Internet DRAFT - draft-chadwick-pkixldap-v3
draft-chadwick-pkixldap-v3
Internet-Draft D.W.Chadwick
PKIX WG University of Salford
Intended Category: Standards Track
Expires: 12 December 1999 12 June, 1999
Internet X.509 Public Key Infrastructure
Operational Protocols - LDAPv3
<draft-chadwick-pkixldap-v3-00.txt>
STATUS OF THIS MEMO
This document is an Internet-Draft and is in full conformance with
all the provisions of Section 10 of RFC2026.
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ABSTRACT
This document describes the features of the Lightweight Directory
Access Protocol v3 that are needed in order to support a public key
infrastructure based on X.509 certificates and CRLs.
1. Introduction
RFC 2559 [1] specifies the subset of LDAPv2 [2] that is necessary to
retrieve X.509 [9] certificates and CRLs from LDAP servers. However
LDAPv2 has a number of deficiencies that may limit its usefulness in
certain circumstances. The most notable of these are:
- LDAPv2 distinguished names must be composed from the IA5
character set and cannot contain accented or non-latin characters,
- LDAPv2 only has a limited number of supported authentication
schemes for binding to the server, in particular the use of hashed
passwords or TLS [3] are not supported,
- LDAPv2 only supports a single directory server. It is the
responsibility of the user to pre-configure his client with the
required set of LDAP servers, and to choose the correct one for each
certificate and CRL retrieval.
It is for these reasons (and others not listed here) that the IETF
have stopped the standardisation of the LDAPv2 protocol and have
replaced it with the LDAPv3 protocol [4]. However the LDAPv3 protocol
is much more complex than the LDAPv2 protocol and many of its
features are not essential for simple PKIX use. This document
describes the features of LDAPv3 that are essential, or not required,
or are optional for servers to support a PKI based on X.509.
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 [5].
2. Features Of Ldapv3 That MUST Be Supported
Attribute descriptions are a superset of attribute type definitions.
They allow attribute subtyping to be specified in the LDAPv3
protocol. The ;binary option is exception to this. This option allows
certificates and CRLs to be asked for and returned as binary values
encoded using the Basic Encoding Rules [11]. The mechanism described
in PKIX LDAPv2 [1] is fully compliant with the ;binary option of
LDAPv3. The ;binary option of attribute descriptions MUST be
supported by all implementations. Other attribute description
options SHOULD NOT be supported by clients. Servers MAY choose to
support them at their discretion.
UTF8 encoding [12] allows the full ISO 10646 character set to be used
in the creation of distinguished names. UTF8 encoding of
distinguished names MUST be supported as specified in RFC2253 [6].
The altServer attribute is used by servers to point to alternative
servers that may be contacted if this server is temporarily
unavailable. This attribute MUST be stored in the root DSE of the
server and MUST be available to clients for retrieval. If no
alternative servers exist this attribute MUST point to the current
server. Clients MAY make use of this feature but do not need to.
Servers MAY store any other operational attributes in the root DSE,
but do not need to.
3. Features Of Ldapv3 That SHOULD Be Supported
In a distributed directory with multiple servers, LDAPv3 supports
referrals as the mechanism to allow one server that cannot fulfil a
client's request, to refer the client to another server that might be
better able to fulfil the request. Servers SHOULD be able to return
referrals to clients. Clients SHOULD be able to receive referrals,
although they are not required to automatically process them and
support multiple asynchronous outgoing connections. As a minimum,
clients SHOULD be able to ask the user if the referrals are be cached
locally and added to the set of servers known to the client.
Partial Search results are returned when a server only has a subset
of the certificates requested by the client. Referrals to other
servers are embedded in the SearchResultReference field. Clients and
servers SHOULD be able to handle SearchResultReferences in the same
way as they handle referrals.
4. Features Of Ldapv3 That SHOULD NOT Be Supported
The client SHOULD NOT support the ModifyDN, Compare and Abandon
operations. The server MAY choose to support these operations at its
discretion.
The LDAPv3 protocol is infinitely extensible via two mechanisms:
extended operations and controls on existing operations. The client
SHOULD NOT generate any LDAPv3 protocol extensions (extended
operations or controls). The server SHOULD NOT return any LDAPv3
protocol extensions (extended operations or controls).
LDAPv3 has the concept of unsolicited notifications that can be sent
from the server to the client. The server SHOULD NOT generate any
unsolicited notifications.
LDAPv3 allows the subschema supported by the server to be published
in a subschema subentry. Subschema publishing is not needed for
normal PKI use, therefore the client SHOULD NOT try to retrieve
either the contents of the subschema subentry or the pointer to it
(held in the subschemaSubentry attribute of the root DSE) from the
server. The server MAY publish its subschema at its discretion.
Operational attributes are attributes stored by the server that hold
administrative information. Clients SHOULD NOT request any
operational attributes from the server other than the altServer
attribute, and the server need not store any operational attributes
other than altServer.
5. Features Of Ldapv3 That MAY Be Supported
If the CPS allows unauthenticated anonymous access to the server,
then the server MUST allow a client to perform a Search operation
(for a "read" or "search" type request) without issuing a prior Bind
operation. The server MUST also allow the client to present a Bind
request with the simple authentication choice and a zero-length OCTET
STRING.
If the CPS allows weak password based authentication for "read" or
"search" access to the server, the client and the server SHOULD
support the DIGEST-MD5 mechanism [7] as specified in [8], and may
support a simple password Bind sequence following the negotiation of
a TLS ciphersuite to provide connection confidentiality, as specified
in [10].
If the CPS requires strong authentication for access to the server
then the client and the server SHOULD support certificate based
authentication as specified in [10].
The parameters of the Search operation for "read" or "search" type
queries will usually be set as specified in RFC 2559. However,
X.509(1997) [9] supports flexible certificate matching by the server,
via the certificateMatch MATCHING-RULE. For example, a client may
search for certificates with a particular validity time, key usage,
policy or other field. If the server supports flexible matching, then
the extensibleMatch filter item MUST be supported. Clients MAY
support the extensibleMatch filter item.
6. Security Considerations
The PKI information to be retrieved from LDAPv3 servers (certificates
and CRLs) is digitally signed and therefore additional integrity
services are NOT REQUIRED. The CPS will specify whether the
information should be publicly available or not. If publicly
available, privacy services will NOT be REQUIRED for retrieval
requests. If not publicly available, privacy services MAY be REQUIRED
and these can be provided by a TLS ciphersuite as specified in clause
5.
For update of the information by CAs either strong authentication or
weaker password based authentication MUST be supported as specified
in clause 5. Additional access controls SHOULD be provided.
Organizations are NOT REQUIRED to provide external CAs or users with
access to their directories.
7 Copyright
Copyright (C) The Internet Society (date). 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. 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
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 must 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.
8. References
[1] S.Boeyen, T. Howes, P. Richard "Internet X.509 Public Key
Infrastructure Operational Protocols - LDAPv2", RFC 2559, April 1999
[2] Yeong, W., Howes, T., and Kille, S. "Lightweight Directory Access
Protocol", RFC 1777, March 1995.
[3] T. Dierks, C. Allen. "The TLS Protocol Version 1.0", RFC 2246,
January 1999.
[4] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
Protocol (v3)", Dec. 1997, RFC 2251
[5] S.Bradner. "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[6] M. Wahl, S. Kille, T. Howes. "Lightweight Directory Access
Protocol (v3): UTF-8 String Representation of Distinguished Names",
RFC2253, December 1997.
[7] Digest md5
[8] P. Leach, C. Newman, "Using Digest Authentication as a SASL
Mechanism", INTERNET DRAFT <draft-leach-digest-sasl-01.txt>, November
1998.
[9] X.509(97)
[10] M. Wahl, H. Alvestrand, J. Hodges, RL "Bob" Morgan.
"Authentication Methods for LDAP" <draft-ietf-ldapext-authmeth-
03.txt>, November 1998
[11] ITU-T Rec. X.690, "Specification of ASN.1 encoding rules: Basic,
Canonical, and Distinguished Encoding Rules", 1994.
[12] F. Yergeau. "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
10 Authors Address
David Chadwick
IS Institute
University of Salford
Salford
England
M5 4WT
Email: d.w.chadwick@iti.salford.ac.uk
Internet-Draft PKIX Operational Protocols - LDAPv3 12 June 1999
