Internet DRAFT - draft-ietf-precis-nickname
draft-ietf-precis-nickname
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.
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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 | <Σ> | GREEK SMALL LETTER SIGMA (U+03C3) |
+---------------------------+-----------------------------------+
| 6 | <σ> | GREEK SMALL LETTER SIGMA (U+03C3) |
+---------------------------+-----------------------------------+
| 7 | <ς> | GREEK SMALL LETTER FINAL SIGMA |
| | | (U+03C2) |
+---------------------------+-----------------------------------+
| 8 | <♚> | BLACK CHESS KING (U+265A) |
+---------------------------+-----------------------------------+
| 9 | <Richard Ⅳ> | <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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