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rfc:rfc1779

Network Working Group S. Kille Request for Comments: 1779 ISODE Consortium Obsoletes: 1485 March 1995 Category: Standards Track

           A String Representation of Distinguished Names

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 The OSI Directory uses distinguished names as the primary keys to
 entries in the directory.  Distinguished Names are encoded in ASN.1.
 When a distinguished name is communicated between to users not using
 a directory protocol (e.g., in a mail message), there is a need to
 have a user-oriented string representation of distinguished name.
 This specification defines a string format for representing names,
 which is designed to give a clean representation of commonly used
 names, whilst being able to represent any distinguished name.

Table of Contents

 1.   Why a notation is needed ...................................   2
 2.   A notation for Distinguished Name ..........................   2
     2.1    Goals ................................................   2
     2.2    Informal definition ..................................   2
     2.3    Formal definition ....................................   4
 3.   Examples ...................................................   6
 4.   Acknowledgements ...........................................   7
 5.   References .................................................   7
 6.   Security Considerations ....................................   8
 7.   Author's Address ...........................................   8

Kille [Page 1] RFC 1779 DN Representation March 1995

1. Why a notation is needed

 Many OSI Applications make use of Distinguished Names (DN) as defined
 in the OSI Directory, commonly known as X.500 [1].  This
 specification assumes familiarity with X.500, and the concept of
 Distinguished Name.  It is important to have a common format to be
 able to unambiguously represent a distinguished name.  This might be
 done to represent a directory name on a business card or in an email
 message.  There is a need for a format to support human to human
 communication, which must be string based (not ASN.1) and user
 oriented.  This notation is targeted towards a general user oriented
 system, and in particular to represent the names of humans.  Other
 syntaxes may be more appropriate for other uses of the directory.
 For example, the OSF Syntax may be more appropriate for some system
 oriented uses.  (The OSF Syntax uses "/" as a separator, and forms
 names in a manner intended to resemble UNIX filenames).

2. A notation for Distinguished Name

2.1 Goals

 The following goals are laid out:
  o  To provide an unambiguous representation of a distinguished name
  o  To be an intuitive format for the majority of names
  o  To be fully general, and able to represent any distinguished name
  o  To be amenable to a number of different layouts to achieve an
     attractive representation.
  o  To give a clear representation of the contents of the
     distinguished name

2.2 Informal definition

 This notation is designed to be convenient for common forms of name.
 Some examples are given.  The author's directory distinguished name
 would be written:
 CN=Steve Kille,
 O=ISODE Consortium, C=GB

Kille [Page 2] RFC 1779 DN Representation March 1995

 This may be folded, perhaps to display in multi-column format.  For
 example:
 CN=Steve Kille,
 O=ISODE Consortium,
 C=GB
 Another name might be:
 CN=Christian Huitema, O=INRIA, C=FR
 Semicolon (";") may be used as an alternate separator.  The
 separators may be mixed, but this usage is discouraged.
 CN=Christian Huitema; O=INRIA; C=FR
 In running text, this would be written as <CN=Christian Huitema;
 O=INRIA; C=FR>.  Another example, shows how different attribute types
 are handled:
 CN=James Hacker,
 L=Basingstoke,
 O=Widget Inc,
 C=GB
 Here is an example of a multi-valued Relative Distinguished Name,
 where the namespace is flat within an organisation, and department is
 used to disambiguate certain names:
 OU=Sales + CN=J. Smith, O=Widget Inc., C=US
 The final examples show both methods quoting of a comma in an
 Organisation name:
 CN=L. Eagle, O="Sue, Grabbit and Runn", C=GB
 CN=L. Eagle, O=Sue\, Grabbit and Runn, C=GB

Kille [Page 3] RFC 1779 DN Representation March 1995

2.3 Formal definition

 A formal definition can now be given.  The structure is specified in
 a BNF grammar in Figure 1.  This BNF uses the grammar defined in RFC
 822, with the terminals enclosed in <> [2].  This definition is in an
 abstract character set, and so may be written in any character set
 supporting the explicitly defined special characters.  The quoting
 mechanism is used for the following cases:
  o  Strings containing ",", "+", "=" or """ , <CR>, "<",
     ">", "#", or ";".
  o  Strings with leading or trailing spaces
  o  Strings containing consecutive spaces
 There is an escape mechanism from the normal user oriented form, so
 that this syntax may be used to print any valid distinguished name.
 This is ugly.  It is expected to be used only in pathological cases.
 There are two parts to this mechanism:
 1.  Attributes types are represented in a (big-endian) dotted
     notation.  (e.g., OID.2.6.53).
 2.  Attribute values are represented in hexadecimal (e.g.  #0A56CF).
     Each pair of hex digits defines an octet, which is the ASN.1 Basic
     Encoding Rules value of the Attribute Value.
 The keyword specification is optional in the BNF, but mandatory for
 this specification.  This is so that the same BNF may be used for the
 related specification on User Friendly Naming [5].  When this
 specification is followed, the attribute type keywords must always be
 present.
 A list of valid keywords for well known attribute types used in
 naming is given in Table 1.  Keywords may contain spaces, but shall
 not have leading or trailing spaces.  This is a list of keywords
 which must be supported.  These are chosen because they appear in
 common forms of name, and can do so in a place which does not
 correspond to the default schema used.  A register of valid keywords
 is maintained by the IANA.

Kille [Page 4] RFC 1779 DN Representation March 1995

 <name> ::= <name-component> ( <spaced-separator> )
        | <name-component> <spaced-separator> <name>
 <spaced-separator> ::= <optional-space>
                 <separator>
                 <optional-space>
 <separator> ::=  "," | ";"
 <optional-space> ::= ( <CR> ) *( " " )
 <name-component> ::= <attribute>
         | <attribute> <optional-space> "+"
           <optional-space> <name-component>
 <attribute> ::= <string>
         | <key> <optional-space> "=" <optional-space> <string>
 <key> ::= 1*( <keychar> ) | "OID." <oid> | "oid." <oid>
 <keychar> ::= letters, numbers, and space
 <oid> ::= <digitstring> | <digitstring> "." <oid>
 <digitstring> ::= 1*<digit>
 <digit> ::= digits 0-9
 <string> ::= *( <stringchar> | <pair> )
          | '"' *( <stringchar> | <special> | <pair> ) '"'
          | "#" <hex>
 <special> ::= "," | "=" | <CR> | "+" | "<" |  ">"
          | "#" | ";"
 <pair> ::= "\" ( <special> | "\" | '"')
 <stringchar> ::= any character except <special> or "\" or '"'
 <hex> ::= 2*<hexchar>
 <hexchar> ::= 0-9, a-f, A-F
             Figure 1:  BNF Grammar for Distinguished Name

Kille [Page 5] RFC 1779 DN Representation March 1995

                     Key     Attribute (X.520 keys)
                     ------------------------------
                     CN      CommonName
                     L       LocalityName
                     ST      StateOrProvinceName
                     O       OrganizationName
                     OU      OrganizationalUnitName
                     C       CountryName
                     STREET  StreetAddress
                    Table 1:  Standardised Keywords
 Only string type attributes are considered, but other attribute
 syntaxes could be supported locally (e.g., by use of the syntexes
 defined in [3].)  It is assumed that the interface will translate
 from the supplied string into an appropriate Directory String
 encoding.  The "+" notation is used to specify multi-component RDNs.
 In this case, the types for attributes in the RDN must be explicit.
 The name is presented/input in a little-endian order (most
 significant component last).  When an address is written in a context
 where there is a need to delimit the entire address (e.g., in free
 text), it is recommended that the delimiters <> are used.  The
 terminator > is a special in the notation to facilitate this
 delimitation.

3. Examples

 This section gives a few examples of distinguished names written
 using this notation:
 CN=Marshall T. Rose, O=Dover Beach Consulting, L=Santa Clara,
 ST=California, C=US
 CN=FTAM Service, CN=Bells, OU=Computer Science,
 O=University College London, C=GB
 CN=Markus Kuhn, O=University of Erlangen, C=DE
 CN=Steve Kille,
 O=ISODE Consortium,
 C=GB

Kille [Page 6] RFC 1779 DN Representation March 1995

 CN=Steve Kille ,
 O =   ISODE Consortium,
 C=GB
 CN=Steve Kille, O=ISODE Consortium, C=GB

4. Acknowledgements

 This work was based on research work done at University College
 London [4], and evolved by the IETF OSI-DS WG.
 Input for this version of the document was received from:  Allan
 Cargille (University of Wisconsin); John Dale (COS); Philip Gladstone
 (Onsett); John Hawthorne (US Air Force); Roland Hedberg (University
 of Umea); Kipp Hickman (Mosaic Communications Corp.)  Markus Kuhn
 (University of Erlangen); Elisabeth Roudier (E3X); Mark Wahl (ISODE
 Consortium).

5. References

 [1] The Directory --- overview of concepts, models and services,
     1993. CCITT X.500 Series Recommendations.
 [2] Crocker, D., "Standard of the Format of ARPA-Internet Text
     Messages", STD 11, RFC 822, University of Delaware, August 1982.
 [3] Yeong, W., Howes, T., and S. Kille, "Lightweight Directory Access
     Protocol", RFC 1777, Performance Systems International,
     University of Michigan, ISODE Consortium, March 1995.
 [4] S.E. Kille. Using the OSI directory to achieve user friendly
     naming. Research Note RN/20/29, Department of Computer Science,
     University College London, February 1990.
 [5] Kille, S., "Using the OSI Directory to Achieve User Friendly
     Naming", RFC 1781, ISODE Consortium, March 1995.

Kille [Page 7] RFC 1779 DN Representation March 1995

6. Security Considerations

 Security issues are not discussed in this memo.

7. Author's Address

 Steve Kille
 ISODE Consortium
 The Dome
 The Square
 Richmond, Surrey
 TW9 1DT
 England
 Phone:  +44-181-332-9091
 EMail:  S.Kille@ISODE.COM
 DN: CN=Steve Kille,
 O=ISODE Consortium, C=GB
 UFN: S. Kille,
 ISODE Consortium, GB

Kille [Page 8]

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