Network Working Group                                 M. Smith, Editor
Request for Comments: DRAFT              Netscape Communications Corp.                        Pearl Crescent, LLC
Obsoletes: RFC 2254                                           T. Howes
Expires: 25 April 13 August 2004                                  Opsware, Inc.
                                                       25 October 2003
                                                      13 February 2004

             LDAP: String Representation of Search Filters

1.  Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   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 as "work in progress."

   The list of current Internet-Drafts can be accessed at

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

   Discussion of this document should take place on the LDAP (v3)
   Revision (ldapbis) Working Group mailing list <ietf->.

   Copyright (C) The Internet Society (2003). (2004).  All Rights Reserved.

2.  Abstract

   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

3.  Table of Contents

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

4.  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 [Roadmap].

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

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

5.  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,
                -- at least one must be present,
                -- 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 <attributedescription>
                                 -- [Models]

        AttributeValue ::= OCTET STRING

        MatchingRuleId ::= LDAPString

        AssertionValue ::= OCTET STRING

        LDAPString ::= OCTET STRING -- UTF-8 encoded,
                                    -- ISO 10646 [ISO10646] characters

   where the LDAPString above is limited to the UTF-8 encoding [UTF-8]
   of the ISO 10646 character set [ISO10646].

   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 defined in [ASN.1], [X.690], with simplifications described in

6.  String Search Filter Definition

   The string representation of an LDAP search filter is a string of
   UTF-8[RFC3629] encoded ISO 10646-1 characters 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 1.3
   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 / greater / less
      equal          = EQUALS
      approx         = TILDE EQUALS
      greater        = RANGLE EQUALS
      less           = 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
                         ; 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 a string strings that
   includes invalid
   are not valid UTF-8 octet sequences. 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
   search filter is a string of UTF-8 encoded ISO 10646-1 characters).

7.  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 ":dn" ":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. 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)

   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

8.  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.

9.  Normative References

   [ASN.1] Specification of ASN.1 encoding rules: Basic, Canonical, and
   Distinguished Encoding Rules, ITU-T Recommendation X.690, 1994.

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

[ISO10646]  Universal Multiple-Octet Coded Character Set (UCS) -
            Architecture and Basic Multilingual Plane, ISO/IEC 10646-1,

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

[Protocol] Sermersheim, J. (editor), "LDAP: The Protocol", draft-
   ietf-ldapbis-protocol-xx.txt,  draft-ietf-ldapbis-protocol-xx.txt, a work in progress.

[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.

   [UTF-8] Yergeau, F., "UTF-8, a transformation format

[X.690]     Specification of ISO 10646",
   draft-yergeau-rfc2279bis-xx.txt, a work in progress. ASN.1 encoding rules: Basic, Canonical, and
            Distinguished Encoding Rules, ITU-T Recommendation X.690,

10.  Informative References


11.  Intellectual Property Rights

   The IETF takes no position regarding the validity or scope of any
   intellectual property 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; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication 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 implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive

12.  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

13.  Authors' Address Addresses

   Mark Smith, Editor
   Netscape Communications Corp.
   360 W. Caribbean Drive
   Sunnyvale, CA 94089
   Pearl Crescent, LLC
   447 Marlpool Dr.
   Saline, MI 48176
   +1 650 937-3477 734 944-2856

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

14.  Full Copyright Statement

   Copyright (C) The Internet Society (2003). (2004). 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

   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

15.  Appendix A: Changes Since RFC 2254

15.1.  Technical Changes

   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 ISO 10646-1 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]

   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."

15.2.  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" and "Intellectual Property Rights" sections:

   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 [ISO10646], [RFC2119], [AuthMeth],
   [Models], and [Roadmap] and updated the UTF-8 reference.  Replaced
   RFC 822 reference with a reference to RFC 2234.

   "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:

16.  Appendix B: Changes Since Previous Document Revision

   This appendix lists all changes relative to the previously published
   revision, draft-ietf-ldapbis-filter-04.txt. draft-ietf-ldapbis-filter-05.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-04.txt. draft-ietf-ldapbis-filter-05.txt.  This section will be
   removed before this document is published as an RFC.

16.1.  Technical Changes

   "Examples" section: Removed the (:=Fred Flintstone) example which is
   not allowed by the protocol.


16.2.  Editorial Changes


   "LDAP Search Filter Definition" section: Revised changed the last two
   sentences LDAPv3 search
   filter ABNF so it matches that used in this section the latest revision of
   [Protocol] and removed the following redundant descriptive text:
   "where the LDAPString above is limited to improve clarity (the updated text now
   begins with the text UTF-8 encoding [UTF-8]
   of the ISO 10646 character set [ISO10646]."

   "String Search Filter Definition" section: Corrected section
   reference to [Models] and replaced this sentence: "Implementations
   SHOULD accept as input a string that includes...."

   Replaced all occurrences of "asterix" includes invalid UTF-8 octet
   sequences." with the correctly spelled
   "asterisk." following: "Implementations SHOULD accept as
   input strings that are not valid UTF-8 strings."

   "Examples" section: Corrected the description of this example:
   (sn:dn: Rubble).

   "Normative References" section: changed UTF-8 reference to point to
   RFC 3629, replaced [ASN.1] with [X.690] for consistency, and indented
   the UTF-8 Internet Draft.

   "Intellectual Property Rights" section: added.

   Author's reference descriptions to enhance readability.

   Authors' Addresses section: New email address contact information for Mark Smith.

   "Full Copyright Statement" section: updated text

   Updated the copyright year to match latest IETF
   guidelines. 2004.

This Internet Draft expires on 25 April 13 August 2004.