draft-pkix-ldap-v3

Last Version:	draft-pkix-ldap-v3-03.txt		Tracker Entry
Date:	04-Nov-2000
Disposition:	expired

Internet-Draft                                       D.W.Chadwick
PKIX WG                       		   University of Salford
Intended Category: Standards Track             	    2 September 2000
Expires: 2 March 2001




                 Internet X.509 Public Key Infrastructure
                      Operational Protocols - LDAPv3
                       <draft-pkix-ldap-v3-03.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.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
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This Internet-Draft expires on 2 March 2001.

Comments and suggestions on this document are encouraged. Comments on
this document should be sent to the PKIX working group discussion
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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.


. 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].


. 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 an 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 RFC2559 (PKIX LDAPv2) [1] is fully compliant with the
;binary option of LDAPv3. The ;binary option of attribute
descriptions MUST be supported by all implementations. When a client
adds, deletes, retrieves or modifies attribute values that are
defined in RFC 2256 [13] to be stored and requested in the binary
form, the attribute type name MUST always be specified with the
;binary attribute option. When the server returns such an attribute
in a search result, the attribute type name MUST include the ;binary
option.  Other attribute description options SHOULD NOT be generated
by clients. Servers MAY choose to support them at their discretion.

Other parameters of the Search operation for "read" or "search" type
queries will usually be set as specified in RFC 2559 [1].

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].

Multiple attribute value assertions (AVAs) within RDN components of
distinguished names MUST be supported and the ordering of the AVAs is
non-deterministic. For example cn=John + serialNumber=123 is the same
as serialNumber=123 + cn=John.

LDAPv3 has the concept of unsolicited notifications that can be sent
from the server to the client. This is used to indicate when the
server is going down, so that a client can distinguish between a
server failure and a network failure. A client MUST be prepared to
accept unsolicited notifications defined in RFC 2251 [4].

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. (The access
controls on this attribute MUST be the same or less than those on
certificates and revocation lists.) 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, except
where mandated in this or other profiles.

If the Certification Practice Statement (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 MUST support
the DIGEST-MD5 mechanism [7] as specified in [8] and [10].

. 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 and
process them, although they are not required to automatically process
them and support multiple asynchronous outgoing connections.

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.

However, the returned referrals SHOULD NOT specify new search
filters, attributes to be returned or user credentials. Servers
SHOULD only return the hostport and DN components and MAY return the
scope component.


. Features Of Ldapv3 that are Not Used by this Profile

A client following this profile need not send the ModifyDN, Compare
and Abandon operations. The server MAY choose to support these
operations at its discretion. (Note that a client wishing to
abnormally terminate a search request may, instead of issuing an
Abandon operation, close the TCP/IP connection.)

The LDAPv3 protocol is infinitely extensible via two mechanisms:
extended operations and controls on existing operations. The client
does not need to generate any LDAPv3 protocol extensions (extended
operations or controls), unless flexible searching for certificates
is supported (see below).  The server SHOULD NOT return any LDAPv3
protocol extensions (extended operations or controls) apart from
those necessary to support the controls already used by the client.


. Features Of Ldapv3 That MAY Be Supported

The default behaviour for LDAPv3 servers is that a user must retrieve
all the attribute values from an attribute, or none of them (subject
of course to having access rights to the values). If the user of an
LDAPv3 server wishes to retrieve a limited number of attribute
values, specifically those that match certain filtering criteria,
(for example a data encryption userCertificate from a user’s entry,
or a revocation list that was current at a particular moment in time)
then this MAY be achieved by using the LDAPv3 valuesReturnFilter
control [15] along with the certificateExactMatch, certificateMatch,
certificateListExactMatch or certificateListMatch matching rules
[14].

If the CPS allows weak password based authentication for "read" or
"search" access to the server, the client and the server 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].


. 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. However, clients that retrieve CRLs
without some way of verifying the server run the risk of being sent a
still current but superceded CRL.

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.


. 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.


. References

[] 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] R. Rivest, "The MD5 Message-Digest Algorithm", RFC 1321, April

[8] P. Leach, C. Newman, "Using Digest Authentication as a SASL
Mechanism", RFC 2831, May 2000.
[9] ITU-T Rec. X.509(97) The  Directory:  Authentication Framework
[10] M. Wahl, H. Alvestrand, J. Hodges, R. Morgan. "Authentication
Methods for LDAP", RFC 2829, May 2000
[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.
[13] M.Wahl. "A Summary of the X.500(96) User Schema for use with
LDAPv3" RFC 2256, Dec 1997
[14] D.Chadwick, "Internet X.509 Public Key Infrastructure,
Additional LDAP Schema for PKIs and PMIs", <draft-pkix-ldap-schema-
.txt>, September 2000
[15] D.Chadwick, "Returning Matched Values with LDAPv3", Internet
Draft <draft-ldapext-matchedval-03.txt>, September 2000


. Authors Address

David Chadwick
IS Institute
University of Salford
Salford
England
M5 4WT

Email: d.w.chadwick@salford.ac.uk

. Changes Made to Version 01

i) Schema removed to a separate document
ii) Selecting individual attribute values updated to reflect new
LDAP Internet Draft
iii) Re-wording of text surrounding the use of ;binary option.

Changes Made to Version 02

i) Added text to Security section about superceded CRLs.
ii) Changed text in section 4 about which controls server can send
to client
iii) Updated references section
iv) Added selective retrieving of CRLs to section 5