CVS libidn/doc/specifications

[libidn-commit]

Update of /home/cvs/libidn/doc/specifications
In directory dopio:/tmp/cvs-serv19705

Added Files:
        draft-ietf-ldapbis-strprep-07.txt 
Log Message:
Add.


--- /home/cvs/libidn/doc/specifications/draft-ietf-ldapbis-strprep-07.txt       
2006/01/24 21:36:33     NONE
+++ /home/cvs/libidn/doc/specifications/draft-ietf-ldapbis-strprep-07.txt       
2006/01/24 21:36:33     1.1






Internet-Draft                                      Kurt D. Zeilenga
Intended Category: Standard Track                OpenLDAP Foundation
Expires in six months                                23 January 2006



                LDAP: Internationalized String Preparation
                   <draft-ietf-ldapbis-strprep-07.txt>



Status of this Memo

  This document is intended to be published as a Standard Track RFC.
  Distribution of this memo is unlimited.  Technical discussion of this
  document will take place on the IETF LDAP Revision Working Group
  mailing list <address@hidden>.  Please send editorial
  comments directly to the editor <address@hidden>.

  By submitting this Internet-Draft, each author represents that any
  applicable patent or other IPR claims of which he or she is aware have
  been or will be disclosed, and any of which he or she becomes aware
  will be disclosed, in accordance with Section 6 of BCP 79.

  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 (2006).  All Rights Reserved.

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







Zeilenga                        LDAPprep                        [Page 1]

Internet-Draft        draft-ietf-ldapbis-strprep-07      23 January 2006


Abstract

  The previous Lightweight Directory Access Protocol (LDAP) technical
  specifications did not precisely define how character string matching
  is to be performed.  This led to a number of usability and
  interoperability problems.  This document defines string preparation
  algorithms for character-based matching rules defined for use in LDAP.


Conventions and Terms

  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>.
  In the lists of mappings and the prohibited characters, the "U+" is
  left off to make the lists easier to read.  The comments for character
  ranges are shown in square brackets (such as "[CONTROL CHARACTERS]")
  and do not come from the standard.

  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].

  The term "combining mark", as used in this specification, refers to
  any Unicode [Unicode] code point which has a mark property (Mn, Mc,
  Me).  Appendix A provides a definitive list of combining marks.


1. Introduction

1.1. Background

  A Lightweight Directory Access Protocol (LDAP) [Roadmap] matching rule
  [Syntaxes] defines an algorithm for determining whether a presented
  value matches an attribute value in accordance with the criteria
  defined for the rule.  The proposition may be evaluated to True,
  False, or Undefined.

      True      - the attribute contains a matching value,

      False     - the attribute contains no matching value,

      Undefined - it cannot be determined whether the attribute contains
                  a matching value or not.



Zeilenga                        LDAPprep                        [Page 2]

Internet-Draft        draft-ietf-ldapbis-strprep-07      23 January 2006


  For instance, the caseIgnoreMatch matching rule may be used to compare
  whether the commonName attribute contains a particular value without
  regard for case and insignificant spaces.


1.2. X.500 String Matching Rules

  "X.520: Selected attribute types" [X.520] provides (amongst other
  things) value syntaxes and matching rules for comparing values
  commonly used in the Directory.  These specifications are inadequate
  for strings composed of Unicode [Unicode] characters.

  The caseIgnoreMatch matching rule [X.520], for example, is simply
  defined as being a case insensitive comparison where insignificant
  spaces are ignored.  For printableString, there is only one space
  character and case mapping is bijective, hence this definition is
  sufficient.  However, for Unicode string types such as
  universalString, this is not sufficient.  For example, a case
  insensitive matching implementation which folded lower case characters
  to upper case would yield different different results than an
  implementation which used upper case to lower case folding.  Or one
  implementation may view space as referring to only SPACE (U+0020), a
  second implementation may view any character with the space separator
  (Zs) property as a space, and another implementation may view any
  character with the whitespace (WS) category as a space.

  The lack of precise specification for character string matching has
  led to significant interoperability problems.  When used in
  certificate chain validation, security vulnerabilities can arise.  To
  address these problems, this document defines precise algorithms for
  preparing character strings for matching.


1.3. Relationship to "stringprep"

  The character string preparation algorithms described in this document
  are based upon the "stringprep" approach [RFC3454].  In "stringprep",
  presented and stored values are first prepared for comparison and so
  that a character-by-character comparison yields the "correct" result.

  The approach used here is a refinement of the "stringprep" [RFC3454]
  approach.  Each algorithm involves two additional preparation steps.

  a) prior to applying the Unicode string preparation steps outlined in
     "stringprep", the string is transcoded to Unicode;

  b) after applying the Unicode string preparation steps outlined in
     "stringprep", the string is modified to appropriately handle



Zeilenga                        LDAPprep                        [Page 3]

Internet-Draft        draft-ietf-ldapbis-strprep-07      23 January 2006


     characters insignificant to the matching rule.

  Hence, preparation of character strings for X.500 matching involves
  the following steps:

      1) Transcode
      2) Map
      3) Normalize
      4) Prohibit
      5) Check Bidi (Bidirectional)
      6) Insignificant Character Handling

  These steps are described in Section 2.

  It is noted that while various tables of Unicode characters included
  or referenced by this specification are derived from Unicode [UNICODE]
  data, these tables are to be considered definitive for the purpose of
  implementing this specification.


1.4. Relationship to the LDAP Technical Specification

  This document is a integral part of the LDAP technical specification
  [Roadmap] which obsoletes the previously defined LDAP technical
  specification [RFC3377] in its entirety.

  This document details new LDAP internationalized character string
  preparation algorithms used by [Syntaxes] and possible other technical
  specifications defining LDAP syntaxes and/or matching rules.


1.5. Relationship to X.500

  LDAP is defined [Roadmap] in X.500 terms as an X.500 access mechanism.
  As such, there is a strong desire for alignment between LDAP and X.500
  syntax and semantics.  The character string preparation algorithms
  described in this document are based upon "Internationalized String
  Matching Rules for X.500" [XMATCH] proposal to ITU/ISO Joint Study
  Group 2.


2. String Preparation

  The following six-step process SHALL be applied to each presented and
  attribute value in preparation for character string matching rule
  evaluation.

      1) Transcode



Zeilenga                        LDAPprep                        [Page 4]

Internet-Draft        draft-ietf-ldapbis-strprep-07      23 January 2006


      2) Map
      3) Normalize
      4) Prohibit
      5) Check bidi
      6) Insignificant Character Handling

  Failure in any step causes the assertion to evaluate to Undefined.

  The character repertoire of this process is Unicode 3.2 [Unicode].

  Note that this six-step process specification is intended to described
  expected matching behavior.   Implementations are free use alternative
  processes so long as the matching rule evaluation behavior provided is
  consistent with the behavior described by this specification.


2.1. Transcode

  Each non-Unicode string value is transcoded to Unicode.

  PrintableString [X.680] value are transcoded directly to Unicode.

  UniversalString, UTF8String, and bmpString [X.680] values need not be
  transcoded as they are Unicode-based strings (in the case of
  bmpString, a subset of Unicode).

  TeletexString [X.680] values are transcoded to Unicode.  As there is
  no standard for mapping TeletexString values to Unicode, the mapping
  is left a local matter.

  For these and other reasons, use of TeletexString is NOT RECOMMENDED.

  The output is the transcoded string.


2.2. Map

  SOFT HYPHEN (U+00AD) and MONGOLIAN TODO SOFT HYPHEN (U+1806) code
  points are mapped to nothing.  COMBINING GRAPHEME JOINER (U+034F) and
  VARIATION SELECTORs (U+180B-180D, FF00-FE0F) code points are also
  mapped to nothing.  The OBJECT REPLACEMENT CHARACTER (U+FFFC) is
  mapped to nothing.

  CHARACTER TABULATION (U+0009), LINE FEED (LF) (U+000A), LINE
  TABULATION (U+000B), FORM FEED (FF) (U+000C), CARRIAGE RETURN (CR)
  (U+000D), and NEXT LINE (NEL) (U+0085) are mapped to SPACE (U+0020).

  All other control code (e.g., Cc) points or code points with a control



Zeilenga                        LDAPprep                        [Page 5]

Internet-Draft        draft-ietf-ldapbis-strprep-07      23 January 2006


  function (e.g., Cf) are mapped to nothing.  The following is a
  complete list of these code points: U+0000-0008, 000E-001F, 007F-0084,
  0086-009F, 06DD, 070F, 180E, 200C-200F, 202A-202E, 2060-2063,
  206A-206F, FEFF, FFF9-FFFB, 1D173-1D17A, E0001, E0020-E007F.

  ZERO WIDTH SPACE (U+200B) is mapped to nothing.  All other code points
  with Separator (space, line, or paragraph) property (e.g, Zs, Zl, or
  Zp) are mapped to SPACE (U+0020).  The following is a complete list of
  these code points: U+0020, 00A0, 1680, 2000-200A, 2028-2029, 202F,
  205F, 3000.

  For case ignore, numeric, and stored prefix string matching rules,
  characters are case folded per B.2 of [RFC3454].

  The output is the mapped string.


2.3. Normalize

  The input string is be normalized to Unicode Form KC (compatibility
  composed) as described in [UAX15].  The output is the normalized
  string.


2.4. Prohibit

  All Unassigned code points are prohibited.  Unassigned code points are
  listed in Table A.1 of [RFC3454].

  Characters which, per Section 5.8 of [Stringprep], change display
  properties or are deprecated are prohibited.  These characters are are
  listed in Table C.8 of [RFC3454].

  Private Use code points are prohibited.  These characters are listed
  in Table C.3 of [RFC3454].

  All non-character code points are prohibited.  These code points are
  listed in Table C.4 of [RFC3454].

  Surrogate codes are prohibited.  These characters are listed in Table
  C.5 of [RFC3454].

  The REPLACEMENT CHARACTER (U+FFFD) code point is prohibited.

  The step fails if the input string contains any prohibited code point.
  Otherwise, the output is the input string.





Zeilenga                        LDAPprep                        [Page 6]

Internet-Draft        draft-ietf-ldapbis-strprep-07      23 January 2006


2.5. Check bidi

  Bidirectional characters are ignored.


2.6. Insignificant Character Handling

  In this step, the string is modified to ensure proper handling of
  characters insignificant to the matching rule.  This modification
  differs from matching rule to matching rule.

  Section 2.6.1 applies to case ignore and exact string matching.
  Section 2.6.2 applies to numericString matching.
  Section 2.6.3 applies to telephoneNumber matching.


2.6.1. Insignificant Space Handling

  For the purposes of this section, a space is defined to be the SPACE
  (U+0020) code point followed by no combining marks.

  NOTE - The previous steps ensure that the string cannot contain any
         code points in the separator class, other than SPACE (U+0020).

  If the input string contains at least one non-space character, then
  the string is modified such that the string starts with exactly one
  space character, ends with exactly one SPACE character, and that any
  inner (non-empty) sequence of space characters is replaced with
  exactly two SPACE characters.  For instance, the input strings
  "foo<SPACE>bar<SPACE><SPACE>", results in the output
  "<SPACE>foo<SPACE><SPACE>bar<SPACE>".

  Otherwise, if the string being prepared is an initial, any, or final
  substring, then the output string is exactly one SPACE character, else
  the output string is exactly two SPACEs.

  Appendix B discusses the rationale for the behavior.


2.6.2. numericString Insignificant Character Handling

  For the purposes of this section, a space is defined to be the SPACE
  (U+0020) code point followed by no combining marks.

  All spaces are regarded as insignificant and are to be removed.

  For example, removal of spaces from the Form KC string:
      "<SPACE><SPACE>123<SPACE><SPACE>456<SPACE><SPACE>"



Zeilenga                        LDAPprep                        [Page 7]

Internet-Draft        draft-ietf-ldapbis-strprep-07      23 January 2006


  would result in the output string:
      "123456"

[387 lines skipped]