PRECIS P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track December 3, 2013
Expires: June 6, 2014
Preparation and Comparison of Nicknames
draft-ietf-precis-nickname-08
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
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This Internet-Draft will expire on June 6, 2014.
Copyright Notice
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Use in Application Protocols . . . . . . . . . . . . . . . . . 6
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
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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]).
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.
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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
equivalents 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.
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
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[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
+---------------------------+-----------------------------------+
| # | 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) |
+---------------------------+-----------------------------------+
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 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) 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.
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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.
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-12 (work in progress),
November 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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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.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version
6.1", 2012,
<http://www.unicode.org/versions/Unicode6.1.0/>.
[UTS39] The Unicode Consortium, "Unicode Technical Standard #39:
Unicode Security Mechanisms", August 2010,
<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,
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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.
Author's Address
Peter Saint-Andre
Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
Phone: +1-303-308-3282
Email: psaintan@cisco.com
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