PRECIS P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track September 23, 2012
Expires: March 25, 2013

Preparation and Comparison of Nicknames


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).

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Table of Contents

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.

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.

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:

Chatroom nicknames in MSRP and XMPP.
Base Class:
Map uppercase and titlecase characters to lowercase.
Additional Mappings:
Map non-ASCII space characters to ASCII space.
The "Bidi Rule" defined in RFC 5893 applies.
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", Internet-Draft draft-ietf-precis-framework-05, 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 Internationalized Domain Names for Applications (IDNA)", RFC 5893, August 2010.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version 6.1", 2012.
[UTR39] The Unicode Consortium, "Unicode Technical Report #39: Unicode Security Mechanisms", August 2010.

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)", Internet-Draft draft-ietf-simple-chat-16, August 2012.
[I-D.yoneya-precis-mappings] YONEYA, Y and T NEMOTO, "Mapping characters for PRECIS classes", Internet-Draft draft-yoneya-precis-mappings-02, 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.

Author's Address

Peter Saint-Andre Cisco Systems, Inc. 1899 Wynkoop Street, Suite 600 Denver, CO 80202 USA Phone: +1-303-308-3282 EMail: