Network Working Group                                 M. Smith, Editor
Request for Comments: DRAFT                        Pearl Crescent, LLC
Obsoletes: RFC 2254                                           T. Howes
Expires: 24 April 2005                                   Opsware, Inc.
                                                       24 October 2004

             LDAP: String Representation of Search Filters

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she become
   aware will be disclosed, in accordance with RFC 3668.

   This document is intended to be published as a Standards Track RFC,
   replacing RFC 2254.  Distribution of this memo is unlimited.
   Technical discussion of this document will take place on the IETF
   LDAP (v3) Revision (ldapbis) Working Group mailing list
   <>.  Please send editorial comments directly
   to the editor <>.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   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 a "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   Copyright (C) The Internet Society (2004).  All Rights Reserved.
   Please see the Full Copyright section near the end of this document
   for more information.

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   LDAP search filters are transmitted in the LDAP protocol using a
   binary representation that is appropriate for use on the network.
   This document defines a human-readable string representation of LDAP
   search filters that is appropriate for use in LDAP URLs and in other

Table of Contents

       Status of this Memo............................................1
       Table of Contents..............................................2
1.     Introduction...................................................2
2.     LDAP Search Filter Definition..................................3
3.     String Search Filter Definition................................4
4.     Examples.......................................................6
5.     Security Considerations........................................7
6.     IANA Considerations............................................7
7.     Normative References...........................................7
8.     Informative References.........................................8
9.     Acknowledgments................................................8
10.    Authors' Addresses.............................................8
11.    Appendix A: Changes Since RFC 2254.............................9
11.1.     Technical Changes...........................................9
11.2.     Editorial Changes...........................................10
12.    Appendix B: Changes Since Previous Document Revision...........11
12.1.     Editorial Changes...........................................11
13.    Intellectual Property Rights...................................11
14.    Full Copyright.................................................12

1.  Introduction

   The Lightweight Directory Access Protocol (LDAP) [Protocol] defines a
   network representation of a search filter transmitted to an LDAP
   server.  Some applications may find it useful to have a common way of
   representing these search filters in a human-readable form; LDAP URLs
   are an example of one such application.  This document defines a
   human-readable string format for representing the full range of
   possible LDAP version 3 search filters, including extended match

   This document is an integral part of the LDAP Technical Specification

   This document replaces RFC 2254.  Changes to RFC 2254 are summarized
   in Appendix A.

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   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14 [RFC2119].

2.  LDAP Search Filter Definition

   An LDAPv3 search filter is defined in Section 4.5.1 of [Protocol] as

        Filter ::= CHOICE {
            and                [0] SET SIZE (1..MAX) OF filter Filter,
            or                 [1] SET SIZE (1..MAX) OF filter Filter,
            not                [2] Filter,
            equalityMatch      [3] AttributeValueAssertion,
            substrings         [4] SubstringFilter,
            greaterOrEqual     [5] AttributeValueAssertion,
            lessOrEqual        [6] AttributeValueAssertion,
            present            [7] AttributeDescription,
            approxMatch        [8] AttributeValueAssertion,
            extensibleMatch    [9] MatchingRuleAssertion }

        SubstringFilter ::= SEQUENCE {
            type    AttributeDescription,
            -- initial and final can occur at most once
            substrings    SEQUENCE SIZE (1..MAX) OF substring CHOICE {
             initial        [0] AssertionValue,
             any            [1] AssertionValue,
             final          [2] AssertionValue } }

        AttributeValueAssertion ::= SEQUENCE {
            attributeDesc   AttributeDescription,
            assertionValue  AssertionValue }

        MatchingRuleAssertion ::= SEQUENCE {
            matchingRule    [1] MatchingRuleId OPTIONAL,
            type            [2] AttributeDescription OPTIONAL,
            matchValue      [3] AssertionValue,
            dnAttributes    [4] BOOLEAN DEFAULT FALSE }

        AttributeDescription ::= LDAPString
                        -- Constrained to <attributedescription>
                        -- [Models]

        AttributeValue ::= OCTET STRING

        MatchingRuleId ::= LDAPString

        AssertionValue ::= OCTET STRING

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        LDAPString ::= OCTET STRING -- UTF-8 encoded,
                                    -- [Unicode] characters

   The AttributeDescription is a string representation of the attribute
   description and is defined in [Protocol].  The AttributeValue and
   AssertionValue OCTET STRING have the form defined in [Syntaxes].  The
   Filter is encoded for transmission over a network using the Basic
   Encoding Rules (BER) defined in [X.690], with simplifications
   described in [Protocol].

3.  String Search Filter Definition

   The string representation of an LDAP search filter is a string of
   UTF-8 [RFC3629] encoded Unicode characters [Unicode] that is defined
   by the following grammar, following the ABNF notation defined in
   [RFC2234].  The productions used that are not defined here are
   defined in section 1.4 (Common ABNF Productions) of [Models] unless
   otherwise noted.  The filter format uses a prefix notation.

      filter         = LPAREN filtercomp RPAREN
      filtercomp     = and / or / not / item
      and            = AMPERSAND filterlist
      or             = VERTBAR filterlist
      not            = EXCLAMATION filter
      filterlist     = 1*filter
      item           = simple / present / substring / extensible
      simple         = attr filtertype assertionvalue
      filtertype     = equal / approx / greaterorequal / lessorequal
      equal          = EQUALS
      approx         = TILDE EQUALS
      greaterorequal = RANGLE EQUALS
      lessorequal    = LANGLE EQUALS
      extensible     = attr [dnattrs]
                             [matchingrule] COLON EQUALS assertionvalue
                       / [dnattrs]
                              matchingrule COLON EQUALS assertionvalue
                       / COLON EQUALS assertionvalue
      present        = attr EQUALS ASTERISK
      substring      = attr EQUALS [initial] any [final]
      initial        = assertionvalue
      any            = ASTERISK *(assertionvalue ASTERISK)
      final          = assertionvalue
      attr           = attributedescription
                         ; The attributedescription rule is defined in
                         ; Section 2.5 of [Models].
      dnattrs        = COLON "dn"
      matchingrule   = COLON oid
      assertionvalue = valueencoding

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      ; The <valueencoding> rule is used to encode an <AssertionValue>
      ; from Section 4.1.6 of [Protocol].
      valueencoding  = 0*(normal / escaped)
      normal         = UTF1SUBSET / UTFMB
      escaped        = ESC HEX HEX
      UTF1SUBSET     = %x01-27 / %x2B-5B / %x5D-7F
                          ; UTF1SUBSET excludes 0x00 (NUL), LPAREN,
                          ; RPAREN, ASTERISK, and ESC.
      EXCLAMATION    = %x21 ; exclamation mark ("!")
      AMPERSAND      = %x26 ; ampersand (or AND symbol) ("&")
      ASTERISK       = %x2A ; asterisk ("*")
      COLON          = %x3A ; colon (":")
      VERTBAR        = %x7C ; vertical bar (or pipe) ("|")
      TILDE          = %x7E ; tilde ("~")

   Note that although both the <substring> and <present> productions in
   the grammar above can produce the "attr=*" construct, this construct
   is used only to denote a presence filter.

   The <valueencoding> rule ensures that the entire filter string is a
   valid UTF-8 string and provides that the octets that represent the
   ASCII characters "*" (ASCII 0x2a), "(" (ASCII 0x28), ")" (ASCII
   0x29), "\" (ASCII 0x5c), and NUL (ASCII 0x00) are represented as a
   backslash "\" (ASCII 0x5c) followed by the two hexadecimal digits
   representing the value of the encoded octet.

   This simple escaping mechanism eliminates filter-parsing ambiguities
   and allows any filter that can be represented in LDAP to be
   represented as a NUL-terminated string. Other octets that are part of
   the <normal> set may be escaped using this mechanism, for example,
   non-printing ASCII characters.

   For AssertionValues that contain UTF-8 character data, each octet of
   the character to be escaped is replaced by a backslash and two hex
   digits, which form a single octet in the code of the character.

   For example, the filter checking whether the "cn" attribute contained
   a value with the character "*" anywhere in it would be represented as

   As indicated by the valueencoding rule, implementations MUST escape
   all octets greater than 0x7F that are not part of a valid UTF-8
   encoding sequence when they generate a string representation of a
   search filter.  Implementations SHOULD accept as input strings that
   are not valid UTF-8 strings. This is necessary because RFC 2254 did
   not clearly define the term "string representation" (and in
   particular did not mention that the string representation of an LDAP

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   search filter is a string of UTF-8 encoded Unicode characters).

4.  Examples

   This section gives a few examples of search filters written using
   this notation.

        (cn=Babs Jensen)
        (!(cn=Tim Howes))
        (&(objectClass=Person)(|(sn=Jensen)(cn=Babs J*)))

   The following examples illustrate the use of extensible matching.

        (cn: Flintstone)
        (cn:=Betty Rubble)
        (sn:dn: Rubble)
        (o:dn:=Ace Industry)
        (:1.2.3:=Wilma Flintstone)

   The first example shows use of the matching rule "".

   The second example demonstrates use of a MatchingRuleAssertion form
   without a matchingRule.

   The third example illustrates the use of the ":oid" notation to
   indicate that matching rule "" should be used when making
   comparisons, and that the attributes of an entry's distinguished name
   should be considered part of the entry when evaluating the match
   (indicated by the use of ":dn").

   The fourth example denotes an equality match, except that DN
   components should be considered part of the entry when doing the

   The fifth example is a filter that should be applied to any attribute
   supporting the matching rule given (since the attr has been omitted).

   The sixth and final example is also a filter that should be applied
   to any attribute supporting the matching rule given.  Attributes
   supporting the matching rule contained in the DN should also be

   The following examples illustrate the use of the escaping mechanism.

        (o=Parens R Us \28for all your parenthetical needs\29)

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   The first example shows the use of the escaping mechanism to
   represent parenthesis characters. The second shows how to represent a
   "*" in an assertion value, preventing it from being interpreted as a
   substring indicator. The third illustrates the escaping of the
   backslash character.

   The fourth example shows a filter searching for the four-byte value
   0x00000004, illustrating the use of the escaping mechanism to
   represent arbitrary data, including NUL characters.

   The fifth example illustrates the use of the escaping mechanism to
   represent various non-ASCII UTF-8 characters.

   The sixth and final example demonstrates assertion of a BER encoded

5.  Security Considerations

   This memo describes a string representation of LDAP search filters.
   While the representation itself has no known security implications,
   LDAP search filters do. They are interpreted by LDAP servers to
   select entries from which data is retrieved.  LDAP servers should
   take care to protect the data they maintain from unauthorized access.

   Please refer to the Security Considerations sections of [Protocol]
   and [AuthMeth] for more information.

6.  IANA Considerations

   This document has no actions for IANA.

7.  Normative References

[AuthMeth]  Harrison, R. (editor), "LDAP: Authentication Methods and
            Connection Level Security Mechanisms",
            draft-ietf-ldapbis-authmeth-xx.txt, a work in progress.

[Models]    Zeilenga, K. (editor), "LDAP: Directory Information Models",
            draft-ietf-ldapbis-models-xx.txt, a work in progress.

[Protocol]  draft-ietf-ldapbis-protocol-xx.txt, a work in progress.

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[RFC2119]   S. Bradner, "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14 (also RFC 2119), March 1997.

[RFC2234]   Crocker, D., Overell, P., "Augmented BNF for Syntax
            Specifications: ABNF", RFC 2234, November 1997.

[RFC3629]   Yergeau, F., "UTF-8, a transformation format of ISO 10646",
            RFC 3629, November 2003.

[Roadmap]   Zeilenga, K. (editor), "LDAP: Technical Specification Road
            Map", draft-ietf-ldapbis-roadmap-xx.txt, a work in progress.

[Syntaxes]  Dally, K. (editor), "LDAP: Syntaxes",
            draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress.

[Unicode]   The Unicode Consortium, "The Unicode Standard, Version
            3.2.0" is defined by "The Unicode Standard, Version 3.0"
            (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), as
            amended by the "Unicode Standard Annex #27: Unicode 3.1"
            ( and by the "Unicode
            Standard Annex #28: Unicode 3.2."

[X.690]     Specification of ASN.1 encoding rules: Basic, Canonical, and
            Distinguished Encoding Rules, ITU-T Recommendation X.690,

8.  Informative References


9.  Acknowledgments

   This document replaces RFC 2254 by Tim Howes.  Changes included in
   this revised specification are based upon discussions among the
   authors, discussions within the LDAP (v3) Revision Working Group
   (ldapbis), and discussions within other IETF Working Groups.  The
   contributions of individuals in these working groups is gratefully

10.  Authors' Addresses

   Mark Smith, Editor
   Pearl Crescent, LLC
   447 Marlpool Dr.
   Saline, MI 48176
   +1 734 944-2856

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   Tim Howes
   Opsware, Inc.
   599 N. Mathilda Ave.
   Sunnyvale, CA 94085
   +1 408 744-7509

11.  Appendix A: Changes Since RFC 2254

11.1.  Technical Changes

   Replaced [ISO 10646] reference with [Unicode].

   The following technical changes were made to the contents of the
   "String Search Filter Definition" section:

   Added statement that the string representation is a string of UTF-8
   encoded Unicode characters.

   Revised all of the ABNF to use common productions from [Models].

   Replaced the "value" rule with a new "assertionvalue" rule within the
   "simple", "extensible", and "substring" ("initial", "any", and
   "final") rules.  This matches a change made in [Syntaxes].

   Revised the "attr", "matchingrule", and "assertionvalue" ABNF to more
   precisely reference productions from the [Models] and [Protocol]

   "String Search Filter Definition" section: replaced "greater" and
   "less" with "greaterorequal" and "lessorequal" to avoid confusion.

   Introduced the "valueencoding" and associated "normal" and "escaped"
   rules to reduce the dependence on descriptive text. The "normal"
   production restricts filter strings to valid UTF-8 sequences.

   Added a third option to the "extensible" production to allow creation
   of a MatchingRuleAssertion that only has a matchValue.

   Added a statement about expected behavior in light of RFC 2254's lack
   of a clear definition of "string representation."

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11.2.  Editorial Changes

   Changed document title to include "LDAP:" prefix.

   IESG Note: removed note about lack of satisfactory mandatory
   authentication mechanisms.

   Header and "Authors' Addresses" sections: added Mark Smith as the
   document editor and updated affiliation and contact information.

   "Table of Contents", "IANA Considerations", and "Intellectual
   Property Rights" sections: added.

   Copyright: updated per latest IETF guidelines.

   "Abstract" section: separated from introductory material.

   "Introduction" section: new section; separated from the Abstract.
   Updated second paragraph to indicate that RFC 2254 is replaced by
   this document (instead of RFC 1960). Added reference to the [Roadmap]

   "LDAP Search Filter Definition" section: made corrections to the
   LDAPv3 search filter ABNF so it matches that used in [Protocol].

   Clarified the definition of 'value' (now 'assertionvalue') to take
   into account the fact that it is not precisely an AttributeAssertion
   from [Protocol] section 4.1.6 (special handling is required for some
   characters).  Added a note that each octet of a character to be
   escaped is replaced by a backslash and two hex digits, which
   represent a single octet.

   "Examples" section: added four additional examples: (seeAlso=),
   (cn:=Betty Rubble), (:1.2.3:=Wilma Flintstone), and
   (\04\02\48\69).  Replaced one occurrence of "a
   value" with "an assertion value".  Corrected the description of this
   example: (sn:dn: Rubble).

   "Security Considerations" section: added references to [Protocol] and

   "Normative References" section: renamed from "References" per new RFC
   guidelines. Changed from [1] style to [Protocol] style throughout the
   document.  Added entries for [Unicode], [RFC2119], [AuthMeth],
   [Models], and [Roadmap] and updated the UTF-8 reference.  Replaced
   RFC 822 reference with a reference to RFC 2234.

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   "Informative References" section: added for clarity.

   "Acknowledgments" section: added.

   "Appendix A: Changes Since RFC 2254" section: added.

   "Appendix B: Changes Since Previous Document Revision" section:

12.  Appendix B: Changes Since Previous Document Revision

   This appendix lists all changes relative to the previously published
   revision, draft-ietf-ldapbis-filter-07.txt.  Note that when
   appropriate these changes are also included in Appendix A, but are
   also included here for the benefit of the people who have already
   reviewed draft-ietf-ldapbis-filter-07.txt.  This section will be
   removed before this document is published as an RFC.

12.1.  Editorial Changes

   "Status of this Memo" section: replaced RFC 3668 (IPR) boilerplate
   paragraph with the version that says "each author" instead of "I."

   "Status of this Memo" section: added 2 paragraphs that were
   accidently removed from the -07 revision (one begins with "The list
   of current Internet-Drafts..." and the other begins with "The list of
   Internet-Draft Shadow Directories...."

13.  Intellectual Property Rights

   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 procedures with respect to rights in RFC 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

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   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

14.  Full Copyright

   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

This Internet Draft expires on 24 April 2005.

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