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Versions: (draft-saintandre-precis-nickname) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 RFC 7700

PRECIS                                                    P. Saint-Andre
Internet-Draft
Intended status: Standards Track                        January 23, 2014
Expires: July 27, 2014


                Preparation and Comparison of Nicknames
                     draft-ietf-precis-nickname-09

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 July 27, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.












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   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
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Use in Application Protocols  . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     6.1.  Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . .   7
     6.2.  Reuse of Unicode  . . . . . . . . . . . . . . . . . . . .   7
     6.3.  Visually Similar Characters . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     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]).



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   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.

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

   A nickname MUST consist only of Unicode code points that conform to
   the "FreeformClass" string class defined in
   [I-D.ietf-precis-framework].

   For preparation purposes (most commonly, when a chatroom client
   generates a nickname from user input for inclusion as a protocol
   element that represents a "nickname slot"), an application MUST at a
   minimum ensure that the string conforms to the "FreeformClass" string
   class defined in [I-D.ietf-precis-framework]; however, it MAY in
   addition perform the normalization and mapping operations specified
   below for comparison purposes.

   For comparison purposes (e.g., when a chatroom server determines if
   two nicknames are in conflict during the authorization process), an
   application MUST treat a nickname as specified below (these rules
   constitute the "NicknameFreeformClass" profile).  The operations
   specified MUST be completed in the order shown (in particular,
   normalization MUST be performed after the other mapping steps and
   before validity-checking against the definition of the PRECIS
   "FreeformClass", consistent with [I-D.ietf-precis-framework]).

   1.  So-called additional mappings MAY be applied, such as those
       defined in [I-D.ietf-precis-mappings].  (Note that mapping of
       fullwidth and halfwidth characters to their decomposition
       mappings is not necessary, since those mappings are performed as
       part of normalization using NFKC as mandated below.)


   2.  Non-ASCII space characters from the "N" category defined under
       Section 6.14 of [I-D.ietf-precis-framework] MUST be mapped to
       U+0020 SPACE.




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   3.  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").


   4.  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").


   5.  Uppercase and titlecase characters MUST be mapped to their
       lowercase equivalents.  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.


   6.  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).


   7.  Finally, the rules for the PRECIS "FreeformClass" MUST be
       applied, as specified in [I-D.ietf-precis-framework].

   For both preparation and comparison, the "Bidi Rule" defined in
   [RFC5893] applies to the directionality of a nickname.

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






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   +---------------------------+-----------------------------------+
   | # | 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.

   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




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   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 Identifiers, etc.).

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:  Map uppercase and titlecase characters to lowercase.

   Normalization:  NFKC.

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

   Exclusions:  None.

   Enforcement:  To be specified by applications.




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   Specification:  RFC XXXX.  [Note to RFC Editor: please change XXXX to
      the 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.

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-13 (work in progress), December
              2013.

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

   [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/>.



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   [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.

   [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-05 (work in
              progress), October 2013.

   [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.



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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

   Peter Saint-Andre

   Email: ietf@stpeter.im









































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