INTERNET-DRAFT Kurt D. Zeilenga
Intended Category: Standard Track OpenLDAP Foundation
Expires: 4 January 2001 4 July 2000
LDAPv3bis Suggestions:
The String Representation of LDAP Search Filters
<draft-zeilenga-ldapv3bis-rfc2254-00.txt>
Status of Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
This document is intended to be, after appropriate review and
revision, submitted to the RFC Editor as a Standard Track document.
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Copyright 2000, The Internet Society. All Rights Reserved.
Please see the Copyright section near the end of this document for
more information.
Forward
This Internet Draft suggests a number of updates to "The String
Representation of LDAP Search Filters" [RFC 2254]. This document is
not intended to be published as an RFC but used to identify LDAPv3bis
work items.
The remainer of this documents incorporates the substantive portion of
RFC 2254 text (less status of memo, appendices, etc). Comments and
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suggested updates to this text are inserted as inline notes prefixed
with '//'.
// Start of RFC 2254 text
2. Abstract
The Lightweight Directory Access Protocol (LDAP) [1] 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. This document defines
a human-readable string format for representing LDAP search filters.
This document replaces RFC 1960, extending the string LDAP filter
definition to include support for LDAP version 3 extended match
filters, and including support for representing the full range of
possible LDAP search filters.
3. LDAP Search Filter Definition
An LDAPv3 search filter is defined in Section 4.5.1 of [1] as follows:
Filter ::= CHOICE {
and [0] SET OF Filter,
or [1] SET OF 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,
SEQUENCE OF CHOICE {
initial [0] LDAPString,
any [1] LDAPString,
final [2] LDAPString
}
}
AttributeValueAssertion ::= SEQUENCE {
attributeDesc AttributeDescription,
attributeValue AttributeValue
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}
MatchingRuleAssertion ::= SEQUENCE {
matchingRule [1] MatchingRuleID OPTIONAL,
type [2] AttributeDescription OPTIONAL,
matchValue [3] AssertionValue,
dnAttributes [4] BOOLEAN DEFAULT FALSE
}
AttributeDescription ::= LDAPString
AttributeValue ::= OCTET STRING
MatchingRuleID ::= LDAPString
AssertionValue ::= OCTET STRING
LDAPString ::= OCTET STRING
where the LDAPString above is limited to the UTF-8 encoding of the ISO
10646 character set [4]. The AttributeDescription is a string
representation of the attribute description and is defined in [1].
The AttributeValue and AssertionValue OCTET STRING have the form
defined in [2]. The Filter is encoded for transmission over a network
using the Basic Encoding Rules defined in [3], with simplifications
described in [1].
4. String Search Filter Definition
The string representation of an LDAP search filter is defined by the
following grammar, following the ABNF notation defined in [5]. The
filter format uses a prefix notation.
filter = "(" filtercomp ")"
filtercomp = and / or / not / item
and = "&" filterlist
or = "|" filterlist
not = "!" filter
filterlist = 1*filter
// replace (to support empty SET OF) with:
// filterlist = 0*filter
item = simple / present / substring / extensible
simple = attr filtertype value
filtertype = equal / approx / greater / less
equal = "="
approx = "~="
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greater = ">="
less = "<="
extensible = attr [":dn"] [":" matchingrule] ":=" value
/ [":dn"] ":" 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]
The attr, matchingrule, and value constructs are as described in the
corresponding section of [1] given above.
If a value should contain any of the following characters
Character ASCII value
---------------------------
* 0x2a
( 0x28
) 0x29
\ 0x5c
NUL 0x00
the character must be encoded as the backslash '\' character (ASCII
0x5c) followed by the two hexadecimal digits representing the ASCII
value of the encoded character. The case of the two hexadecimal digits
is not significant.
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 characters besides the
ones listed above may be escaped using this mechanism, for example,
non-printing characters.
For example, the filter checking whether the "cn" attribute contained
a value with the character "*" anywhere in it would be represented as
"(cn=*\2a*)".
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.
5. Examples
This section gives a few examples of search filters written using this
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notation.
(cn=Babs Jensen)
(!(cn=Tim Howes))
(&(objectClass=Person)(|(sn=Jensen)(cn=Babs J*)))
(o=univ*of*mich*)
// Add (for empty SET OF):
// The following filters evaluate to true or false,
// respectively.
// (&)
// (|)
The following examples illustrate the use of extensible matching.
(cn:1.2.3.4.5:=Fred Flintstone)
(sn:dn:2.4.6.8.10:=Barney Rubble)
(o:dn:=Ace Industry)
(:dn:2.4.6.8.10:=Dino)
The second example illustrates the use of the ":dn" notation to
indicate that matching rule "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.
The third example denotes an equality match, except that DN components
should be considered part of the entry when doing the match.
The fourth example is a filter that should be applied to any attribute
supporting the matching rule given (since the attr has been left off).
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)
The first example shows the use of the escaping mechanism to represent
parenthesis characters. The second shows how to represent a "*" in a
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
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represent arbitrary data, including NUL characters.
The final example illustrates the use of the escaping mechanism to
represent various non-ASCII UTF-8 characters.
6. Security Considerations
// Add consideration requiring the use of strong authentication
// to update the directory.
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.
7. References
[1] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December 1997.
[2] Wahl, M., Coulbeck, A., Howes, T., and S. Kille, "Lightweight
Directory Access Protocol (v3): Attribute Syntax Definitions", RFC
2252, December 1997.
[3] Specification of ASN.1 encoding rules: Basic, Canonical, and
Distinguished Encoding Rules, ITU-T Recommendation X.690, 1994.
[4] Yergeau, F., "UTF-8, a transformation format of Unicode and ISO
10646", RFC 2044, October 1996.
[5] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, August 1982.
// Remainder trimmed
// End of RFC 2254 text
Additional Information
Discussions regarding these suggestions may directed to the author:
Kurt D. Zeilenga
OpenLDAP Foundation
<Kurt@OpenLDAP.org>
or the LDAPext Working Group mailing list:
<ietf-ldapext@netscape.com>
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