Request for Comments: 4043 Bull
Category: Standards Track T. Gindin
IBM
May 2005
Internet X.509 Public Key Infrastructure
Permanent Identifier
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document defines 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.
Table of Contents
1. Introduction.................................................. 2
2. Definition of a Permanent Identifier.......................... 3
3. IANA Considerations........................................... 6
4. Security Considerations....................................... 6
5. References.................................................... 7
5.1. Normative References.................................... 7
5.2. Informative References.................................. 8
Appendix A. ASN.1 Syntax.......................................... 9
A.1. 1988 ASN.1 Module....................................... 9
A.2. 1993 ASN.1 Module....................................... 10
Appendix B. OID’s for organizations............................... 11
B.1. Using IANA (Internet Assigned Numbers Authority)........ 11
B.2. Using an ISO Member Body................................ 12
B.3. Using an ICD (International Code Designator) From
British Standards Institution to Specify a New or
an Existing Identification Scheme....................... 12
Authors’ Addresses................................................ 14
Full Copyright Statement.......................................... 15
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 [RFC2119].
This specification is based on [RFC3280], 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. 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, as defined in
[X.509] and [RFC3280].
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 a serialNumber attribute,
-- if there is such an 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 value of the
serialNumber attribute (as defined in section 5.2.9 of [X.520])
from the deepest RDN of the subject DN is the value to be taken
for the identifierValue. In such a case, there MUST be at least
one serialNumber attribute in the subject DN, otherwise the
PermanentIdentifier SHALL NOT be used.
The assigner field is optional.
When the assigner field is present, then it is an OID which
identifies a naming space, i.e., both an Assigner Authority and
the type of that field. 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.
The various combinations are detailed below:
1. Both the assigner and the identifierValue fields are present:
The identifierValue is the value for that type of identifier. The
assigner field identifies the Assigner Authority and the type of
permanent identifier being identified.
The permanent identifier is globally unique among all CAs. In
such a case, two permanent identifiers of this type match if and
only if their assigner fields match and the contents of the
identifierValue field in the two permanent identifiers consist of
the same Unicode code points presented in the same order.
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:
If there are one or more RDNs containing a serialNumber attribute
(alone or accompanied by other attributes), then the value
contained in the serialNumber of the deepest such RDN SHALL be
used as the identifierValue; otherwise, the Permanent Identifier
definition is invalid and the Permanent Identifier SHALL NOT be
used.
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.
4. The assigner field is present and the identifierValue field is
absent:
If there are one or more RDNs containing a serialNumber attribute
(alone or accompanied by other attributes), then the value
contained in the serialNumber of the deepest such RDN SHALL be
used as the identifierValue; otherwise, the Permanent Identifier
definition is invalid and the Permanent Identifier SHALL NOT be
used.
The assigner field identifies the Assigner Authority and the type
of permanent identifier being identified.
The permanent identifier is globally unique among all CAs. In
such a case, two permanent identifiers of this type match if and
only if their assigner fields match and the contents of the
serialNumber attributes within the subject DN’s of those same
certificates match using the caseIgnoreMatch rule.
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. IANA Considerations
No IANA actions are necessary. However, a Private Enterprise Number
may be used to construct an OID for the assigner field (see Annex
B.1.).
4. 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., the assigner field is
not present), then two certificates from the same CA can be compared.
When two certificates contain 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.,
the assigner field 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. Such a name 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 an assigner field 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.
When the above checks fail, the permanent 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 [RFC3852] section
10.2.4 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.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[X.501] ITU-T Rec X.501 | ISO 9594-2: 2001: Information technology
- Open Systems Interconnection - The Directory: Models,
February 2001.
5.2. Informative References
[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
3852, July 2004.
[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.
Appendix A. ASN.1 Syntax
As in RFC 2459, 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 "as is" by an 1997-compliant ASN.1 parser.
In case of discrepancies between these modules, the 1988 module is
the normative one.
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 [UTF-8].
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 [RFC3280]
-- Permanent identifier Object Identifier and Syntax
id-on OBJECT IDENTIFIER ::= { id-pkix 8 }
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
}
END
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 [RFC3280]
ATTRIBUTE
FROM InformationFramework {joint-iso-itu-t ds(5) module(1)
informationFramework(1) 4};
-- from [X.501]
-- Permanent identifier Object Identifiers
id-on OBJECT IDENTIFIER ::= { id-pkix 8 }
id-on-permanentIdentifier OBJECT IDENTIFIER ::= { id-on 3 }
-- 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
Appendix B. OID’s for Organizations
In order to construct an OID for the assigner field, organizations
need first to have a registered OID for themselves. Such an OID must
be obtained from a registration authority following [X.660]. 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.
Appendix 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:
http://www.iana.org/assignments/enterprise-numbers
Appendix 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