PRECIS P. Saint-Andre Internet-Draft Filament Obsoletes: 7700 (if approved) May 1, 2017 Intended status: Standards Track Expires: November 2, 2017 Preparation, Enforcement, and Comparison of Internationalized Strings Representing Nicknames draft-ietf-precis-7700bis-07 Abstract This document describes methods for handling Unicode strings representing memorable, human-friendly names (called "nicknames", "display names", or "petnames") for people, devices, accounts, websites, and other entities. This document obsoletes RFC 7700. 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on November 2, 2017. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Saint-Andre Expires November 2, 2017 [Page 1] Internet-Draft PRECIS: Nickname May 2017 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Nickname Profile . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Enforcement . . . . . . . . . . . . . . . . . . . . . . . 5 2.4. Comparison . . . . . . . . . . . . . . . . . . . . . . . 5 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Use in Application Protocols . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6.1. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 8 6.2. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 8 6.3. Visually Similar Characters . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.1. Normative References . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . 9 Appendix A. Changes from RFC 7700 . . . . . . . . . . . . . . . 10 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction 1.1. Overview A number of technologies and applications provide the ability for a person to choose a memorable, human-friendly name in a communications context, or to set such a name for another entity such as a device, account, contact, or website. Such names are variously called "nicknames" (e.g., in chat room applications), "display names" (e.g., in Internet mail), or "petnames" (see [PETNAME-SYSTEMS]); for consistency, these are all called "nicknames" in this document. Nicknames are commonly supported in technologies for textual chat rooms, e.g., Internet Relay Chat [RFC2811] and multi-party chat technologies based on the Extensible Messaging and Presence Protocol (XMPP) [RFC6120] [XEP-0045], the Message Session Relay Protocol (MSRP) [RFC4975] [RFC7701], and Centralized Conferencing (XCON) [RFC5239] [XCON-SYSTEM]. Recent chat room technologies also allow internationalized nicknames because they support code points from outside the ASCII range [RFC20], typically by means of the Unicode coded character set [Unicode]. Although such nicknames tend to be Saint-Andre Expires November 2, 2017 [Page 2] Internet-Draft PRECIS: Nickname May 2017 used primarily for display purposes, they are sometimes used for programmatic purposes as well (e.g., kicking users or avoiding nickname conflicts). A similar usage enables a person to set their own preferred display name or to set a preferred display name for another user (e.g., the "display-name" construct in the Internet message format [RFC5322] and [XEP-0172] in XMPP). Memorable, human-friendly names are also used in contexts other than personal messaging, such as names for devices (e.g., in a network visualization application), websites (e.g., for bookmarks in a web browser), accounts (e.g., in a web interface for a list of payees in a bank account), people (e.g., in a contact list application), and the like. The rules specified in this document can be applied in all of the foregoing contexts. To increase the likelihood that memorable, human-friendly names will work in ways that make sense for typical users throughout the world, this document defines rules for preparing, enforcing, and comparing internationalized nicknames. 1.2. Terminology Many important terms used in this document are defined in [RFC7564], [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 [RFC2119]. 2. Nickname Profile 2.1. Rules The following rules apply within the Nickname profile of the PRECIS FreeformClass. 1. Width Mapping Rule: There is no width-mapping rule (such a rule is not necessary because width mapping is performed as part of normalization using Normalization Form KC (NFKC) as specified below). 2. Additional Mapping Rule: The additional mapping rule consists of the following sub-rules. Saint-Andre Expires November 2, 2017 [Page 3] Internet-Draft PRECIS: Nickname May 2017 1. Map any instances of non-ASCII space to ASCII space (U+0020); a non-ASCII space is any Unicode code point having a general category of "Zs", naturally with the exception of U+0020. (The inclusion of only ASCII space prevents confusion with various non-ASCII space code points, many of which are difficult to reproduce across different input methods.) 2. Remove any instances of the ASCII space character at the beginning or end of a nickname (e.g., "stpeter " is mapped to "stpeter"). 3. Map interior sequences of more than one ASCII space character to a single ASCII space character (e.g., "St Peter" is mapped to "St Peter"). 3. Case Mapping Rule: Apply the Unicode toLower() operation, as defined in the Unicode Standard [Unicode]. 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 presented to a human user at the same time. (As explained below, this is typically appropriate only for comparison, not for enforcement.) 4. Normalization Rule: Apply Unicode Normalization Form KC. 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 code points 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). 5. Directionality Rule: There is no directionality rule. The "Bidi Rule" (defined in [RFC5893]) and similar rules are unnecessary and inapplicable to nicknames, because it is perfectly acceptable for a given nickname to be presented differently in different layout systems (e.g., a user interface that is configured to handle primarily a right-to-left script versus an interface that is configured to handle primarily a left-to-right script), as long as the presentation is consistent in any given layout system. Saint-Andre Expires November 2, 2017 [Page 4] Internet-Draft PRECIS: Nickname May 2017 2.2. Preparation An entity that prepares a string for subsequent enforcement according to this profile MUST ensure that the string consists only of Unicode code points that conform to the FreeformClass string class defined in [RFC7564]. 2.3. Enforcement An entity that performs enforcement according to this profile MUST prepare a string as described in Section 2.2 and MUST also apply the following rules specified in Section 2.1 in the order shown: 1. Additional Mapping Rule 2. Normalization Rule Note: An entity SHOULD NOT apply the Case Mapping Rule during enforcement, because typically it is appropriate only during comparison. After all of the foregoing rules have been enforced, the entity MUST ensure that the nickname is not zero bytes in length (this is done after enforcing the rules to prevent applications from mistakenly omitting a nickname entirely, because when internationalized strings are accepted, a non-empty sequence of characters can result in a zero-length nickname after canonicalization). 2.4. Comparison An entity that performs comparison of two strings according to this profile MUST prepare each string as specified in Section 2.2 and MUST apply the following rules specified in Section 2.1 in the order shown: 1. Additional Mapping Rule 2. Case Mapping Rule 3. Normalization Rule The two strings are to be considered equivalent if and only if they are an exact octet-for-octet match (sometimes called "bit-string identity"). 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 (note that the Saint-Andre Expires November 2, 2017 [Page 5] Internet-Draft PRECIS: Nickname May 2017 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 | | | +---------------------------+-----------------------------------+ | 2 | | | +---------------------------+-----------------------------------+ | 3 | | | +---------------------------+-----------------------------------+ | 4 | | | +---------------------------+-----------------------------------+ | 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) | +---------------------------+-----------------------------------+ | 9 | | | +---------------------------+-----------------------------------+ Regarding examples 5, 6, and 7: applying the Unicode toLower() operation to GREEK CAPITAL LETTER SIGMA (U+03A3) results in GREEK SMALL LETTER SIGMA (U+03C3), however the toLower() operation does not modify GREEK SMALL LETTER FINAL SIGMA (U+03C2); therefore, the comparison operation defined in Section 2.4 would result in matching of the nicknames in examples 5 and 6 but not the nicknames in examples 5 and 7 or 6 and 7. 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. Regarding example 9: applying the Unicode toLower() operation to ROMAN NUMERAL FOUR (U+2163) results in SMALL ROMAN NUMERAL FOUR (U+2173), and applying NFKC to SMALL ROMAN NUMERAL FOUR (U+2173) results in LATIN SMALL LETTER I (U+0069) LATIN SMALL LETTER V (U+0086). 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) or application definition to specify the protocol slots in which nickname strings can appear, the Saint-Andre Expires November 2, 2017 [Page 6] Internet-Draft PRECIS: Nickname May 2017 entities that are expected to enforce the rules governing nickname strings, and when in protocol processing or interface handling the rules need to be enforced. See Section 6 of [RFC7564] for guidelines about using PRECIS profiles in applications. 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 code points 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 IDs, etc.). Entities that enforce the rules specified in this document are encouraged to be liberal in what they accept by following this procedure: 1. Where possible, map characters (e.g, through width mapping, additional mapping, case mapping, or normalization) and accept the mapped string. 2. If mapping is not possible (e.g., because a character is disallowed in the FreeformClass), reject the string. Implementation experience has shown that applying the rules for the Nickname profile is not an idempotent procedure for all code points. Therefore, implementations might need to apply the rules more than once to a nickname string. 5. IANA Considerations The IANA shall add the following entry to the PRECIS Profiles Registry: Name: Nickname Base Class: FreeformClass Applicability: Nicknames in messaging and text conferencing technologies; petnames for devices, accounts, and people; and other uses of nicknames or petnames. Saint-Andre Expires November 2, 2017 [Page 7] Internet-Draft PRECIS: Nickname May 2017 Replaces: None Width Mapping Rule: None (handled via NFKC) Additional Mapping Rule: 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. Case Mapping Rule: Map uppercase and titlecase code points to lowercase using the Unicode toLower() operation. Normalization Rule: NFKC Directionality Rule: None Enforcement: To be specified by applications. Specification: RFC 7700 (this document) 6. Security Considerations 6.1. Reuse of PRECIS The security considerations described in [RFC7564] 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 code points in nicknames. 6.3. Visually Similar Characters [RFC7564] describes some of the security considerations related to visually similar characters, also called "confusable characters" or "confusables". Although the mapping rules defined in 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 Saint-Andre Expires November 2, 2017 [Page 8] Internet-Draft PRECIS: Nickname May 2017 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts for Internationalized Domain Names for Applications (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010, . [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in Internationalization in the IETF", BCP 166, RFC 6365, DOI 10.17487/RFC6365, September 2011, . [RFC7564] Saint-Andre, P. and M. Blanchet, "PRECIS Framework: Preparation, Enforcement, and Comparison of Internationalized Strings in Application Protocols", RFC 7564, DOI 10.17487/RFC7564, May 2015, . [Unicode] The Unicode Consortium, "The Unicode Standard", . [UTS39] The Unicode Consortium, "Unicode Technical Standard #39: Unicode Security Mechanisms", November 2013, . 7.2. Informative References [Err4570] RFC Errata, "Erratum ID 4570", RFC 7700, . [PETNAME-SYSTEMS] Stiegler, M., "An Introduction to Petname Systems", updated June 2012, February 2005, . [RFC20] Cerf, V., "ASCII format for network interchange", STD 80, RFC 20, DOI 10.17487/RFC0020, October 1969, . [RFC2811] Kalt, C., "Internet Relay Chat: Channel Management", RFC 2811, DOI 10.17487/RFC2811, April 2000, . Saint-Andre Expires November 2, 2017 [Page 9] Internet-Draft PRECIS: Nickname May 2017 [RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed., "The Message Session Relay Protocol (MSRP)", RFC 4975, DOI 10.17487/RFC4975, September 2007, . [RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for Centralized Conferencing", RFC 5239, DOI 10.17487/RFC5239, June 2008, . [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008, . [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120, March 2011, . [RFC7700] Saint-Andre, P., "Preparation, Enforcement, and Comparison of Internationalized Strings Representing Nicknames", RFC 7700, DOI 10.17487/RFC7700, December 2015, . [RFC7701] Niemi, A., Garcia-Martin, M., and G. Sandbakken, "Multi- party Chat Using the Message Session Relay Protocol (MSRP)", RFC 7701, DOI 10.17487/RFC7701, December 2015, . [XCON-SYSTEM] Barnes, M., Boulton, C., and S. Loreto, "Chatrooms within a Centralized Conferencing (XCON) System", Work in Progress, draft-boulton-xcon-session-chat-08, July 2012. [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. Changes from RFC 7700 The following changes were made from [RFC7700]. o Addressed [Err4570] by removing the directionality rule and adding the normalization rule to Section 2.3. Saint-Andre Expires November 2, 2017 [Page 10] Internet-Draft PRECIS: Nickname May 2017 o In accordance with working group discussions and updates to [RFC7564], removed the use of the Unicode CaseFold() operation in favor of the Unicode toLower() operation. o Clarified several editorial matters. o Updated references. Appendix B. Acknowledgements Thanks to William Fisher for his implementation feedback, especially regarding idempotence. Thanks to Sam Whited for his feedback and for submitting [Err4570]. See [RFC7700] for acknowledgements related to the specification that this document supersedes. Author's Address Peter Saint-Andre Filament P.O. Box 787 Parker, CO 80134 USA Phone: +1 720 256 6756 Email: peter@filament.com URI: https://filament.com/ Saint-Andre Expires November 2, 2017 [Page 11]