Network Working Group M. Smith, Editor
Request for Comments: DRAFT Pearl Crescent, LLC
Obsoletes: RFC 2254 T. Howes
Expires: 16 May 2005 Opsware, Inc.
16 November 2004
LDAP: String Representation of Search Filters
<draft-ietf-ldapbis-filter-09.txt>
Status of this Memo
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This document is intended to be published as a Standards Track RFC,
replacing RFC 2254. Distribution of this memo is unlimited.
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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 [LDAPURL] and
in other applications.
Table of Contents
Status of this Memo............................................1
Abstract.......................................................2
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.............................................9
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. Technical Changes...........................................11
12.2. Editorial Changes...........................................12
Intellectual Property Rights...................................12
Full Copyright.................................................13
1. Introduction
The Lightweight Directory Access Protocol (LDAP) [Roadmap] 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
filters.
This document is a integral part of the LDAP technical specification
[Roadmap] which obsoletes the previously defined LDAP technical
specification, RFC 3377, in its entirety.
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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 [Protocol] 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 } }
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
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MatchingRuleId ::= LDAPString
AssertionValue ::= OCTET STRING
LDAPString ::= OCTET STRING -- UTF-8 encoded,
-- [Unicode] characters
The AttributeDescription, as defined in [Protocol], is a string
representation of the attribute description that is discussed in
[Models]. 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 )
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].
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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
"(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
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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.
The third example illustrates the use of the ":oid" notation to
indicate that 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.
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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.
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",
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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.
[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"
(http://www.unicode.org/reports/tr27/) and by the "Unicode
Standard Annex #28: Unicode 3.2."
8. Informative References
[LDAPURL] Smith, M. (editor), "LDAP: Uniform Resource Locator",
draft-ietf-ldapbis-url-xx.txt, a work in progress.
[X.690] Specification of ASN.1 encoding rules: Basic, Canonical, and
Distinguished Encoding Rules, ITU-T Recommendation X.690,
1994.
9. Acknowledgments
This document replaces RFC 2254 by Tim Howes. RFC 2254 was a product
of the IETF ASID Working Group.
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 acknowledged.
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10. Authors' Addresses
Mark Smith, Editor
Pearl Crescent, LLC
447 Marlpool Dr.
Saline, MI 48176
USA
+1 734 944-2856
[email protected]
Tim Howes
Opsware, Inc.
599 N. Mathilda Ave.
Sunnyvale, CA 94085
USA
+1 408 744-7509
[email protected]
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].
Added "(" and ")" around the components of the <extensible>
subproductions for clarity.
Revised the "attr", "matchingrule", and "assertionvalue" ABNF to more
precisely reference productions from the [Models] and [Protocol]
documents.
"String Search Filter Definition" section: replaced "greater" and
"less" with "greaterorequal" and "lessorequal" to avoid confusion.
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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 statement about expected behavior in light of RFC 2254's lack
of a clear definition of "string representation."
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]
document.
"LDAP Search Filter Definition" section: made corrections to the LDAP
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
(1.3.6.1.4.1.1466.0=\04\02\48\69). Replaced one occurrence of "a
value" with "an assertion value". Corrected the description of this
example: (sn:dn:2.4.6.8.10:=Barney Rubble). Replaced the numeric OID
in the first extensible match example with "caseExactMatch" to
demonstrate use of the descriptive form. Used "DN" (uppercase) in
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the last extensible match example to remind the reader to treat the
<dnattrs> production as case insensitive. Reworded the description
of the fourth escaping mechanism example to avoid making assumptions
about byte order. Added text to the fifth escaping mechanism example
to spell out what the non-ASCII characters are in Unicode terms.
"Security Considerations" section: added references to [Protocol] and
[AuthMeth].
"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.
"Informative References" section: (new section) moved [X.690] to this
section. Added a reference to [LDAPURL].
"Acknowledgments" section: added.
"Appendix A: Changes Since RFC 2254" section: added.
"Appendix B: Changes Since Previous Document Revision" section:
added.
Surrounded the names of all ABNF productions with "<" and ">" where
they are used in descriptive text.
Replaced all occurrences of "LDAPv3" with "LDAP."
12. Appendix B: Changes Since Previous Document Revision
This appendix lists all changes relative to the previously published
revision, draft-ietf-ldapbis-filter-08.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-08.txt. This section will be
removed before this document is published as an RFC.
12.1. Technical Changes
Removed the third option from the "extensible" production that
allowed creation of a MatchingRuleAssertion that only had a
matchValue (disallowed By [Protocol]). Added "(" and ")" around the
components of the <extensible> subproductions for clarity.
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12.2. Editorial Changes
"Introduction" section: referenced [Roadmap] upon first use of LDAP
and expanded the paragraph that begins "This document is an integral
part of the LDAP technical specification..." to match the text used
in [Protocol].
"LDAP Search Filter Definition" section: reworded the last paragraph
for clarity.
"Examples" section: Replaced the numeric OID in the first extensible
match example with "caseExactMatch" to demonstrate use of the
descriptive form. Used "DN" (uppercase) in the last extensible match
example to remind the reader to treat the <dnattrs> production as
case insensitive. Reworded the description of the fourth escaping
mechanism example to avoid making assumptions about byte order.
Added text to the fifth escaping mechanism example to spell out what
the non-ASCII characters are in Unicode terms.
References: added [LDAPURL] and moved [X.690] to "Informative
References."
"Acknowledgements" section: added the sentence "RFC 2254 was a
product of the IETF ASID Working Group."
Changed these two sections to unnumbered ones: "Intellectual Property
Rights" and "Full Copyright."
Surrounded the names of all ABNF productions with "<" and ">" where
they are used in descriptive text.
Replaced all occurrences of "LDAPv3" with "LDAP."
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
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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
[email protected].
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
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 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.
This Internet Draft expires on 16 May 2005.
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