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





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  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 }




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           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.








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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.







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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: [email protected]
  mail: [email protected]
  telephoneNumber: + 781 442 0926
  telephoneNumber: 555-9999



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  dn: cn=David Chadwick,ou=isi,o=salford,dc=ac,dc=uk
  cn: David Chadwick
  sn: Chadwick
  objectClass: organizationalPerson
  objectClass: person
  objectClass: inetOrgPerson
  mail: [email protected]

  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: [email protected]
  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



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   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: [email protected]
  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}




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  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 <[email protected]>
     Usage: Control
     Specification: RFC3876
     Author/Change Controller: IESG
     Comments: none





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  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.









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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.




















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10.  Authors' Addresses

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

  Phone: +44 161 295 5351
  EMail: [email protected]


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

  EMail: [email protected]
































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11.  Full Copyright Statement

  Copyright (C) The Internet Society (2004).

  This document is subject to the rights, licenses and restrictions
  contained in BCP 78, and except as set forth therein, the authors
  retain all their rights.

  This document and the information contained herein are provided on an
  "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/S HE
  REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
  INTERNET ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

  The IETF takes no position regarding the validity or scope of any
  Intellectual Property Rights or other rights that might be claimed to
  pertain to the implementation or use of the technology described in
  this document or the extent to which any license under such rights
  might or might not be available; nor does it represent that it has
  made any independent effort to identify any such rights.  Information
  on the IETF's procedures with respect to rights in IETF Documents can
  be found in BCP 78 and BCP 79.

  Copies of IPR disclosures made to the IETF Secretariat and any
  assurances of licenses to be made available, or the result of an
  attempt made to obtain a general license or permission for the use of
  such proprietary rights by implementers or users of this
  specification can be obtained from the IETF on-line IPR repository at
  http://www.ietf.org/ipr.

  The IETF invites any interested party to bring to its attention any
  copyrights, patents or patent applications, or other proprietary
  rights that may cover technology that may be required to implement
  this standard.  Please address the information to the IETF at ietf-
  [email protected].

Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.







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