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PRECIS                                                    P. Saint-Andre
Internet-Draft                                                      &yet
Intended status: Standards Track                       September 3, 2015
Expires: March 6, 2016


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

Abstract

   This document describes methods for handling Unicode strings
   representing memorable, human-friendly names (variously called
   "nicknames", "display names", or "petnames") for people, devices,
   accounts, websites, and other entities.

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
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   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 March 6, 2016.

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
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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.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Nickname Profile  . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Rules . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Preparation . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Enforcement . . . . . . . . . . . . . . . . . . . . . . .   5
     2.4.  Comparison  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Use in Application Protocols  . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
     6.1.  Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . .   8
     6.2.  Reuse of Unicode  . . . . . . . . . . . . . . . . . . . .   8
     6.3.  Visually Similar Characters . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
     7.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

1.1.  Overview

   A number of technologies and applications provide the ability for a
   person to choose a memorable, human-friendly name in a communications
   context, or to set such a name for another entity entity such as a
   device, account, contact, or website.  Such names are variously
   called "nicknames" (e.g., in chatroom applications), "display names"
   (e.g., in Internet mail), or "petnames" (see [1]); for consistency,
   these are all called "nicknames" in this document.

   Nicknames are commonly supported in technologies for textual
   chatrooms, e.g., Internet Relay Chat [RFC2811] and 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).



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   A similar usage enables a person to set their own preferred display
   name or to set a preferred display name for another user (e.g., the
   "display-name" construct in the Internet message format [RFC5322] and
   [XEP-0172] in XMPP).

   Memorable, human-friendly names are also used in contexts other than
   personal messaging, such as names 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 application), and
   the like.

   The rules specified in this document can be applied in all of the
   foregoing contexts.

   To increase the likelihood that memorable, human-friendly names 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 [RFC7564],
   [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

2.1.  Rules

   The following rules apply within the Nickname profile of the PRECIS
   FreeformClass.

   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.

       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.



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       2.  Any 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 as defined in the Unicode Standard [Unicode] (at the time
       of this writing, the algorithm is specified in Chapter 3 of
       [Unicode7.0]).  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: There is no directionality rule.  The "Bidi
       Rule" (defined in [RFC5893]) and similar rules are unnecessary
       and inapplicable to nicknames, because it is perfectly acceptable
       for a given nickname to be presented differently in different
       layout systems (e.g., a user interface that is configured to
       handle primarily a right-to-left script vs. an interface that is
       configured to handle primarily a left-to-right script), as long
       as the presentation is consistent in any given layout system.

2.2.  Preparation

   An entity that prepares a string for subsequent enforcement 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 [RFC7564].  In addition, the entity MUST ensure that the
   string is encoded as UTF-8 [RFC3629].







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2.3.  Enforcement

   An entity that performs enforcement according to this profile MUST
   prepare a string as described in Section 2.2 section and MUST also
   apply the rules specified in Section 2.1.  The rules MUST be applied
   in the order shown.

   After all of the foregoing rules have been enforced, the entity MUST
   ensure that the nickname is not zero bytes in length (this is done
   after enforcing the rules to prevent applications from mistakenly
   omitting a nickname entirely, because when internationalized
   characters are accepted a non-empty sequence of characters can result
   in a zero-length nickname after canonicalization).

2.4.  Comparison

   An entity that performs comparison of two strings according to this
   profile MUST prepare each string and enforce the rules as specified
   in Section 2.2 and Section 2.3.  The two strings are to be considered
   equivalent if they are an exact octet-for-octet match (sometimes
   called "bit-string identity").

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 (note that the
   characters < and > are used to delineate the actual nickname and are
   not part of the nickname strings).






















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   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)         |
   +---------------------------+-----------------------------------+
   | 9 | <Richard &#x2163;>    | <richard iv>                      |
   +---------------------------+-----------------------------------+

   Regarding examples 5, 6, and 7: applying Unicode Default Case Folding
   to GREEK CAPITAL LETTER SIGMA (U+03A3) results in GREEK SMALL LETTER
   SIGMA (U+03C3), and doing so 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.
   Regarding example 9: applying Unicode Default Case Folding to ROMAN
   NUMERAL FOUR (U+2163) results in SMALL ROMAN NUMERAL FOUR (U+2173),
   and applying NFKC to SMALL ROMAN NUMERAL FOUR (U+2173) results in
   LATIN SMALL LETTER I (U+0069) LATIN SMALL LETTER V (U+0086).

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




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   rules need to be enforced.  See Section 6 of [RFC7564] 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.

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.



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   Case Mapping Rule:  Map uppercase and titlecase characters to
      lowercase using Unicode Default Case Folding.

   Normalization Rule:  NFKC.

   Directionality Rule:  None.

   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 [RFC7564] 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

   [RFC7564] 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

   [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.






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

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

   [RFC7564]  Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
              Preparation, Enforcement, and Comparison of
              Internationalized Strings in Application Protocols", RFC
              7564, May 2015.

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

   [Unicode7.0]
              The Unicode Consortium, "The Unicode Standard, Version
              7.0.0", 2014,
              <http://www.unicode.org/versions/Unicode7.0.0/>.

   [Unicode]  The Unicode Consortium, "The Unicode Standard",
              2015-present, <http://www.unicode.org/versions/latest/>.

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.

   [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.





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

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

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

7.3.  URIs

   [1] http://www.skyhunter.com/marcs/petnames/IntroPetNames.html

Appendix A.  Acknowledgements

   Thanks to Kim Alvefur, Mary Barnes, Ben Campbell, Dave Cridland,
   Miguel Garcia, Salvatore Loreto, Enrico Marocco, Matt Miller, and
   Yoshiro YONEYA for their reviews and comments.

   Paul Kyzivat and Melinda Shore reviewed the document for the General
   Area Review Team and Operations Directorate, respectively.

   During IESG review, Ben Campbell and Kathleen Moriarty provided
   comments that led to further improvements.

   Thanks to Matt Miller as document shepherd, Pete Resnick and Andrew
   Sullivan as IANA designated experts, Marc Blanchet and Alexey
   Melnikov as working group chairs, and Barry Leiba as area director.

   The author wishes to acknowledge Cisco Systems, Inc., for employing
   him during his work on earlier draft versions of this document.

Author's Address

   Peter Saint-Andre
   &yet

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




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