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rfc:rfc7700

Internet Engineering Task Force (IETF) P. Saint-Andre Request for Comments: 7700 &yet Category: Standards Track December 2015 ISSN: 2070-1721

            Preparation, Enforcement, and Comparison of
          Internationalized Strings Representing Nicknames

Abstract

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

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7700.

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
 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.

Saint-Andre Standards Track [Page 1] RFC 7700 PRECIS: Nickname December 2015

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 ................................................5
    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
 Acknowledgements ..................................................11
 Author's Address ..................................................11

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 such as a device,
 account, contact, or website.  Such names are variously called
 "nicknames" (e.g., in chat room applications), "display names" (e.g.,
 in Internet mail), or "petnames" (see [PETNAME-SYSTEMS]); for
 consistency, these are all called "nicknames" in this document.
 Nicknames are commonly supported in technologies for textual chat
 rooms, 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] [RFC7701], and Centralized Conferencing (XCON)
 [RFC5239] [XCON-SYSTEM].  Recent chat room 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).

Saint-Andre Standards Track [Page 2] RFC 7700 PRECIS: Nickname December 2015

 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
 [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 Normalization Form KC (NFKC) as specified
     below).

Saint-Andre Standards Track [Page 3] RFC 7700 PRECIS: Nickname December 2015

 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.
     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: Unicode Default Case Folding MUST be applied,
     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
     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 versus 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.

Saint-Andre Standards Track [Page 4] RFC 7700 PRECIS: Nickname December 2015

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 string class defined in
 [RFC7564].  In addition, the entity MUST ensure that the string is
 encoded as UTF-8 [RFC3629].

2.3. Enforcement

 An entity that performs enforcement according to this profile MUST
 prepare a string as described in Section 2.2 and MUST also apply the
 following rules specified in Section 2.1 in the order shown:
 1.  Additional Mapping Rule
 2.  Normalization Rule
 3.  Directionality Rule
 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 as specified in Section 2.2 and MUST
 apply the following rules specified in Section 2.1 in the order
 shown:
 1.  Additional Mapping Rule
 2.  Case Mapping Rule
 3.  Normalization Rule
 4.  Directionality Rule
 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).

Saint-Andre Standards Track [Page 5] RFC 7700 PRECIS: Nickname December 2015

 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 SIGMA (U+03C3) |
 +---------------------------+-----------------------------------+
 | 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 the same is true of GREEK SMALL LETTER FINAL
 SIGMA (U+03C2); therefore, the comparison operation defined in
 Section 2.4 would result in matching of the nicknames in examples 5,
 6, and 7.  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
 rules need to be enforced.  See Section 6 of [RFC7564] for guidelines
 about using PRECIS profiles in applications.

Saint-Andre Standards Track [Page 6] RFC 7700 PRECIS: Nickname December 2015

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

Saint-Andre Standards Track [Page 7] RFC 7700 PRECIS: Nickname December 2015

 Normalization Rule:  NFKC
 Directionality Rule:  None
 Enforcement:  To be specified by applications.
 Specification:  RFC 7700 (this document)

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 in 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,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
            10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
            2003, <http://www.rfc-editor.org/info/rfc3629>.

Saint-Andre Standards Track [Page 8] RFC 7700 PRECIS: Nickname December 2015

 [RFC5893]  Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts
            for Internationalized Domain Names for Applications
            (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010,
            <http://www.rfc-editor.org/info/rfc5893>.
 [RFC6365]  Hoffman, P. and J. Klensin, "Terminology Used in
            Internationalization in the IETF", BCP 166, RFC 6365,
            DOI 10.17487/RFC6365, September 2011,
            <http://www.rfc-editor.org/info/rfc6365>.
 [RFC7564]  Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
            Preparation, Enforcement, and Comparison of
            Internationalized Strings in Application Protocols",
            RFC 7564, DOI 10.17487/RFC7564, May 2015,
            <http://www.rfc-editor.org/info/rfc7564>.
 [Unicode]  The Unicode Consortium, "The Unicode Standard",
            <http://www.unicode.org/versions/latest/>.
 [Unicode7.0]
            The Unicode Consortium, "The Unicode Standard, Version
            7.0.0", 2014,
            <http://www.unicode.org/versions/Unicode7.0.0/>.
 [UTS39]    The Unicode Consortium, "Unicode Technical Standard #39:
            Unicode Security Mechanisms", November 2013,
            <http://unicode.org/reports/tr39/>.

7.2. Informative References

 [PETNAME-SYSTEMS]
            Stiegler, M., "An Introduction to Petname Systems",
            updated June 2012, February 2005,
            <http://www.skyhunter.com/marcs/petnames/
            IntroPetNames.html>.
 [RFC20]    Cerf, V., "ASCII format for network interchange", STD 80,
            RFC 20, DOI 10.17487/RFC0020, October 1969,
            <http://www.rfc-editor.org/info/rfc20>.
 [RFC2811]  Kalt, C., "Internet Relay Chat: Channel Management",
            RFC 2811, DOI 10.17487/RFC2811, April 2000,
            <http://www.rfc-editor.org/info/rfc2811>.
 [RFC4975]  Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed.,
            "The Message Session Relay Protocol (MSRP)", RFC 4975,
            DOI 10.17487/RFC4975, September 2007,
            <http://www.rfc-editor.org/info/rfc4975>.

Saint-Andre Standards Track [Page 9] RFC 7700 PRECIS: Nickname December 2015

 [RFC5239]  Barnes, M., Boulton, C., and O. Levin, "A Framework for
            Centralized Conferencing", RFC 5239, DOI 10.17487/RFC5239,
            June 2008, <http://www.rfc-editor.org/info/rfc5239>.
 [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
            DOI 10.17487/RFC5322, October 2008,
            <http://www.rfc-editor.org/info/rfc5322>.
 [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
            Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
            March 2011, <http://www.rfc-editor.org/info/rfc6120>.
 [RFC7701]  Niemi, A., Garcia-Martin, M., and G. Sandbakken, "Multi-
            party Chat Using the Message Session Relay Protocol
            (MSRP)", RFC 7701, DOI 10.17487/RFC7701, December 2015,
            <http://www.rfc-editor.org/info/rfc7701>.
 [XCON-SYSTEM]
            Barnes, M., Boulton, C., and S. Loreto, "Chatrooms within
            a Centralized Conferencing (XCON) System", Work in
            Progress, draft-boulton-xcon-session-chat-08, July 2012.
 [XEP-0045]
            Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February
            2012, <http://xmpp.org/extensions/xep-0045.html>.
 [XEP-0172]
            Saint-Andre, P. and V. Mercier, "User Nickname", XSF
            XEP 0172, March 2012,
            <http://xmpp.org/extensions/xep-0172.html>.

Saint-Andre Standards Track [Page 10] RFC 7700 PRECIS: Nickname December 2015

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/

Saint-Andre Standards Track [Page 11]

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