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: sean.mullan@hotmail.com
mail: mullan@east.sun.com
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: 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
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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: 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}
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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 <d.w.chadwick@salford.ac.uk>
Usage: Control
Specification: RFC3876
Author/Change Controller: IESG
Comments: none
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RFC 3876 Returning Matched Values with LDAPv3 September 2004
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: 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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RFC 3876 Returning Matched Values with LDAPv3 September 2004
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
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Acknowledgement
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Internet Society.
Chadwick & Mullan Standards Track [Page 12]