rfc4515.txt

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Network Working Group                                      M. Smith, Ed.
Request for Comments: 4515                           Pearl Crescent, LLC
Obsoletes: 2254                                                 T. Howes
Category: Standards Track                                  Opsware, Inc.
                                                               June 2006


             Lightweight Directory Access Protocol (LDAP):
                String Representation of Search Filters

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 (2006).

Abstract

   Lightweight Directory Access Protocol (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 (RFC 4516) and in other
   applications.

Table of Contents

   1. Introduction ....................................................2
   2. LDAP Search Filter Definition ...................................2
   3. String Search Filter Definition .................................3
   4. Examples ........................................................5
   5. Security Considerations .........................................7
   6. Normative References ............................................7
   7. Informative References ..........................................8
   8. Acknowledgements ................................................8
   Appendix A: Changes Since RFC 2254 .................................9
      A.1. Technical Changes ..........................................9
      A.2. Editorial Changes ..........................................9







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1.  Introduction

   The Lightweight Directory Access Protocol (LDAP) [RFC4510] 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
   [RFC4516] 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 filters.

   This document is a integral part of the LDAP technical specification
   [RFC4510], which obsoletes the previously defined LDAP technical
   specification, RFC 3377, in its entirety.

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

   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 [RFC2119].

2.  LDAP Search Filter Definition

   An LDAP search filter is defined in Section 4.5.1 of [RFC4511] as
   follows:

        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 } }





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        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>
                        -- [RFC4512]

        AttributeValue ::= OCTET STRING

        MatchingRuleId ::= LDAPString

        AssertionValue ::= OCTET STRING

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

   The AttributeDescription, as defined in [RFC4511], is a string
   representation of the attribute description that is discussed in
   [RFC4512].  The AttributeValue and AssertionValue OCTET STRING have
   the form defined in [RFC4517].  The Filter is encoded for
   transmission over a network using the Basic Encoding Rules (BER)
   defined in [X.690], with simplifications described in [RFC4511].

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
   [RFC4234].  The productions used that are not defined here are
   defined in Section 1.4 (Common ABNF Productions) of [RFC4512] 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



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      equal          = EQUALS
      approx         = TILDE EQUALS
      greaterorequal = RANGLE EQUALS
      lessorequal    = LANGLE EQUALS
      extensible     = ( attr [dnattrs]
                           [matchingrule] COLON EQUALS assertionvalue )
                       / ( [dnattrs]
                            matchingrule 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 [RFC4512].
      dnattrs        = COLON "dn"
      matchingrule   = COLON oid
      assertionvalue = valueencoding
      ; The <valueencoding> rule is used to encode an <AssertionValue>
      ; from Section 4.1.6 of [RFC4511].
      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.







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RFC 4515     LDAP: String Representation of Search Filters     June 2006


   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
   "(cn=*\2a*)".

   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
   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*)))
        (o=univ*of*mich*)
        (seeAlso=)

   The following examples illustrate the use of extensible matching.

        (cn:caseExactMatch:=Fred Flintstone)
        (cn:=Betty Rubble)
        (sn:dn:2.4.6.8.10:=Barney Rubble)
        (o:dn:=Ace Industry)
        (:1.2.3:=Wilma Flintstone)
        (:DN:2.4.6.8.10:=Dino)

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

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





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   The third example illustrates the use of the ":oid" notation to
   indicate that the matching rule identified by the OID "2.4.6.8.10"
   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
   match.

   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
   considered.

   The following examples illustrate the use of the escaping mechanism.

        (o=Parens R Us \28for all your parenthetical needs\29)
        (cn=*\2A*)
        (filename=C:\5cMyFile)
        (bin=\00\00\00\04)
        (sn=Lu\c4\8di\c4\87)
        (1.3.6.1.4.1.1466.0=\04\02\48\69)

   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-octet value
   00 00 00 04 (hex), 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.  Specifically, there
   are 5 characters in the <assertionvalue> portion of this example:
   LATIN CAPITAL LETTER L (U+004C), LATIN SMALL LETTER U (U+0075), LATIN
   SMALL LETTER C WITH CARON (U+010D), LATIN SMALL LETTER I (U+0069),
   and LATIN SMALL LETTER C WITH ACUTE (U+0107).

   The sixth and final example demonstrates assertion of a BER-encoded
   value.




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