7 INTERNET-DRAFT Editor: Kurt D. Zeilenga
8 Intended Category: Standard Track OpenLDAP Foundation
9 Expires in six months 4 May 2003
13 LDAP: String Representation of Distinguished Names
14 <draft-ietf-ldapbis-dn-10.txt>
19 This document is an Internet-Draft and is in full conformance with all
20 provisions of Section 10 of RFC2026.
22 This document is intended to be, after appropriate review and
23 revision, submitted to the RFC Editor as a Standard Track document
24 replacing RFC 2253. Distribution of this memo is unlimited.
25 Technical discussion of this document will take place on the IETF LDAP
26 Revision (LDAPbis) Working Group mailing list
27 <ietf-ldapbis@openldap.org>. Please send editorial comments directly
28 to the document editor <Kurt@OpenLDAP.org>.
30 Internet-Drafts are working documents of the Internet Engineering Task
31 Force (IETF), its areas, and its working groups. Note that other
32 groups may also distribute working documents as Internet-Drafts.
33 Internet-Drafts are draft documents valid for a maximum of six months
34 and may be updated, replaced, or obsoleted by other documents at any
35 time. It is inappropriate to use Internet-Drafts as reference
36 material or to cite them other than as ``work in progress.''
38 The list of current Internet-Drafts can be accessed at
39 <http://www.ietf.org/ietf/1id-abstracts.txt>. The list of
40 Internet-Draft Shadow Directories can be accessed at
41 <http://www.ietf.org/shadow.html>.
43 Copyright 2003, The Internet Society. All Rights Reserved.
45 Please see the Copyright section near the end of this document for
51 The X.500 Directory uses distinguished names (DNs) as primary keys to
52 entries in the directory. This document defines the string
53 representation used in the Lightweight Directory Access Protocol
54 (LDAP) to transfer distinguished names. The string representation is
58 Zeilenga LDAP: Distinguished Names [Page 1]
60 INTERNET-DRAFT draft-ietf-ldapbis-dn-10.txt 4 May 2003
63 designed to give a clean representation of commonly used distinguished
64 names, while being able to represent any distinguished name.
69 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
70 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
71 document are to be interpreted as described in BCP 14 [RFC2119].
74 1. Background and Intended Usage
76 In X.500-based directory systems [X.500], including those accessed
77 using the Lightweight Directory Access Protocol (LDAP) [Roadmap],
78 distinguished names (DNs) are used to unambiguously refer to a
79 directory entry [X.501][Models].
81 The structure of a DN [X.501] is described in terms of ASN.1 [X.680].
82 In the X.500 Directory Access Protocol [X.511] (and other ITU-defined
83 directory protocols), DNs are encoded using the Basic Encoding Rules
84 (BER) [X.690]. In LDAP, DNs are represented in string form.
86 It is important to have a common format to be able to unambiguously
87 represent a distinguished name. The primary goal of this
88 specification is ease of encoding and decoding. A secondary goal is
89 to have names that are human readable. It is not expected that LDAP
90 implementations with a human user interface would display these
91 strings directly to the user, but would most likely be performing
92 translations (such as expressing attribute type names in one of the
93 local national languages).
95 This document defines the string representation of Distinguished Names
96 used in LDAP [Protocol][Syntaxes]. Section 2 details the RECOMMENDED
97 algorithm for converting a DN from its ASN.1 structured representation
98 to a string. Section 3 details how to convert a DN from a string to a
99 ASN.1 structured representation.
101 While other documents may define other algorithms for converting a DN
102 from its ASN.1 structured representation to a string, all algorithms
103 MUST produce strings which adhere to the requirements of Section 3.
105 This document does not define a canonical string representation for
106 DNs. Comparison of DNs for equality is to be performed in accordance
107 with the distinguishedNameMatch matching rule [Syntaxes].
109 This document is an integral part of the LDAP Technical Specification
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119 This document obsoletes RFC 2253. Changes since RFC 2253 are
120 summarized in Appendix B.
122 This specification assumes familiarity with X.500 [X.500], and the
123 concept of Distinguished Name [X.501][Models].
126 2. Converting DistinguishedName from ASN.1 to a String
128 X.501 [X.501] defines the ASN.1 [X.680] structure of distinguished
129 name. The following is a variant provided for discussion purposes.
131 DistinguishedName ::= RDNSequence
133 RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
135 RelativeDistinguishedName ::= SET SIZE (1..MAX) OF
136 AttributeTypeAndValue
138 AttributeTypeAndValue ::= SEQUENCE {
140 value AttributeValue }
142 This section defines the RECOMMENDED algorithm for converting a
143 distinguished name from an ASN.1 structured representation to an UTF-8
144 [RFC2279] encoded Universal Character Set (UCS) [ISO10646] character
145 string representation. Other documents may describe other algorithms
146 for converting a distinguished name to a string, but only strings
147 which conform to the grammar defined in Section 3 MUST be produced by
148 LDAP implementations.
151 2.1. Converting the RDNSequence
153 If the RDNSequence is an empty sequence, the result is the empty or
156 Otherwise, the output consists of the string encodings of each
157 RelativeDistinguishedName in the RDNSequence (according to Section
158 2.2), starting with the last element of the sequence and moving
159 backwards toward the first.
161 The encodings of adjoining RelativeDistinguishedNames are separated by
162 a comma ("," U+002C) character.
165 2.2. Converting RelativeDistinguishedName
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175 When converting from an ASN.1 RelativeDistinguishedName to a string,
176 the output consists of the string encodings of each
177 AttributeTypeAndValue (according to Section 2.3), in any order.
179 Where there is a multi-valued RDN, the outputs from adjoining
180 AttributeTypeAndValues are separated by a plus sign ("+" U+002B)
184 2.3. Converting AttributeTypeAndValue
186 The AttributeTypeAndValue is encoded as the string representation of
187 the AttributeType, followed by an equals ("=" U+003D) character,
188 followed by the string representation of the AttributeValue. The
189 encoding of the AttributeValue is given in Section 2.4.
191 If the AttributeType is defined to have a short name and that short
192 name is known to be registered [REGISTRY] as identifying the
193 AttributeType, that short name, a <descr>, is used. Otherwise the
194 AttributeType is encoded as the dotted-decimal encoding, a
195 <numericoid>, of its OBJECT IDENTIFIER. The <descr> and <numericoid>
196 is defined in [Models].
198 Implementations are not expected dynamically update their knowledge of
199 registered short names. However, implementations SHOULD provide a
200 mechanism to allow its knowledge of registered short names to be
204 2.4. Converting an AttributeValue from ASN.1 to a String
206 If the AttributeType is of the dotted-decimal form, the AttributeValue
207 is represented by an number sign ("#" U+0023) character followed by
208 the hexadecimal encoding of each of the octets of the BER encoding of
209 the X.500 AttributeValue. This form is also used when the syntax of
210 the AttributeValue does not have a native string encoding defined for
211 it or the native string encoding is not restricted to UTF-8 encoded
212 UCS (or a subset of UCS) characters. This form may also be used in
213 other cases, such as when a reversible string representation is
214 desired (see Section 5.2).
216 Otherwise, if the AttributeValue is of a syntax which has a native
217 string encoding, the value is converted first to a UTF-8 encoded UCS
218 string according to its syntax specification (see for example Section
219 6 of [Syntaxes]). If that UTF-8 encoded UCS string does not have any
220 of the following characters which need escaping, then that string can
221 be used as the string representation of the value.
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228 INTERNET-DRAFT draft-ietf-ldapbis-dn-10.txt 4 May 2003
231 - a space (" " U+0020) or number sign ("#" U+0023) occurring at
232 the beginning of the string;
234 - a space (" " U+0020) character occurring at the end of the
237 - one of the characters """, "+", ",", ";", "<", ">", or "\"
238 (U+0022, U+002B, U+002C, U+003B, U+003C, U+003E, or U+005C
241 - the null (U+0000) character.
243 Other characters may be escaped.
245 Each octet of the character to be escaped is replaced by a backslash
246 and two hex digits, which form a single octet in the code of the
247 character. Alternatively, if and only if the character to be escaped
250 " ", """, "#", "+", ",", ";", "<", "=", ">", or "\"
251 (U+0020, U+0022, U+0023, U+002B, U+002C, U+003B,
252 U+003C, U+003D, U+003E, U+005C respectively)
254 it can be prefixed by a backslash ("\" U+0005C).
256 Examples of the escaping mechanism are shown in Section 4.
259 3. Parsing a String back to a Distinguished Name
261 The string representation of Distinguished Names is restricted to
262 UTF-8 [RFC2279] encoded characters from the Universal Character Set
263 (UCS) [ISO10646]. The structure of this string representation is
264 specified using the following Augmented BNF [RFC2234] grammar:
266 distinguishedName = [ relativeDistinguishedName
267 *( COMMA relativeDistinguishedName ) ]
269 relativeDistinguishedName = attributeTypeAndValue
270 *( PLUS attributeTypeAndValue )
272 attributeTypeAndValue = attributeType EQUALS attributeValue
274 attributeType = descr / numericoid
276 attributeValue = string / hexstring
278 ; The UTF-8 string shall not contain NULL, ESC, or
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284 INTERNET-DRAFT draft-ietf-ldapbis-dn-10.txt 4 May 2003
287 ; one of escaped, shall not start with SHARP or SPACE,
288 ; and shall must not end with SPACE.
289 string = [ (leadchar / pair)
290 [ *( stringchar / pair ) ( trailchar / pair ) ] ]
292 leadchar = LUTF1 / UTFMB
293 LUTF1 = %x01-1F / %x21 / %x24-2A / %x2D-3A /
294 %x3D / %x3F-5B / %x5D-7F
296 trailchar = TUTF1 / UTFMB
297 TUTF1 = %x01-1F / %x21 / %x23-2A / %x2D-3A /
298 %x3D / %x3F-5B / %x5D-7F
300 stringchar = SUTF1 / UTFMB
301 SUTF1 = %x01-21 / %x23-2A / %x2D-3A /
302 %x3D / %x3F-5B / %x5D-7F
304 pair = ESC ( ESC / special / hexpair )
306 special = escaped / SPACE / SHARP / EQUALS
308 escaped = DQUOTE / PLUS / COMMA / SEMI / LANGLE / RANGLE
310 hexstring = SHARP 1*hexpair
314 where the productions <descr>, <numericoid>, <COMMA>, <DQUOTE>,
315 <EQUALS>, <ESC>, <HEX>, <LANGLE>, <NULL>, <PLUS>, <RANGLE>, <SEMI>,
316 <SPACE>, <SHARP>, <UTFMB> are defined in [Models].
318 Each <attributeType>, either a <descr> or a <numericoid>, refers to an
319 attribute type of an attribute value assertion (AVA). The
320 <attributeType> is followed by a <EQUALS> and an <attributeValue>.
321 The <attributeValue> is either in <string> or <hexstring> form.
323 If in <string> form, a LDAP string representation asserted value can
324 be obtained by replacing (left-to-right, non-recursively) each <pair>
325 appearing in the <string> as follows:
326 replace <ESC><ESC> with <ESC>;
327 replace <ESC><special> with <special>;
328 replace <ESC><hexpair> with the octet indicated by the <hexpair>.
330 If in <hexstring> form, a BER representation can be obtained from
331 converting each <hexpair> of the <hexstring> to the octet indicated by
334 One or more attribute values assertions, separated by <PLUS>, for a
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340 INTERNET-DRAFT draft-ietf-ldapbis-dn-10.txt 4 May 2003
343 relative distinguished name.
345 Zero or more relative distinguished names, separated by <COMMA>, for a
348 Implementations MUST recognize AttributeType name strings
349 (descriptors) listed in the following table, but MAY recognize other
352 String X.500 AttributeType
353 ------ --------------------------------------------
354 CN commonName (2.5.4.3)
355 L localityName (2.5.4.7)
356 ST stateOrProvinceName (2.5.4.8)
357 O organizationName (2.5.4.10)
358 OU organizationalUnitName (2.5.4.11)
359 C countryName (2.5.4.6)
360 STREET streetAddress (2.5.4.9)
361 DC domainComponent (0.9.2342.19200300.100.1.25)
362 UID userId (0.9.2342.19200300.100.1.1)
364 Implementations MAY recognize other DN string representations
365 (such as that described in RFC 1779). However, as there is no
366 requirement that alternative DN string representations to be
367 recognized (and, if so, how), implementations SHOULD only generate
368 DN strings in accordance with Section 2 of this document.
373 This notation is designed to be convenient for common forms of
374 name. This section gives a few examples of distinguished names
375 written using this notation. First is a name containing three
376 relative distinguished names (RDNs):
378 UID=jsmith,DC=example,DC=net
380 Here is an example name containing three RDNs, in which the first
383 OU=Sales+CN=J. Smith,DC=example,DC=net
385 This example shows the method of escaping of a comma in a common
388 CN=John Smith\, III,DC=example,DC=net
390 An example name in which a value contains a carriage return
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401 CN=Before\0dAfter,DC=example,DC=net
403 An example name in which an RDN was of an unrecognized type. The
404 value is the BER encoding of an OCTET STRING containing two octets
407 1.3.6.1.4.1.1466.0=#04024869,DC=example,DC=com
409 Finally, an example of an RDN commonName value consisting of 5
412 Unicode Letter Description UCS code UTF-8 Escaped
413 ------------------------------- -------- ------ --------
414 LATIN CAPITAL LETTER L U+004C 0x4C L
415 LATIN SMALL LETTER U U+0075 0x75 u
416 LATIN SMALL LETTER C WITH CARON U+010D 0xC48D \C4\8D
417 LATIN SMALL LETTER I U+0069 0x69 i
418 LATIN SMALL LETTER C WITH ACUTE U+0107 0xC487 \C4\87
420 could be written in printable ASCII (useful for debugging purposes):
425 5. Security Considerations
427 The following security considerations are specific to the handling of
428 distinguished names. LDAP security considerations are discussed in
429 [Protocol] and other documents comprising the LDAP Technical
430 Specification [Roadmap].
435 Distinguished Names typically consist of descriptive information about
436 the entries they name, which can be people, organizations, devices or
437 other real-world objects. This frequently includes some of the
438 following kinds of information:
440 - the common name of the object (i.e. a person's full name)
441 - an email or TCP/IP address
442 - its physical location (country, locality, city, street address)
443 - organizational attributes (such as department name or affiliation)
445 Most countries have privacy laws regarding the publication of
446 information about people.
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455 5.2. Use of Distinguished Names in Security Applications
457 The transformations of an AttributeValue value from its X.501 form to
458 an LDAP string representation are not always reversible back to the
459 same BER (Basic Encoding Rules) or DER (Distinguished Encoding rules)
460 form. An example of a situation which requires the DER form of a
461 distinguished name is the verification of an X.509 certificate.
463 For example, a distinguished name consisting of one RDN with one AVA,
464 in which the type is commonName and the value is of the TeletexString
465 choice with the letters 'Sam' would be represented in LDAP as the
466 string CN=Sam. Another distinguished name in which the value is still
467 'Sam' but of the PrintableString choice would have the same
468 representation CN=Sam.
470 Applications which require the reconstruction of the DER form of the
471 value SHOULD NOT use the string representation of attribute syntaxes
472 when converting a distinguished name to the LDAP format. Instead,
473 they SHOULD use the hexadecimal form prefixed by the number sign ('#')
474 as described in the first paragraph of Section 2.3.
479 This document is an update to RFC 2253, by Mark Wahl, Tim Howes, and
480 Steve Kille. RFC 2253 was a product of the IETF ASID Working Group.
482 This document is a product of the IETF LDAPBIS Working Group.
485 7. Document Editor's Address
492 8. Normative References
494 [X.501] "The Directory -- Models," ITU-T Rec. X.501(1993).
496 [X.680] ITU-T, "Abstract Syntax Notation One (ASN.1) -
497 Specification of Basic Notation", X.680, 1994.
499 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
500 Requirement Levels", BCP 14 (also RFC 2119).
502 [RFC2234] Crocker, D., and P. Overell, "Augmented BNF for Syntax
506 Zeilenga LDAP: Distinguished Names [Page 9]
508 INTERNET-DRAFT draft-ietf-ldapbis-dn-10.txt 4 May 2003
511 Specifications: ABNF", RFC 2234, November 1997.
513 [RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
514 10646", RFC 2279, January 1998.
516 [Models] K. Zeilenga (editor), "LDAP: Directory Information
517 Models", draft-ietf-ldapbis-models-xx.txt, a work in
520 [Roadmap] K. Zeilenga, "LDAP: Technical Specification Road Map",
521 draft-ietf-ldapbis-roadmap-xx.txt, a work in progress.
523 [Protocol] J. Sermersheim (editor), "LDAP: The Protocol",
524 draft-ietf-ldapbis-protocol-xx.txt, a work in progress.
526 [Syntaxes] S. Legg (editor), "LDAP: Syntaxes",
527 draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress.
529 [Schema] K. Dally (editor), "LDAP: User Schema",
530 draft-ietf-ldapbis-user-schema-xx.txt, a work in
533 [ISO10646] Universal Multiple-Octet Coded Character Set (UCS) -
534 Architecture and Basic Multilingual Plane, ISO/IEC
538 9. Informative References
540 [X.500] "The Directory -- overview of concepts, models and
541 services," ITU-T Rec. X.500(1993).
543 [X.690] ITU-T, "Specification of ASN.1 encoding rules: Basic,
544 Canonical, and Distinguished Encoding Rules", X.690,
547 [RFC3383] K. Zeilenga, "IANA Considerations for LDAP", BCP 64 (also
548 RFC 3383), September 2002.
550 [RFC2849] G. Good, "The LDAP Data Interchange Format (LDIF) -
551 Technical Specification", RFC 2849, June 2000.
554 Appendix A. Presentation Issues
556 This appendix is provided for informational purposes only, it is not a
557 normative part of this specification.
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567 The string representation described in this document is not intended
568 to be presented to humans without translation. However, at times it
569 may be desirable to present non-translated DN strings to users. This
570 section discusses presentation issues associated with non-translated
571 DN strings. Presentation of translated DN strings issues are not
572 discussed in this appendix. Transcoding issues are also not discussed
575 This appendix provides guidance for applications presenting DN strings
576 to users. This section is not comprehensive, it does not discuss all
577 presentation issues which implementors may face.
579 Not all user interfaces are capable of displaying the full set of UCS
580 characters. Some UCS characters are not displayable.
582 It is recommended that human interfaces use the optional hex pair
583 escaping mechanism (Section 2.3) to produce a string representation
584 suitable for display to the user. For example, an application can
585 generate a DN string for display which escapes all non-printable
586 characters appearing in the AttributeValue's string representation (as
587 demonstrated in the final example of Section 4).
589 When a DN string is displayed in free form text, it is often necessary
590 to distinguish the DN string from surrounding text. While this is
591 often done with white space (as demonstrated in Section 4), it is
592 noted that DN strings may end with white space. Careful readers of
593 Section 3 will note that characters "<" (U+003C) and ">" (U+003E) may
594 only appear in the DN string if escaped. These characters are
595 intended to be used in free form text to distinguish a DN string from
596 surrounding text. For example, <CN=Sam\ > distinguished the string
597 representation of the DN comprised of one RDN consisting of the AVA:
598 the commonName (CN) value "Sam " from the surrounding text. It should
599 be noted to the user that the wrapping "<" and ">" characters are not
600 part of the DN string.
602 DN strings can be quite long. It is often desirable to line-wrap
603 overly long DN strings in presentations. Line wrapping should be done
604 by inserting white space after the RDN separator character or, if
605 necessary, after the AVA separator character. It should be noted to
606 the user that the inserted white space is not part of the DN string
607 and is to be removed before use in LDAP. For example,
609 The following DN string is long:
610 CN=Kurt D. Zeilenga,OU=Engineering,L=Redwood Shores,
611 O=OpenLDAP Foundation,ST=California,C=US
612 so it has been line-wrapped for readability. The extra white
613 space is to be removed before the DN string is used in LDAP.
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623 It is not advised to insert white space otherwise as it may not be
624 obvious to the user which white space is part of the DN string and
625 which white space was added for readability.
627 Another alternative is to use the LDAP Data Interchange Format (LDIF)
628 [RFC2849]. For example,
630 # This entry has a long DN...
631 dn: CN=Kurt D. Zeilenga,OU=Engineering,L=Redwood Shores,
632 O=OpenLDAP Foundation,ST=California,C=US
638 Appendix B. Changes made since RFC 2253
640 This appendix is provided for informational purposes only, it is not a
641 normative part of this specification.
643 The following substantive changes were made to RFC 2253:
644 - Removed IESG Note. The IESG Note has been addressed.
645 - Clarified (in Section 1), that this document does not define a
646 canonical string representation.
647 - Replaced specification of additional requirements for LDAPv2
648 implementations which also support LDAPv3 (RFC 2253, Section 4)
649 with a statement (in Section 3) allowing recognition of
650 alternative string representations.
651 - Clarified (in Section 2.3) that the "published" table of names
652 which may be appear in DNs is the table which Section 2.3
653 provides. Remove "as an example" language. Noted this table is
654 not extensible. Added statement (in Section 3) allowing
655 recognition of additional names. Added security considerations
656 (Section 5.3) regarding the use of other names.
657 - Updated Section 2.3 to indicate attribute type name strings are
659 - Updated Section 2.4 to allow hex pair escaping of all characters
660 and clarified escaping for when multiple octet UTF-8 characters
662 - Rewrote Section 3 to use ABNF as defined in RFC 2234.
663 - Rewrote Section 3 ABNF to be consistent with 2.4.
664 - Updated Section 3 to describe how to parse elements of the
667 - Added reference to documentations containing general LDAP security
669 - Added discussion of presentation issues (Appendix A).
670 - Added this appendix.
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679 In addition, numerous editorial changes were made.
682 Copyright 2003, The Internet Society. All Rights Reserved.
684 This document and translations of it may be copied and furnished to
685 others, and derivative works that comment on or otherwise explain it
686 or assist in its implementation may be prepared, copied, published and
687 distributed, in whole or in part, without restriction of any kind,
688 provided that the above copyright notice and this paragraph are
689 included on all such copies and derivative works. However, this
690 document itself may not be modified in any way, such as by removing
691 the copyright notice or references to the Internet Society or other
692 Internet organizations, except as needed for the purpose of
693 developing Internet standards in which case the procedures for
694 copyrights defined in the Internet Standards process must be followed,
695 or as required to translate it into languages other than English.
697 The limited permissions granted above are perpetual and will not be
698 revoked by the Internet Society or its successors or assigns.
700 This document and the information contained herein is provided on an
701 "AS IS" basis and THE AUTHORS, THE INTERNET SOCIETY, AND THE INTERNET
702 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
703 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
704 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
705 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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