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Network Working Group                                            M. WahlRequest for Comments: 2253                           Critical Angle Inc.Obsoletes:1779                                                 S. KilleCategory: Standards Track                                     Isode Ltd.                                                                T. Howes                                           Netscape Communications Corp.                                                           December 1997Lightweight Directory Access Protocol (v3):UTF-8 String Representation of Distinguished NamesStatus 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.Copyright Notice   Copyright (C) The Internet Society (1997).  All Rights Reserved.IESG Note   This document describes a directory access protocol that provides   both read and update access.  Update access requires secure   authentication, but this document does not mandate implementation of   any satisfactory authentication mechanisms.   In accordance withRFC 2026, section 4.4.1, this specification is   being approved by IESG as a Proposed Standard despite this   limitation, for the following reasons:   a. to encourage implementation and interoperability testing of      these protocols (with or without update access) before they      are deployed, and   b. to encourage deployment and use of these protocols in read-only      applications.  (e.g. applications where LDAPv3 is used as      a query language for directories which are updated by some      secure mechanism other than LDAP), and   c. to avoid delaying the advancement and deployment of other Internet      standards-track protocols which require the ability to query, but      not update, LDAPv3 directory servers.Wahl, et. al.              Proposed Standard                    [Page 1]

RFC 2253               LADPv3 Distinguished Names          December 1997   Readers are hereby warned that until mandatory authentication   mechanisms are standardized, clients and servers written according to   this specification which make use of update functionality are   UNLIKELY TO INTEROPERATE, or MAY INTEROPERATE ONLY IF AUTHENTICATION   IS REDUCED TO AN UNACCEPTABLY WEAK LEVEL.   Implementors are hereby discouraged from deploying LDAPv3 clients or   servers which implement the update functionality, until a Proposed   Standard for mandatory authentication in LDAPv3 has been approved and   published as an RFC.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.   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 inRFC 2119 [6].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 one of the local national languages).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 RelativeDistinguishedNameWahl, et. al.              Proposed Standard                    [Page 2]

RFC 2253               LADPv3 Distinguished Names          December 1997       RelativeDistinguishedName ::= SET SIZE (1..MAX) OF        AttributeTypeAndValue       AttributeTypeAndValue ::= SEQUENCE {        type  AttributeType,        value AttributeValue }   The following sections define 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 insection 2.4.   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:Wahl, et. al.              Proposed Standard                    [Page 3]

RFC 2253               LADPv3 Distinguished Names          December 1997                    String  X.500 AttributeType                    ------------------------------                    CN      commonName                    L       localityName                    ST      stateOrProvinceName                    O       organizationName                    OU      organizationalUnitName                    C       countryName                    STREET  streetAddress                    DC      domainComponent                    UID     userid2.4.  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 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 (see for example section 6 of   [4]).   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 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 insection 5.Wahl, et. al.              Proposed Standard                    [Page 4]

RFC 2253               LADPv3 Distinguished Names          December 19973. Parsing a String back to a Distinguished Name   The structure of the string is specified in a BNF grammar, based on   the grammar defined inRFC 822 [5].  Server implementations parsing a   DN string generated by an LDAPv2 client MUST also accept (and ignore)   the variants given insection 4 of this document.distinguishedName = [name]                    ; may be empty stringname       = name-component *("," name-component)name-component = attributeTypeAndValue *("+" attributeTypeAndValue)attributeTypeAndValue = attributeType "=" attributeValueattributeType = (ALPHA 1*keychar) / oidkeychar    = ALPHA / DIGIT / "-"oid        = 1*DIGIT *("." 1*DIGIT)attributeValue = stringstring     = *( stringchar / pair )             / "#" hexstring             / QUOTATION *( quotechar / pair ) QUOTATION ; only from v2quotechar     = <any character except "\" or QUOTATION >special    = "," / "=" / "+" / "<" /  ">" / "#" / ";"pair       = "\" ( special / "\" / QUOTATION / hexpair )stringchar = <any character except one of special, "\" or QUOTATION >hexstring  = 1*hexpairhexpair    = hexchar hexcharhexchar    = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"             / "a" / "b" / "c" / "d" / "e" / "f"ALPHA      =  <any ASCII alphabetic character>                                         ; (decimal 65-90 and 97-122)DIGIT      =  <any ASCII decimal digit>  ; (decimal 48-57)QUOTATION  =  <the ASCII double quotation mark character '"' decimal 34>Wahl, et. al.              Proposed Standard                    [Page 5]

RFC 2253               LADPv3 Distinguished Names          December 19974.  Relationship withRFC 1779 and LDAPv2   The syntax given in this document is more restrictive than the syntax   inRFC 1779.  Implementations parsing a string generated by an LDAPv2   client MUST accept the syntax ofRFC 1779.  Implementations MUST NOT,   however, generate any of theRFC 1779 encodings which are not   described above insection 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.   Implementations MUST allow an oid in the attribute type to be   prefixed by one of the character strings "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 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=GBWahl, et. al.              Proposed Standard                    [Page 6]

RFC 2253               LADPv3 Distinguished Names          December 1997   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 5 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\876.  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] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory       Access  Protocol (v3)",RFC 2251, December 1997.   [4] Wahl, M., Coulbeck, A., Howes, T. and S. Kille, "Lightweight       Directory Access Protocol (v3): Attribute Syntax Definitions",RFC 2252, December 1997.   [5] Crocker, D., "Standard of the Format of ARPA-Internet Text       Messages", STD 11,RFC 822, August 1982.   [6] Bradner, S., "Key words for use in RFCs to Indicate Requirement       Levels",RFC 2119.Wahl, et. al.              Proposed Standard                    [Page 7]

RFC 2253               LADPv3 Distinguished Names          December 19977.  Security Considerations7.1. Disclosure   Distinguished Names typically consist of descriptive information   about the entries they name, which can be people, organizations,   devices or other real-world objects.  This frequently includes some   of the following kinds of information:   - the common name of the object (i.e. a person's full name)   - an email or TCP/IP address   - its physical location (country, locality, city, street address)   - organizational attributes (such as department name or affiliation)   Most countries have privacy laws regarding the publication of   information about people.7.2. Use of Distinguished Names in Security Applications   The transformations of an AttributeValue value from its X.501 form to   an LDAP string representation are not always reversible back to the   same BER or DER form.  An example of a situation which requires the   DER form of a distinguished name is the verification of an X.509   certificate.   For example, a distinguished name consisting of one RDN with one AVA,   in which the type is commonName and the value is of the TeletexString   choice with the letters 'Sam' would be represented in LDAP as the   string CN=Sam.  Another distinguished name in which the value is   still 'Sam' but of the PrintableString choice would have the same   representation CN=Sam.   Applications which require the reconstruction of the DER form of the   value SHOULD NOT use the string representation of attribute syntaxes   when converting a distinguished name to the LDAP format.  Instead,   they SHOULD use the hexadecimal form prefixed by the octothorpe ('#')   as described in the first paragraph ofsection 2.4.8.  Authors' Addresses   Mark Wahl   Critical Angle Inc.   4815 W. Braker Lane #502-385   Austin, TX 78759   USA   EMail:  M.Wahl@critical-angle.comWahl, et. al.              Proposed Standard                    [Page 8]

RFC 2253               LADPv3 Distinguished Names          December 1997   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, MS MV068   Mountain View, CA 94043   USA   Phone:  +1 650 937-3419   EMail:   howes@netscape.comWahl, et. al.              Proposed Standard                    [Page 9]

RFC 2253               LADPv3 Distinguished Names          December 19979.  Full Copyright Statement   Copyright (C) The Internet Society (1997).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Wahl, et. al.              Proposed Standard                   [Page 10]