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Versions: 00 01 02 03 rfc2253                                           
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
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   Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe),
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   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 ::= 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

    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.

   <distinguishedName> ::= <name> | ""               -- empty string

   <name> ::= <name-component> | <name-component> "," <name>

   <name-component> ::= <attributeTypeAndValue>
           | <attributeTypeAndValue> "+" <name-component>

   <attributeTypeAndValue> ::=
       <attributeType> "=" <attributeValue>

   <attributeType> ::= 1*( <keychar> ) | <oid>
   <keychar> ::= letters, digits and '-'

   <oid> ::= 1* ( <oidchar> )
   <oidchar> ::= digits and '.'

   <attributeValue> ::= <string>

   <string> ::= *( <stringchar> | <pair> )
            | "#" <hexstring>
            | '"' *( <stringchar> | <special> | <pair> ) '"'  -- only from v2

   <special> ::= "," | "=" | "+" | "<" |  ">" | "#" | ";"

   <pair> ::= "\" ( <special> | "\" | '"' | <hexpair> )
   <stringchar> ::= any character except <special> or "\" or '"'

   <hexstring> 1* ( <hexpair> )
   <hexpair> ::= <hexchar><hexchar>
   <hexchar> ::= 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 <name-component> and ',', between <attributeTypeAndValue>
   and '+', between <attributeType> and '=', and between '=' and
   <attributeValue>.  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

   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:


   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

   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 I            U00000069  0x69   i
   LATIN SMALL LETTER C WITH ACUTE U00000107  0xC487 \C4\87

   Could be written in printable ASCII (useful for debugging purposes):


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

   EMail:  M.Wahl@critical-angle.com

   Steve Kille
   Isode Ltd.
   The Dome
   The Square
   Richmond, Surrey
   TW9 1DT

   Phone:  +44-181-332-9091
   EMail:  S.Kille@ISODE.COM

   Tim Howes
   Netscape Communications Corp.
   501 E. Middlefield Rd
   Mountain View, CA 94043

   Phone:  +1 415 254-1900
   EMail:   howes@netscape.com

INTERNET-DRAFT        draft-ietf-asid-ldapv3-dn-02.txt     March 1997