Network Working Group Tim Howes INTERNET DRAFT Netscape Communications Corp. OBSOLETES: RFC 1960 May 1997 The String Representation of LDAP Search Filters <draft-ietf-asid-ldapv3-filter-02.txt> 1. Status of this Memo This document is an Internet-Draft. Internet-Drafts are working docu- ments of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). 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 defin- ition to include support for LDAP version 3 extended match filters, and including support for representing the full range of possible LDAP search filters. Howes [Page 1]
RFC DRAFT May 1997 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 } 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 Howes [Page 2]
RFC DRAFT May 1997 where the LDAPString above is limited to the UTF-8 encoding of the ISO 10646 character set [4]. The AttributeDescription is a string represen- tation of the attribute description and is defined in [1]. The Attribu- teValue 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 item = simple / present / substring / extensible simple = attr filtertype value filtertype = equal / approx / greater / less equal = "=" approx = "~=" 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. Howes [Page 3]
RFC DRAFT May 1997 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 charac- ters. 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 notation. (cn=Babs Jensen) (!(cn=Tim Howes)) (&(objectClass=Person)(|(sn=Jensen)(cn=Babs J*))) (o=univ*of*mich*) 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, Howes [Page 4]
RFC DRAFT May 1997 and that the attributes of an entry's distinguished name should be con- sidered 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\c7) 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 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 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] Lightweight Directory Access Protocol (v3), M. Wahl, T. Howes, S. Kille, Internet Draft draft-ietf-asid-ldapv3-protocol-04.txt, March, 1997. [2] Lightweight Directory Access Protocol (v3): Attribute Syntax Defin- itions, M. Wahl, A. Coulbeck, T. Howes, S. Kille, Internet Draft draft-ietf-asid-ldapv3-attributes-04.txt, March, 1997. Howes [Page 5]
RFC DRAFT May 1997 [3] Specification of ASN.1 encoding rules: Basic, Canonical, and Dis- tinguished Encoding Rules, ITU-T Recommendation X.690, 1994. [4] UTF-8, a transformation format of Unicode and ISO 10646, F. Yer- geau, draft-yergeau-utf8-rev-00.txt, April, 1997. [5] Standard for the Format of ARPA Internet Text Messages, D. Crocker, RFC 822, August, 1982. 8. Author's Address Tim Howes Netscape Communications Corp. 501 E. Middlefield Road Mountain View, CA 94043 USA +1 415 937-3419 howes@netscape.com Howes [Page 6]
