PRECIS P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track March 5, 2012
Expires: September 04, 2012

Preparation and Comparison of Nicknames
draft-saintandre-precis-nickname-00

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 Extensible Messaging and Presence Protocol (XMPP) and the Message Session Relay Protocol (MSRP).

Status of this Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on September 04, 2012.

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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 the outside the ASCII range, typically by means of the Unicode character set [UNICODE]. Although such nicknames are often 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 nickname input and comparison 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 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 NOT be zero bytes in length and MUST NOT be more than 1023 bytes in length (the latter restriction is derived from the length restriction on XMPP resourceparts, see [RFC6122]). This rule is to be enforced after any mapping or normalization of code points.

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 (e.g., when a chatroom client generates a nickname from user input for inclusion as a nickname protocol element), an application MUST only ensure that the string conforms to the "FreeClass" base string class defined in [I-D.ietf-precis-framework]; however, it MAY also perform the mapping and normalization operations specified below for comparison.

For comparison purposes (e.g., when a chatroom server determines if two nicknames match during the authorization process), an application MUST treat a nickname as follows, where the operations specified MUST be completed in the order shown:

  1. Non-ASCII space characters from the "N" category defined under Section 6.14 of [I-D.ietf-precis-framework] MUST be mapped to SPACE [U+0020].

  2. Uppercase and titlecase characters MUST be mapped to their lowercase equivalents. In applications that prohibit matching 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 room at the same time.

  3. All characters MUST be mapped using Unicode Normalization Form KC (NFKC). Because NFKC is more "aggressive" in finding matches than other normalization forms (in the language 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., ROMAN NUMERAL FOUR [U+2163] would match the combination of LATIN CAPITAL LETTER I [U+0049] and LATIN CAPITAL LETTER V [U+0056]).

For both preparation and comparision, the "Bidi Rule" provided 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, respectively.

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

[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 under Section 2 are designed in part to reduce the possibility of confusion about nicknames, this document does not yet provide more detailed recommendations regarding the handling of visually similar characters, such as those in [UTR39]. However, a future version of this document might provide such recommendations.

4. IANA Considerations

The IANA shall add an entry to the PRECIS Usage Registry for reuse of the PRECIS FreeClass for preparation and comparision of nicknames, as follows:

Application Protocol:
MSRP and XMPP.
Base Class:
FreeClass
Subclassing:
No.
Directionality:
The "Bidi Rule" defined in RFC 5893 applies.
Casemapping:
None.
Normalization:
NFC.
Specification:
RFC XXXX.

5. References

5.1. Normative References

[I-D.ietf-precis-framework] Blanchet, M and P Saint-Andre, "Precis Framework: Handling Internationalized Strings in Protocols", Internet-Draft draft-ietf-precis-framework-01, October 2011.
[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-14, March 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.
[RFC6122] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Address Format", RFC 6122, March 2011.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version 6.1", 2012.
[UTR39] The Unicode Consortium, "Unicode Technical Report #39: Unicode Security Mechanisms", August 2010.
[XEP-0045] Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February 2012.

5.2. Informative References

[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.

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