PRECIS P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track September 23, 2012
Expires: March 27, 2013
Preparation and Comparison of Nicknames
draft-ietf-precis-nickname-02
Abstract
This document describes how to prepare and compare Unicode strings
representing nicknames, primarily as used within textual chatrooms.
This profile is intended to be used by chatroom technologies based on
both the Message Session Relay Protocol (MSRP) and the Extensible
Messaging and Presence Protocol (XMPP).
Status of this Memo
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This Internet-Draft will expire on March 27, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
3.1. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . . 5
3.3. Visually Similar Characters . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
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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], Multi-User Chat (MUC) based on the
Extensible Messaging and Presence Protocol (XMPP) [XEP-0045], and
multi-party chat based on the Message Session Relay Protocol (MSRP)
[I-D.ietf-simple-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).
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]. Relevant XMPP
terms are defined in [RFC6120] and [XEP-0045], and relevant MSRP
terms are defined in [RFC4975] and [I-D.ietf-simple-chat].
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 "FreeClass" base 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 "FreeClass" base
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 follows, where the operations
specified MUST be completed in the order shown (in particular,
normalization MUST be performed before all other mapping steps and
validity checks, consistent with [I-D.ietf-precis-framework]):
1. 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).
2. 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.
3. 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.
4. Other mappings MAY be applied, such as those defined in
[I-D.yoneya-precis-mappings]. (Note that mapping of fullwidth
and halfwidth characters to their decomposition mappings is not
necessary, since those mappings are performed as part of
normalization using NFKC.)
For both preparation and comparison, the "Bidi Rule" defined in
[RFC5893] applies to the directionality of a nickname.
3. Security Considerations
3.1. Reuse of PRECIS
The security considerations described in [I-D.ietf-precis-framework]
apply to the "FreeClass" base string class used in this document for
nicknames.
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3.2. Reuse of Unicode
The security considerations described in [UTR39] apply to the use of
Unicode characters in nicknames.
3.3. Visually Similar Characters
Section 10.5 of [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 in [UTR39].
4. IANA Considerations
The IANA shall add the following entry to the PRECIS Usage Registry:
Applicability: Chatroom nicknames in MSRP and XMPP.
Base Class: FreeClass.
Subclass: No.
Replaces: N/A.
Normalization: NFKC.
Casemapping: Map uppercase and titlecase characters to lowercase.
Additional Mappings: Map non-ASCII space characters to ASCII space.
Directionality: The "Bidi Rule" defined in RFC 5893 applies.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
5. References
5.1. Normative References
[I-D.ietf-precis-framework]
Saint-Andre, P. and M. Blanchet, "Precis Framework:
Handling Internationalized Strings in Protocols",
draft-ietf-precis-framework-05 (work in progress),
August 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
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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/>.
[UTR39] The Unicode Consortium, "Unicode Technical Report #39:
Unicode Security Mechanisms", August 2010,
<http://unicode.org/reports/tr39/>.
5.2. Informative References
[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-16 (work in progress), August 2012.
[I-D.yoneya-precis-mappings]
YONEYA, Y. and T. NEMOTO, "Mapping characters for PRECIS
classes", draft-yoneya-precis-mappings-02 (work in
progress), July 2012.
[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.
[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.
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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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