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+Network Working Group M. Wahl
+Request for Comments: 2253 Critical Angle Inc.
+Obsoletes: 1779 S. Kille
+Category: Standards Track Isode Ltd.
+ T. Howes
+ Netscape Communications Corp.
+ December 1997
+
+
+ Lightweight Directory Access Protocol (v3):
+ UTF-8 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.
+
+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 with RFC 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 in RFC 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 RelativeDistinguishedName
+
+
+
+
+
+
+Wahl, 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 in section 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 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 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 in section 5.
+
+
+
+
+Wahl, et. al. Proposed Standard [Page 4]
+
+RFC 2253 LADPv3 Distinguished Names December 1997
+
+
+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 [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] ; may be empty string
+
+name = name-component *("," name-component)
+
+name-component = attributeTypeAndValue *("+" attributeTypeAndValue)
+
+attributeTypeAndValue = attributeType "=" attributeValue
+
+attributeType = (ALPHA 1*keychar) / oid
+keychar = ALPHA / DIGIT / "-"
+
+oid = 1*DIGIT *("." 1*DIGIT)
+
+attributeValue = string
+
+string = *( stringchar / pair )
+ / "#" hexstring
+ / QUOTATION *( quotechar / pair ) QUOTATION ; only from v2
+
+quotechar = <any character except "\" or QUOTATION >
+
+special = "," / "=" / "+" / "<" / ">" / "#" / ";"
+
+pair = "\" ( special / "\" / QUOTATION / hexpair )
+stringchar = <any character except one of special, "\" or QUOTATION >
+
+hexstring = 1*hexpair
+hexpair = hexchar hexchar
+
+hexchar = 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 1997
+
+
+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.
+
+ 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=GB
+
+
+
+
+Wahl, 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\87
+
+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] 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 1997
+
+
+7. Security Considerations
+
+7.1. 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 of section 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.com
+
+
+
+
+Wahl, 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.com
+
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+Wahl, et. al. Proposed Standard [Page 9]
+
+RFC 2253 LADPv3 Distinguished Names December 1997
+
+
+9. 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.
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+Wahl, et. al. Proposed Standard [Page 10]
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