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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                                                      &yet
Intended status: Standards Track                       December 23, 2014
Expires: June 26, 2015


 Preparation, Enforcement, and Comparison of Internationalized Strings
                         Representing Nicknames
                     draft-ietf-precis-nickname-14

Abstract

   This document describes methods for handling Unicode strings
   representing nicknames.

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 June 26, 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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   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Nickname Profile  . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Preparation . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Enforcement . . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Comparison  . . . . . . . . . . . . . . . . . . . . . . .   4
   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]).

   Nicknames (sometimes called "petnames") are also used in contexts
   other than messaging, such as petnames for devices (e.g., in a
   network visualization application), websites (e.g., for bookmarks in
   a web browser), accounts (e.g., in a web interface for a list of
   payees in a bank account), people (e.g., in a contact list




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   application), and the like.  The rules specified in this document can
   also be applied to such usages.

   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, enforcing, 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.  Nickname Profile

   Detailed rules for the preparation, enforcement, and comparison of
   nicknames are provided in the following sections, which define the
   Nickname profile of the PRECIS FreeformClass (on the differences
   among preparation, enforcement, and comparison, refer to
   [I-D.ietf-precis-framework]).

2.1.  Preparation

   An entity that prepares a string according to this profile 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 according to this profile MUST
   prepare a string as described in the previous section and MUST also
   apply the rules specified below for the Nickname profile (these rules
   MUST be applied in the order shown).

   1.  Width Mapping Rule: There is no width-mapping rule (such a rule
       is not necessary because width mapping is performed as part of
       normalization using NFKC as specified below).

   2.  Additional Mapping Rule: The additional mapping rule consists of
       the following sub-rules.




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       1.  Any instances of non-ASCII space MUST be mapped to ASCII
           space (U+0020); a non-ASCII space is any Unicode code point
           having a general category of "Zs", naturally with the
           exception of U+0020.

       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").

   3.  Case Mapping Rule: 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 presented to a human user at the same
       time.

   4.  Normalization Rule: 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).

   5.  Directionality Rule: Applications MUST apply the "Bidi Rule"
       defined in [RFC5893] to strings that contain right-to-left
       characters (i.e., each of the six conditions of the Bidi Rule
       must be satisfied).

2.3.  Comparison

   An entity that performs comparison of two strings according to this
   profile MUST prepare each string and enforce the rules as specified
   in the previous two sections.  The two strings are to be considered
   equivalent if they are an exact octet-for-octet match (sometimes
   called "bit-string identity").







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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 and trailing spaces     |
   +---------------------------------+---------------------------------+
   | 10 | <foo      bar>             | Multiple 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) or application definition to
   specify the protocol slots in which nickname strings can appear, the
   entities that are expected to enforce the rules governing nickname
   strings, and when in protocol processing or interface handling the
   rules need to be enforced.  See Section 6 of
   [I-D.ietf-precis-framework] for guidelines about using PRECIS
   profiles in applications.

   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, 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:  Nickname.

   Base Class:  FreeformClass.

   Applicability:  Nicknames in messaging and text conferencing
      technologies; petnames for devices, accounts, and people; and
      other uses of nicknames or petnames.

   Replaces:  None.

   Width Mapping Rule:  None (handled via NFKC).

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

   Normalization Rule:  NFKC.

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

   Enforcement:  To be specified by applications.

   Specification:  RFC XXXX.  [Note to RFC Editor: please change "XXXX"
      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-21 (work in progress), December
              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.

   [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.

   Peter Saint-Andre wishes to acknowledge Cisco Systems, Inc., for
   employing him during his work on earlier versions of this document.

Author's Address

   Peter Saint-Andre
   &yet

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



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