Network Working Group S. Boeyen
Request for Comments: 2587 Entrust
Category: Standards Track T. Howes
Netscape
P. Richard
Xcert
June 1999

Internet X.509 Public Key InfrastrUCture
LDAPv2 Schema

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 (1999). All Rights Reserved.

1. Abstract

The schema defined in this document is a minimal schema to support
PKIX in an LDAPv2 environment, as defined in RFC2559. Only PKIX-
specific components are specified here. LDAP servers, acting as PKIX
repositories should support the auxiliary object classes defined in
this specification and integrate this schema specification with the
generic and other application-specific schemas as appropriate,
depending on the services to be supplied by that server.

The key Words 'MUST', 'SHALL', 'REQUIRED', 'SHOULD', 'RECOMMENDED',
and 'MAY' in this document are to be interpreted as described in RFC
2119.

2. Introduction

This specification is part of a multi-part standard for development
of a Public Key Infrastructure (PKI) for the Internet. LDAPv2 is one
mechanism defined for Access to a PKI repository. Other mechanisms,
such as http, are also defined. If an LDAP server, accessed by LDAPv2
is used to provide a repository, the minimum requirement is that the
repository support the addition of X.509 certificates to Directory

entries. Certificate Revocation List (CRL)is one mechanism for
publishing revocation information in a repository. Other mechanisms,
such as http, are also defined.

This specification defines the attributes and object classes to be
used by LDAP servers acting as PKIX repositories and to be understood
by LDAP clients communicating with such repositories to query, add,
modify and delete PKI information. Some object classes and attributes
defined in X.509 are duplicated here for completeness. For end
entities and Certification Authorities (CA), the earlier X.509
defined object classes mandated inclusion of attributes which are
optional for PKIX. Also, because of the mandatory attribute
specification, this would have required dynamic modification of the
object class attribute should the attributes not always be present in
entries. For these reasons, alternative object classes are defined in
this document for use by LDAP servers acting as PKIX repositories.

3. PKIX Repository Objects

The primary PKIX objects to be represented in a repository are:

- End Entities
- Certification Authorities (CA)

These objects are defined in RFC2459.

3.1. End Entities

For purposes of PKIX schema definition, the role of end entities as
subjects of certificates is the major ASPect relevant to this
specification. End entities may be human users, or other types of
entities to which certificates may be issued. In some cases, the
entry for the end entity may already exist and the PKI-specific
information is added to the existing entry. In other cases the entry
may not exist prior to the issuance of a certificate, in which case
the entity adding the certificate may also need to create the entry.
Schema elements used to represent the non PKIX aspects of an entry,
such as the structural object class used to represent organizational
persons, may vary, depending on the particular environment and set of
applications served and are outside the scope of this specification.

The following auxiliary object class MAY be used to represent
certificate subjects:

pkiUser OBJECT-CLASS ::= {
SUBCLASS OF { top}
KIND auxiliary
MAY CONTAIN {userCertificate}
ID joint-iso-ccitt(2) ds(5) objectClass(6) pkiUser(21)}

userCertificate ATTRIBUTE ::= {
WITH SYNTAX Certificate
EQUALITY MATCHING RULE certificateExactMatch
ID joint-iso-ccitt(2) ds(5) attributeType(4) userCertificate(36) }

An end entity may oBTain one or more certificates from one or more
Certification Authorities. The userCertificate attribute MUST be
used to represent these certificates in the directory entry
representing that user.

3.2. Certification Authorities

As with end entities, Certification Authorities are typically
represented in directories as auxiliary components of entries
representing a more generic object, such as organizations,
organizational units etc. The non PKIX-specific schema elements for
these entries, such as the structural object class of the object, are
outside the scope of this specification.

The following auxiliary object class MAY be used to represent
Certification Authorities:

pkiCA OBJECT-CLASS ::= {
SUBCLASS OF { top}
KIND auxiliary
MAY CONTAIN {cACertificate
certificateRevocationList
authorityRevocationList
crossCertificatePair }
ID joint-iso-ccitt(2) ds(5) objectClass(6) pkiCA(22)}

cACertificate ATTRIBUTE ::= {
WITH SYNTAX Certificate
EQUALITY MATCHING RULE certificateExactMatch
ID joint-iso-ccitt(2) ds(5) attributeType(4) cACertificate(37) }

crossCertificatePairATTRIBUTE::={
WITH SYNTAX CertificatePair
EQUALITY MATCHING RULE certificatePairExactMatch
ID joint-iso-ccitt(2) ds(5) attributeType(4) crossCertificatePair(40)}

The cACertificate attribute of a CA's directory entry shall be used
to store self-issued certificates (if any) and certificates issued to
this CA by CAs in the same realm as this CA.

The forward elements of the crossCertificatePair attribute of a CA's
directory entry shall be used to store all, except self-issued
certificates issued to this CA. Optionally, the reverse elements of
the crossCertificatePair attribute, of a CA's directory entry may
contain a subset of certificates issued by this CA to other CAs.
When both the forward and the reverse elements are present in a
single attribute value, issuer name in one certificate shall match
the subject name in the other and vice versa, and the subject public
key in one certificate shall be capable of verifying the digital
signature on the other certificate and vice versa.

When a reverse element is present, the forward element value and the
reverse element value need not be stored in the same attribute value;
in other words, they can be stored in either a single attribute value
or two attribute values.

In the case of V3 certificates, none of the above CA certificates
shall include a basicConstraints extension with the cA value set to
FALSE.

The definition of realm is purely a matter of local policy.

certificateRevocationListATTRIBUTE::={
WITH SYNTAX CertificateList
EQUALITY MATCHING RULE certificateListExactMatch
ID joint-iso-ccitt(2) ds(5) attributeType(4)
certificateRevocationList(39)}

The certificateRevocationList attribute, if present in a particular
CA's entry, contains CRL(s) as defined in RFC2459.

authorityRevocationListATTRIBUTE::={
WITH SYNTAX CertificateList
EQUALITY MATCHING RULE certificateListExactMatch
ID joint-iso-ccitt(2) ds(5) attributeType(4)
authorityRevocationList(38)}

The authorityRevocationList attribute, if present in a particular
CA's entry, includes revocation information regarding certificates
issued to other CAs.

3.2.1. CRL distribution points

CRL distribution points are an optional mechanism, specified in RFC
2459, which MAY be used to distribute revocation information.

A patent statement regarding CRL distribution points can be found at
the end of this document.

If a CA elects to use CRL distribution points, the following object
class is used to represent these.

cRLDistributionPoint OBJECT-CLASS::= {
SUBCLASS OF { top }
KIND structural
MUST CONTAIN { commonName }
MAY CONTAIN { certificateRevocationList
authorityRevocationList
deltaRevocationList }
ID joint-iso-ccitt(2) ds(5) objectClass(6) cRLDistributionPoint(19) }

The certificateRevocationList and authorityRevocationList attributes
are as defined above.

The commonName attribute and deltaRevocationList attributes, defined
in X.509, are duplicated below.

commonName ATTRIBUTE::={
SUBTYPE OF name
WITH SYNTAX DirectoryString
ID joint-iso-ccitt(2) ds(5) attributeType(4) commonName(3) }

deltaRevocationList ATTRIBUTE ::= {
WITH SYNTAX CertificateList
EQUALITY MATCHING RULE certificateListExactMatch
ID joint-iso-ccitt(2) ds(5) attributeType(4)
deltaRevocationList(53) }

3.2.2. Delta CRLs

Delta CRLs are an optional mechanism, specified in RFC2459, which
MAY be used to enhance the distribution of revocation information.

If a CA elects to use delta CRLs, the following object class is used
to represent these.

deltaCRL OBJECT-CLASS::= {
SUBCLASS OF { top }
KIND auxiliary
MAY CONTAIN { deltaRevocationList }
ID joint-iso-ccitt(2) ds(5) objectClass(6) deltaCRL(23) }

4. Security Considerations

Since the elements of information which are key to the PKI service
(certificates and CRLs) are both digitally signed pieces of
information, no additional integrity service is REQUIRED.

Security considerations with respect to retrieval, addition,
deletion, and modification of the information supported by this
schema definition are addressed in RFC2559.

5. References

[1] Yeong, Y., Howes, T. and S. Kille, "Lightweight Directory Access
Protocol", RFC1777, March 1995.

[2] Bradner, S., "Key Words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC2119, March 1997.

6 Intellectual Property Rights

The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this
document. For more information consult the online list of claimed
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.

7. Authors' Addresses

Sharon Boeyen
Entrust Technologies Limited
750 Heron Road
Ottawa, Ontario
Canada K1V 1A7

EMail: sharon.boeyen@entrust.com

Tim Howes
Netscape Communications Corp.
501 E. Middlefield Rd.
Mountain View, CA 94043
USA

EMail: howes@netscape.com

Patrick Richard
Xcert Software Inc.
Suite 1001, 701 W. Georgia Street
P.O. Box 10145
Pacific Centre
Vancouver, B.C.
Canada V7Y 1C6

EMail: patr@xcert.com

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