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INTERNET-DRAFT                           Editor: Kurt D. Zeilenga
Intended Category: Standard Track                OpenLDAP Foundation
Expires in six months                            10 February 2005
Obsoletes: RFC 2253



            LDAP: String Representation of Distinguished Names
                      <draft-ietf-ldapbis-dn-16.txt>



Status of Memo

  This document is intended to be, after appropriate review and
  revision, submitted to the RFC Editor as a Standard Track document
  replacing RFC 2253.  Distribution of this memo is unlimited.
  Technical discussion of this document will take place on the IETF LDAP
  Revision (LDAPBIS) Working Group mailing list
  <address@hidden>.  Please send editorial comments directly
  to the document editor <address@hidden>.

  By submitting this Internet-Draft, I accept the provisions of Section
  4 of RFC 3667.  By submitting this Internet-Draft, I certify that any
  applicable patent or other IPR claims of which I am aware have been
  disclosed, or will be disclosed, and any of which I become aware will
  be disclosed, in accordance with RFC 3668.

  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."

  The list of current Internet-Drafts can be accessed at
  http://www.ietf.org/1id-abstracts.html

  The list of Internet-Draft Shadow Directories can be accessed at
  http://www.ietf.org/shadow.html


  Copyright (C) The Internet Society (2005).  All Rights Reserved.

  Please see the Full Copyright section near the end of this document
  for more information.



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Abstract

  The X.500 Directory uses distinguished names (DNs) as primary keys to
  entries in the directory.  This document defines the string
  representation used in the Lightweight Directory Access Protocol
  (LDAP) to transfer distinguished names.  The string representation is
  designed to give a clean representation of commonly used distinguished
  names, while being able to represent any distinguished name.


1.  Background and Intended Usage

  In X.500-based directory systems [X.500], including those accessed
  using the Lightweight Directory Access Protocol (LDAP) [Roadmap],
  distinguished names (DNs) are used to unambiguously refer to directory
  entries [X.501][Models].

  The structure of a DN [X.501] is described in terms of ASN.1 [X.680].
  In the X.500 Directory Access Protocol [X.511] (and other ITU-defined
  directory protocols), DNs are encoded using the Basic Encoding Rules
  (BER) [X.690].  In LDAP, DNs are represented in the string form
  described in this document.

  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
  implementations 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).

  This document defines the string representation of Distinguished Names
  used in LDAP [Protocol][Syntaxes].  Section 2 details the RECOMMENDED
  algorithm for converting a DN from its ASN.1 structured representation
  to a string.  Section 3 details how to convert a DN from a string to a
  ASN.1 structured representation.

  While other documents may define other algorithms for converting a DN
  from its ASN.1 structured representation to a string, all algorithms
  MUST produce strings which adhere to the requirements of Section 3.

  This document does not define a canonical string representation for
  DNs.  Comparison of DNs for equality is to be performed in accordance
  with the distinguishedNameMatch matching rule [Syntaxes].

  This document is a integral part of the LDAP technical specification
  [Roadmap] which obsoletes the previously defined LDAP technical



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  specification, RFC 3377, in its entirety.  This document obsoletes RFC
  2253.  Changes since RFC 2253 are summarized in Appendix B.

  This specification assumes familiarity with X.500 [X.500] and the
  concept of Distinguished Name [X.501][Models].


1.1. Conventions

  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].

  Character names in this document use the notation for code points and
  names from the Unicode Standard [Unicode].  For example, the letter
  "a" may be represented as either <U+0061> or <LATIN SMALL LETTER A>.

  Note: a glossary of terms used in Unicode can be found in [Glossary].
  Information on the Unicode character encoding model can be found in
  [CharModel].


2.  Converting DistinguishedName from ASN.1 to a String

  X.501 [X.501] defines the ASN.1 [X.680] structure of distinguished
  name.  The following is a variant provided for discussion purposes.

      DistinguishedName ::= RDNSequence

      RDNSequence ::= SEQUENCE OF RelativeDistinguishedName

      RelativeDistinguishedName ::= SET SIZE (1..MAX) OF
          AttributeTypeAndValue

      AttributeTypeAndValue ::= SEQUENCE {
          type  AttributeType,
          value AttributeValue }

  This section defines the RECOMMENDED algorithm for converting a
  distinguished name from an ASN.1 structured representation to an UTF-8
  [RFC3629] encoded Unicode [Unicode] character string representation.
  Other documents may describe other algorithms for converting a
  distinguished name to a string, but only strings which conform to the
  grammar defined in Section 3 SHALL be produced by LDAP
  implementations.


2.1. Converting the RDNSequence



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  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 Section
  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 (',' U+002C) character.


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 Section 2.3), in any order.

  Where there is a multi-valued RDN, the outputs from adjoining
  AttributeTypeAndValues are separated by a plus sign ('+' U+002B)
  character.


2.3.  Converting AttributeTypeAndValue

  The AttributeTypeAndValue is encoded as the string representation of
  the AttributeType, followed by an equals sign ('=' U+003D) character,
  followed by the string representation of the AttributeValue.  The
  encoding of the AttributeValue is given in Section 2.4.

  If the AttributeType is defined to have a short name (descriptor)
  [Models] and that short name is known to be registered
  [REGISTRY][BCP64bis] as identifying the AttributeType, that short
  name, a <descr>, is used.  Otherwise the AttributeType is encoded as
  the dotted-decimal encoding, a <numericoid>, of its OBJECT IDENTIFIER.
  The <descr> and <numericoid> is defined in [Models].

  Implementations are not expected to dynamically update their knowledge
  of registered short names.  However, implementations SHOULD provide a
  mechanism to allow its knowledge of registered short names to be
  updated.


2.4.  Converting an AttributeValue from ASN.1 to a String

  If the AttributeType is of the dotted-decimal form, the AttributeValue
  is represented by an number sign ('#' U+0023) character followed by
  the hexadecimal encoding of each of the octets of the BER encoding of



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  the X.500 AttributeValue.  This form is also used when the syntax of
  the AttributeValue does not have a LDAP-specific [Syntaxes, Section
  3.1] string encoding defined for it or the LDAP-specific string
  encoding is not restricted to UTF-8 encoded Unicode characters.  This
  form may also be used in other cases, such as when a reversible string
  representation is desired (see Section 5.2).

  Otherwise, if the AttributeValue is of a syntax which has a
  LDAP-specific string encoding, the value is converted first to a UTF-8
  encoded Unicode string according to its syntax specification (see
  [Syntaxes, Section 3.3] for examples).  If that UTF-8 encoded Unicode
  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.

      - a space (' ' U+0020) or number sign ('#' U+0023) occurring at
        the beginning of the string;

      - a space (' ' U+0020) character occurring at the end of the
        string;

      - one of the characters '"', '+', ',', ';', '<', '>',  or '\'
        (U+0022, U+002B, U+002C, U+003B, U+003C, U+003E, or U+005C
        respectively);

      - the null (U+0000) character.

  Other characters may be escaped.

  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.  Alternatively, if and only if the character to be escaped
  is one of

      ' ', '"', '#', '+', ',', ';', '<', '=', '>', or '\'
      (U+0020, U+0022, U+0023, U+002B, U+002C, U+003B,
       U+003C, U+003D, U+003E, U+005C respectively)

  it can be prefixed by a backslash ('\' U+005C).

  Examples of the escaping mechanism are shown in Section 4.


3. Parsing a String back to a Distinguished Name

  The string representation of Distinguished Names is restricted to
  UTF-8 [RFC3629] encoded Unicode [Unicode] characters.  The structure
  of this string representation is specified using the following



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  Augmented BNF [RFC2234] grammar:

      distinguishedName = [ relativeDistinguishedName
          *( COMMA relativeDistinguishedName ) ]
      relativeDistinguishedName = attributeTypeAndValue
          *( PLUS attributeTypeAndValue )
      attributeTypeAndValue = attributeType EQUALS attributeValue
      attributeType = descr / numericoid
      attributeValue = string / hexstring

      ; The following characters are to be escaped when they appear
      ; in the value to be encoded: ESC, one of <escaped>, leading
      ; SHARP or SPACE, trailing SPACE, and NULL.
      string =   [ ( leadchar / pair ) [ *( stringchar / pair )
         ( trailchar / pair ) ] ]

      leadchar = LUTF1 / UTFMB
      LUTF1 = %x01-1F / %x21 / %x24-2A / %x2D-3A /
         %x3D / %x3F-5B / %x5D-7F

      trailchar  = TUTF1 / UTFMB
      TUTF1 = %x01-1F / %x21 / %x23-2A / %x2D-3A /
         %x3D / %x3F-5B / %x5D-7F

      stringchar = SUTF1 / UTFMB
      SUTF1 = %x01-21 / %x23-2A / %x2D-3A /
         %x3D / %x3F-5B / %x5D-7F

      pair = ESC ( ESC / special / hexpair )
      special = escaped / SPACE / SHARP / EQUALS
      escaped = DQUOTE / PLUS / COMMA / SEMI / LANGLE / RANGLE
      hexstring = SHARP 1*hexpair
      hexpair = HEX HEX

  where the productions <descr>, <numericoid>, <COMMA>, <DQUOTE>,
  <EQUALS>, <ESC>, <HEX>, <LANGLE>, <NULL>, <PLUS>, <RANGLE>, <SEMI>,
  <SPACE>, <SHARP>, <UTFMB> are defined in [Models].

  Each <attributeType>, either a <descr> or a <numericoid>, refers to an
  attribute type of an attribute value assertion (AVA).  The
  <attributeType> is followed by a <EQUALS> and an <attributeValue>.
  The <attributeValue> is either in <string> or <hexstring> form.

  If in <string> form, a LDAP string representation asserted value can
  be obtained by replacing (left-to-right, non-recursively) each <pair>
  appearing in the <string> as follows:
      replace <ESC><ESC> with <ESC>;
      replace <ESC><special> with <special>;



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      replace <ESC><hexpair> with the octet indicated by the <hexpair>.

  If in <hexstring> form, a BER representation can be obtained from
  converting each <hexpair> of the <hexstring> to the octet indicated by
  the <hexpair>.

  One or more attribute values assertions, separated by <PLUS>, for a
  relative distinguished name.

  Zero or more relative distinguished names, separated by <COMMA>, for a
  distinguished name.

  Implementations MUST recognize AttributeType name strings
  (descriptors) listed in the following table, but MAY recognize other
  name strings.

      String  X.500 AttributeType
      ------  --------------------------------------------
      CN      commonName (2.5.4.3)
      L       localityName (2.5.4.7)
      ST      stateOrProvinceName (2.5.4.8)
      O       organizationName (2.5.4.10)
      OU      organizationalUnitName (2.5.4.11)
      C       countryName (2.5.4.6)
      STREET  streetAddress (2.5.4.9)
      DC      domainComponent (0.9.2342.19200300.100.1.25)
      UID     userId (0.9.2342.19200300.100.1.1)

  Implementations MAY recognize other DN string representations (such as
  that described in RFC 1779).  However, as there is no requirement that
  alternative DN string representations to be recognized (and, if so,
  how), implementations SHOULD only generate DN strings in accordance
  with Section 2 of this document.


4.  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):

      UID=jsmith,DC=example,DC=net

  Here is an example name containing three RDNs, in which the first RDN
  is multi-valued:

      OU=Sales+CN=J. Smith,DC=example,DC=net



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  This example shows the method of escaping of a special characters
  appearing in a common name:


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