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Saint-Andre 3 Internet-Draft &yet 4 Intended status: Standards Track September 3, 2015 5 Expires: March 6, 2016 7 Preparation, Enforcement, and Comparison of Internationalized Strings 8 Representing Nicknames 9 draft-ietf-precis-nickname-19 11 Abstract 13 This document describes methods for handling Unicode strings 14 representing memorable, human-friendly names (variously called 15 "nicknames", "display names", or "petnames") for people, devices, 16 accounts, websites, and other entities. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on March 6, 2016. 35 Copyright Notice 37 Copyright (c) 2015 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. Nickname Profile . . . . . . . . . . . . . . . . . . . . . . 3 56 2.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 4 58 2.3. Enforcement . . . . . . . . . . . . . . . . . . . . . . . 5 59 2.4. Comparison . . . . . . . . . . . . . . . . . . . . . . . 5 60 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5 61 4. Use in Application Protocols . . . . . . . . . . . . . . . . 6 62 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 63 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 64 6.1. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 8 65 6.2. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 8 66 6.3. Visually Similar Characters . . . . . . . . . . . . . . . 8 67 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 68 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 69 7.2. Informative References . . . . . . . . . . . . . . . . . 9 70 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 10 71 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10 72 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 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 entity such as a 81 device, account, contact, or website. Such names are variously 82 called "nicknames" (e.g., in chatroom applications), "display names" 83 (e.g., in Internet mail), or "petnames" (see [1]); for consistency, 84 these are all called "nicknames" in this document. 86 Nicknames are commonly supported in technologies for textual 87 chatrooms, 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] [I-D.ietf-simple-chat], and Centralized Conferencing 91 (XCON) [RFC5239] [I-D.boulton-xcon-session-chat]. Recent chatroom 92 technologies also allow internationalized nicknames because they 93 support characters from outside the ASCII range [RFC20], typically by 94 means of the Unicode character set [Unicode]. Although such 95 nicknames tend to be used primarily for display purposes, they are 96 sometimes used for programmatic purposes as well (e.g., kicking users 97 or avoiding 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 RFC 127 2119 [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 NFKC as specified below). 140 2. Additional Mapping Rule: The additional mapping rule consists of 141 the following sub-rules. 143 1. Any instances of non-ASCII space MUST be mapped to ASCII 144 space (U+0020); a non-ASCII space is any Unicode code point 145 having a general category of "Zs", naturally with the 146 exception of U+0020. 148 2. Any instances of the ASCII space character at the beginning 149 or end of a nickname MUST be removed (e.g., "stpeter " is 150 mapped to "stpeter"). 152 3. Interior sequences of more than one ASCII space character 153 MUST be mapped to a single ASCII space character (e.g., 154 "St Peter" is mapped to "St Peter"). 156 3. Case Mapping Rule: Uppercase and titlecase characters MUST be 157 mapped to their lowercase equivalents using Unicode Default Case 158 Folding as defined in the Unicode Standard [Unicode] (at the time 159 of this 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 Normalization Form KC (NFKC). Because NFKC is more "aggressive" 168 in finding matches than other normalization forms (in the 169 terminology of Unicode, it performs both canonical and 170 compatibility decomposition before recomposing code points), this 171 rule helps to reduce the possibility of confusion by increasing 172 the number of characters that would match (e.g., U+2163 ROMAN 173 NUMERAL FOUR would match the combination of U+0049 LATIN CAPITAL 174 LETTER I and U+0056 LATIN 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 vs. an interface that is 182 configured to handle primarily a left-to-right script), as long 183 as the presentation is consistent in any given layout system. 185 2.2. Preparation 187 An entity that prepares a string for subsequent enforcement according 188 to this profile MUST ensure that the string consists only of Unicode 189 code points that conform to the "FreeformClass" base string class 190 defined in [RFC7564]. In addition, the entity MUST ensure that the 191 string is encoded as UTF-8 [RFC3629]. 193 2.3. Enforcement 195 An entity that performs enforcement according to this profile MUST 196 prepare a string as described in Section 2.2 section and MUST also 197 apply the rules specified in Section 2.1. The rules MUST be applied 198 in the order shown. 200 After all of the foregoing rules have been enforced, the entity MUST 201 ensure that the nickname is not zero bytes in length (this is done 202 after enforcing the rules to prevent applications from mistakenly 203 omitting a nickname entirely, because when internationalized 204 characters are accepted a non-empty sequence of characters can result 205 in a zero-length nickname after canonicalization). 207 2.4. Comparison 209 An entity that performs comparison of two strings according to this 210 profile MUST prepare each string and enforce the rules as specified 211 in Section 2.2 and Section 2.3. The two strings are to be considered 212 equivalent if they are an exact octet-for-octet match (sometimes 213 called "bit-string identity"). 215 3. Examples 217 The following examples illustrate a small number of nicknames that 218 are consistent with the format defined above, along with the output 219 string resulting from application of the PRECIS rules (note that the 220 characters < and > are used to delineate the actual nickname and are 221 not part of the nickname strings). 223 Table 1: A sample of legal nicknames 225 +---------------------------+-----------------------------------+ 226 | # | Nickname | Output for Comparison | 227 +---------------------------+-----------------------------------+ 228 | 1 | | | 229 +---------------------------+-----------------------------------+ 230 | 2 | | | 231 +---------------------------+-----------------------------------+ 232 | 3 | | | 233 +---------------------------+-----------------------------------+ 234 | 4 | | | 235 +---------------------------+-----------------------------------+ 236 | 5 | <Σ> | GREEK SMALL LETTER SIGMA (U+03C3) | 237 +---------------------------+-----------------------------------+ 238 | 6 | <σ> | GREEK SMALL LETTER SIGMA (U+03C3) | 239 +---------------------------+-----------------------------------+ 240 | 7 | <ς> | GREEK SMALL LETTER FINAL SIGMA | 241 | | | (U+03C2) | 242 +---------------------------+-----------------------------------+ 243 | 8 | <♚> | BLACK CHESS KING (U+265A) | 244 +---------------------------+-----------------------------------+ 245 | 9 | | | 246 +---------------------------+-----------------------------------+ 248 Regarding examples 5, 6, and 7: applying Unicode Default Case Folding 249 to GREEK CAPITAL LETTER SIGMA (U+03A3) results in GREEK SMALL LETTER 250 SIGMA (U+03C3), and doing so during comparison would result in 251 matching the nicknames in examples 5 and 6; however, because the 252 PRECIS mapping rules do not account for the special status of GREEK 253 SMALL LETTER FINAL SIGMA (U+03C2), the nicknames in examples 5 and 7 254 or examples 6 and 7 would not be matched. Regarding example 8: 255 symbol characters such as BLACK CHESS KING (U+265A) are allowed by 256 the PRECIS FreeformClass and thus can be used in nicknames. 257 Regarding example 9: applying Unicode Default Case Folding to ROMAN 258 NUMERAL FOUR (U+2163) results in SMALL ROMAN NUMERAL FOUR (U+2173), 259 and applying NFKC to SMALL ROMAN NUMERAL FOUR (U+2173) results in 260 LATIN SMALL LETTER I (U+0069) LATIN SMALL LETTER V (U+0086). 262 4. Use in Application Protocols 264 This specification defines only the PRECIS-based rules for handling 265 of nickname strings. It is the responsibility of an application 266 protocol (e.g., MSRP, XCON, or XMPP) or application definition to 267 specify the protocol slots in which nickname strings can appear, the 268 entities that are expected to enforce the rules governing nickname 269 strings, and when in protocol processing or interface handling the 270 rules need to be enforced. See Section 6 of [RFC7564] for guidelines 271 about using PRECIS profiles in applications. 273 Above and beyond the PRECIS-based rules specified here, application 274 protocols can also define application-specific rules governing 275 nickname strings (rules regarding the minimum or maximum length of 276 nicknames, further restrictions on allowable characters or character 277 ranges, safeguards to mitigate the effects of visually similar 278 characters, etc.). 280 Naturally, application protocols can also specify rules governing the 281 actual use of nicknames in applications (reserved nicknames, 282 authorization requirements for using nicknames, whether certain 283 nicknames can be prohibited, handling of duplicates, the relationship 284 between nicknames and underlying identifiers such as SIP URIs or 285 Jabber IDs, etc.). 287 Entities that enforce the rules specified in this document are 288 encouraged to be liberal in what they accept by following this 289 procedure: 291 1. Where possible, map characters (e.g, through width mapping, 292 additional mapping, case mapping, or normalization) and accept 293 the mapped string. 295 2. If mapping is not possible (e.g., because a character is 296 disallowed in the FreeformClass), reject the string. 298 5. IANA Considerations 300 The IANA shall add the following entry to the PRECIS Profiles 301 Registry: 303 Name: Nickname. 305 Base Class: FreeformClass. 307 Applicability: Nicknames in messaging and text conferencing 308 technologies; petnames for devices, accounts, and people; and 309 other uses of nicknames or petnames. 311 Replaces: None. 313 Width Mapping Rule: None (handled via NFKC). 315 Additional Mapping Rule: Map non-ASCII space characters to ASCII 316 space, strip leading and trailing space characters, map interior 317 sequences of multiple space characters to a single ASCII space. 319 Case Mapping Rule: Map uppercase and titlecase characters to 320 lowercase using Unicode Default Case Folding. 322 Normalization Rule: NFKC. 324 Directionality Rule: None. 326 Enforcement: To be specified by applications. 328 Specification: RFC XXXX. [Note to RFC Editor: please change "XXXX" 329 to the RFC number issued for this specification.] 331 6. Security Considerations 333 6.1. Reuse of PRECIS 335 The security considerations described in [RFC7564] apply to the 336 "FreeformClass" string class used in this document for nicknames. 338 6.2. Reuse of Unicode 340 The security considerations described in [UTS39] apply to the use of 341 Unicode characters in nicknames. 343 6.3. Visually Similar Characters 345 [RFC7564] describes some of the security considerations related to 346 visually similar characters, also called "confusable characters" or 347 "confusables". 349 Although the mapping rules defined under Section 2 of this document 350 are designed in part to reduce the possibility of confusion about 351 nicknames, this document does not provide more detailed 352 recommendations regarding the handling of visually similar 353 characters, such as those provided in [UTS39]. 355 7. References 357 7.1. Normative References 359 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 360 Requirement Levels", BCP 14, RFC 2119, March 1997. 362 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 363 10646", STD 63, RFC 3629, November 2003. 365 [RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for 366 Internationalized Domain Names for Applications (IDNA)", 367 RFC 5893, August 2010. 369 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 370 Internationalization in the IETF", BCP 166, RFC 6365, 371 September 2011. 373 [RFC7564] Saint-Andre, P. and M. Blanchet, "PRECIS Framework: 374 Preparation, Enforcement, and Comparison of 375 Internationalized Strings in Application Protocols", RFC 376 7564, May 2015. 378 [UTS39] The Unicode Consortium, "Unicode Technical Standard #39: 379 Unicode Security Mechanisms", November 2013, 380 . 382 [Unicode7.0] 383 The Unicode Consortium, "The Unicode Standard, Version 384 7.0.0", 2014, 385 . 387 [Unicode] The Unicode Consortium, "The Unicode Standard", 388 2015-present, . 390 7.2. Informative References 392 [I-D.boulton-xcon-session-chat] 393 Barnes, M., Boulton, C., and S. Loreto, "Chatrooms within 394 a Centralized Conferencing (XCON) System", draft-boulton- 395 xcon-session-chat-08 (work in progress), July 2011. 397 [I-D.ietf-simple-chat] 398 Niemi, A., Garcia, M., and G. Sandbakken, "Multi-party 399 Chat Using the Message Session Relay Protocol (MSRP)", 400 draft-ietf-simple-chat-18 (work in progress), January 401 2013. 403 [RFC20] Cerf, V., "ASCII format for network interchange", RFC 20, 404 October 1969. 406 [RFC2811] Kalt, C., "Internet Relay Chat: Channel Management", RFC 407 2811, April 2000. 409 [RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message 410 Session Relay Protocol (MSRP)", RFC 4975, September 2007. 412 [RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for 413 Centralized Conferencing", RFC 5239, June 2008. 415 [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, 416 October 2008. 418 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 419 Protocol (XMPP): Core", RFC 6120, March 2011. 421 [XEP-0045] 422 Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February 423 2012. 425 [XEP-0172] 426 Saint-Andre, P. and V. Mercier, "User Nickname", XSF XEP 427 0172, March 2012. 429 7.3. URIs 431 [1] http://www.skyhunter.com/marcs/petnames/IntroPetNames.html 433 Appendix A. Acknowledgements 435 Thanks to Kim Alvefur, Mary Barnes, Ben Campbell, Dave Cridland, 436 Miguel Garcia, Salvatore Loreto, Enrico Marocco, Matt Miller, and 437 Yoshiro YONEYA for their reviews and comments. 439 Paul Kyzivat and Melinda Shore reviewed the document for the General 440 Area Review Team and Operations Directorate, respectively. 442 During IESG review, Ben Campbell and Kathleen Moriarty provided 443 comments that led to further improvements. 445 Thanks to Matt Miller as document shepherd, Pete Resnick and Andrew 446 Sullivan as IANA designated experts, Marc Blanchet and Alexey 447 Melnikov as working group chairs, and Barry Leiba as area director. 449 The author wishes to acknowledge Cisco Systems, Inc., for employing 450 him during his work on earlier draft versions of this document. 452 Author's Address 454 Peter Saint-Andre 455 &yet 457 Email: peter@andyet.com 458 URI: https://andyet.com/