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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PRECIS P. Saint-Andre 3 Internet-Draft Filament 4 Obsoletes: 7700 (if approved) June 27, 2017 5 Intended status: Standards Track 6 Expires: December 29, 2017 8 Preparation, Enforcement, and Comparison of Internationalized Strings 9 Representing Nicknames 10 draft-ietf-precis-7700bis-08 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 December 29, 2017. 36 Copyright Notice 38 Copyright (c) 2017 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 . . . . . . . . . . . . . . . . . . . . . . . 5 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 . . . . . . . . . . . . . . . . . . 9 70 7.2. Informative References . . . . . . . . . . . . . . . . . 9 71 Appendix A. Changes from RFC 7700 . . . . . . . . . . . . . . . 11 72 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 11 73 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 75 1. Introduction 77 1.1. Overview 79 A number of technologies and applications provide the ability for a 80 person to choose a memorable, human-friendly name in a communications 81 context, or to set such a name for another entity such as a device, 82 account, contact, or website. Such names are variously called 83 "nicknames" (e.g., in chat room applications), "display names" (e.g., 84 in Internet mail), or "petnames" (see [PETNAME-SYSTEMS]); for 85 consistency, these are all called "nicknames" in this document. 87 Nicknames are commonly supported in technologies for textual chat 88 rooms, e.g., Internet Relay Chat [RFC2811] and multi-party chat 89 technologies based on the Extensible Messaging and Presence Protocol 90 (XMPP) [RFC6120] [XEP-0045], the Message Session Relay Protocol 91 (MSRP) [RFC4975] [RFC7701], and Centralized Conferencing (XCON) 92 [RFC5239] [XCON-SYSTEM]. Recent chat room technologies also allow 93 internationalized nicknames because they support code points from 94 outside the ASCII range [RFC20], typically by means of the Unicode 95 coded character set [Unicode]. Although such nicknames tend to be 96 used primarily for display purposes, they are sometimes used for 97 programmatic purposes as well (e.g., kicking users or avoiding 98 nickname conflicts). 100 A similar usage enables a person to set their own preferred display 101 name or to set a preferred display name for another user (e.g., the 102 "display-name" construct in the Internet message format [RFC5322] and 103 [XEP-0172] in XMPP). 105 Memorable, human-friendly names are also used in contexts other than 106 personal messaging, such as names for devices (e.g., in a network 107 visualization application), websites (e.g., for bookmarks in a web 108 browser), accounts (e.g., in a web interface for a list of payees in 109 a bank account), people (e.g., in a contact list application), and 110 the like. 112 The rules specified in this document can be applied in all of the 113 foregoing contexts. 115 To increase the likelihood that memorable, human-friendly names will 116 work in ways that make sense for typical users throughout the world, 117 this document defines rules for preparing, enforcing, and comparing 118 internationalized nicknames. 120 1.2. Terminology 122 Many important terms used in this document are defined in 123 [I-D.ietf-precis-7564bis], [RFC6365], and [Unicode]. 125 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 126 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 127 "OPTIONAL" in this document are to be interpreted as described in 128 [RFC2119]. 130 2. Nickname Profile 132 2.1. Rules 134 The following rules apply within the Nickname profile of the PRECIS 135 FreeformClass defined in the PRECIS framework specification 136 [I-D.ietf-precis-7564bis]. 138 1. Width Mapping Rule: There is no width-mapping rule (such a rule 139 is not necessary because width mapping is performed as part of 140 normalization using Normalization Form KC (NFKC) as specified 141 below). 143 2. Additional Mapping Rule: The additional mapping rule consists of 144 the following sub-rules. 146 1. Map any instances of non-ASCII space to ASCII space (U+0020); 147 a non-ASCII space is any Unicode code point having a general 148 category of "Zs", naturally with the exception of U+0020. 149 (The inclusion of only ASCII space prevents confusion with 150 various non-ASCII space code points, many of which are 151 difficult to reproduce across different input methods.) 153 2. Remove any instances of the ASCII space character at the 154 beginning or end of a nickname (e.g., "stpeter " is mapped to 155 "stpeter"). 157 3. Map interior sequences of more than one ASCII space character 158 to a single ASCII space character (e.g., "St Peter" is 159 mapped to "St Peter"). 161 3. Case Mapping Rule: Apply the Unicode toLower() operation, as 162 defined in the Unicode Standard [Unicode]. In applications that 163 prohibit conflicting nicknames, this rule helps to reduce the 164 possibility of confusion by ensuring that nicknames differing 165 only by case (e.g., "stpeter" vs. "StPeter") would not be 166 presented to a human user at the same time. (As explained below, 167 this is typically appropriate only for comparison, not for 168 enforcement.) 170 4. Normalization Rule: Apply Unicode Normalization Form KC. Because 171 NFKC is more "aggressive" in finding matches than other 172 normalization forms (in the terminology of Unicode, it performs 173 both canonical and compatibility decomposition before recomposing 174 code points), this rule helps to reduce the possibility of 175 confusion by increasing the number of code points that would 176 match (e.g., U+2163 ROMAN NUMERAL FOUR would match the 177 combination of U+0049 LATIN CAPITAL LETTER I and U+0056 LATIN 178 CAPITAL LETTER V). 180 5. Directionality Rule: There is no directionality rule. The "Bidi 181 Rule" (defined in [RFC5893]) and similar rules are unnecessary 182 and inapplicable to nicknames, because it is perfectly acceptable 183 for a given nickname to be presented differently in different 184 layout systems (e.g., a user interface that is configured to 185 handle primarily a right-to-left script versus an interface that 186 is configured to handle primarily a left-to-right script), as 187 long as the presentation is consistent in any given layout 188 system. 190 2.2. Preparation 192 An entity that prepares a string for subsequent enforcement according 193 to this profile MUST ensure that the string consists only of Unicode 194 code points that conform to the FreeformClass string class defined in 195 [I-D.ietf-precis-7564bis]. 197 2.3. Enforcement 199 An entity that performs enforcement according to this profile MUST 200 prepare a string as described in Section 2.2 and MUST also apply the 201 following rules specified in Section 2.1 in the order shown: 203 1. Additional Mapping Rule 204 2. Normalization Rule 206 Note: An entity SHOULD apply the Case Mapping Rule only during 207 comparison. 209 After all of the foregoing rules have been enforced, the entity MUST 210 ensure that the nickname is not zero bytes in length (this is done 211 after enforcing the rules to prevent applications from mistakenly 212 omitting a nickname entirely, because when internationalized strings 213 are accepted, a non-empty sequence of characters can result in a 214 zero-length nickname after canonicalization). 216 2.4. Comparison 218 An entity that performs comparison of two strings according to this 219 profile MUST prepare each string as specified in Section 2.2 and MUST 220 apply the following rules specified in Section 2.1 in the order 221 shown: 223 1. Additional Mapping Rule 224 2. Case Mapping Rule 225 3. Normalization Rule 227 The two strings are to be considered equivalent if and only if they 228 are an exact octet-for-octet match (sometimes called "bit-string 229 identity"). 231 3. Examples 233 The following examples illustrate a small number of nicknames that 234 are consistent with the format defined above, along with the output 235 string resulting from application of the PRECIS rules (note that the 236 characters < and > are used to delineate the actual nickname and are 237 not part of the nickname strings). 239 Table 1: A Sample of Legal Nicknames 241 +---------------------------+-----------------------------------+ 242 | # | Nickname | Output for Comparison | 243 +---------------------------+-----------------------------------+ 244 | 1 | | | 245 +---------------------------+-----------------------------------+ 246 | 2 | | | 247 +---------------------------+-----------------------------------+ 248 | 3 | | | 249 +---------------------------+-----------------------------------+ 250 | 4 | | | 251 +---------------------------+-----------------------------------+ 252 | 5 | <Σ> | GREEK SMALL LETTER SIGMA (U+03C3) | 253 +---------------------------+-----------------------------------+ 254 | 6 | <σ> | GREEK SMALL LETTER SIGMA (U+03C3) | 255 +---------------------------+-----------------------------------+ 256 | 7 | <ς> | GREEK SMALL LETTER FINAL SIGMA | 257 | | | (U+03C2) | 258 +---------------------------+-----------------------------------+ 259 | 8 | <♚> | BLACK CHESS KING (U+265A) | 260 +---------------------------+-----------------------------------+ 261 | 9 | | | 262 +---------------------------+-----------------------------------+ 264 Regarding examples 5, 6, and 7: applying the Unicode toLower() 265 operation to GREEK CAPITAL LETTER SIGMA (U+03A3) results in GREEK 266 SMALL LETTER SIGMA (U+03C3), however the toLower() operation does not 267 modify GREEK SMALL LETTER FINAL SIGMA (U+03C2); therefore, the 268 comparison operation defined in Section 2.4 would result in matching 269 of the nicknames in examples 5 and 6 but not the nicknames in 270 examples 5 and 7 or 6 and 7. Regarding example 8: symbol characters 271 such as BLACK CHESS KING (U+265A) are allowed by the PRECIS 272 FreeformClass and thus can be used in nicknames. Regarding example 273 9: applying the Unicode toLower() operation to ROMAN NUMERAL FOUR 274 (U+2163) results in SMALL ROMAN NUMERAL FOUR (U+2173), and applying 275 NFKC to SMALL ROMAN NUMERAL FOUR (U+2173) results in LATIN SMALL 276 LETTER I (U+0069) LATIN SMALL LETTER V (U+0086). 278 4. Use in Application Protocols 280 This specification defines only the PRECIS-based rules for handling 281 of nickname strings. It is the responsibility of an application 282 protocol (e.g., MSRP, XCON, or XMPP) or application definition to 283 specify the protocol slots in which nickname strings can appear, the 284 entities that are expected to enforce the rules governing nickname 285 strings, and when in protocol processing or interface handling the 286 rules need to be enforced. See Section 6 of 288 [I-D.ietf-precis-7564bis] for guidelines about using PRECIS profiles 289 in applications. 291 Above and beyond the PRECIS-based rules specified here, application 292 protocols can also define application-specific rules governing 293 nickname strings (rules regarding the minimum or maximum length of 294 nicknames, further restrictions on allowable code points or character 295 ranges, safeguards to mitigate the effects of visually similar 296 characters, etc.). 298 Naturally, application protocols can also specify rules governing the 299 actual use of nicknames in applications (reserved nicknames, 300 authorization requirements for using nicknames, whether certain 301 nicknames can be prohibited, handling of duplicates, the relationship 302 between nicknames and underlying identifiers such as SIP URIs or 303 Jabber IDs, etc.). 305 Entities that enforce the rules specified in this document are 306 encouraged to be liberal in what they accept by following this 307 procedure: 309 1. Where possible, map characters (e.g, through width mapping, 310 additional mapping, case mapping, or normalization) and accept 311 the mapped string. 313 2. If mapping is not possible (e.g., because a character is 314 disallowed in the FreeformClass), reject the string. 316 Implementation experience has shown that applying the rules for the 317 Nickname profile is not an idempotent procedure for all code points. 318 Therefore, implementations might need to apply the rules more than 319 once to a nickname string. 321 5. IANA Considerations 323 The IANA shall add the following entry to the PRECIS Profiles 324 Registry: 326 Name: Nickname 328 Base Class: FreeformClass 330 Applicability: Nicknames in messaging and text conferencing 331 technologies; petnames for devices, accounts, and people; and 332 other uses of nicknames or petnames. 334 Replaces: None 335 Width Mapping Rule: None (handled via NFKC) 337 Additional Mapping Rule: Map non-ASCII space characters to ASCII 338 space, strip leading and trailing space characters, map interior 339 sequences of multiple space characters to a single ASCII space. 341 Case Mapping Rule: Map uppercase and titlecase code points to 342 lowercase using the Unicode toLower() operation. 344 Normalization Rule: NFKC 346 Directionality Rule: None 348 Enforcement: To be specified by applications. 350 Specification: [[this document]] 352 6. Security Considerations 354 6.1. Reuse of PRECIS 356 The security considerations described in [I-D.ietf-precis-7564bis] 357 apply to the FreeformClass string class used in this document for 358 nicknames. 360 6.2. Reuse of Unicode 362 The security considerations described in [UTS39] apply to the use of 363 Unicode code points in nicknames. 365 6.3. Visually Similar Characters 367 [I-D.ietf-precis-7564bis] describes some of the security 368 considerations related to visually similar characters, also called 369 "confusable characters" or "confusables", and provides some examples 370 of such characters. 372 Although the mapping rules defined in Section 2 of this document are 373 designed, in part, to reduce the possibility of confusion about 374 nicknames, this document does not provide more-detailed 375 recommendations regarding the handling of visually similar 376 characters, such as those provided in [UTS39]. 378 7. References 379 7.1. Normative References 381 [I-D.ietf-precis-7564bis] 382 Saint-Andre, P. and M. Blanchet, "PRECIS Framework: 383 Preparation, Enforcement, and Comparison of 384 Internationalized Strings in Application Protocols", 385 draft-ietf-precis-7564bis-08 (work in progress), June 386 2017. 388 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 389 Requirement Levels", BCP 14, RFC 2119, 390 DOI 10.17487/RFC2119, March 1997, 391 . 393 [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts 394 for Internationalized Domain Names for Applications 395 (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010, 396 . 398 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 399 Internationalization in the IETF", BCP 166, RFC 6365, 400 DOI 10.17487/RFC6365, September 2011, 401 . 403 [Unicode] The Unicode Consortium, "The Unicode Standard", 404 . 406 [UTS39] The Unicode Consortium, "Unicode Technical Standard #39: 407 Unicode Security Mechanisms", November 2013, 408 . 410 7.2. Informative References 412 [Err4570] RFC Errata, "Erratum ID 4570", RFC 7700, 413 . 415 [PETNAME-SYSTEMS] 416 Stiegler, M., "An Introduction to Petname Systems", 417 updated June 2012, February 2005, 418 . 421 [RFC20] Cerf, V., "ASCII format for network interchange", STD 80, 422 RFC 20, DOI 10.17487/RFC0020, October 1969, 423 . 425 [RFC2811] Kalt, C., "Internet Relay Chat: Channel Management", 426 RFC 2811, DOI 10.17487/RFC2811, April 2000, 427 . 429 [RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed., 430 "The Message Session Relay Protocol (MSRP)", RFC 4975, 431 DOI 10.17487/RFC4975, September 2007, 432 . 434 [RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for 435 Centralized Conferencing", RFC 5239, DOI 10.17487/RFC5239, 436 June 2008, . 438 [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, 439 DOI 10.17487/RFC5322, October 2008, 440 . 442 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 443 Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120, 444 March 2011, . 446 [RFC7700] Saint-Andre, P., "Preparation, Enforcement, and Comparison 447 of Internationalized Strings Representing Nicknames", 448 RFC 7700, DOI 10.17487/RFC7700, December 2015, 449 . 451 [RFC7701] Niemi, A., Garcia-Martin, M., and G. Sandbakken, "Multi- 452 party Chat Using the Message Session Relay Protocol 453 (MSRP)", RFC 7701, DOI 10.17487/RFC7701, December 2015, 454 . 456 [XCON-SYSTEM] 457 Barnes, M., Boulton, C., and S. Loreto, "Chatrooms within 458 a Centralized Conferencing (XCON) System", Work in 459 Progress, draft-boulton-xcon-session-chat-08, July 2012. 461 [XEP-0045] 462 Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February 463 2012, . 465 [XEP-0172] 466 Saint-Andre, P. and V. Mercier, "User Nickname", XSF 467 XEP 0172, March 2012, 468 . 470 Appendix A. Changes from RFC 7700 472 The following changes were made from [RFC7700]. 474 o Addressed [Err4570] by removing the directionality rule and adding 475 the normalization rule to Section 2.3. 477 o In accordance with working group discussions and updates to 478 [I-D.ietf-precis-7564bis], removed the use of the Unicode 479 CaseFold() operation in favor of the Unicode toLower() operation. 481 o Clarified several editorial matters. 483 o Updated references. 485 Appendix B. Acknowledgements 487 Thanks to William Fisher for his implementation feedback, especially 488 regarding idempotence. 490 Thanks to Sam Whited for his feedback and for submitting [Err4570]. 492 See [RFC7700] for acknowledgements related to the specification that 493 this document supersedes. 495 Author's Address 497 Peter Saint-Andre 498 Filament 499 P.O. Box 787 500 Parker, CO 80134 501 USA 503 Phone: +1 720 256 6756 504 Email: peter@filament.com 505 URI: https://filament.com/