PKIX Working Group D. Pinkas (Bull)
INTERNET-DRAFT T. Gindin (IBM)
Expires: February 2004 August 2003
Target category: Standard Track
Internet X.509 Public Key Infrastructure
Permanent Identifier
<draft-ietf-pkix-pi-07.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of [RFC 2026].
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Copyright (C) The Internet Society (2002). All Rights Reserved.
Please send comments on this document to the ietf-pkix@imc.org
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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 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 consists of an identifier value assigned
within a given naming space by the organization which is
authoritative for that naming space. Such an organization is known
as 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 or
be representable as a URI.
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.
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 support of most of the world's writing systems
using a single character set.
The IdentifierType field, when present, identifies both the
Assigner Authority and the type of that field.
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When the IdentifierType field is missing, then it is assumed that
the Assigner Authority is the CA itself and that there is only one
type of such identifier for the CA.
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 Assigner Authority, 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.
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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.
The content and the format of the IdentifierValue are 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.
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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.
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
Rue Jean-Jaurs. 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
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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
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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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 is 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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C. Permanent URIs for organizations
URIs are delivered in conformance with ICANN rules, i.e. "Uniform
Domain Name Dispute Resolution Policy". http://www.icann.org/udrp/
Currently, once a URI has been assigned to an organization, the URI
will continue to be assigned to that organization as long as it pays
for it. However, in case there is no more payment, the domain name
which controls that URI can be re-assigned to another organization
asking for it.
This means that URI's are not assigned permanently.
C.1. How can URI's be made pseudo-permanent?
There are two main approaches that may be used singly or in combination:
- continue to pay the renewal fee forever, or
- choose a URI structure that is very unlikely going to be re-used,
C.2. Why should a URI be left unpaid?
While a cessation of operation of the organization is an obvious
reason, a merger with another organization often implies a change in the
name and thus the URI is abandoned. Unless provisions are specifically
made to address the issue, payments will cease and the URI may be
re-assigned.
C.3. How to choose a URI structure which is unlikely to be re-used?
Adding the year of issue directly after the first part of the URI-PATH
is such an approach, or adding the year of issue as a path segment in
an HTTP or FTP URL.
C.4. How to understand what the URI means?
This is more of a concern for the CA's making use of them than for the
Relying Parties. There are two approaches to solve this problem:
- find a document from the organization owning the URI specifying
the meaning of the URI's,
- find out the meaning directly by dereferencing the URI. This is
the preferred approach, as long as the URI is maintained by its
original owner.
C.5. Recommendations
Care should be taken by organizations acting as an Assigner Authority
when choosing a permanent URI as the means to identify a Permanent
Identifier. They should:
a) define rules for the assignment of permanent URI's,
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b) take provisions to maintain the URI as long as possible,
c) choose the ways to enable third parties to understand the meaning
of each permanent identifier, either using URI dereferencing, or
publication in a document or both.
C.6. Examples
C.6.1. W3C
W3C has provisions in its statutes to continue to pay forever for
"www.w3.org". In addition, permanent URI's must be constructed as
follows: the year of issue must be the second element in the URI,
e.g. http://www.w3.org/1999/
http://www.w3.org/2001/XMLSchema
http://www.w3.org/2000/09/xmldsig
The definition of such URI's may be either found by dereferencing them
or by looking at the W3C document which defines it.
C.6.2 ETSI
ETSI has chosen a name space that is very unlikely to be re-used.
ETSI has defined a URI Namespace for use specifically as identifiers
within XML code which is published as part of an ETSI specification.
The root namespace is: http://uri.etsi.org
XML uses URIs, or Universal Resource Identifiers, in order to clearly
identify an XML module, or an object defined within an XML file.
URIs used in XML files look like HTTP URLs, but they are unique
Identifiers, not Locators, i.e. the URI does not necessarily point
to any specific location or page.
The ETSI URI Namespace is structured into 3 domains:
* Deliverable Based Domain,
* Common Domain,
* ETSI Identified Organization Domain.
The Deliverable Based Domain is used for URIs which are assigned in
one ETSI specification and are unrelated to other URIs assigned in
other specifications. Every ETSI specification has a URI root which
can be associated with it, whether or not it is actually used in the
specification. This URI root is defined as follows:
http://uri.etsi.org/xxxxx/
where xxxxx is the five digit number obtained by removing the first
digit of the ETSI Document number, and any part or sub-part numbers.
Leading zeros are NOT stripped. The resulting number is independent
of ETSI deliverable type.
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Example 1: The value obtained for TS 101 123 is "01123". The value
obtained for ES 201 123 is also "01123", since the assignment of ETSI
document numbers is independent of ETSI document type. Technically,
TS 101 123 and ES 201 123 are just two different versions of the same
document.
Both will result in the following URI root:
http://uri.etsi.org/01123/
Example 2: The value obtained for ES 201 915-4 is ô01915ö.
The URI root obtained is:
http://uri.etsi.org/01915/
Example 3: The value obtained for EN 300 822 is 00822.
The URI root obtained is:
http://uri.etsi.org/00822/
There is no necessity to register either the ETSI Deliverable Based URI
root, or any sub-structure or individual URIs based on this URI root,
with the ETSI Secretariat. The ETSI document number, uniquely assigned
by the ETSI Secretariat, is sufficient to guarantee uniqueness and to
identify the location of a URI definition.
The ETSI technical body which drafts the specification, is responsible
for assignment and management of any URIs in its specification.
Some real examples are:
http://uri.etsi.org/01903/v1.1.1/
http://uri.etsi.org/01903/v1.1.1/#SignedProperties
The definition of such URI's may be either found by dereferencing them
or by looking at the ETSI document which defines it.
D. 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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Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process shall be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. This
document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL
NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY
OR FITNESS FOR A PARTICULAR PURPOSE.
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