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.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.

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

Copyright Notice

Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 1.1. Overview
• 1.2. Terminology
• 2. Rules
• 3. Security Considerations
• 3.1. Reuse of PRECIS
• 3.2. Reuse of Unicode
• 3.3. Visually Similar Characters
• 4. IANA Considerations
• 5. References
• 5.1. Normative References
• 5.2. Informative References
• Author's Address

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

5.2. Informative References

Author's Address