Returning Matched Values with the Lightweight Directory Access Protocol version 3 (LDAPv3)
draft-ietf-ldapext-matchedval-07

Internet-Draft                                      David Chadwick
LDAPExt WG                                         University of Salford      
Intended Category: Standards Track                     Sean Mullan
                                                    Sun Microsystems
Expires: 8 March 2003                             8 September 2002

                   Returning Matched Values with LDAPv3
                  <draft-ietf-ldapext-matchedval-07.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
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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 version 3 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 the Lightweight 
Directory Access Protocol version 3 (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 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 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 [4].

2. The valuesReturnFilter Control

The valuesReturnFilter control is either 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 control is marked as critical, and either the server does not  
support the control or the control is applied to an operation other 
than Search, then the server MUST return an 
unavailableCriticalExtension error.  If the control is not marked as 
critical, and either the server does not support the control or the 
control is applied to an operation other than Search, then the server
MUST ignore the control.

The object identifier for this control is 1.2.826.0.1.3344810.2.3.

The controlValue is an OCTET STRING, whose value is the BER encoding 
[15], as per Section 5.1 of RFC 2251 [2], of a value of the ASN.1 
[14] type ValuesReturnFilter.

        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,
--- at least one of the above must be present
                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 is 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 is 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 user attribute. 
If the AttributeDescriptionList contains a "+" then the control 
MUST be applied against every operational attribute.

3. Relationship to X.500

The control is a superset of the matchedValuesOnly (MVO) boolean of 
the X.500 Directory Access Protocol (DAP) [5] Search argument, as 
amended in the latest version [6]. Close examination of the 
matchedValuesOnly boolean by the LDAP Extensions (LDAPEXT) Working 
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 LDAPEXT 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 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 LDAP Data Interchange Format (LDIF)[8].

The string representation of the valuesReturnFilter in the examples 
below uses the following ABNF [12] notation:

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

where item is as defined below (adapted from RFC2254 [11]). 
 
          item       = simple / present / substring / extensible
        simple     = attr filtertype value
        filtertype = equal / approx / greater / less
        equal      = "="
        approx     = "~="
        greater    = ">="
        less       = "<="
        extensible = attr [":" matchingrule] ":=" value
                     / ":" matchingrule ":=" value
        present    = attr "=*"
        substring  = attr "=" [initial] any [final]
        initial    = value
        any        = "*" *(value "*")
        final      = value
        attr       = AttributeDescription from Section 4.1.5 of [1]
        matchingrule = MatchingRuleId from Section 4.1.9 of [1]
        value      = AttributeValue from Section 4.1.6 of [1]

(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 organizationalPerson object classes 
located somewhere beneath the distinguished name dc=ac,dc=uk.

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

dn: cn=David Chadwick,ou=isi,o=salford,dc=ac,dc=uk 
cn: David Chadwick
sn: Chadwick
objectClass: organizationalPerson
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" or "*". 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
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). 

dn: cn=subschema subentry,o=myorg
cn: subschema subentry
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 obj
 ectIdentifierMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 )
attributeTypes: ( 2.5.18.2 NAME 'modifyTimestamp' EQUALITY gen
 eralizedTimeMatch ORDERING generalizedTimeOrderingMatch SYN
 TAX 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 obj
 ectIdentifierFirstComponentMatch SYNTAX 1.3.
 6.1.4.1.1466.115.121.1.37 USAGE directoryOperation )
attributeTypes: ( 1.2.3.4.5 NAME 'gunk' EQUALITY caseIgnoreMat
 ch SUBSTR caseIgnoreSubstringsMatch SYNTAX 1.3.
 6.1.4.1.1466.115.121.1.44{64} )
attributeTypes: ( 2.5.21.5 NAME 'attributeTypes' EQUALITY obj
 ectIdentifierFirstComponentMatch 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
attributeTypes: ( 1.2.3.4.5 NAME 'gunk' EQUALITY caseIgnoreMat
 ch 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. Note that this example requires the 
LDAP server to support the certificateExactMatch matching rule 
defined in [9] as the EQUALITY matching rule for userCertificate.

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

dn: cn=David Chadwick,ou=people,o=University of Salford,c=gb
cn: David Chadwick
objectClass: person 
objectClass: organizationalPerson 
objectClass: pkiUser 
objectClass: inetOrgPerson
sn: Chadwick
mail: d.w.chadwick@salford.ac.uk
userCertificate;binary: {binary representation of a certificate with 
a serial number of 2468 issued by o=truetrust ltd,c=gb}
userCertificate;binary: {binary representation of certificate with a 
serial number of 1357 issued by o=truetrust ltd,c=gb}
userCertificate;binary: {binary representation of certificate with a 
serial number of 1234 issued by dc=certsRus,dc=com}

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 ((userCertificate=1357$o=truetrust ltd,c=gb)).

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

dn: cn=David Chadwick,ou=people,o=University of Salford,c=gb
userCertificate;binary: {binary representation of certificate with a 
serial number of 1357 issued by o=truetrust ltd,c=gb}

6. Security Considerations

This 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. IANA Considerations

Registrigration of the Matched Values control as an LDAP Protocol 
Mechanism [16] is requested:

    Subject: Request for LDAP Protocol Mechanism Registration

    Object Identifier: 1.2.826.0.1.3344810.2.3
    Description: Matched Values Control
    Person & email address to contact for further information:
      David Chadwick <d.w.chadwick@salford.ac.uk>
    Usage: Control
    Specification: RFCxxxx 
    Author/Change Controller: IESG
    Comments: none

This document uses the OID 1.2.826.0.1.3344810.2.3 to identify the 
matchedValues control described here. This OID was assigned by 
TrueTrust Ltd, under its BSI assigned English/Welsh Registered 
Company number [13].

8. Acknowledgements

The authors would like to thank members of the LDAPExt list for their 
constructive comments on earlier versions of this 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.

9. 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.

10. References

Normative

[1] S. Bradner. "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] S.Bradner. "Key words for use in RFCs to Indicate Requirement 
Levels", RFC 2119, March 1997.
[14] ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998, 
Information Technology - Abstract Syntax Notation One (ASN.1): 
Specification of Basic Notation
[15] ITU-T Recommendation X.690 (1997) | ISO/IEC 8825-1,2,3:1998 
Information technology - ASN.1 encoding rules: Specification of Basic 
Encoding Rules (BER), Canonical Encoding Rules (CER) and 
Distinguished Encoding Rules (DER)
[16] K. Zeilenga. "IANA Considerations for LDAP" <draft-ietf-ldapbis-
iana-09.txt>, August 2002

Informative

[5] ITU-T Rec. X.511, "The Directory: Abstract Service Definition", 
1993.
[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-06.txt>, October 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", Internet Draft <draft-pkix-ldap-
pki-schema-00.txt>, June 2002
[10] T. Howes, M. Wahl, A. Anantha, "LDAP Control Extension for 
Server Side Sorting of Search Results", RFC 2891, August 2000
[11] T. Howes. "The String Representation of LDAP Search Filters". 
RFC 2254, December 1997.
[12] D. Crocker, Ed. "Augmented BNF for Syntax Specifications: ABNF." 
RFC 2234. November 1997.
[13] BRITISH STANDARD BS 7453 Part 1. Procedures for UK Registration 
for Open System Standards Part 1: Procedures for the UK Name 
Registration Authority.

11. 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

12. Changes since version 2

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

Changes since version 3

i)      Mandated that at least one of type and matchingRule in 
simpleMatchingAssertion be present
ii)     Fixed LDIF mistakes in the examples
iii)    Additional minor editorials only

Changes since version 4

i)      corrected the ABNF for single items of valuesReturnFilter

Changes since version 5

i)      added some adapted BNFL from [11] into the examples 
(specifically the [":dn"] component was removed)
ii)     general editorial tidying up prior to Last Call

Changes since version 6

i)      First example had all attributes (*) added to it
ii)     References to ASN.1 standards added
iii)    Syntax error in third example corrected
iv)     IANA considerations section added