LDAP Matched Values: Returning Matched Values with the Lightweight Directory Access Protocol version 3 (LDAPv3)

Network Working Group                                        D. Chadwick
Request for Comments: 3876                         University of Salford
Category: Standards Track                                      S. Mullan
                                                        Sun Microsystems
                                                          September 2004


                   Returning Matched Values with the
        Lightweight Directory Access Protocol version 3 (LDAPv3)

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 (2004).

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 BCP 14, 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, 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
   [6], as per Section 5.1 of RFC 2251 [2], of a value of the ASN.1 [5]
   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 values.

   Note.  If the AttributeDescriptionList (see [2]) 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) [8] Search argument, as
   amended in the latest version [9].  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 was evaluated as 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 [13] and duplicate entries [10].  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 an LDAP Data Interchange Format
   (LDIF)[11].

   The string representation of the valuesReturnFilter in the examples
   below uses the following ABNF [15] notation:

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

   where item is as defined below (adapted from RFC2254 [14]).

      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 [12] as the EQUALITY matching rule for userCertificate.

   The entry below represents 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
   scalable, and more practical when combined with X.509 certificate
   matching rules at the server, 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

   The Matched Values control as an LDAP Protocol Mechanism [7] has been
   registered as follows:

      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: RFC3876
      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 [16].

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.  References

9.1.  Normative References

   [1]  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
        9, RFC 2026, October 1996.

   [2]  Wahl, M., Howes, T., and S. Kille, "Lightweight Directory Access
        Protocol (w3)", RFC 2251, December 1997.

   [3]  Wahl, M., Coulbeck, A., Howes, T., and S. Kille, "Lightweight
        Directory Access Protocol (v3): Attribute Syntax Definitions",
        RFC 2252, December 1997.

   [4]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [5]  ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998,
        Information Technology - Abstract Syntax Notation One (ASN.1):
        Specification of Basic Notation

   [6]  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)

   [7]  Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
        Considerations for the Lightweight Directory Access Protocol
        (LDAP)", BCP 64, RFC 3383, September 2002.

9.2.  Informative References

   [8]  ITU-T Rec. X.511, "The Directory: Abstract Service Definition",
        1993.

   [9]  ISO/IEC 9594 / ITU-T Rec X.511 (2001) The Directory: Abstract
        Service Definition.

   [10] Sermersheim, J., "LDAP Control for a Duplicate Entry
        Representation of Search Results", Work in Progress, October
        2000.

   [11] Good, G., "The LDAP Data Interchange Format (LDIF) - Technical
        Specification", RFC 2849, June 2000.

   [12] Chadwick, D. and S.Legg, "Internet X.509 Public Key
        Infrastructure - Additional LDAP Schema for PKIs", Work in
        Progress, June 2002

   [13] Howes, T., Wahl, M., and A. Anantha, "LDAP Control Extension for
        Server Side Sorting of Search Results", RFC 2891, August 2000.

   [14] Howes, T., "The String Representation of LDAP Search Filters",
        RFC 2254, December 1997.

   [15] Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.

   [16] BRITISH STANDARD BS 7453 Part 1. Procedures for UK Registration
        for Open System Standards Part 1: Procedures for the UK Name
        Registration Authority.

10.  Authors' Addresses

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

   Phone: +44 161 295 5351
   EMail: d.w.chadwick@salford.ac.uk


   Sean Mullan
   Sun Microsystems
   One Network Drive
   Burlington, MA 01803
   USA

   EMail: sean.mullan@sun.com

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