Network Working Group M. Wahl INTERNET-DRAFT Critical Angle Inc. Obsoletes: RFC 1779 S. Kille Isode Ltd. T. Howes Netscape Communications Corp. Expires in six months from March 24, 1997 Intended Category: Standards Track Lightweight Directory Access Protocol (v3): UTF-8 String Representation of Distinguished Names Status of this Memo This document is an Internet-Draft. 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-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). Abstract The X.500 Directory uses distinguished names as the primary keys to entries in the directory. Distinguished Names are encoded in ASN.1 in the X.500 Directory protocols. In the Lightweight Directory Access Protocol, a string representation of distinguished names is transferred. This specification defines the string format for representing names, which is designed to give a clean representation of commonly used distinguished names, while being able to represent any distinguished name. 1. Background This specification assumes familiarity with X.500 [1], and the concept of Distinguished Name. It is important to have a common format to be able to unambiguously represent a distinguished name. The primary goal of this specification is ease of encoding and decoding. A secondary goal is to have names that are human readable. It is not expected that LDAP clients with a human user interface would display these strings directly to the user, but would most likely be performing translations (such as expressing attribute type names in the local national language). INTERNET-DRAFT draft-ietf-asid-ldapv3-dn-02.txt March 1997 Wahl,Kille,Howes String Representations of Distinguished Names Page 2 2. Converting DistinguishedName from ASN.1 to a String In X.501 [2] the ASN.1 structure of distinguished name is defined as: DistinguishedName ::= RDNSequence RDNSequence ::= SEQUENCE OF RelativeDistinguishedName RelativeDistinguishedName ::= SET SIZE (1..MAX) OF AttributeTypeAndValue AttributeTypeAndValue ::= SEQUENCE { type AttributeType, value AttributeValue } The following sections defines the algorithm for converting from an ASN.1 structured representation to a UTF-8 string representation. 2.1. Converting the RDNSequence If the RDNSequence is an empty sequence, the result is the empty or zero length string. Otherwise, the output consists of the string encodings of each RelativeDistinguishedName in the RDNSequence (according to 2.2), starting with the last element of the sequence and moving backwards toward the first. The encodings of adjoining RelativeDistinguishedNames are separated by a comma character (',' ASCII 44). 2.2. Converting RelativeDistinguishedName When converting from an ASN.1 RelativeDistinguishedName to a string, the output consists of the string encodings of each AttributeTypeAndValue (according to 2.3), in any order. Where there is a multi-valued RDN, the outputs from adjoining AttributeTypeAndValues are separated by a plus ('+' ASCII 43) character. 2.3. Converting AttributeTypeAndValue The AttributeTypeAndValue is encoded as the string representation of the AttributeType, followed by an equals character ('=' ASCII 61), followed by the string representation of the AttributeValue. The encoding of the AttributeValue is given in section 2.4. INTERNET-DRAFT draft-ietf-asid-ldapv3-dn-02.txt March 1997 Wahl,Kille,Howes String Representations of Distinguished Names Page 3 If the AttributeType is in a published table of attribute types associated with LDAP [4], then the type name string from that table is used, otherwise it is encoded as the dotted-decimal encoding of the AttributeType's OBJECT IDENTIFIER. The dotted-decimal notation is described in [3]. As an example, strings for a few of the attribute types frequently seen in RDNs include: String X.500 AttributeType ------------------------------ CN commonName L localityName ST stateOrProvinceName O organizationName OU organizationalUnitName C countryName STREET streetAddress DC domainComponent UID userid 2.4. Converting an AttributeValue from ASN.1 to a String If the AttributeValue is of a type which does not have a string representation defined for it, then it is simply encoded as an octothorpe character ('#' ASCII 35) followed by the hexadecimal representation of the each of the bytes of the BER encoding of the X.500 AttributeValue. This form SHOULD be used if the AttributeType is of the dotted-decimal form. Otherwise, if the AttributeValue is of a type which has a string representation, the value is converted first to a UTF-8 string according to its syntax specification. If the UTF-8 string does not have any of the following characters which need escaping, then that string can be used as the string representation of the value. o a space or "#" character occurring at the beginning of the string o a space character occurring at the end of the string o one of the characters ",", "+", """, "\", "<", ">" or ";" Implementations MAY escape other characters. If a character to be escaped is a one of the list shown above, then it is prefixed by a backslash ('\' ASCII 92). Otherwise the character to be escaped is replaced by a backslash and two hex digits, which form a single byte in the code of the character. Examples of the escaping mechanism are shown in section 5. INTERNET-DRAFT draft-ietf-asid-ldapv3-dn-02.txt March 1997 Wahl,Kille,Howes String Representations of Distinguished Names Page 4 3. Parsing a String back to a Distinguished Name The structure of the string is specified in a BNF grammar, based on the grammar defined in RFC 822, with the terminals enclosed in <> [5]. Server implementations parsing a DN string generated by an LDAPv2 client MUST also accept (and ignore) the variants given in section 4 of this document. ::= | "" -- empty string ::= | "," ::= | "+" ::= "=" ::= 1*( ) | ::= letters, digits and '-' ::= 1* ( ) ::= digits and '.' ::= ::= *( | ) | "#" | '"' *( | | ) '"' -- only from v2 ::= "," | "=" | "+" | "<" | ">" | "#" | ";" ::= "\" ( | "\" | '"' | ) ::= any character except or "\" or '"' 1* ( ) ::= ::= 0-9, a-f, A-F 4. Relationship with RFC 1779 and LDAPv2 The syntax given in this document is more restrictive than the syntax in RFC 1779. Implementations parsing a string generated by an LDAPv2 client MUST accept the syntax of RFC 1779. Implementations MUST NOT, however, generate any of the RFC 1779 encodings which are not described above in section 2. Implementations MUST allow a semicolon character to be used instead of a comma to separate RDNs in a distinguished name, and MUST also allow whitespace characters to be present on either side of the comma or semicolon. The whitespace characters are ignored, and the semicolon replaced with a comma. INTERNET-DRAFT draft-ietf-asid-ldapv3-dn-02.txt March 1997 Wahl,Kille,Howes String Representations of Distinguished Names Page 5 Implementations MUST allow an oid in the attribute type to be prefixed by the characters "oid." or "OID.". Implementations MUST allow for space (' ' ASCII 32) characters to be present between and ',', between and '+', between and '=', and between '=' and . These space characters are ignored when parsing. Implementations MUST allow a value to be surrounded by quote ('"' ASCII 34) characters, which are not part of the value. Inside the quoted value, the following characters can occur without any escaping: ",", "=", "+", "<", ">", "#" and ";" 5. Examples This notation is designed to be convenient for common forms of name. This section gives a few examples of distinguished names written using this notation. First is a name containing three relative distinguished names (RDNs): CN=Steve Kille,O=Isode Limited,C=GB Here is an example name containing three RDNs, in which the first RDN is multi-valued: OU=Sales+CN=J. Smith,O=Widget Inc.,C=US This example shows the method of quoting of a comma in an organization name: CN=L. Eagle,O=Sue\, Grabbit and Runn,C=GB An example name in which a value contains a carriage return character: CN=Before\0DAfter,O=Test,C=GB An example name in which an RDN was of an unrecognized type. The value is the BER encoding of an OCTET STRING containing two bytes 0x48 and 0x69. 1.3.6.1.4.1.1466.0=#04024869,O=Test,C=GB Finally, an example of an RDN surname value consisting of five letters: Unicode Letter Description 10646 code UTF-8 Quoted =============================== ========== ====== ======= LATIN CAPITAL LETTER L U0000004C 0x4C L LATIN SMALL LETTER U U00000075 0x75 u LATIN SMALL LETTER C WITH CARON U0000010D 0xC48D \C4\8D LATIN SMALL LETTER I U00000069 0x69 i LATIN SMALL LETTER C WITH ACUTE U00000107 0xC487 \C4\87 Could be written in printable ASCII (useful for debugging purposes): SN=Lu\C4\8Di\C4\C7 INTERNET-DRAFT draft-ietf-asid-ldapv3-dn-02.txt March 1997 Wahl,Kille,Howes String Representations of Distinguished Names Page 6 6. References [1] The Directory -- overview of concepts, models and services. ITU-T Rec. X.500(1993). [2] The Directory -- Models. ITU-T Rec. X.501(1993). [3] M. Wahl, S. Kille, T. Howes, "Lightweight Directory Access Protocol (v3)", INTERNET DRAFT, draft-ietf-asid-ldapv3-protocol-04.txt. March 1997. [4] M. Wahl, S. Kille, T. Howes, A. Coulbeck, "Lightweight Directory Access Protocol (v3): Standard and Pilot Attribute Definitions", INTERNET DRAFT, draft-ietf-asid-ldapv3-attributes-04.txt. March 1997. [5] D. Crocker, "Standard of the Format of ARPA-Internet Text Messages", STD 11, RFC 822, August 1982. 6. Security Considerations Security issues are not discussed in this memo. 7. Author's Address Mark Wahl Critical Angle Inc. 4815 W. Braker Lane #502-385 Austin, TX 78759 USA EMail: M.Wahl@critical-angle.com Steve Kille Isode Ltd. The Dome The Square Richmond, Surrey TW9 1DT England Phone: +44-181-332-9091 EMail: S.Kille@ISODE.COM Tim Howes Netscape Communications Corp. 501 E. Middlefield Rd Mountain View, CA 94043 USA Phone: +1 415 254-1900 EMail: howes@netscape.com INTERNET-DRAFT draft-ietf-asid-ldapv3-dn-02.txt March 1997