Internet-Draft                                      Kurt D. Zeilenga
Intended Category: Standard Track                OpenLDAP Foundation
Expires in six months                                    4 June 2004                                9 February 2005

                LDAP: Internationalized String Preparation
                   <draft-ietf-ldapbis-strprep-04.txt>
                   <draft-ietf-ldapbis-strprep-05.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
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  mailing list <ietf-ldapbis@openldap.org>.  Please send editorial
  comments directly to the editor <Kurt@OpenLDAP.org>.

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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 C A provides a complete 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.

  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 [StringPrep].  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"
  [StringPrep] 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
     characters insignificant to the matching rules are
     removed. 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 Removal Handling

  These steps are described in Section 2.

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

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

  This process is intended to act upon non-empty character strings.  If
  the string to prepare is empty, this process is not applied and the
  assertion is evaluated to Undefined.

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

2.1. Transcode

  Each non-Unicode string value is transcoded to Unicode.

  TeletexString [X.680][T.61] values are transcoded to Unicode as
  described in Appendix A.

  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 TelexString 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
  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 [StringPrep].

  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 [StringPrep].

  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 [StringPrep].

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

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

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

  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.

2.5. Check bidi

  This step fails if the input string does not conform to the the
  bidirectional character restrictions detailed in 6 of [Stringprep].
  Otherwise, the output is the input string.

  Bidirectional characters are ignored.

2.6. Insignificant Character Removal Handling

  In this step, the string is modified to ensure proper handling of
  characters insignificant to the matching rule are to be
  removed.  The characters to be removed differ 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 Removal 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 consists entirely of spaces or is empty, contains at least one non-space character, then
  the
  output string is a modified such that the string consisting of starts with exactly one
  space (e.g. " ").

  Otherwise, the following spaces are removed:
    - leading spaces (i.e. those preceding the first character that is
      not a space);
    - trailing spaces (i.e. those following the last character character, ends with exactly one SPACE character, and that is
      not a space);
    - multiple consecutive spaces (these are taken as equivalent to a
      single any
  inner (non-empty) sequence of space character). characters is replaced with
  exactly two SPACE characters.  For example, removal of spaces from instance, the Form KC string:
      "<SPACE><SPACE>foo<SPACE><SPACE>bar<SPACE><SPACE>"
  would result input strings
  "foo<SPACE>bar<SPACE><SPACE>", results in the output string:
      "foo<SPACE>bar"
  and
  "<SPACE>foo<SPACE><SPACE>bar<SPACE>".

  Otherwise, if the Form KC string:
      "<SPACE><SPACE><SPACE>"
  would result in string being prepared is an initial, any, or final
  substring, then the output string:
      "<SPACE>". 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 Removal 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 not significant.  If the input string
  consists entirely of spaces or is empty, the output is a string
  consisting of exactly one space (e.g. " ").  Otherwise, all spaces insignificant and are to be removed.

  For example, removal of spaces from the Form KC string:
      "<SPACE><SPACE>123<SPACE><SPACE>456<SPACE><SPACE>"
  would result in the output string:
      "123456"
  and the Form KC string:
      "<SPACE><SPACE><SPACE>"
  would result in the output string:
      "<SPACE>".
      "" (an empty string).

2.6.3. telephoneNumber Insignificant Character Removal Handling

  For the purposes of this section, a hyphen is defined to be
  HYPHEN-MINUS (U+002D), ARMENIAN HYPHEN (U+058A), HYPHEN (U+2010),
  NON-BREAKING HYPHEN (U+2011), MINUS SIGN (U+2212), SMALL HYPHEN-MINUS
  (U+FE63), or FULLWIDTH HYPHEN-MINUS (U+FF0D) code point followed by no
  combining marks and a space is defined to be the SPACE (U+0020) code
  point followed by no combining marks.

  All hyphens and spaces are considered insignificant.  If the string
  contains only spaces and hyphens or is empty, then the output is a
  string consisting of one space.  Otherwise, all hyphens insignificant and spaces are to be
  removed.

  For example, removal of hyphens and spaces from the Form KC string:
      "<SPACE><HYPHEN>123<SPACE><SPACE>456<SPACE><HYPHEN>"
  would result in the output string:
      "123456"
  and the Form KC string:
      "<HYPHEN><HYPHEN><HYPHEN>"
  would result in the (empty) output string:
      "<SPACE>".
      "".

3. Security Considerations

  "Preparation for International Strings ('stringprep')" [StringPrep]
  security considerations generally apply to the algorithms described
  here.

4. Contributors

  Appendix A and B of this document were authored by Howard Chu
  <hyc@symas.com> of Symas Corporation (based upon information provided
  in RFC 1345).

5. Acknowledgments

  The approach used in this document is based upon design principles and
  algorithms described in "Preparation of Internationalized Strings
  ('stringprep')" [StringPrep] by Paul Hoffman and Marc Blanchet.  Some
  additional guidance was drawn from Unicode Technical Standards,
  Technical Reports, and Notes.

  This document is a product of the IETF LDAP Revision (LDAPBIS) Working
  Group.

6.

5. Author's Address

  Kurt D. Zeilenga
  OpenLDAP Foundation

  Email: Kurt@OpenLDAP.org

7.

6. References

  [[Note to the RFC Editor: please replace the citation tags used in
  referencing Internet-Drafts with tags of the form RFCnnnn.]]

7.1. RFCnnnn where
  possible.]]

6.1. Normative References

  [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14 (also RFC 2119), March 1997.

  [Roadmap]     Zeilenga, K. (editor), "LDAP: Technical Specification
                Road Map", draft-ietf-ldapbis-roadmap-xx.txt, a work in
                progress.

  [StringPrep]  Hoffman P. and M. Blanchet, "Preparation of
                Internationalized Strings ('stringprep')",
                draft-hoffman-rfc3454bis-xx.txt, a work in progress.

  [Syntaxes]    Legg, S. (editor), "LDAP: Syntaxes and Matching Rules",
                draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress.

  [Unicode]     The Unicode Consortium, "The Unicode Standard, Version
                3.2.0" is defined by "The Unicode Standard, Version 3.0"
                (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5),
                as amended by the "Unicode Standard Annex #27: Unicode
                3.1" (http://www.unicode.org/reports/tr27/) and by the
                "Unicode Standard Annex #28: Unicode 3.2"
                (http://www.unicode.org/reports/tr28/).

  [UAX15]       Davis, M. and M. Duerst, "Unicode Standard Annex #15:
                Unicode Normalization Forms, Version 3.2.0".
                <http://www.unicode.org/unicode/reports/tr15/tr15-22.html>,
                March 2002.

  [X.680]       International Telecommunication Union -
                Telecommunication Standardization Sector, "Abstract
                Syntax Notation One (ASN.1) - Specification of Basic
                Notation", X.680(1997) (also ISO/IEC 8824-1:1998).

  [T.61]        CCITT (now ITU), "Character Repertoire and Coded
                Character Sets for the International Teletex Service",
                T.61, 1988.

7.2.

6.2. Informative References

  [X.500]       International Telecommunication Union -
                Telecommunication Standardization Sector, "The Directory
                -- Overview of concepts, models and services,"
                X.500(1993) (also ISO/IEC 9594-1:1994).

  [X.501]       International Telecommunication Union -
                Telecommunication Standardization Sector, "The Directory
                -- Models," X.501(1993) (also ISO/IEC 9594-2:1994).

  [X.520]       International Telecommunication Union -
                Telecommunication Standardization Sector, "The
                Directory: Selected Attribute Types", X.520(1993) (also
                ISO/IEC 9594-6:1994).

  [Glossary]    The Unicode Consortium, "Unicode Glossary",
                <http://www.unicode.org/glossary/>.

  [CharModel]   Whistler, K. and M. Davis, "Unicode Technical Report
                #17, Character Encoding Model", UTR17,
                <http://www.unicode.org/unicode/reports/tr17/>, August
                2000.

  [XMATCH]      Zeilenga, K., "Internationalized String Matching Rules
                for X.500", draft-zeilenga-ldapbis-strmatch-xx.txt, a
                work in progress.

  [RFC1345]     Simonsen, K., "Character Mnemonics & Character Sets",
                RFC 1345, June 1992.

Appendix A. Teletex (T.61) to Unicode

  This appendix defines an algorithm for transcoding [T.61] characters
  to [Unicode] characters for use in string preparation for LDAP
  matching rules.  Combining Marks

  This appendix is normative.

  The transcoding algorithm is derived from the T.61-8bit definition
  provided in [RFC1345].  With a few exceptions, the T.61 character
  codes from x00 to x7f are equivalent to the corresponding [Unicode]
  code points, and their values are left unchanged by this algorithm.
  E.g.

  0300-034F 0360-036F 0483-0486 0488-0489 0591-05A1 05A3-05B9 05BB-05BC
  05BF 05C1-05C2 05C4 064B-0655 0670 06D6-06DC 06DE-06E4 06E7-06E8
  06EA-06ED 0711 0730-074A 07A6-07B0 0901-0903 093C 093E-094F 0951-0954
  0962-0963 0981-0983 09BC 09BE-09C4 09C7-09C8 09CB-09CD 09D7 09E2-09E3
  0A02 0A3C 0A3E-0A42 0A47-0A48 0A4B-0A4D 0A70-0A71 0A81-0A83 0ABC
  0ABE-0AC5 0AC7-0AC9 0ACB-0ACD 0B01-0B03 0B3C 0B3E-0B43 0B47-0B48
  0B4B-0B4D 0B56-0B57 0B82 0BBE-0BC2 0BC6-0BC8 0BCA-0BCD 0BD7 0C01-0C03
  0C3E-0C44 0C46-0C48 0C4A-0C4D 0C55-0C56 0C82-0C83 0CBE-0CC4 0CC6-0CC8
  0CCA-0CCD 0CD5-0CD6 0D02-0D03 0D3E-0D43 0D46-0D48 0D4A-0D4D 0D57
  0D82-0D83 0DCA 0DCF-0DD4 0DD6 0DD8-0DDF 0DF2-0DF3 0E31 0E34-0E3A
  0E47-0E4E 0EB1 0EB4-0EB9 0EBB-0EBC 0EC8-0ECD 0F18-0F19 0F35 0F37 0F39
  0F3E-0F3F 0F71-0F84 0F86-0F87 0F90-0F97 0F99-0FBC 0FC6 102C-1032
  1036-1039 1056-1059 1712-1714 1732-1734 1752-1753 1772-1773 17B4-17D3
  180B-180D 18A9 20D0-20EA 302A-302F 3099-309A FB1E FE00-FE0F FE20-FE23
  1D165-1D169 1D16D-1D172 1D17B-1D182 1D185-1D18B 1D1AA-1D1AD

Appendix B.  Substrings Matching
  In absence of substrings matching, the T.61 code x20 is identical to (U+0020).  The exceptions are insignificant space handling
  for these T.61 codes that are undefined: x23, x24, x5c, x5e, x60, x7b,
  x7d, and x7e.

  The codes from x80 to x9f are also equivalent to case ignore/exact matching could be simplified.   Specifically,
  the corresponding
  Unicode code points.  This is specified for completeness only, handling could be as
  these codes are control require all sequences of one or more spaces
  be replaced with one space and, if string contains non-space
  characters, removal of all all leading spaces and will be mapped to nothing in trailing spaces.

  In the LDAP String Preparation Mapping step.

  The remaining T.61 codes are mapped below in Table A.1.  Table
  positions marked "??" are undefined.

  Input strings containing undefined T.61 codes SHALL produce an
  Undefined presence of substrings matching, this simplified space handling
  this simplified space handling would lead to unexpected and
  undesirable matching result. behavior.  For diagnostic purposes, this algorithm
  does instance:
  1) (CN=foo\20*\20bar) would match the CN value "foobar" but not fail for undefined input codes.  Instead, undefined codes
    "foo<SPACE>bar" nor "foo<SPACE><SPACE>bar";
  2) (CN=*\20foobar\20*) would match "foobar", but (CN=*\20*foobar*\20*)
    would not;
  3) (CN=foo\20*\20bar) would match "foo<SPACE>X<SPACE>bar" but not
    "foo<SPACE><SPACE>bar".

  The first case illustrates that this simplified space handling would
  cause leading and trailing spaces in substrings of the input are mapped string to the Unicode REPLACEMENT CHARACTER (U+FFFD).
  As the LDAP String Preparation Prohibit step disallows the REPLACEMENT
  CHARACTER from appearing in its output, this transcoding yields the
  desired effect.

  Note: RFC 1345 listed the non-spacing accent codepoints be
  regarded as residing in
        the range starting at (U+E000).  In the current Unicode
        standard, the (U+E000) range is reserved for Private Use, insignificant.  However, only leading and trailing (as
  well as multiple consecutive spaces) of the non-spacing accents string (as a whole) are in the range starting at (U+0300).
  insignificant.

  The tables here use the (U+0300) range for these accents.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   a0| 00a0 | 00a1 | 00a2 | 00a3 | 0024 | 00a5 | 0023 | 00a7 |
   a8| 00a8 |  ??  |  ??  | 00ab |  ??  |  ??  |  ??  |  ??  |
   b0| 00b0 | 00b1 | 00b2 | 00b3 | 00d7 | 00b5 | 00b6 | 00b7 |
   b8| 00f7 |  ??  |  ??  | 00bb | 00bc | 00bd | 00be | 00bf |
   c0|  ??  | 0300 | 0301 | 0302 | 0303 | 0304 | 0306 | 0307 |
   c8| 0308 |  ??  | 030a | 0327 | 0332 | 030b | 0328 | 030c |
   d0|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   d8|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   e0| 2126 | 00c6 | 00d0 | 00aa |  ??  | 0126 | 0132 | 013f |
   e8| 0141 | 00d8 | 0152 | 00ba | 00de | 0166 | 014a | 0149 |
   f0| 0138 | 00e6 | 0111 | 00f0 | 0127 | 0131 | 0133 | 0140 |
   f8| 0142 | 00f8 | 0153 | 00df | 00fe | 0167 | 014b |  ??  |
   --+------+------+------+------+------+------+------+------+
            Table A.1:  Mapping of 8-bit T.61 codes to Unicode

  T.61 also defines a number of accented characters second case illustrates that are formed by
  combining an accent prefix followed by this simplified space handling would
  cause sub-partitioning failures.  That is, if a base character.  These
  prefixes are in the code range xc1 to xcf. If prepared any substring
  matches a prefix character
  appears at the end partition of a string, the result is undefined.  Otherwise
  these sequences are mapped to Unicode attribute value, then an assertion
  constructed by substituting the
  corresponding non-spacing accent code (as listed in Table A.1) for the
  accent prefix, and exchanging the order so subdividing that substring into multiple substrings
  should also match.

  The third case illustrates that this simplified space handling causes
  another partitioning failure.  Though both the base character
  precedes the accent.

Appendix B. Additional Teletex (T.61) to Unicode Tables

  All initial or final
  strings match different portions of "foo<SPACE>X<SPACE>bar" with
  neither matching the accented characters in T.61 have X portion, they don't match a corresponding code point
  in Unicode.  For string consisting
  of the sake two matched portions less the unmatched X portion.

  In designing an appropriate approach for space handling for substrings
  matching, one must study key aspects of X.500 case exact/ignore
  matching.  X.520 [X.520] says:
      The [substrings] rule returns TRUE if there is a partitioning of completeness,
      the combined character
  codes are presented attribute value (into portions) such that:
      - the specified substrings (initial, any, final) match different
        portions of the value in the order of the strings sequence;
      - initial, if present, matches the first portion of the value;
      - final, if present, matches the last portion of the value;
      - any, if present, matches some arbitrary portion of the value.

  That is, the substrings assertion (CN=foo\20*\20bar) matches the
  attribute value "foo<SPACE><SPACE>bar" as the value can be partitioned
  into the portions "foo<SPACE>" and "<SPACE>bar" meeting the above
  requirements.

  X.520 also says:
      [T]he following tables.  This spaces are regarded as not significant:
      - leading spaces (i.e. those preceding the first character that is informational
  only; for matching purposes it
        not a space);
      - trailing spaces (i.e. those following the last character that is sufficient
        not a space);
      - multiple consecutive spaces (these are taken as equivalent to a
        single space character).

  This statement applies to map the non-spacing
  accent assertion values and exchange the order attribute values
  as whole strings, and not individually to substrings of an assertion
  value.  In particular, the character pair as specified in
  Appendix A.   This appendix is informative.

B.1. Combinations with SPACE

  Accents may statements should be combined with a <SPACE> taken to mean that
  if an assertion value and attribute value match without any
  consideration to generate insignificant characters, then that assertion value
  should also match any attribute value which differs only by inclusion
  or removal of insignificant characters.

  Hence, the accent assertion (CN=foo\20*\20bar) matches
  "foo<SPACE><SPACE><SPACE>bar" and "foo<SPACE>bar" as these values
  only differ from "foo<SPACE><SPACE>bar" by
  itself.  For each accent code, the result inclusion or removal
  of combining with <SPACE> is
  listed in Table B.1.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   c0|  ??  | 0060 | 00b4 | 005e | 007e | 00af | 02d8 | 02d9 |
   c8| 00a8 |  ??  | 02da | 00b8 |  ??  | 02dd | 02db | 02c7 |
   --+------+------+------+------+------+------+------+------+
       Table B.1:  Mapping insignificant spaces.

  Astute readers of T.61 Accents with <SPACE> to Unicode

B.2. Combinations for xc1: (Grave accent)

  T.61 has predefined characters for combinations with A, E, I, O, and
  U.  Unicode this text will also defines combinations for N, W, and Y.  All of these
  combinations note that there are special
  cases where the specified space handling does not ignore spaces
  which could be considered insignificant.   For instance, the assertion
  (CN=\20*\20*\20) does not match "<SPACE><SPACE><SPACE>"
  (insignificant spaces present in Table B.2.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 00c0 |  ??  |  ??  |  ??  | 00c8 |  ??  |  ??  |
   48|  ??  | 00cc |  ??  |  ??  |  ??  |  ??  | 01f8 | 00d2 |
   50|  ??  |  ??  |  ??  |  ??  |  ??  | 00d9 |  ??  | 1e80 |
   58|  ??  | 1ef2 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 00e0 |  ??  |  ??  |  ??  | 00e8 |  ??  |  ??  |
   68|  ??  | 00ec |  ??  |  ??  |  ??  |  ??  | 01f9 | 00f2 |
   70|  ??  |  ??  |  ??  |  ??  |  ??  | 00f9 |  ??  | 1e81 |
   78|  ??  | 1ef3 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
           Table B.2: Mapping of T.61 Grave Accent Combinations

B.3. Combinations for xc2: (Acute accent)

  T.61 has predefined characters for combinations with A, E, I, O, U, Y,
  C, L, N, R, S, and Z.  Unicode also defines G, K, M, P, and W.  All of
  these combinations are present in Table B.3.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 00c1 |  ??  | 0106 |  ??  | 00c9 |  ??  | 01f4 |
   48|  ??  | 00cd |  ??  | 1e30 | 0139 | 1e3e | 0143 | 00d3 |
   50| 1e54 |  ??  | 0154 | 015a |  ??  | 00da |  ??  | 1e82 |
   58|  ??  | 00dd | 0179 |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 00e1 |  ??  | 0107 |  ??  | 00e9 |  ??  | 01f5 |
   68|  ??  | 00ed |  ??  | 1e31 | 013a | 1e3f | 0144 | 00f3 |
   70| 1e55 |  ??  | 0155 | 015b |  ??  | 00fa |  ??  | 1e83 |
   78|  ??  | 00fd | 017a |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
           Table B.3: Mapping of T.61 Acute Accent Combinations

B.4. Combinations for xc3: (Circumflex)

  T.61 has predefined characters for combinations with A, E, I, O, U, Y,
  C, G, H, J, S, and W.  Unicode also defines the combination for Z.
  All of these combinations are value) nor " " (insignificant
  spaces not present in Table B.4.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 00c2 |  ??  | 0108 |  ??  | 00ca |  ??  | 011c |
   48| 0124 | 00ce | 0134 |  ??  |  ??  |  ??  |  ??  | 00d4 |
   50|  ??  |  ??  |  ??  | 015c |  ??  | 00db |  ??  | 0174 |
   58|  ??  | 0176 | 1e90 |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 00e2 |  ??  | 0109 |  ??  | 00ea |  ??  | 011d |
   68| 0125 | 00ee | 0135 |  ??  |  ??  |  ??  |  ??  | 00f4 |
   70|  ??  |  ??  |  ??  | 015d |  ??  | 00fb |  ??  | 0175 |
   78|  ??  | 0177 | 1e91 |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
        Table B.4: Mapping of T.61 Circumflex Accent Combinations

B.5. Combinations for xc4: (Tilde)

  T.61 has predefined characters for combinations with A, I, O, U, and
  N.  Unicode also defines E, V, and Y.  All of value).   However, as these combinations are
  present in Table B.5.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 00c3 |  ??  |  ??  |  ??  | 1ebc |  ??  |  ??  |
   48|  ??  | 0128 |  ??  |  ??  |  ??  |  ??  | 00d1 | 00d5 |
   50|  ??  |  ??  |  ??  |  ??  |  ??  | 0168 | 1e7c |  ??  |
   58|  ??  | 1ef8 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 00e3 |  ??  |  ??  |  ??  | 1ebd |  ??  |  ??  |
   68|  ??  | 0129 |  ??  |  ??  |  ??  |  ??  | 00f1 | 00f5 |
   70|  ??  |  ??  |  ??  |  ??  |  ??  | 0169 | 1e7d |  ??  |
   78|  ??  | 1ef9 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
           Table B.5: Mapping of T.61 Tilde Accent Combinations

B.6. Combinations for xc5: (Macron)

  T.61 has predefined characters for combinations with A, E, I, O, and
  U.  Unicode also defines Y, G, cases have no
  practical application that cannot be met by simple assertions, e.g.
  (cn=\20), and AE.  All of these combinations are
  present this minor anomaly can only be fully addressed by a
  preparation algorithm to be used in Table B.6.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 0100 |  ??  |  ??  |  ??  | 0112 |  ??  | 1e20 |
   48|  ??  | 012a |  ??  |  ??  |  ??  |  ??  |  ??  | 014c |
   50|  ??  |  ??  |  ??  |  ??  |  ??  | 016a |  ??  |  ??  |
   58|  ??  | 0232 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 0101 |  ??  |  ??  |  ??  | 0113 |  ??  | 1e21 |
   68|  ??  | 012b |  ??  |  ??  |  ??  |  ??  |  ??  | 014d |
   70|  ??  |  ??  |  ??  |  ??  |  ??  | 016b |  ??  |  ??  |
   78|  ??  | 0233 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   e0|  ??  | 01e2 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   f0|  ??  | 01e3 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
          Table B.6: Mapping of T.61 Macron Accent Combinations

B.7. Combinations for xc6: (Breve)

  T.61 has predefined characters for combinations conjunction with A, U, and G.

  Unicode also defines E, I, and O.  All of these combinations are
  present in Table B.7.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 0102 |  ??  |  ??  |  ??  | 0114 |  ??  | 011e |
   48|  ??  | 012c |  ??  |  ??  |  ??  |  ??  |  ??  | 014e |
   50|  ??  |  ??  |  ??  |  ??  |  ??  | 016c |  ??  |  ??  |
   58|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 0103 |  ??  |  ??  |  ??  | 0115 |  ??  | 011f |
   68|  ??  | 012d |  ??  |  ??  |  ??  |  ??  | 00f1 | 014f |
   70|  ??  |  ??  |  ??  |  ??  |  ??  | 016d |  ??  |  ??  |
   78|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
           Table B.7: Mapping of T.61 Breve Accent Combinations

B.8. Combinations for xc7: (Dot Above)

  T.61 has predefined characters for C, E, G, I, and Z.  Unicode also
  defines A, O, B, D, F, H, M, N, P, R, S, T, W, X, and Y.  All of these
  combinations are present in Table B.8.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 0226 | 1e02 | 010a | 1e0a | 0116 | 1e1e | 0120 |
   48| 1e22 | 0130 |  ??  |  ??  |  ??  | 1e40 | 1e44 | 022e |
   50| 1e56 |  ??  | 1e58 | 1e60 | 1e6a |  ??  |  ??  | 1e86 |
   58| 1e8a | 1e8e | 017b |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 0227 | 1e03 | 010b | 1e0b | 0117 | 1e1f | 0121 |
   68| 1e23 |  ??  |  ??  |  ??  |  ??  | 1e41 | 1e45 | 022f |
   70| 1e57 |  ??  | 1e59 | 1e61 | 1e6b |  ??  |  ??  | 1e87 |
   78| 1e8b | 1e8f | 017c |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
         Table B.8: Mapping of T.61 Dot Above Accent Combinations

B.9. Combinations for xc8: (Diaeresis)

  T.61 has predefined characters for A, E, I, O, U, and Y.  Unicode also
  defines H, W, X, and t.  All of these combinations are present in
  Table B.9.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 00c4 |  ??  |  ??  |  ??  | 00cb |  ??  |  ??  |
   48| 1e26 | 00cf |  ??  |  ??  |  ??  |  ??  |  ??  | 00d6 |
   50|  ??  |  ??  |  ??  |  ??  |  ??  | 00dc |  ??  | 1e84 |
   58| 1e8c | 0178 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 00e4 |  ??  |  ??  |  ??  | 00eb |  ??  |  ??  |
   68| 1e27 | 00ef |  ??  |  ??  |  ??  |  ??  |  ??  | 00f6 |
   70|  ??  |  ??  |  ??  |  ??  | 1e97 | 00fc |  ??  | 1e85 |
   78| 1e8d | 00ff |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
         Table B.8: Mapping of T.61 Diaeresis Accent Combinations

B.10. Combinations for xca: (Ring Above)

  T.61 has predefined characters for A, and U.  Unicode also defines w
  and y.  All of these combinations are present in Table B.10.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 00c5 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   48|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   50|  ??  |  ??  |  ??  |  ??  |  ??  | 016e |  ??  |  ??  |
   58|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 00e5 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   68|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   70|  ??  |  ??  |  ??  |  ??  |  ??  | 016f |  ??  | 1e98 |
   78|  ??  | 1e99 |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
        Table B.10: Mapping of T.61 Ring Above Accent Combinations

B.11. Combinations for xcb: (Cedilla)

  T.61 has predefined characters for C, G, K, L, N, R, S, and T.
  Unicode also defines E, D, and H.  All of these combinations are
  present in Table B.11.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  |  ??  |  ??  | 00c7 | 1e10 | 0228 |  ??  | 0122 |
   48| 1e28 |  ??  |  ??  | 0136 | 013b |  ??  | 0145 |  ??  |
   50|  ??  |  ??  | 0156 | 015e | 0162 |  ??  |  ??  |  ??  |
   58|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  |  ??  |  ??  | 00e7 | 1e11 | 0229 |  ??  | 0123 |
   68| 1e29 |  ??  |  ??  | 0137 | 013c |  ??  | 0146 |  ??  |
   70|  ??  |  ??  | 0157 | 015f | 0163 |  ??  |  ??  |  ??  |
   78|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
         Table B.11: Mapping of T.61 Cedilla Accent Combinations

B.12. Combinations for xcd: (Double Acute Accent)

  T.61 has predefined characters for O, and U.  These combinations are
  present in Table B.12.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   48|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  | 0150 |
   50|  ??  |  ??  |  ??  |  ??  |  ??  | 0170 |  ??  |  ??  |
   68|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  | 0151 |
   70|  ??  |  ??  |  ??  |  ??  |  ??  | 0171 |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
       Table B.12: Mapping of T.61 Double Acute Accent Combinations

B.13. Combinations for xce: (Ogonek)

  T.61 has predefined characters for A, E, I,
  character-by-character partitioning and U.  Unicode also
  defines matching, the combination for O.  All of these combinations are present
  in Table B.13.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 0104 |  ??  |  ??  |  ??  | 0118 |  ??  |  ??  |
   48|  ??  | 012e |  ??  |  ??  |  ??  |  ??  |  ??  | 01ea |
   50|  ??  |  ??  |  ??  |  ??  |  ??  | 0172 |  ??  |  ??  |
   58|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 0105 |  ??  |  ??  |  ??  | 0119 |  ??  |  ??  |
   68|  ??  | 012f |  ??  |  ??  |  ??  |  ??  |  ??  | 01eb |
   70|  ??  |  ??  |  ??  |  ??  |  ??  | 0173 |  ??  |  ??  |
   78|  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
          Table B.13: Mapping of T.61 Ogonek Accent Combinations

B.14. Combinations for xcf: (Caron)

  T.61 has predefined characters for C, D, E, L, N, R, S, T, and Z.
  Unicode also defines A, I, O, U, G, H, j,and K.  All of these
  combinations are present in Table B.14.

     |    0 |    1 |    2 |    3 |    4 |    5 |    6 |    7 |
   --+------+------+------+------+------+------+------+------+
   40|  ??  | 01cd |  ??  | 010c | 010e | 011a |  ??  | 01e6 |
   48| 021e | 01cf |  ??  | 01e8 | 013d |  ??  | 0147 | 01d1 |
   50|  ??  |  ??  | 0158 | 0160 | 0164 | 01d3 |  ??  |  ??  |
   58|  ??  |  ??  | 017d |  ??  |  ??  |  ??  |  ??  |  ??  |
   60|  ??  | 01ce |  ??  | 010d | 010f | 011b |  ??  | 01e7 |
   68| 021f | 01d0 | 01f0 | 01e9 | 013e |  ??  | 0148 | 01d2 |
   70|  ??  |  ??  | 0159 | 0161 | 0165 | 01d4 |  ??  |  ??  |
   78|  ??  |  ??  | 017e |  ??  |  ??  |  ??  |  ??  |  ??  |
   --+------+------+------+------+------+------+------+------+
          Table B.14: Mapping of T.61 Caron Accent Combinations

Appendix C.  Combining Marks

  This appendix anomaly is normative.

  0300-034F 0360-036F 0483-0486 0488-0489 0591-05A1 05A3-05B9 05BB-05BC
  05BF 05C1-05C2 05C4 064B-0655 0670 06D6-06DC 06DE-06E4 06E7-06E8
  06EA-06ED 0711 0730-074A 07A6-07B0 0901-0903 093C 093E-094F 0951-0954
  0962-0963 0981-0983 09BC 09BE-09C4 09C7-09C8 09CB-09CD 09D7 09E2-09E3
  0A02 0A3C 0A3E-0A42 0A47-0A48 0A4B-0A4D 0A70-0A71 0A81-0A83 0ABC
  0ABE-0AC5 0AC7-0AC9 0ACB-0ACD 0B01-0B03 0B3C 0B3E-0B43 0B47-0B48
  0B4B-0B4D 0B56-0B57 0B82 0BBE-0BC2 0BC6-0BC8 0BCA-0BCD 0BD7 0C01-0C03
  0C3E-0C44 0C46-0C48 0C4A-0C4D 0C55-0C56 0C82-0C83 0CBE-0CC4 0CC6-0CC8
  0CCA-0CCD 0CD5-0CD6 0D02-0D03 0D3E-0D43 0D46-0D48 0D4A-0D4D 0D57
  0D82-0D83 0DCA 0DCF-0DD4 0DD6 0DD8-0DDF 0DF2-0DF3 0E31 0E34-0E3A
  0E47-0E4E 0EB1 0EB4-0EB9 0EBB-0EBC 0EC8-0ECD 0F18-0F19 0F35 0F37 0F39
  0F3E-0F3F 0F71-0F84 0F86-0F87 0F90-0F97 0F99-0FBC 0FC6 102C-1032
  1036-1039 1056-1059 1712-1714 1732-1734 1752-1753 1772-1773 17B4-17D3
  180B-180D 18A9 20D0-20EA 302A-302F 3099-309A FB1E FE00-FE0F FE20-FE23
  1D165-1D169 1D16D-1D172 1D17B-1D182 1D185-1D18B 1D1AA-1D1AD
  considered acceptable.

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