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 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 August 17, 2014. YONEYA & Nemoto Expires August 17, 2014 [Page 1] Internet-Draft precis mapping February 2014 Copyright Notice Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . . . 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 YONEYA & Nemoto Expires August 17, 2014 [Page 2] Internet-Draft precis mapping February 2014 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 YONEYA & Nemoto Expires August 17, 2014 [Page 3] Internet-Draft precis mapping February 2014 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 YONEYA & Nemoto Expires August 17, 2014 [Page 4] Internet-Draft precis mapping February 2014 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. YONEYA & Nemoto Expires August 17, 2014 [Page 5] Internet-Draft precis mapping February 2014 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", , 2012. [Casefolding] The Unicode Consortium, "CaseFolding-6.3.0.txt", Unicode Character Database, July 2011, , . [Specialcasing] The Unicode Consortium, "SpecialCasing-6.3.0.txt", Unicode Character Database, July 2011, , . 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. YONEYA & Nemoto Expires August 17, 2014 [Page 6] Internet-Draft precis mapping February 2014 [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 | - | +----------------------+-------------+-----------+------+---------+ YONEYA & Nemoto Expires August 17, 2014 [Page 7] Internet-Draft precis mapping February 2014 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". YONEYA & Nemoto Expires August 17, 2014 [Page 8] Internet-Draft precis mapping February 2014 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". YONEYA & Nemoto Expires August 17, 2014 [Page 9] Internet-Draft precis mapping February 2014 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 YONEYA & Nemoto Expires August 17, 2014 [Page 10] Internet-Draft precis mapping February 2014 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 YONEYA & Nemoto Expires August 17, 2014 [Page 11]