Internet DRAFT - draft-ietf-precis-mappings
draft-ietf-precis-mappings
Network Working Group Y. YONEYA
Internet-Draft JPRS
Intended status: Informational T. Nemoto
Expires: May 4, 2016 Keio University
November 1, 2015
Mapping characters for PRECIS classes
draft-ietf-precis-mappings-12
Abstract
The framework for preparation, enforcement, and comparison of
internationalized strings ("PRECIS") defines several classes of
strings for use in application protocols. Because many protocols
perform case-sensitive or case-insensitive string comparison, it
necessary to define methods for case mapping. In addition, both the
Internationalized Domain Names in Applications (IDNA) and the PRECIS
problem statement describe mappings for internationalized strings
that are not limited to case, but include width mapping and mapping
of delimiters and other special characters that can be taken into
consideration. This document provides guidelines for designers of
PRECIS profiles and describes several mappings that can be applied
between receiving user input and passing permitted code points to
internationalized protocols. In particular, this document describes
both locale-dependent and context-depending case mappings as well as
additional mappings for delimiters and special characters.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on May 4, 2016.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
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 . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Mapping type list each protocol . . . . . . . . . . 8
A.1. Mapping type list for each protocol . . . . . . . . . . . 8
Appendix B. The reason why local case mapping is alternative to
case mapping in PRECIS framework . . . . . . . . . . 8
Appendix C. Limitation to local case mapping . . . . . . . . . . 9
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 9
D.1. Changes since -00 . . . . . . . . . . . . . . . . . . . . 9
D.2. Changes since -01 . . . . . . . . . . . . . . . . . . . . 9
D.3. Changes since -02 . . . . . . . . . . . . . . . . . . . . 10
D.4. Changes since -03 . . . . . . . . . . . . . . . . . . . . 10
D.5. Changes since -04 . . . . . . . . . . . . . . . . . . . . 10
D.6. Changes since -05 . . . . . . . . . . . . . . . . . . . . 10
D.7. Changes since -06 . . . . . . . . . . . . . . . . . . . . 11
D.8. Changes since -07 . . . . . . . . . . . . . . . . . . . . 11
D.9. Changes since -08 . . . . . . . . . . . . . . . . . . . . 11
D.10. Changes since -09 . . . . . . . . . . . . . . . . . . . . 11
D.11. Changes since -10 . . . . . . . . . . . . . . . . . . . . 12
D.12. Changes since -11 . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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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
[RFC7564]. The case and width mappings defined in the PRECIS
framework do not handle other mappings such as delimiter characters,
special characters, and locale-dependent or context-dependent case;
these mappings are also important in order to increase the
probability that the resulting strings compare as users expect. 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 delimiter mapping and special
mapping rules described here are applied as "additional mappings"
beyond those defined in the PRECIS framework, whereas the "local case
mapping" rule provides locale-dependent and context-dependent
alternative case mappings for specific target characters.
2. Protocol dependent mappings
The PRECIS framework defines several protocol-independent mappings.
The additional mappings and local case 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
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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
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 such as CHARACTER TABULATION(U+0009) or IDEOGRAPHIC
SPACE(U+3000) 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
results that users expect when character case is changed (e.g., map
uppercase to lowercase) between input and use in a protocol. Local
case mapping selectively affects characters whose case mapping
depends on locale and/or context.
(Note: The term "locale" in this document practically means
"language" or "language and region" because the locale based on that
language configuration of applications on POSIX is selected by
"locale" information and referred "Note" in section 2.1.1 of BCP 47
[RFC5646].)
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 language is 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 the PRECIS
framework does not consider such locale or context because it is a
common framework for internationalization. Local case mapping
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defined in this document corresponds to demands from applications
which supports users' locale and/or context. The complete set of
possible target characters for local case mapping are the characters
specified in the SpecialCasing.txt [Specialcasing] file in the
Section 3.13 of the Unicode Standard [Unicode], but the specific set
of target characters selected for local case mapping depends on
locale and/or context, as further explained in the SpecialCasing.txt
file.
The case folding method for a selected target character is to map
into lower case as defined in SpecialCasing.txt. The case folding
method for all other, non-target characters is as specified in the
Section 5.2.3 of the PRECIS framework . When an application supports
users' locale and/or context, use of local case mapping can increase
the probability that string comparisons yield the results that users
expect.
If a PRECIS profile selects Unicode Default Case Folding as the
preferred method of case mapping, the profile designers may consider
whether local case mapping can be applied. And if it can be applied,
it is better to add "alternatively, local case mapping might be
applicable" after "Unicode Default Case Folding" so that application
developers are aware of the alternative. See the Appendix B for a
description of why local case mapping can be an alternative.
3. Order of operations
Delimiter mapping and special mapping as described in this document
are expected to be applied as the "Additional Mapping Rule" mentioned
in the Section 5.2.2 of the PRECIS framework. Although the delimited
mapping and special mapping could be applied in either order, this
document recommends the following order to minimize the effect of
code point changes introduced by the mappings and to be acceptable to
the widest user community:
1. Delimiter mapping
2. Special mapping
4. Security Considerations
Detailed security considerations for PRECIS strings are discussed in
the PRECIS framework specification [RFC7564]. This document inherits
the considerations as well.
As with Mapping Characters for IDNA2008 [RFC5895], this document
suggests creating mappings that might cause confusion for some users
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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, David Black, Heather
Flanagan, Joe Hildebrand, John Klensin, Marc Blanchet, Pete Resnick
and Peter Saint-Andre, et al. gave important suggestion for this
document during working group discussions.
7. References
7.1. Normative References
[RFC7564] Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation, Enforcement, and Comparison of
Internationalized Strings in Application Protocols",
RFC 7564, DOI 10.17487/RFC7564, May 2015,
<http://www.rfc-editor.org/info/rfc7564>.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
7.0.0", <http://www.unicode.org/versions/Unicode7.0.0/>,
2012.
[Casefolding]
The Unicode Consortium, "CaseFolding-7.0.0.txt", Unicode
Character Database, July 2011,
<http://www.unicode.org/Public/7.0.0/ucd/CaseFolding.txt>.
[Specialcasing]
The Unicode Consortium, "SpecialCasing-7.0.0.txt", Unicode
Character Database, July 2011,
<http://www.unicode.org/Public/7.0.0/ucd/
SpecialCasing.txt>.
7.2. Informative References
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454,
DOI 10.17487/RFC3454, December 2002,
<http://www.rfc-editor.org/info/rfc3454>.
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[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, DOI 10.17487/RFC3490, March 2003,
<http://www.rfc-editor.org/info/rfc3490>.
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)",
RFC 3491, DOI 10.17487/RFC3491, March 2003,
<http://www.rfc-editor.org/info/rfc3491>.
[RFC3722] Bakke, M., "String Profile for Internet Small Computer
Systems Interface (iSCSI) Names", RFC 3722,
DOI 10.17487/RFC3722, April 2004,
<http://www.rfc-editor.org/info/rfc3722>.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<http://www.rfc-editor.org/info/rfc3748>.
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names
and Passwords", RFC 4013, DOI 10.17487/RFC4013, February
2005, <http://www.rfc-editor.org/info/rfc4013>.
[RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
RFC 4314, DOI 10.17487/RFC4314, December 2005,
<http://www.rfc-editor.org/info/rfc4314>.
[RFC4518] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Internationalized String Preparation", RFC 4518,
DOI 10.17487/RFC4518, June 2006,
<http://www.rfc-editor.org/info/rfc4518>.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <http://www.rfc-editor.org/info/rfc5646>.
[RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for
Internationalized Domain Names in Applications (IDNA)
2008", RFC 5895, DOI 10.17487/RFC5895, September 2010,
<http://www.rfc-editor.org/info/rfc5895>.
[RFC6122] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format", RFC 6122,
DOI 10.17487/RFC6122, March 2011,
<http://www.rfc-editor.org/info/rfc6122>.
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[RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and
Problem Statement for the Preparation and Comparison of
Internationalized Strings (PRECIS)", RFC 6885,
DOI 10.17487/RFC6885, March 2013,
<http://www.rfc-editor.org/info/rfc6885>.
[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 |
| IMAP (RFC 4314) | o | - | - | o |
| LDAP (RFC 4518) | o | - | o | o |
+----------------------+-------------+-----------+------+---------+
Appendix B. The reason why local case mapping is alternative to case
mapping in PRECIS framework
Local case mapping is alternative to Unicode Default Case Folding
instead of being applied sequentially. Because, one outstanding
issue regarding full case folding for characters is, some lowercase
characters like "LATIN SMALL LETTER SHARP S" (U+00DF) (hereinafter
referred to as "eszett") and ligatures like "LATIN SMALL LIGATURE FF"
(U+FB00) that described in section Unconditional mappings of
SpecialCasing.txt become a different codepoint by performing the case
mapping using Unicode Default Case Folding in the PRECIS framework.
In particular, German's eszett can not keep the locale because eszett
becomes two "LATIN SMALL LETTER S"s (U+0073 U+0073) by performing the
case mapping using Unicode Default Case Folding. On the other hand,
eszett doesn't become a different codepoint by performing the case
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mapping in SpecialCasing.txt. Therefore, if it is necessary to keep
locale of characters, PRECIS profile designers should select local
case mapping as alternative to Unicode Default Case Folding.
Appendix C. Limitation to local case mapping
As described in the section Section 2.3, the possible target
characters of local case mapping are specified in SpecialCasing.txt.
The Unicode Standard (at least, up to version 7.0.0) does not define
any context-dependent 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"). Thus, local case mapping is not applicable to small sigma
or final sigma, so case mapping in the PRECIS framework always maps
final sigma to small sigma, independent of context, as also specified
by Unicode Default Case Folding. (Note: Following comments are from
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
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".
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.
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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".
D.6. Changes since -05
o Correct some sentences in this document.
o Modify the local case mapping's rule and target characters in the
Section 2.3 "Local case mapping". This is to avoid user's
confusion towards Greek's final sigma and German's eszett.
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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".
D.8. Changes since -07
o Modify the Section 1 "Introduction".
o Modify the local case mapping's rule and target characters in the
Section 2.3 "Local case mapping".
o Modify the Section 3 "Order of operations".
D.9. Changes since -08
o Updated the Unicode version 6.3 to 7.0 in this document.
D.10. Changes since -09
o Modify the Section 1 "Introduction" to clarify to the discussion
of string matching and the use of mappings from the
SpecialCasing.txt.
o Modify the Section 2.3 "Local case mapping" to clarify to the
discussion of string matching and the use of mappings from the
SpecialCasing.txt.
o Modify the Appendix B "The reason why local case mapping is
alternative to case mapping in PRECIS framework" to state the
result of the case mapping in SpecialCasing.txt of eszett.
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o Clarify the Appendix C "Limitation to local case mapping".
D.11. Changes since -10
o Modify the "Abstract" to clarify to sentences.
o Modify the Section 1 "Introduction" to clarify to a sentence.
o Modify the Section 2.2 "Special mapping" to add examples.
o Modify the Section 2.3 "Local case mapping" to clarify to
sentences. And add a note to explain the term "locale" in this
document.
o Modify the Section 3 "Order of operations" to clarify to
sentences.
o Correct a sentence in the Section 4 "Security Considerations".
o Modify a sentence in the Section 6 "Acknowledgment".
o Change the references from [I-D.ietf-precis-framework] to
[RFC7564] in the Section 7 "Normative References".
o Removed SASL and XMPP in the table of the Appendix A. "Mapping
type list each protocol".
o Modify the Appendix B "The reason why local case mapping is
alternative to case mapping in PRECIS framework" to clarify to
sentences.
o Modify the Appendix C "Limitation to local case mapping" to
clarify to sentences.
D.12. Changes since -11
o Correct a few sentence in the Section 2.3 "Local case mapping" to
address comments by the IESG review.
o Removed citation part which includes "RECOMMENDED" (RFC 2119 word)
in the Section 2.3 "Local case mapping" to avoid readers'
confusion.
o Modify the Section 4 "Security Considerations" to add a reference
to RFC7564.
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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
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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