the same entity if their
permanent identifiers match, whatever the content of the DN or
other subjectAltName components may be.
Since the use of permanent identifiers may conflict with privacy,
CAs SHOULD advertise to purchasers of certificates the use of
permanent identifiers in certificates.
2. Definition of a Permanent Identifier
This Permanent Identifier is a name defined as a form of otherName
from the GeneralName structure in SubjectAltName.
A CA which includes a permanent identifier in a certificate is
certifying that any public key certificate containing the same
values for that identifier refers to the same entity.
The use of a permanent identifier is OPTIONAL. The permanent
identifier is defined as follows:
id-on-permanentIdentifier OBJECT IDENTIFIER ::= { id-on 3 }
PermanentIdentifier ::= SEQUENCE {
identifierValue UTF8String OPTIONAL
-- if absent, use the serialNumber attribute
if there is a single such attribute present
in the subject DN
assigner OBJECT IDENTIFIER OPTIONAL,
-- if absent, the assigner is
the certificate issuer
}
The identifierValue field is optional.
When the identifierValue field is present, then the identifierValue
supports one syntax: UTF8String.
When the identifierValue field is absent, then the serialNumber
attribute from the subject DN is the value to be taken for the
identifierValue. In such a case, there MUST NOT more than one
serialNumber attribute in the subject DN, otherwise the
PermanentIdentifier SHALL NOT be used.
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The assigner field is optional.
When the assigner field is present, then it is an OID which
identifies both the Assigner Authority and the type of that field.
In such a case, the identifierValue field MUST be present.
Characteristically, the prefix of the OID identifies the Assigner
Authority, and a suffix is used to identify the type of permanent
identifier.
When the assigner field is absent, then the permanent identifier is
locally unique to the CA.
Only the following three combinations are allowed :
1- Both the assigner and the identifierValue fields are present:
The assigner field identifies the Assigner Authority and the type
of permanent identifier being identified. The identifierValue is
the value for that type of identifier. The permanent identifier is
globally unique among all CAs. In such a case, two permanent
identifiers of this type match if and only if the contents of the
identifierValue field in the two permanent identifiers consist of
the same Unicode code points presented in the same order and the
assigner field match.
2 - The assigner field is absent and the identifierValue field is
present:
The Assigner Authority is the CA that has issued the certificate.
The identifierValue is given by the CA and the permanent identifier
is only local to the CA that has issued the certificate. In such
a case, two permanent identifiers of this type match if and only if
the issuer DN's in the certificates which contain them match using
the distinguishedNameMatch rule, as defined in X.501 and the two
values of the identifierValue field consist of the same Unicode
code points presented in the same order.
3 - Both the assigner and the identifierValue fields are absent:
The value of the single serialNumber attribute included in the
subject DN SHALL be considered as the identifier value assigned
within the naming space of the certificate issuer. The permanent
identifier is only local to the CA that has issued the certificate.
In such a case, two permanent identifiers of this type match if
and only if the issuer DN's in the certificates which contain them
match and the serialNumber attributes within the subject DN's of
those same certificates also match using the caseIgnoreMatch rule.
The following combination is NOT allowed:
The assigner field is present and the identifierValue field is
absent.
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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
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.
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. It is the responsibility of the CA to verify that
the permanent identifier being included in the certificate refers
to the subject being certified.
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 longer present in the
current certificate.
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 that are
issued under the same issuer DN and which contain the same
permanent identifier extension without a identifierType do not
necessarily refer to the same entity.
Additional checks need to be done, e.g. to check if the public key
values of the two CAs which have issued the certificates to be
compared are identical or if the sequence of CA names in the
certification path from the trust anchor to the CA are identical.
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When the above checks fail, the permanents identifiers may still
match if there has been a CA key rollover. In such a case the
checking is more complicated.
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.
The permanent identifier allows organizations to create links
between different certificates associated with an entity issued
with or without overlapping validity periods. This ability to link
different certificates may conflict with privacy. It is therefore
important that a CA clearly disclose any plans to issue certificates
which include a permanent identifier to potential subjects of those
certificates.
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.
[RFC 3280] R. Housley, W. Ford, W. Polk, and D. Solo, "Internet X.509
Public Key Infrastructure: Certificate and CRL Profile", April 2002.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
3.2.0" is defined by "The Unicode Standard, Version 3.0"
(Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), as amended
by the "Unicode Standard Annex #27: Unicode 3.1"
(http://www.unicode.org/reports/tr27/) and by the "Unicode Standard
Annex #28: Unicode 3.2" (http://www.unicode.org/reports/tr28/).
[ISO10646] Universal Multiple-Octet Coded Character Set (UCS) -
Architecture and Basic Multilingual Plane, ISO/IEC 10646-1: 1993.
[UTF-8] RFC 2279. F. Yergeau. UTF-8, a transformation format of
ISO 10646, January 1998.
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.
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[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
Rue Jean-Jaurå°. BP 68
78340 Les Clayes-sous-Bois
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.
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 A
ASN.1 definitions
As in RFC 3280, ASN.1 modules are supplied in two different variants
of the ASN.1 syntax.
This section describes data objects used by conforming PKI components
in an "ASN.1-like" syntax. This syntax is a hybrid of the 1988 and
1993 ASN.1 syntaxes. The 1988 ASN.1 syntax is augmented with 1993
the UNIVERSAL Type UTF8String.
The ASN.1 syntax does not permit the inclusion of type statements in
the ASN.1 module, and the 1993 ASN.1 standard does not permit use of
the new UNIVERSAL types in modules using the 1988 syntax. As a
result, this module does not conform to either version of the ASN.1
standard.
Appendix A.1 may be parsed by an 1988 ASN.1-parser by replacing the
definitions for the UNIVERSAL Types with the 1988 catch-all "ANY".
Appendix A.2 may be parsed by an 1993 ASN.1-parser by removing the
UTF8String choice from the definition of IdentifierValue in the
module. Appendix A.2 may be parsed "as is" by an 1997 ASN.1 parser.
In case of discrepancies between these modules, the 1988 module is
the normative one.
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APPENDIX 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-perm-id-88(28) }
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
-- UTF8String, / move hyphens before slash if UTF8String does not
-- resolve with your compiler
-- The content of this type conforms to RFC 2279.
id-pkix
FROM PKIX1Explicit88 { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-pkix1-explicit(18) } ;
-- from [RFC 3280]
-- 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 }
id-mod-perm-id-88 OBJECT IDENTIFIER ::= { id-mod 28 }
PermanentIdentifier ::= SEQUENCE {
identifierValue UTF8String OPTIONAL,
-- if absent, use the serialNumber attribute
if there is a single such attribute present
in the subject DN
assigner OBJECT IDENTIFIER OPTIONAL
-- if absent, the assigner is
the certificate issuer
}
END
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APPENDIX 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-perm-id-93(29) }
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
id-pkix
FROM PKIX1Explicit88 { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-pkix1-explicit(18) } ;
-- from [RFC 3280]
-- 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 }
id-mod-perm-id-93 OBJECT IDENTIFIER ::= { id-mod 29 }
-- permanent identifier
permanentIdentifier ATTRIBUTE ::= {
WITH SYNTAX PermanentIdentifier
ID id-on-permanentIdentifier }
PermanentIdentifier ::= SEQUENCE {
identifierValue UTF8String OPTIONAL,
-- if absent, use the serialNumber attribute
if there is a single such attribute present
in the subject DN
assigner OBJECT IDENTIFIER OPTIONAL
-- if absent, the assigner is
the certificate issuer
}
END
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APPENDIX 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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B.3. Using an ICD (International Code Designator) from British Standards
Institution to specify a new or an existing identification scheme
The International Code Designator (ICD) is used to uniquely identify an
ISO 6523 compliant organization identification scheme. ISO 6523 is a
standard that defines the proper structure of an identifier and the
registration procedure for an ICD.
The conjunction of the ICD with an identifier issued by the registration
authority is worldwide unique.
The basic structure of the code contains the following components:
- the ICD value: The International Code Designator issued to the
identification scheme makes the identifier worldwide unique
(up to 4 digits),
- the Organization, usually a company or governmental body
(up to 35 characters),
- an Organization Part (OPI - Organization Part Identifier).
An identifier allocated to a particular Organization Part
(optional, up to 35 characters)
The ICD is also equivalent to an object identifier (OID) under the arc
{1(iso). 3(identified organization)}.
On behalf of ISO, British Standards Institution (BSI) is the
Registration Authority for organizations under the arc {iso (1) org(3)}.
This means BSI registers code issuing authorities (=organizations) by
ICD values which are equivalent to OIDs of the form {iso (1) org(3)
icd(xxxx)}. The corresponding IdentifierValue is the code value of the
scheme identified by icd(xxxx).
Example:
The ICD 0012 was allocated to European Computer Manufacturers
Association : ECMA. Thus the OID is 1(iso). 3(identified organization).
12.
For registration with BSI, a "Sponsoring Authority" has to vouch for the
Applying organization. Registration is not free. Recognized "Sponsoring
Authorities" are: ISO Technical Committees or (Sub)Committees, Member
Bodies of ISO or International Organizations having a liaison status
with ISO or with any of its Technical (Sub)Committees.
An example of a Sponsoring Authority is the EDIRA Association
(EDI/EC Registration Authority, web: http://www.edira.org,
email:info@edira.org).
The numerical list of all ICDs that have been issued is posted on its
webpage: http://www.edira.org/documents.htm#icd-List
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