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draft-resman-idna2008-mappings
IDNABIS P. Resnick
Internet-Draft Qualcomm Incorporated
Intended status: Informational P. Hoffman
Expires: April 22, 2010 VPN Consortium
October 19, 2009
Mapping Characters in IDNA
draft-ietf-idnabis-mappings-05
Status of this Memo
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document authors. All rights reserved.
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Provisions Relating to IETF Documents in effect on the date of
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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 that
can be 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]. A general implementation procedure for
mapping is given in section 2.
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. 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 application 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
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straightforward:
1. Upper case characters are mapped to their lower case equivalents
by using the algorithm for mapping case in Unicode characters.
2. 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.
3. All characters are mapped using Unicode Normalization Form C
(NFC).
4. [I-D.ietf-idnabis-protocol] is specified such that the protocol
acts on the indvidual labels of the domain name. If an
implementation of this mapping is also performing the step of
separation of the parts of a domain name into labels by using the
FULL STOP character (U+002E), the following character can be
mapped to the FULL STOP before label separation occurs:
* IDEOGRAPHIC FULL STOP (U+3002)
There are other characters that are used as "full stops" that one
could consider mapping as label separators, but their use as such
has not been investigated thoroughly.
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>.
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o The <http://www.unicode.org/Public/UNIDATA/UCD.html> web page has
useful descriptions of the contents of these files.
If the 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 form a minimal set of mappings that an application should
strongly consider doing. Of course, there are many others that might
be done.
3. IANA Considerations
This memo includes no request to IANA.
4. 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).
5. Acknowledgements
This document is the product of the IDNAbis Working Group and
contains contributions from many people in the Working Group.
6. Normative References
[I-D.ietf-idnabis-protocol]
Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol",
draft-ietf-idnabis-protocol-16 (work in progress),
September 2009.
[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/>).
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Authors' Addresses
Peter W. Resnick
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/
Paul Hoffman
VPN Consortium
127 Segre Place
Santa Cruz, CA 95060
US
Phone: 1-831-426-9827
Email: paul.hoffman@vpnc.org
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