One document matched: draft-ietf-idnabis-mappings-01.txt

Differences from draft-ietf-idnabis-mappings-00.txt




IDNABIS                                                  P. Resnick, Ed.
Internet-Draft                                     Qualcomm Incorporated
Intended status: Standards Track                              P. Hoffman
Expires: January 4, 2010                                  VPN Consortium
                                                            July 3, 2009


                       Mapping Characters in IDNA
                     draft-ietf-idnabis-mappings-01

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may contain material
   from IETF Documents or IETF Contributions published or made publicly
   available before November 10, 2008.  The person(s) controlling the
   copyright in some of this material may not have granted the IETF
   Trust the right to allow modifications of such material outside the
   IETF Standards Process.  Without obtaining an adequate license from
   the person(s) controlling the copyright in such materials, this
   document may not be modified outside the IETF Standards Process, and
   derivative works of it may not be created outside the IETF Standards
   Process, except to format it for publication as an RFC or to
   translate it into languages other than English.

   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/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on January 4, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




Resnick & Hoffman        Expires January 4, 2010                [Page 1]

Internet-Draft                IDNA Mapping                     July 2009


   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   In the original version of the Internationalized Domain Names in
   Applications (IDNA) protocol, any Unicode code points taken from user
   input were mapped into a set of Unicode code points that "make
   sense", which were then encoded and passed to the domain name system
   (DNS).  The current version of IDNA presumes that the input to the
   protocol comes from a set of "permitted" code points, which it then
   encodes and passes to the DNS, but does not specify what to do with
   the result of user input.  This document describes the actions taken
   by an implementation between user input and passing permitted code
   points to the new IDNA protocol.


1.  Introduction

   This document describes the operations that can be applied to user
   input in order to get it into a form acceptable by the
   Internationalized Domain Names in Applications (IDNA) protocol
   [I-D.ietf-idnabis-protocol].  The document describes the underlying
   architectural principles (in section 2 and the general implementation
   procedure (in section 3).

   It should be noted that this document does not specify the behavior
   of a protocol that appears "on the wire".  It describes an operation
   that is to be applied to user input in order to prepare that user
   input for use in an "on the network" protocol.  As unusual as this
   may be for an IETF protocol document, it is a necessary operation to
   maintain interoperability.


2.  Architectural Principles

   An application that implements the IDNA protocol
   [I-D.ietf-idnabis-protocol] will always take any user input and
   convert it to a set of Unicode code points.  That user input may be
   acquired by any of several different input methods, all with
   differing conversion processes to be taken into consideration (e.g.,
   typed on a keyboard, written by hand onto some sort of digitizer,
   spoken into a microphone and interpreted by a speech-to-text engine,
   etc.).  The process of taking any particular user input and mapping
   it into a Unicode code point may be a simple one: If a user strikes



Resnick & Hoffman        Expires January 4, 2010                [Page 2]

Internet-Draft                IDNA Mapping                     July 2009


   the "A" key on a US English keyboard, without any modifiers such as
   the "Shift" key held down, in order to draw a Latin small letter A
   ("a"), many (perhaps most) modern operating system input methods will
   produce to the calling application the code point U+0061, encoded in
   a single octet.

   Sometimes the process is somewhat more complicated: a user might
   strike a particular set of keys to represent a combining macron
   followed by striking the "A" key in order to draw a Latin small
   letter A with a macron above it.  Depending on the operating system,
   the input method chosen by the user, and even the parameters with
   which the application communicates with the input method, the result
   might be the code point U+0101 (encoded as two octets in UTF-8 or
   UTF-16, four octets in UTF-32, etc.), the code point U+0061 followed
   by the code point U+0304 (again, encoded in three or more octets,
   depending upon the encoding used) or even the code point U+FF41
   followed by the code point U+0304 (and encoded in some form).  And
   these examples leave aside the issue of operating systems and input
   methods that do not use Unicode code points for their character set.

   In every case, applications (with the help of the operating systems
   on which they run and the input methods used) need to perform a
   mapping from user input into Unicode code points.

   The original version of the IDNA protocol [RFC3490] used a model
   whereby input was taken from the user, mapped (via whatever input
   method mechanisms were used) to a set of Unicode code points, and
   then further mapped to a set of Unicode code points using the
   Nameprep profile specified in [RFC3491].  In this procedure, there
   are two separate mapping steps: First, a mapping done by the input
   method (which might be controlled by the operating system, the
   application, or some combination) and then a second mapping performed
   by the Nameprep portion of the IDNA protocol.  The mapping done in
   Nameprep includes a particular mapping table to re-map some
   characters to other characters, a particular normalization, and a set
   of prohibited characters.

   Note that the result of the two step mapping process means that the
   mapping chosen by the operating system or application in the first
   step might differ significantly from the mapping supplied by the
   Nameprep profile in the second step.  This has advantages and
   disadvantages.  Of course, the second mapping regularizes what gets
   looked up in the DNS, making for better interoperability between
   implementations which use the Nameprep mapping.  However, the
   application or operating system may choose mappings in their input
   methods, which when passed through the second (Nameprep) mapping
   result in characters that are "surprising" to the end user.




Resnick & Hoffman        Expires January 4, 2010                [Page 3]

Internet-Draft                IDNA Mapping                     July 2009


   The other important feature of the original version of the IDNA
   protocol is that, with very few exceptions, it assumes that any set
   of Unicode code points provided to the Nameprep mapping can be mapped
   into a string of Unicode code points that are "sensible", even if
   that means mapping some code points to nothing (that is, removing the
   code points from the string).  This allowed maximum flexibility in
   input strings.

   The present version of IDNA differs significantly in approach from
   the original version.  First and foremost, it does not provide
   explicit mapping instructions.  Instead, it assumes that the
   application (perhaps via an operating system input method) will do
   whatever mapping it requires to convert input into Unicode code
   points.  This has the advantage of giving flexibility to the
   application to choose a mapping that is suitable for its user given
   specific user requirements, and avoids the two-step mapping of the
   original protocol.  Instead of a mapping, the current version of IDNA
   provides a set of categories that can be used to specify the valid
   code points allowed in a domain name.

   In principle, an application ought to take user input of a domain
   name and convert it to the set of Unicode code points that represent
   the domain name the user intends.  As a practical matter, of course,
   determining user intent is a tricky business, so an application needs
   to choose a reasonable mapping from user input.  That may differ
   based on the particular circumstances of a user, depending on locale,
   language, type of input method, etc.  It is up to the application to
   make a reasonable choice.


3.  The General Procedure

   This section defines a general algorithm that applications ought to
   implement in order to produce Unicode code points that will be valid
   under the IDNA protocol.  An application might implement the full
   mapping as described below, or can choose a different mapping.  In
   fact, an appliction might want to implement a full mapping that is
   substantially compatible with the original IDNA protocol instead of
   the algorithm given here.

   The general algorithm that an application (or the input method
   provided by an operating system) ought to use is relatively
   straightforward and generally follows section 5 of
   [I-D.ietf-idnabis-protocol]:

   1.  All characters are mapped using Unicode Normalization Form C
       (NFC).




Resnick & Hoffman        Expires January 4, 2010                [Page 4]

Internet-Draft                IDNA Mapping                     July 2009


   2.  Upper case characters are mapped to their lower case equivalents
       by using the algorithm for mapping Unicode characters.

   3.  Full-width and half-width characters (those defined with
       Decomposition Types <wide> and <narrow>) are mapped to their
       decomposition mappings as shown in the Unicode character
       database.

   Definitions for the rules in this algorithm can be found in
   [Unicode51].  Specifically:

   o  Unicode Normalization Form C can be found in Annex #15 of
      [Unicode51].

   o  In order to map upper case characters to their lower case
      equivalents (defined in section 3.13 of [Unicode51]), first map
      characters to the "Lowercase_Mapping" property (the "<lower>"
      entry in the second column) in
      <http://www.unicode.org/Public/UNIDATA/SpecialCasing.txt>, if any.
      Then, map characters to the "Simple_Lowercase_Mapping" property
      (the fourteenth column) in
      <http://www.unicode.org/Public/UNIDATA/UnicodeData.txt>, if any.

   o  In order to map full-width and half-width characters to their
      decomposition mappings, map any character whose
      "Decomposition_Type" (contained in the first part of of the sixth
      column) in <http://www.unicode.org/Public/UNIDATA/UnicodeData.txt>
      is either "<wide>" or "<narrow>" to the "Decomposition_Mapping" of
      that character (contained in the second part of the sixth column)
      in <http://www.unicode.org/Public/UNIDATA/UnicodeData.txt>.

   o  The <http://www.unicode.org/Public/UNIDATA/UCD.html> web page has
      useful descriptions of the contents of these files.

   If this mappings in this document are applied to versions of Unicode
   later than Unicode 5.1, the later versions of the Unicode Standard
   should be consulted.

   These are a minimal set of mappings that an application should
   strongly consider doing.  Of course, there are many others that might
   be done.


4.  IANA Considerations

   This memo includes no request to IANA.





Resnick & Hoffman        Expires January 4, 2010                [Page 5]

Internet-Draft                IDNA Mapping                     July 2009


5.  Security Considerations

   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 (nor in the
   other IDNA-related documents).


6.  Normative References

   [I-D.ietf-idnabis-protocol]
              Klensin, J., "Internationalized Domain Names in
              Applications (IDNA): Protocol",
              draft-ietf-idnabis-protocol-12 (work in progress),
              May 2009.

   [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.

   [Unicode51]
              The Unicode Consortium, "The Unicode Standard, Version
              5.1.0", 2008.

              defined by: The Unicode Standard, Version 5.0, Boston, MA,
              Addison-Wesley, 2007, ISBN 0-321-48091-0, as amended by
              Unicode 5.1.0
              (<http://www.unicode.org/versions/Unicode5.1.0/>).


Authors' Addresses

   Peter W. Resnick (editor)
   Qualcomm Incorporated
   5775 Morehouse Drive
   San Diego, CA  92121-1714
   US

   Phone: +1 858 651 4478
   Email: presnick@qualcomm.com
   URI:   http://www.qualcomm.com/~presnick/






Resnick & Hoffman        Expires January 4, 2010                [Page 6]

Internet-Draft                IDNA Mapping                     July 2009


   Paul Hoffman
   VPN Consortium
   127 Segre Place
   Santa Cruz, CA  95060
   US

   Phone: 1-831-426-9827
   Email: paul.hoffman@vpnc.org











































Resnick & Hoffman        Expires January 4, 2010                [Page 7]



PAFTECH AB 2003-20242024-03-28 16:10:00