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Internet-Draft                                      David Chadwick
LDAPExt WG                                         University of Salford
Intended Category: Standards Track                     Sean Mullan
                                                       Sun Microsystems
Expires: 2 March 2001                             September 2 2000


Returning Matched Values with LDAPv3
<draft-ietf-ldapext-matchedval-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 [1].

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

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 LDAPExt working group discussion
list:
                ietf-ldapext@netscape.com

or directly to the authors.


ABSTRACT

This document describes a control for the Lightweight Directory
Access Protocol v3 that is used to return a subset of attribute
values from an entry, specifically, only those values that match a
"values return" filter. Without support for this control, a client
must retrieve all of an attribute's values and search for specific
values locally.


1. Introduction

When reading an attribute from an entry using LDAPv3 [2], it is
normally only possible to read either the attribute type, or the
attribute type and all its values. It is not possible to selectively
read just a few of the attribute values. If an attribute holds many
values, for example, the userCertificate attribute, or the subschema
publishing operational attributes objectClasses and attributeTypes
[3], then it may be desirable for the user to be able to selectively
retrieve a subset of the values, specifically, those attribute values
that match some user defined selection criteria. Without the control
specified in this [ID/standard/document] a client must read all of
the attribute's values and filter out the unwanted values,
necessitating the client to implement the matching rules. It also
requires the client to potentially read and process many irrelevant
values, which can be inefficient if the values are large or complex,
or there are many values stored per attribute.

This [ID/Standard/document] specifies an LDAPv3 control to enable a
user to return only those values that matched (i.e. returned TRUE to)
one or more elements of a newly defined "values return" filter. This
control can be especially useful when used in conjunction with
extensible matching rules that match on one or more components of
complex binary attribute values.

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. The valuesReturnFilter Control

The valuesReturnFilter control MAY be critical or non-critical as
determined by the user. It only has meaning for the Search operation,
and SHOULD only be added to the Search operation by the client. If
the server supports the control and it is present on a Search
operation, the server MUST obey the control regardless of the value
of the criticality flag.

If the server does not support the control, or the control is applied
to an operation other than Search, the control MUST be ignored by the
server unless it is marked critical when an
unavailableCriticalExtension error MUST be returned.

The object identifier for this control is 1.2.826.0.1.3344810.2.3


The controlValue is

        ValuesReturnFilter ::= SEQUENCE OF SimpleFilterItem

        SimpleFilterItem ::= CHOICE {
                equalityMatch   [3] AttributeValueAssertion,
                substrings      [4] SubstringFilter,
                greaterOrEqual  [5] AttributeValueAssertion,
                lessOrEqual     [6] AttributeValueAssertion,
                present         [7] AttributeDescription,
                approxMatch     [8] AttributeValueAssertion,
                extensibleMatch [9] SimpleMatchingAssertion }

         SimpleMatchingAssertion ::= SEQUENCE {
                matchingRule    [1] MatchingRuleId OPTIONAL,
                type            [2] AttributeDescription OPTIONAL,
                matchValue      [3] AssertionValue}

All the above data types have their standard meanings as defined in
[2].

If the server supports this control, the server MUST make use of the
control as follows:

(1) The Search Filter is first executed in order to determine
which entries satisfy the Search criteria (these are the
filtered entries). The control has no impact on this step.

(2) If the typesOnly parameter of the Search Request is TRUE,
the control has no effect and the Search Request SHOULD be
processed as if the control had not been specified.

(3) If the attributes parameter of the Search Request consists
of a list containing only the attribute with OID "1.1"
(specifying that no attributes are to be returned), the control
has no effect and the Search Request SHOULD be processed as if
the control had not been specified.

(4) For each attribute listed in the attributes parameter of the
Search Request, the server MUST apply the control as follows to
each entry in the set of filtered entries:

i) Every attribute value that evaluates TRUE against one or
more elements of the ValuesReturnFilter is placed in the
corresponding SearchResultEntry.
ii) Every attribute value that evaluates FALSE or undefined
against all elements of the ValuesReturnFilter is not
placed in the corresponding SearchResultEntry. An
attribute that has no values selected is returned with an
empty set of vals.

Note. If the AttributeDescriptionList is empty or comprises "*"
then the control MUST be applied against every attribute.


3. Relationship to X.500

The control is a superset of the matchedValuesOnly (MVO) boolean of
the X.500 DAP [4] Search argument, as amended in the latest version
[6]. Close examination of the matchedValuesOnly boolean by the
LDAPExt group revealed ambiguities and complexities in the MVO
boolean that could not easily be resolved. For example, it was not
clear if the MVO boolean governed only those attribute values that
contributed to the overall truth of the filter, or all of the
attribute values even if the filter item containing the attribute
evaluated to false. For this reason the LDAP group decided to replace
the MVO boolean with a simple filter that removes any uncertainty as
to whether an attribute value has been selected or not.


4. Relationship to other LDAP Controls

The purpose of this control is to select zero, one or more attribute
values from each requested attribute in a filtered entry, and to
discard the remainder. Once the attribute values have been discarded
by this control they MUST NOT be re-instated into the Search results
by other controls.

This control acts independently of other LDAP controls such as server
side sorting [10] and duplicate entries [7]. However, there might be
interactions between this control and other controls so that a
different set of Search Result Entries are returned, or the entries
are returned in a different order, depending upon the sequencing of
this control and other controls in the LDAP request. For example,
with server side sorting, if sorting is done first, and value return
filtering second, the set of Search Results may appear to be in the
wrong order since the value filtering may remove the attribute values
upon which the ordering was done. (The sorting document specifies
that entries without any sort key attribute values should be treated
as coming after all other attribute values.) Similarly with duplicate
entries, if duplication is performed before value filtering, the set
of Search Result Entries may contain identical duplicate entries,
each with an empty set of attribute values, because the value
filtering removed the attribute values that were used to duplicate
the results.

For these reasons it is recommended that the ValuesReturnFilter
control in a SearchRequest SHOULD precede other controls that affect
the number and ordering of SearchResultEntrys.


5. Examples

All entries are provided in LDIF format [8].

The string representation of the valuesReturnFilter in the examples
below is:

    valuesReturnFilterElement = "(" item ")"
    valuesReturnFilter = 1*valuesReturnFilterElement


(1) The first example shows how the control can be set to return all
attribute values from one attribute type (e.g. telephoneNumber) and a
subset of values from another attribute type (e.g. mail).

The entries below represent organisationalPerson object classes
located somewhere beneath the distinguished name dc=ac, dc=uk.

cn: Sean Mullan
sn: Mullan
dn: cn=Sean Mullan, ou=people, dc=sun, dc=ac, dc=uk
objectClass: organisationalPerson
objectClass: person
objectClass: inetOrgPerson
mail: sean.mullan@hotmail.com
mail: mullan@east.sun.com
telephoneNumber: + 781 442 0926
telephoneNumber: 555-9999

cn: David Chadwick
sn: Chadwick
dn: cn=David Chadwick, ou=isi, o=salford, dc=ac, dc=uk
objectClass: organisationalPerson
objectClass: person
objectClass: inetOrgPerson
mail: d.w.chadwick@salford.ac.uk

An LDAP search operation is specified with a baseObject set to the
DN of the search base (i.e. dc=ac, dc=uk), a subtree scope, a filter
set to (sn=mullan), and the list of attributes to be returned set to
"mail, telephoneNumber". In addition, a ValuesReturnFilter control is
set to "(mail=*hotmail.com),(telephoneNumber=*)"

The search results returned by the server would consist of the
following entry:

dn: cn=Sean Mullan, ou=people, dc=sun, dc=ac, dc=uk
cn: Sean Mullan
mail: sean.mullan@hotmail.com
telephoneNumber: + 781 442 0926
telephoneNumber: 555-9999

Note that the control has no effect on the values returned for the
"telephoneNumber" attribute (all of the values are returned), since
the control specified that all values should be returned.


(2) The second example shows how one might retrieve a single
attribute type subschema definition for the "gunk" attribute with OID
1.2.3.4.5 from the subschema subentry

Assume the subschema subentry is held below the root entry with DN
cn=subschema subentry, o=myorg and this holds an attributeTypes
operational attribute holding the descriptions of the 35 attributes
known to this server (each description is held as a single attribute
value of the attributeTypes attribute).

cn: subschema subentry
dn: cn=subschema subentry, o=myorg
objectClass: subschema
attributeTypes: ( 2.5.4.3 NAME 'cn' SUP name )
attributeTypes: ( 2.5.4.6 NAME 'c' SUP name SINGLE-VALUE )
attributeTypes: ( 2.5.4.0 NAME 'objectClass' EQUALITY
objectIdentifierMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 )
attributeTypes: ( 2.5.18.2 NAME 'modifyTimestamp' EQUALITY
generalizedTimeMatch ORDERING generalizedTimeOrderingMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 SINGLE-VALUE NO-USER-
MODIFICATION USAGE directoryOperation )
attributeTypes: ( 2.5.21.6 NAME 'objectClasses' EQUALITY
objectIdentifierFirstComponentMatch SYNTAX
1.3.6.1.4.1.1466.115.121.1.37 USAGE directoryOperation )
attributeTypes: ( 1.2.3.4.5 NAME 'gunk' EQUALITY caseIgnoreMatch
SUBSTR caseIgnoreSubstringsMatch SYNTAX
1.3.6.1.4.1.1466.115.121.1.44{64} )
attributeTypes: ( 2.5.21.5 NAME 'attributeTypes' EQUALITY
objectIdentifierFirstComponentMatch SYNTAX
1.3.6.1.4.1.1466.115.121.1.3 USAGE directoryOperation )

plus another 28 - you get the idea.


The user creates an LDAP search operation with a baseObject set to
cn=subschema subentry, o=myorg, a scope of base, a filter set to
(objectClass=subschema), the list of attributes to be returned set to
"attributeTypes", and the ValuesReturnFilter set to
(attributeTypes=1.2.3.4.5)

The search result returned by the server would consist of the
following entry:

dn: cn=subschema subentry, o=myorg
cn: subschema subentry
attributeTypes: ( 1.2.3.4.5 NAME 'gunk' EQUALITY caseIgnoreMatch
SUBSTR caseIgnoreSubstringsMatch SYNTAX
1.3.6.1.4.1.1466.115.121.1.44{64} )


(3) The final example shows how the control can be used to match on a
userCertificate attribute value with a particular key usage bit set
(in this case the key encipherment bit). Note that this example
requires the LDAP server to support the certificateMatch matching
rule defined in [9] and extensible matching.

The entry below represent a pkiUser object class stored in the
directory.

dn: cn=David Chadwick + serialNumber=123456, ou=people, o=University
of Salford, c=gb
cn: David Chadwick + serialNumber=123456
objectClass: person
objectClass: organisationalPerson
objectClass: pkiUser
objectClass: inetOrgPerson
sn: Chadwick
mail: d.w.chadwick@salford.ac.uk
userCertificate: {binary representation of certificate including key
usage bit of digitalSignature (0)}
userCertificate: {binary representation of certificate including key
usage bit of nonRepudiation (1)}
userCertificate: {binary representation of certificate including key
usage bit of key encipherment (2)}
userCertificate: {binary representation of certificate including key
usage bit of data encipherment (3)}

An LDAP search operation is specified with a baseObject set to
o=University of Salford, c=gb, a subtree scope, a filter set to
(sn=chadwick) and the list of attributes to be returned set to
"userCertificate;binary". In addition, a ValuesReturnFilter control
is set to (2.5.13.35, userCertificate, USE'001'B)

The search result returned by the server would consist of the
following entry:

dn: cn=David Chadwick + serialNumber=123456, ou=people, o=University
of Salford, c=gb
userCertificate;binary: {binary representation of certificate with
key usage bit of key encipherment (2)}


6. Security Considerations

This [ID/standard/document] does not primarily discuss security
issues.

Note however that attribute values MUST only be returned if the
access controls applied by the LDAP server allow them to be returned,
and in this respect the effect of the ValuesReturnFilter control is
of no consequence.

Note that the ValuesReturnFilter control may have a positive effect
on the deployment of public key infrastructures. Certain PKI
operations, like searching for specific certificates, become more
practical when combined with X.509 certificate matching rules at the
server, and more scalable, since the control avoids the downloading
of potentially large numbers of irrelevant certificates which would
have to be processed and filtered locally (which in some cases is
very difficult to perform).


7. Acknowledgements

The authors would like to thank members of the LDAPExt list for their
constructive comments on earlier versions of this
[ID/standard/document], and in particular to Harald Alvestrand who
first suggested having an attribute return filter and Bruce
Greenblatt who first proposed a syntax for this control.

8. 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.


9. References

[1] S.Brabner. "The Internet Standards Process -- Revision 3", RFC
2026, October 1996.
[2] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
Protocol (v3)", Dec. 1997, RFC 2251
[3] M. Wahl, A. Coulbeck, T. Howes, S. Kille, "Lightweight Directory
Access Protocol (v3): Attribute Syntax Definitions", RFC 2252, Dec
1997
[4] ITU-T Rec. X.511, "The Directory: Abstract Service Definition",
1993.
[5] S.Bradner. "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[6] Draft ISO/IEC 9594 / ITU-T Rec X.511 (2001) The Directory:
Abstract Service Definition.
[7] J. Sermersheim. "LDAP Control for a Duplicate Entry
Representation of Search Results", Internet Draft <draft-ietf-
ldapext-ldapv3-dupent-04.txt>, July 2000.
[8] G. Good. "The LDAP Data Interchange Format (LDIF) - Technical
Specification". RFC 2849, June 2000.
[9] D. Chadwick, S.Legg. "Internet X.509 Public Key Infrastructure -
Additional LDAP Schema for PKIs and PMIs", Internet Draft <draft-
pkix-ldap-schema-01.txt>, September 2000
[10] T. Howes, M. Wahl, A. Anantha, "LDAP Control Extension for
Server Side Sorting of Search Results", RFC 2891, August 2000

10. Authors Addresses

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

Email: d.w.chadwick@salford.ac.uk
Tel: +44 161 295 5351

Sean Mullan
Sun Microsystems
East Point Business Park
Dublin 3
Ireland
Tel: +353 1 853 0655
Email: sean.mullan@sun.com


11. Changes since version 2

i) Revised the examples to be more appropriate
ii) Section on interactions with other LDAP controls added
iii) Removed EditorÆs note concerning present filter
iv) Tightened wording about its applicability to other operations
and use of criticality field


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