Mapping characters for PRECIS classes
draft-ietf-precis-mappings-07

Network Working Group                                          Y. YONEYA
Internet-Draft                                                      JPRS
Intended status: Informational                                 T. Nemoto
Expires: August 17, 2014                                 Keio University
                                                       February 13, 2014

                 Mapping characters for PRECIS classes
                     draft-ietf-precis-mappings-07

Abstract

   The framework for preparation and comparison of internationalized
   strings ("PRECIS") defines several classes of strings for preparation
   and comparison.  Case mapping is defined because many protocols
   perform case-sensitive or case-insensitive string comparison and so
   preparation of the string is mandatory.  The Internationalized Domain
   Names in Applications (IDNA) and the PRECIS problem statement
   describes mappings for internationalized strings that are not limited
   to case, but include width mapping and mapping of delimiters and
   other specials that can be taken into consideration.  This document
   provides guidelines for authors of protocol profiles of the PRECIS
   framework and describes several mappings that can be applied between
   receiving user input and passing permitted code points to
   internationalized protocols.  The mappings described here are
   expected to be applied as an additional mapping and alternative to
   Unicode Default Case Folding as case mapping in the PRECIS framework.

Status of This Memo

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   This Internet-Draft will expire on August 17, 2014.

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Copyright Notice

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Protocol dependent mappings . . . . . . . . . . . . . . . . .   3
     2.1.  Delimiter mapping . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Special mapping . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Local case mapping  . . . . . . . . . . . . . . . . . . .   4
   3.  Order of operations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Mapping type list each protocol  . . . . . . . . . .   7
     A.1.  Mapping type list for each protocol . . . . . . . . . . .   7
   Appendix B.  The reason why local case mapping is alternative to
                case mapping in PRECIS framework . . . . . . . . . .   8
   Appendix C.  Limitation to local case mapping . . . . . . . . . .   8
   Appendix D.  Change Log . . . . . . . . . . . . . . . . . . . . .   8
     D.1.  Changes since -00 . . . . . . . . . . . . . . . . . . . .   8
     D.2.  Changes since -01 . . . . . . . . . . . . . . . . . . . .   9
     D.3.  Changes since -02 . . . . . . . . . . . . . . . . . . . .   9
     D.4.  Changes since -03 . . . . . . . . . . . . . . . . . . . .   9
     D.5.  Changes since -04 . . . . . . . . . . . . . . . . . . . .   9
     D.6.  Changes since -05 . . . . . . . . . . . . . . . . . . . .  10
     D.7.  Changes since -06 . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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1.  Introduction

   In many cases, user input of internationalized strings is generated
   through the use of an input method editor ("IME") or through copy-
   and-paste from free text.  Users generally do not care about the case
   and/or width of input characters because they consider those
   characters to be functionally equivalent or visually identical.
   Furthermore, users rarely switch the IME state to input special
   characters such as protocol elements.  For Internationalized Domain
   Names ("IDNs"), the IDNA Mapping specification [RFC5895] describes
   methods for handling these issues.  For PRECIS strings, case mapping
   and width mapping are defined in the PRECIS framework specification
   [I-D.ietf-precis-framework].  Further, the handling of mappings other
   than case and width, such as delimiter, special, and local case, are
   also important in order to increase the probability that strings
   match as users expect.  This document provides guidelines for authors
   of protocol profiles of the PRECIS framework and describes mappings
   that can be applied between receiving user input and passing
   permitted code points to internationalized protocols.  The mappings
   described in this document are expected to be applied as additional
   mapping and alternative to Unicode Default Case Folding as case
   mapping in the PRECIS framework.

2.  Protocol dependent mappings

   The PRECIS framework defines several protocol-independent mappings.
   Two additional mappings and one alternative mapping defined in this
   document are protocol-dependent, i.e., they depend on the rules for a
   particular application protocol.

2.1.  Delimiter mapping

   Some application protocols define delimiters for their own use,
   resulting in the fact that the delimiters are different for each
   protocol.  The delimiter mapping table should therefore be based on a
   well-defined mapping table for each protocol.

   Delimiter mapping is used to map characters that are similar to
   protocol delimiters into the canonical delimiter characters.  For
   example, there are width-compatible characters that correspond to the
   '@' in email addresses and the ':' and '/' in URIs.  The '+', '-',
   '<' and '>' characters are other common delimiters that might require
   such mapping.  For the FULL STOP character (U+002E), a delimiter in
   the visual presentation of domain names, some IMEs produce a
   character such as IDEOGRAPHIC FULL STOP (U+3002) when a user types
   FULL STOP on the keyboard.  In all these cases, the visually similar
   characters that can come from user input need to be mapped to the

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   correct protocol delimiter characters before the string is passed to
   the protocol.

2.2.  Special mapping

   Aside from delimiter characters, certain protocols have characters
   which need to be mapped in ways that are different from the rules
   specified in the PRECIS framework (e.g., mapping non-ASCII space
   characters to ASCII space).  In this document, these mappings are
   called "special mappings".  They are different for each protocol.
   Therefore, the special mapping table should be based on a well-
   defined mapping table for each protocol.  Examples of special mapping
   are the following;

   o  White spaces are mapped to SPACE (U+0020)

   o  Some characters such as control characters are mapped to nothing
      (Deletion)

   As examples, EAP [RFC3748], SASLprep [RFC4013], IMAP4 ACL [RFC4314]
   and LDAPprep [RFC4518] define the rule that some codepoints for the
   non-ASCII space are mapped to SPACE (U+0020).

2.3.  Local case mapping

   The purpose of local case mapping is to increase the probability of a
   matching result from the comparison between uppercase and lowercase
   characters, targeting characters which mapping depends on locale or
   locale and context.

   As an example of locale and context-dependent mapping, LATIN CAPITAL
   LETTER I ("I", U+0049) is normally mapped to LATIN SMALL LETTER I
   ("i", U+0069); however, if the case of Turkish (or one of several
   other languages), unless an I is before a dot_above, the character
   should be mapped to LATIN SMALL LETTER DOTLESS I (U+0131).

   Case mapping using Unicode Default Case Folding in PRECIS framework
   does not consider such locale or context because it is a common
   framework for internationalization.  Local case mapping defined in
   this document corresponds to demands from applications which supports
   users' locale and/or context.  The target characters of local case
   mapping are characters defined in the SpecialCasing.txt
   [Specialcasing] file in section 3.13 of the Unicode Standard
   [Unicode].

   If a codepoint is a target, the case folding method for the codepoint
   is mapping into lower case as defined in SpecialCasing.txt.  On the
   other hand, if a codepoint is not a target, the case folding method

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   for the codepoint is the same with case mapping in PRECIS framework.
   This local case mapping provides alternative case folding method to
   Unicode Default Case Folding as case mapping in the PRECIS framework,
   therefore if a PRECIS profile chooses local case mapping, it should
   not choose case mapping.  The reason for this is written in the
   Appendix B.

3.  Order of operations

   The mappings described in this document are expected to be applied as
   additional mappings and alternative to Unicode Default Case Folding
   as case mapping in the PRECIS framework.  The mappings described in
   this document could be applied in any order.  This section specifies
   a particular order to minimize the effect of codepoint changes
   introduced by the mappings.  This mapping order is very general and
   has been designed to be acceptable to the widest user community.

   1.  Delimiter mapping

   2.  Special mapping

   3.  Local case mapping

4.  Security Considerations

   As well as Mapping Characters for IDNA2008 [RFC5895], this document
   suggests creating mappings that might cause confusion for some users
   while alleviating confusion in other users.  Such confusion is not
   covered in any depth in this document.

5.  IANA Considerations

   This document has no actions for the IANA.

6.  Acknowledgment

   Martin Duerst suggested a need for the case folding about the mapping
   (map final sigma to sigma, German sz to ss,.).

   Alexey Melnikov, Andrew Sullivan, Barry Leiba, Heather Flanagan, Joe
   Hildebrand, John Klensin, Marc Blanchet, Pete Resnick and Peter
   Saint-Andre, et al. gave important suggestion for this document
   during at WG meeting and WG LC.

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7.  References

7.1.  Normative References

   [I-D.ietf-precis-framework]
              Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
              Preparation and Comparison of Internationalized Strings in
              Application Protocols", draft-ietf-precis-framework-14
              (work in progress), February 2014.

   [Unicode]  The Unicode Consortium, "The Unicode Standard, Version
              6.3.0", <http://www.unicode.org/versions/Unicode6.3.0/>,
              2012.

   [Casefolding]
              The Unicode Consortium, "CaseFolding-6.3.0.txt", Unicode
              Character Database, July 2011,
              <http://www.unicode.org/Public/6.3.0/ucd/CaseFolding.txt>,
              .

   [Specialcasing]
              The Unicode Consortium, "SpecialCasing-6.3.0.txt", Unicode
              Character Database, July 2011, <http://www.unicode.org/
              Public/6.3.0/ucd/SpecialCasing.txt>, .

7.2.  Informative References

   [RFC3454]  Hoffman, P. and M. Blanchet, "Preparation of
              Internationalized Strings ("stringprep")", RFC 3454,
              December 2002.

   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
              "Internationalizing Domain Names in Applications (IDNA)",
              RFC 3490, March 2003.

   [RFC3491]  Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
              Profile for Internationalized Domain Names (IDN)", RFC
              3491, March 2003.

   [RFC3722]  Bakke, M., "String Profile for Internet Small Computer
              Systems Interface (iSCSI) Names", RFC 3722, April 2004.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
              3748, June 2004.

   [RFC4013]  Zeilenga, K., "SASLprep: Stringprep Profile for User Names
              and Passwords", RFC 4013, February 2005.

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   [RFC4314]  Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
              RFC 4314, December 2005.

   [RFC4518]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): Internationalized String Preparation", RFC 4518,
              June 2006.

   [RFC5895]  Resnick, P. and P. Hoffman, "Mapping Characters for
              Internationalized Domain Names in Applications (IDNA)
              2008", RFC 5895, September 2010.

   [RFC6122]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Address Format", RFC 6122, March 2011.

   [RFC6885]  Blanchet, M. and A. Sullivan, "Stringprep Revision and
              Problem Statement for the Preparation and Comparison of
              Internationalized Strings (PRECIS)", RFC 6885, March 2013.

   [ISO.3166-1]
              International Organization for Standardization, "Codes for
              the representation of names of countries and their
              subdivisions - Part 1: Country codes", ISO Standard 3166-
              1:1997, 1997.

Appendix A.  Mapping type list each protocol

A.1.  Mapping type list for each protocol

   This table is the mapping type list for each protocol.  Values marked
   "o" indicate that the protocol use the type of mapping.  Values
   marked "-" indicate that the protocol doesn't use the type of
   mapping.

   +----------------------+-------------+-----------+------+---------+
   |     Protocol and     |    Width    | Delimiter | Case | Special |
   |     mapping RFC      |    (NFKC)   |           |      |         |
   +----------------------+-------------+-----------+------+---------+
   |   IDNA  (RFC 3490)   |      -      |     o     |   -  |    -    |
   |   IDNA  (RFC 3491)   |      o      |     -     |   o  |    -    |
   |   iSCSI (RFC 3722)   |      o      |     -     |   o  |    -    |
   |   EAP   (RFC 3748)   |      o      |     -     |   -  |    o    |
   |   SASL  (RFC 4013)   |      o      |     -     |   -  |    o    |
   |   IMAP  (RFC 4314)   |      o      |     -     |   -  |    o    |
   |   LDAP  (RFC 4518)   |      o      |     -     |   o  |    o    |
   |   XMPP  (RFC 6120)   |      -      |     -     |   o  |    -    |
   +----------------------+-------------+-----------+------+---------+

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Appendix B.  The reason why local case mapping is alternative to case
             mapping in PRECIS framework

   One outstanding issue regarding full case folding for characters is,
   the character "LATIN SMALL LETTER SHARP S" (U+00DF) (hereinafter
   referred to as "eszett") becomes two "LATIN SMALL LETTER S"s (U+0073
   U+0073) by performing the case mapping using Unicode Default Case
   Folding in the PRECIS framework.  If local case mapping in this
   document is not an alternative to case mapping in PRECIS framework,
   PRECIS profile designers can select both mappings, therefore,
   German's eszett can not keep the locale if the case mapping in the
   PRECIS framework was performed after the local case mapping.

Appendix C.  Limitation to local case mapping

   As described in section Section 2.3, target characters of local case
   mapping are characters defined in SpecialCasing.txt.  The Unicode
   Standard (at least, up to version 6.3.0) does not define mappings
   between "GREEK SMALL LETTER SIGMA" (U+03C3) (hereinafter referred to
   as "small sigma") and "GREEK SMALL LETTER FINAL SIGMA" (U+03C2)
   (hereinafter referred to as "final sigma") depend on context.  Thus,
   final sigma is always mapped to small sigma by local case mapping.
   (Cf. Followings are comments in SpecialCasing.txt.)

      # Note: the following cases are not included, since they would
      case-fold in lowercasing
      # 03C3; 03C2; 03A3; 03A3; Final_Sigma; # GREEK SMALL LETTER SIGMA
      # 03C2; 03C3; 03A3; 03A3; Not_Final_Sigma; # GREEK SMALL LETTER

   Local case mapping follows Unicode definition, so mapping of small
   sigma and final sigma is up to the definition.

Appendix D.  Change Log

D.1.  Changes since -00

   o  Modify the Section 4.3 "Local case mapping" to specify the method
      to calculate codepoints that local case mapping targets.

   o  Add the Section 6 "Open issues".

   o  Modify the Section 7 "IANA Considerations".

   o  Modify the Section 8 "Security Considerations".

   o  Remove the "The initial PRECIS local case mapping registrations".

   o  Add the Appendix C "Code points list for local case mapping".

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   o  Add the Appendix D "Change Log".

D.2.  Changes since -01

   o  Unified PRECIS notation in all capital letters as well as other
      documents.

   o  Removed the Section 1 "Types of mapping" and the Section 2
      "Protocol independent mapping" because width mapping is now in
      framework document.

   o  Added relationship between the framework document and this
      document in the Section 3 "Order of operations".

   o  Updated the Section 4 "Open issues" to address new issue raised on
      mailing list.

   o  Move the Section 6 "IANA Considerations" after the Section 5
      "Security Considerations".

   o  Remove the Appendix B "Codepoints which need special mapping" and
      mentioned related documents in the Section 2.2 .

D.3.  Changes since -02

   o  Removed the "Open issues".

D.4.  Changes since -03

   o  Modify the Section 1 "Introduction" in more clear text.

   o  Modify the Section 2.3 "Local case mapping" to clarify the purpose
      of the local case mapping and an example, and add restriction to
      use with PRECIS framework.

   o  Change the format in the Appendix B "Code points list for local
      case mapping".

   o  Split the Section 7 "References" into "Normative References" and
      "Informative References"

   o  Update the Unicode version 6.2 to 6.3 in this document.

D.5.  Changes since -04

   o  Correct a sentence in the Section 2.3 "Local case mapping".

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D.6.  Changes since -05

   o  Correct some sentences in this document.

   o  Modify the local case mapping's rule and target characters in
      Section 2.3 "Local case mapping".  This is to avoid user's
      confusion towards Greek's final sigma and German's eszett.

   o  Add the Section 4 "Open issues".

   o  Modify the Section 8 "Security Considerations".

   o  Modify the table format in the Appendix A. "Mapping type list each
      protocol".

   o  Removed the Appendix B "Code points list for local case mapping".

   o  Add the Appendix B "Local case mapping vs Case mapping".

D.7.  Changes since -06

   o  Removed the Section 4 "Open issues".

   o  Change the title of the Appendix B "Local case mapping vs Case
      mapping" to "The reason why local case mapping is alternative to
      case mapping in PRECIS framework".

   o  Add the Appendix C "Limitation to local case mapping".

Authors' Addresses

   Yoshiro YONEYA
   JPRS
   Chiyoda First Bldg. East 13F
   3-8-1 Nishi-Kanda
   Chiyoda-ku, Tokyo  101-0065
   Japan

   Phone: +81 3 5215 8451
   Email: yoshiro.yoneya@jprs.co.jp

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   Takahiro Nemoto
   Keio University
   Graduate School of Media Design
   4-1-1 Hiyoshi, Kohoku-ku
   Yokohama, Kanagawa  223-8526
   Japan

   Phone: +81 45 564 2517
   Email: t.nemo10@kmd.keio.ac.jp

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