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Saint-Andre 3 Internet-Draft Filament 4 Obsoletes: 7700 (if approved) April 5, 2016 5 Intended status: Standards Track 6 Expires: October 7, 2016 8 Preparation, Enforcement, and Comparison of Internationalized Strings 9 Representing Nicknames 10 draft-ietf-precis-7700bis-00 12 Abstract 14 This document describes methods for handling Unicode strings 15 representing memorable, human-friendly names (called "nicknames", 16 "display names", or "petnames") for people, devices, accounts, 17 websites, and other entities. This document obsoletes RFC 7700. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on October 7, 2016. 36 Copyright Notice 38 Copyright (c) 2016 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 2 55 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Nickname Profile . . . . . . . . . . . . . . . . . . . . . . 3 57 2.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 4 59 2.3. Enforcement . . . . . . . . . . . . . . . . . . . . . . . 5 60 2.4. Comparison . . . . . . . . . . . . . . . . . . . . . . . 5 61 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5 62 4. Use in Application Protocols . . . . . . . . . . . . . . . . 6 63 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 64 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 65 6.1. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 8 66 6.2. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 8 67 6.3. Visually Similar Characters . . . . . . . . . . . . . . . 8 68 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 69 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 70 7.2. Informative References . . . . . . . . . . . . . . . . . 9 71 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10 72 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 74 1. Introduction 76 1.1. Overview 78 A number of technologies and applications provide the ability for a 79 person to choose a memorable, human-friendly name in a communications 80 context, or to set such a name for another entity such as a device, 81 account, contact, or website. Such names are variously called 82 "nicknames" (e.g., in chat room applications), "display names" (e.g., 83 in Internet mail), or "petnames" (see [PETNAME-SYSTEMS]); for 84 consistency, these are all called "nicknames" in this document. 86 Nicknames are commonly supported in technologies for textual chat 87 rooms, e.g., Internet Relay Chat [RFC2811] and multi-party chat 88 technologies based on the Extensible Messaging and Presence Protocol 89 (XMPP) [RFC6120] [XEP-0045], the Message Session Relay Protocol 90 (MSRP) [RFC4975] [RFC7701], and Centralized Conferencing (XCON) 91 [RFC5239] [XCON-SYSTEM]. Recent chat room technologies also allow 92 internationalized nicknames because they support characters from 93 outside the ASCII range [RFC20], typically by means of the Unicode 94 character set [Unicode]. Although such nicknames tend to be used 95 primarily for display purposes, they are sometimes used for 96 programmatic purposes as well (e.g., kicking users or avoiding 97 nickname conflicts). 99 A similar usage enables a person to set their own preferred display 100 name or to set a preferred display name for another user (e.g., the 101 "display-name" construct in the Internet message format [RFC5322] and 102 [XEP-0172] in XMPP). 104 Memorable, human-friendly names are also used in contexts other than 105 personal messaging, such as names for devices (e.g., in a network 106 visualization application), websites (e.g., for bookmarks in a web 107 browser), accounts (e.g., in a web interface for a list of payees in 108 a bank account), people (e.g., in a contact list application), and 109 the like. 111 The rules specified in this document can be applied in all of the 112 foregoing contexts. 114 To increase the likelihood that memorable, human-friendly names will 115 work in ways that make sense for typical users throughout the world, 116 this document defines rules for preparing, enforcing, and comparing 117 internationalized nicknames. 119 1.2. Terminology 121 Many important terms used in this document are defined in [RFC7564], 122 [RFC6365], and [Unicode]. 124 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 125 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 126 "OPTIONAL" in this document are to be interpreted as described in 127 [RFC2119]. 129 2. Nickname Profile 131 2.1. Rules 133 The following rules apply within the Nickname profile of the PRECIS 134 FreeformClass. 136 1. Width Mapping Rule: There is no width-mapping rule (such a rule 137 is not necessary because width mapping is performed as part of 138 normalization using Normalization Form KC (NFKC) as specified 139 below). 141 2. Additional Mapping Rule: The additional mapping rule consists of 142 the following sub-rules. 144 1. Any instances of non-ASCII space MUST be mapped to ASCII 145 space (U+0020); a non-ASCII space is any Unicode code point 146 having a general category of "Zs", naturally with the 147 exception of U+0020. 149 2. Any instances of the ASCII space character at the beginning 150 or end of a nickname MUST be removed (e.g., "stpeter " is 151 mapped to "stpeter"). 153 3. Interior sequences of more than one ASCII space character 154 MUST be mapped to a single ASCII space character (e.g., 155 "St Peter" is mapped to "St Peter"). 157 3. Case Mapping Rule: Unicode Default Case Folding MUST be applied, 158 as defined in the Unicode Standard [Unicode] (at the time of this 159 writing, the algorithm is specified in Chapter 3 of 160 [Unicode7.0]). In applications that prohibit conflicting 161 nicknames, this rule helps to reduce the possibility of confusion 162 by ensuring that nicknames differing only by case (e.g., 163 "stpeter" vs. "StPeter") would not be presented to a human user 164 at the same time. 166 4. Normalization Rule: The string MUST be normalized using Unicode 167 NFKC. Because NFKC is more "aggressive" in finding matches than 168 other normalization forms (in the terminology of Unicode, it 169 performs both canonical and compatibility decomposition before 170 recomposing code points), this rule helps to reduce the 171 possibility of confusion by increasing the number of characters 172 that would match (e.g., U+2163 ROMAN NUMERAL FOUR would match the 173 combination of U+0049 LATIN CAPITAL LETTER I and U+0056 LATIN 174 CAPITAL LETTER V). 176 5. Directionality Rule: There is no directionality rule. The "Bidi 177 Rule" (defined in [RFC5893]) and similar rules are unnecessary 178 and inapplicable to nicknames, because it is perfectly acceptable 179 for a given nickname to be presented differently in different 180 layout systems (e.g., a user interface that is configured to 181 handle primarily a right-to-left script versus an interface that 182 is configured to handle primarily a left-to-right script), as 183 long as the presentation is consistent in any given layout 184 system. 186 2.2. Preparation 188 An entity that prepares a string for subsequent enforcement according 189 to this profile MUST ensure that the string consists only of Unicode 190 code points that conform to the FreeformClass string class defined in 192 [RFC7564]. In addition, the entity MUST ensure that the string is 193 encoded as UTF-8 [RFC3629]. 195 2.3. Enforcement 197 An entity that performs enforcement according to this profile MUST 198 prepare a string as described in Section 2.2 and MUST also apply the 199 following rules specified in Section 2.1 in the order shown: 201 1. Additional Mapping Rule 202 2. Normalization Rule 203 3. Directionality Rule 205 After all of the foregoing rules have been enforced, the entity MUST 206 ensure that the nickname is not zero bytes in length (this is done 207 after enforcing the rules to prevent applications from mistakenly 208 omitting a nickname entirely, because when internationalized 209 characters are accepted, a non-empty sequence of characters can 210 result in a zero-length nickname after canonicalization). 212 2.4. Comparison 214 An entity that performs comparison of two strings according to this 215 profile MUST prepare each string as specified in Section 2.2 and MUST 216 apply the following rules specified in Section 2.1 in the order 217 shown: 219 1. Additional Mapping Rule 220 2. Case Mapping Rule 221 3. Normalization Rule 222 4. Directionality Rule 224 The two strings are to be considered equivalent if they are an exact 225 octet-for-octet match (sometimes called "bit-string identity"). 227 3. Examples 229 The following examples illustrate a small number of nicknames that 230 are consistent with the format defined above, along with the output 231 string resulting from application of the PRECIS rules (note that the 232 characters < and > are used to delineate the actual nickname and are 233 not part of the nickname strings). 235 Table 1: A Sample of Legal Nicknames 237 +---------------------------+-----------------------------------+ 238 | # | Nickname | Output for Comparison | 239 +---------------------------+-----------------------------------+ 240 | 1 | | | 241 +---------------------------+-----------------------------------+ 242 | 2 | | | 243 +---------------------------+-----------------------------------+ 244 | 3 | | | 245 +---------------------------+-----------------------------------+ 246 | 4 | | | 247 +---------------------------+-----------------------------------+ 248 | 5 | <Σ> | GREEK SMALL LETTER SIGMA (U+03C3) | 249 +---------------------------+-----------------------------------+ 250 | 6 | <σ> | GREEK SMALL LETTER SIGMA (U+03C3) | 251 +---------------------------+-----------------------------------+ 252 | 7 | <ς> | GREEK SMALL LETTER SIGMA (U+03C3) | 253 +---------------------------+-----------------------------------+ 254 | 8 | <♚> | BLACK CHESS KING (U+265A) | 255 +---------------------------+-----------------------------------+ 256 | 9 | | | 257 +---------------------------+-----------------------------------+ 259 Regarding examples 5, 6, and 7: applying Unicode Default Case Folding 260 to GREEK CAPITAL LETTER SIGMA (U+03A3) results in GREEK SMALL LETTER 261 SIGMA (U+03C3), and the same is true of GREEK SMALL LETTER FINAL 262 SIGMA (U+03C2); therefore, the comparison operation defined in 263 Section 2.4 would result in matching of the nicknames in examples 5, 264 6, and 7. Regarding example 8: symbol characters such as BLACK CHESS 265 KING (U+265A) are allowed by the PRECIS FreeformClass and thus can be 266 used in nicknames. Regarding example 9: applying Unicode Default 267 Case Folding to ROMAN NUMERAL FOUR (U+2163) results in SMALL ROMAN 268 NUMERAL FOUR (U+2173), and applying NFKC to SMALL ROMAN NUMERAL FOUR 269 (U+2173) results in LATIN SMALL LETTER I (U+0069) LATIN SMALL LETTER 270 V (U+0086). 272 4. Use in Application Protocols 274 This specification defines only the PRECIS-based rules for handling 275 of nickname strings. It is the responsibility of an application 276 protocol (e.g., MSRP, XCON, or XMPP) or application definition to 277 specify the protocol slots in which nickname strings can appear, the 278 entities that are expected to enforce the rules governing nickname 279 strings, and when in protocol processing or interface handling the 280 rules need to be enforced. See Section 6 of [RFC7564] for guidelines 281 about using PRECIS profiles in applications. 283 Above and beyond the PRECIS-based rules specified here, application 284 protocols can also define application-specific rules governing 285 nickname strings (rules regarding the minimum or maximum length of 286 nicknames, further restrictions on allowable characters or character 287 ranges, safeguards to mitigate the effects of visually similar 288 characters, etc.). 290 Naturally, application protocols can also specify rules governing the 291 actual use of nicknames in applications (reserved nicknames, 292 authorization requirements for using nicknames, whether certain 293 nicknames can be prohibited, handling of duplicates, the relationship 294 between nicknames and underlying identifiers such as SIP URIs or 295 Jabber IDs, etc.). 297 Entities that enforce the rules specified in this document are 298 encouraged to be liberal in what they accept by following this 299 procedure: 301 1. Where possible, map characters (e.g, through width mapping, 302 additional mapping, case mapping, or normalization) and accept 303 the mapped string. 305 2. If mapping is not possible (e.g., because a character is 306 disallowed in the FreeformClass), reject the string. 308 5. IANA Considerations 310 The IANA shall add the following entry to the PRECIS Profiles 311 Registry: 313 Name: Nickname 315 Base Class: FreeformClass 317 Applicability: Nicknames in messaging and text conferencing 318 technologies; petnames for devices, accounts, and people; and 319 other uses of nicknames or petnames. 321 Replaces: None 323 Width Mapping Rule: None (handled via NFKC) 325 Additional Mapping Rule: Map non-ASCII space characters to ASCII 326 space, strip leading and trailing space characters, map interior 327 sequences of multiple space characters to a single ASCII space. 329 Case Mapping Rule: Map uppercase and titlecase characters to 330 lowercase using Unicode Default Case Folding. 332 Normalization Rule: NFKC 334 Directionality Rule: None 336 Enforcement: To be specified by applications. 338 Specification: RFC 7700 (this document) 340 6. Security Considerations 342 6.1. Reuse of PRECIS 344 The security considerations described in [RFC7564] apply to the 345 FreeformClass string class used in this document for nicknames. 347 6.2. Reuse of Unicode 349 The security considerations described in [UTS39] apply to the use of 350 Unicode characters in nicknames. 352 6.3. Visually Similar Characters 354 [RFC7564] describes some of the security considerations related to 355 visually similar characters, also called "confusable characters" or 356 "confusables". 358 Although the mapping rules defined in Section 2 of this document are 359 designed, in part, to reduce the possibility of confusion about 360 nicknames, this document does not provide more-detailed 361 recommendations regarding the handling of visually similar 362 characters, such as those provided in [UTS39]. 364 7. References 366 7.1. Normative References 368 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 369 Requirement Levels", BCP 14, RFC 2119, March 1997. 371 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 372 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 373 2003, . 375 [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts 376 for Internationalized Domain Names for Applications 377 (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010, 378 . 380 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 381 Internationalization in the IETF", BCP 166, RFC 6365, DOI 382 10.17487/RFC6365, September 2011, 383 . 385 [RFC7564] Saint-Andre, P. and M. Blanchet, "PRECIS Framework: 386 Preparation, Enforcement, and Comparison of 387 Internationalized Strings in Application Protocols", RFC 388 7564, DOI 10.17487/RFC7564, May 2015, 389 . 391 [UTS39] The Unicode Consortium, "Unicode Technical Standard #39: 392 Unicode Security Mechanisms", November 2013, 393 . 395 [Unicode7.0] 396 The Unicode Consortium, "The Unicode Standard, Version 397 7.0.0", 2014, 398 . 400 [Unicode] The Unicode Consortium, "The Unicode Standard", 401 . 403 7.2. Informative References 405 [PETNAME-SYSTEMS] 406 Stiegler, M., "An Introduction to Petname Systems", 407 updated June 2012, February 2005, 408 . 411 [RFC20] Cerf, V., "ASCII format for network interchange", STD 80, 412 RFC 20, DOI 10.17487/RFC0020, October 1969, 413 . 415 [RFC2811] Kalt, C., "Internet Relay Chat: Channel Management", RFC 416 2811, DOI 10.17487/RFC2811, April 2000, 417 . 419 [RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed., 420 "The Message Session Relay Protocol (MSRP)", RFC 4975, DOI 421 10.17487/RFC4975, September 2007, 422 . 424 [RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for 425 Centralized Conferencing", RFC 5239, DOI 10.17487/RFC5239, 426 June 2008, . 428 [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 429 10.17487/RFC5322, October 2008, 430 . 432 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 433 Protocol (XMPP): Core", RFC 6120, March 2011. 435 [RFC7701] Niemi, A., Garcia-Martin, M., and G. Sandbakken, "Multi- 436 party Chat Using the Message Session Relay Protocol 437 (MSRP)", RFC 7701, DOI 10.17487/RFC7701, December 2015, 438 . 440 [XCON-SYSTEM] 441 Barnes, M., Boulton, C., and S. Loreto, "Chatrooms within 442 a Centralized Conferencing (XCON) System", Work in 443 Progress, draft-boulton-xcon-session-chat-08, July 2012. 445 [XEP-0045] 446 Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February 447 2012, . 449 [XEP-0172] 450 Saint-Andre, P. and V. Mercier, "User Nickname", XSF XEP 451 0172, March 2012, 452 . 454 Appendix A. Acknowledgements 456 Thanks to Kim Alvefur, Mary Barnes, Ben Campbell, Dave Cridland, 457 Miguel Garcia, Salvatore Loreto, Enrico Marocco, Matt Miller, and 458 Yoshiro YONEYA for their reviews and comments. 460 Paul Kyzivat and Melinda Shore reviewed the document for the General 461 Area Review Team and Operations Directorate, respectively. 463 During IESG review, Ben Campbell and Kathleen Moriarty provided 464 comments that led to further improvements. 466 Thanks to Matt Miller as Document Shepherd, Pete Resnick and Andrew 467 Sullivan as IANA Designated Experts, Marc Blanchet and Alexey 468 Melnikov as working group Chairs, and Barry Leiba as Area Director. 470 The author wishes to acknowledge Cisco Systems, Inc., for employing 471 him during his work on earlier draft versions of this document. 473 Author's Address 475 Peter Saint-Andre 476 Filament 478 Email: peter@filament.com 479 URI: https://filament.com/