Preparation, Enforcement, and Comparison of Internationalized Strings Representing Nicknames
draft-ietf-precis-nickname-19

PRECIS                                                    P. Saint-Andre
Internet-Draft                                                      &yet
Intended status: Standards Track                         October 1, 2014
Expires: April 4, 2015


                Preparation and Comparison of Nicknames
                     draft-ietf-precis-nickname-10

Abstract

   This document describes how to prepare and compare Unicode strings
   representing nicknames, primarily for use within textual chatrooms.
   This profile is intended to be used by messaging and text
   conferencing technologies such as the Extensible Messaging and
   Presence Protocol (XMPP), the Message Session Relay Protocol (MSRP),
   and Centralized Conferencing (XCON).

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
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   This Internet-Draft will expire on April 4, 2015.

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
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Preparation . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Enforcement . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Use in Application Protocols  . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     6.1.  Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . .   7
     6.2.  Reuse of Unicode  . . . . . . . . . . . . . . . . . . . .   7
     6.3.  Visually Similar Characters . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

1.1.  Overview

   Technologies for textual chatrooms customarily enable participants to
   specify a nickname for use in the room; e.g., this is true of
   Internet Relay Chat [RFC2811] as well as multi-party chat
   technologies based on the Extensible Messaging and Presence Protocol
   (XMPP) [RFC6120] [XEP-0045], the Message Session Relay Protocol
   (MSRP) [RFC4975] [I-D.ietf-simple-chat], and Centralized Conferencing
   (XCON) [RFC5239] [I-D.boulton-xcon-session-chat].  Recent chatroom
   technologies also allow internationalized nicknames because they
   support characters from outside the ASCII range [RFC20], typically by
   means of the Unicode character set [UNICODE].  Although such
   nicknames tend to be used primarily for display purposes, they are
   sometimes used for programmatic purposes as well (e.g., kicking users
   or avoiding nickname conflicts).  Note too that nicknames can be used
   not only in chatrooms but also more generally as a user's preferred
   display name (see for instance [XEP-0172]).

   To increase the likelihood that nicknames will work in ways that make
   sense for typical users throughout the world, this document defines
   rules for preparing and comparing internationalized nicknames.




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1.2.  Terminology

   Many important terms used in this document are defined in
   [I-D.ietf-precis-framework], [RFC6365], and [UNICODE].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

2.  Rules

   This document distinguishes between three different actions that an
   entity can take:

   o  Enforcement entails applying to all of the rules specified for the
      NicknameFreeformClass profile to an individual string.
      Enforcement is typically the responsibility of a chatroom server,
      conference focus, or similar entity.

   o  Comparison entails applying all of the rules to two separate
      strings, for the purpose of determining if the two strings are
      equivalent.

   o  Preparation entails only ensuring that the characters in an
      individual string are allowed by the PRECIS FreeformClass.
      Preparation is typically the responsibility of a client or user
      agent.

   Detailed rules are provided in the following sections.

2.1.  Preparation

   An entity that prepares a string for inclusion in a nickname slot
   MUST ensure that the string consists only of Unicode code points that
   conform to the "FreeformClass" base string class defined in
   [I-D.ietf-precis-framework].  In addition, the string MUST be encoded
   as UTF-8 [RFC3629].

2.2.  Enforcement

   An entity that performs enforcement in nickname slots MUST prepare a
   string as described in the previous section and MUST also apply the
   width-mapping rules, additional-mapping, special-mapping, case-
   mapping, normalization, and exclusion rules for the
   NicknameFreeformClass profile described below (these rules MUST be
   applied in the order shown).




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   1.  There is no width-mapping rule (this is not necessary because
       width mapping is performed as part of normalization using NFKC as
       specified below).

   2.  So-called additional mappings MAY be applied, such as mapping of
       characters that are similar to common delimiters (such as '@',
       ':', '/', '+', '-', and '.', e.g., mapping of IDEOGRAPHIC FULL
       STOP (U+3002) to FULL STOP (U+002E)); the PRECIS mappings
       document [I-D.ietf-precis-mappings] describes such mappings in
       more detail.

   3.  The special-mapping rule consists of the following:

       1.  Non-ASCII space characters from the "N" category defined
           under Section 7.14 of [I-D.ietf-precis-framework] MUST be
           mapped to U+0020 SPACE.

       2.  Leading and trailing whitespace (i.e., one or more instances
           of the ASCII space character at the beginning or end of a
           nickname) MUST be removed (e.g., "stpeter " is mapped to
           "stpeter").

       3.  Interior sequences of more than one ASCII space character
           MUST be mapped to a single ASCII space character (e.g.,
           "St  Peter" is mapped to "St Peter").

   4.  Uppercase and titlecase characters MUST be mapped to their
       lowercase equivalents using Unicode Default Case Folding.  In
       applications that prohibit conflicting nicknames, this rule helps
       to reduce the possibility of confusion by ensuring that nicknames
       differing only by case (e.g., "stpeter" vs. "StPeter") would not
       be allowed in a chatroom at the same time.

   5.  The string MUST be normalized using Unicode Normalization Form KC
       (NFKC).  Because NFKC is more "aggressive" in finding matches
       than other normalization forms (in the terminology of Unicode, it
       performs both canonical and compatibility decomposition before
       recomposing code points), this rule helps to reduce the
       possibility of confusion by increasing the number of characters
       that would match (e.g., U+2163 ROMAN NUMERAL FOUR would match the
       combination of U+0049 LATIN CAPITAL LETTER I and U+0056 LATIN
       CAPITAL LETTER V).

   6.  There is no exclusion rule.

   With regard to directionality, applications MUST apply the "Bidi
   Rule" defined in [RFC5893] (i.e., each of the six conditions of the
   Bidi Rule must be satisfied).



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3.  Examples

   The following examples illustrate a small number of nicknames that
   are consistent with the format defined above, along with the output
   string resulting from application of the PRECIS rules, which would be
   used for comparison purposes (note that the characters < and > are
   used to delineate the actual nickname and are not part of the
   nickname strings).

   Table 1: A sample of legal nicknames

   +---------------------------+-----------------------------------+
   | # | Nickname              | Output for Comparison             |
   +---------------------------+-----------------------------------+
   | 1 | <Foo>                 | <foo>                             |
   +---------------------------+-----------------------------------+
   | 2 | <foo>                 | <foo>                             |
   +---------------------------+-----------------------------------+
   | 3 | <Foo Bar>             | <foo bar>                         |
   +---------------------------+-----------------------------------+
   | 4 | <foo bar>             | <foo bar>                         |
   +---------------------------+-----------------------------------+
   | 5 | <&#x3A3;>             | GREEK SMALL LETTER SIGMA (U+03C3) |
   +---------------------------+-----------------------------------+
   | 6 | <&#x3C3;>             | GREEK SMALL LETTER SIGMA (U+03C3) |
   +---------------------------+-----------------------------------+
   | 7 | <&#x3C2;>             | GREEK SMALL LETTER FINAL SIGMA    |
   |   |                       | (U+03C2)                          |
   +---------------------------+-----------------------------------+
   | 8 | <&#x265A;>            | BLACK CHESS KING (U+265A)         |
   +---------------------------+-----------------------------------+

   Regarding examples 5, 6, and 7: case-mapping of GREEK CAPITAL LETTER
   SIGMA (U+03A3) to lowercase (i.e., to GREEK SMALL LETTER SIGMA,
   U+03C3) during comparison would result in matching the nicknames in
   examples 5 and 6; however, because the PRECIS mapping rules do not
   account for the special status of GREEK SMALL LETTER FINAL SIGMA
   (U+03C2), the nicknames in examples 5 and 7 or examples 6 and 7 would
   not be matched.  Regarding example 8: symbol characters such as BLACK
   CHESS KING (U+265A) are allowed by the PRECIS FreeformClass and thus
   can be used in nicknames.

   The following examples illustrate strings that are not valid
   nicknames because they violate the format defined above.







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   Table 2: A sample of strings that violate the nickname rules

   +---------------------------------+---------------------------------+
   | # | Non-Nickname string         | Notes                           |
   +---------------------------------+---------------------------------+
   | 9 | <  foo  >                   | Leading spaces                  |
   +---------------------------------+---------------------------------+
   | 10| <>                          | Zero-length string              |
   +---------------------------------+---------------------------------+

4.  Use in Application Protocols

   This specification defines only the PRECIS-based rules for handling
   of nickname strings.  It is the responsibility of an application
   protocol (e.g., MSRP, XCON, or XMPP) to specify the protocol slots in
   which nickname strings can appear, as well as the entities that are
   expected to enforce the rules governing nickname strings in that
   protocol (e.g., chat servers, chat clients, or both).

   Above and beyond the PRECIS-based rules specified here, application
   protocols can also define application-specific rules governing
   nickname strings (rules regarding the minimum or maximum length of
   nicknames, further restrictions on allowable characters or character
   ranges, safeguards to mitigate the effects of visually similar
   characters, etc.).

   Naturally, application protocols can also specify rules governing the
   actual use of nicknames in applications (reserved nicknames,
   authorization requirements for using nicknames, whether certain
   nicknames can be prohibited, handling of duplicates, the relationship
   between nicknames and underlying identifiers such as SIP URIs or
   Jabber IDs, etc.).

   Entities that enforce the rules specified in this document are
   encouraged to be liberal in what they accept by following this
   procedure:

   1.  Where possible, map characters (e.g, through width mapping,
       additional mapping, special mapping, case mapping, or
       normalization) and accept the mapped string.

   2.  If mapping is not possible (e.g., because a character is
       disallowed in the FreeformClass), reject the string.








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5.  IANA Considerations

   The IANA shall add the following entry to the PRECIS Profiles
   Registry:

   Name:  NicknameFreeformClass.

   Applicability:  Nicknames in messaging and text conferencing
      technologies such as MSRP, XCON, and XMPP.

   Base Class:  FreeformClass.

   Replaces:  None.

   Width Mapping:  None (handled via NFKC).

   Additional Mappings:  Map non-ASCII space characters to ASCII space,
      strip leading and trailing space characters, map interior
      sequences of multiple space characters to a single ASCII space.

   Case Mapping:  For comparison purposes, map uppercase and titlecase
      characters to lowercase using Unicode Default Case Folding.

   Normalization:  NFKC.

   Directionality:  The "Bidi Rule" defined in RFC 5893 applies.

   Exclusions:  None.

   Enforcement:  To be specified by applications.

   Specification:  this document.  [Note to RFC Editor: please change
      "this document" to the RFC number issued for this specification.]

6.  Security Considerations

6.1.  Reuse of PRECIS

   The security considerations described in [I-D.ietf-precis-framework]
   apply to the "FreeformClass" string class used in this document for
   nicknames.

6.2.  Reuse of Unicode

   The security considerations described in [UTS39] apply to the use of
   Unicode characters in nicknames.





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6.3.  Visually Similar Characters

   [I-D.ietf-precis-framework] describes some of the security
   considerations related to visually similar characters, also called
   "confusable characters" or "confusables".

   Although the mapping rules defined under Section 2 of this document
   are designed in part to reduce the possibility of confusion about
   nicknames, this document does not provide more detailed
   recommendations regarding the handling of visually similar
   characters, such as those provided in [UTS39].

7.  References

7.1.  Normative References

   [I-D.ietf-precis-framework]
              Saint-Andre, P. and M. Blanchet, "Precis Framework:
              Handling Internationalized Strings in Protocols", draft-
              ietf-precis-framework-18 (work in progress), September
              2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC5893]  Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
              Internationalized Domain Names for Applications (IDNA)",
              RFC 5893, August 2010.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard, Version
              6.3", 2013,
              <http://www.unicode.org/versions/Unicode6.3.0/>.

   [UTS39]    The Unicode Consortium, "Unicode Technical Standard #39:
              Unicode Security Mechanisms", November 2013,
              <http://unicode.org/reports/tr39/>.

7.2.  Informative References

   [I-D.boulton-xcon-session-chat]
              Barnes, M., Boulton, C., and S. Loreto, "Chatrooms within
              a Centralized Conferencing (XCON) System", draft-boulton-
              xcon-session-chat-08 (work in progress), July 2011.





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   [I-D.ietf-simple-chat]
              Niemi, A., Garcia, M., and G. Sandbakken, "Multi-party
              Chat Using the Message Session Relay Protocol (MSRP)",
              draft-ietf-simple-chat-18 (work in progress), January
              2013.

   [I-D.ietf-precis-mappings]
              Yoneya, Y. and T. NEMOTO, "Mapping characters for PRECIS
              classes", draft-ietf-precis-mappings-08 (work in
              progress), June 2014.

   [RFC20]    Cerf, V., "ASCII format for network interchange", RFC 20,
              October 1969.

   [RFC2811]  Kalt, C., "Internet Relay Chat: Channel Management", RFC
              2811, April 2000.

   [RFC4975]  Campbell, B., Mahy, R., and C. Jennings, "The Message
              Session Relay Protocol (MSRP)", RFC 4975, September 2007.

   [RFC5239]  Barnes, M., Boulton, C., and O. Levin, "A Framework for
              Centralized Conferencing", RFC 5239, June 2008.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, March 2011.

   [RFC6365]  Hoffman, P. and J. Klensin, "Terminology Used in
              Internationalization in the IETF", BCP 166, RFC 6365,
              September 2011.

   [XEP-0045]
              Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February
              2012.

   [XEP-0172]
              Saint-Andre, P. and V. Mercier, "User Nickname", XSF XEP
              0172, March 2012.

Appendix A.  Acknowledgements

   Thanks to Kim Alvefur, Mary Barnes, Dave Cridland, Miguel Garcia,
   Salvatore Loreto, and Enrico Marocco for their reviews and comments.

Author's Address







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   Peter Saint-Andre
   &yet

   Email: peter@andyet.com
   URI:   https://andyet.com/














































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