1 2 3 4 5 6 7Network Working Group P. Hoffman 8Request for Comments: 3491 IMC & VPNC 9Category: Standards Track M. Blanchet 10 Viagenie 11 March 2003 12 13 14 Nameprep: A Stringprep Profile for 15 Internationalized Domain Names (IDN) 16 17Status of this Memo 18 19 This document specifies an Internet standards track protocol for the 20 Internet community, and requests discussion and suggestions for 21 improvements. Please refer to the current edition of the "Internet 22 Official Protocol Standards" (STD 1) for the standardization state 23 and status of this protocol. Distribution of this memo is unlimited. 24 25Copyright Notice 26 27 Copyright (C) The Internet Society (2003). All Rights Reserved. 28 29Abstract 30 31 This document describes how to prepare internationalized domain name 32 (IDN) labels in order to increase the likelihood that name input and 33 name comparison work in ways that make sense for typical users 34 throughout the world. This profile of the stringprep protocol is 35 used as part of a suite of on-the-wire protocols for 36 internationalizing the Domain Name System (DNS). 37 381. Introduction 39 40 This document specifies processing rules that will allow users to 41 enter internationalized domain names (IDNs) into applications and 42 have the highest chance of getting the content of the strings 43 correct. It is a profile of stringprep [STRINGPREP]. These 44 processing rules are only intended for internationalized domain 45 names, not for arbitrary text. 46 47 This profile defines the following, as required by [STRINGPREP]. 48 49 - The intended applicability of the profile: internationalized 50 domain names processed by IDNA. 51 52 - The character repertoire that is the input and output to 53 stringprep: Unicode 3.2, specified in section 2. 54 55 56 57 58Hoffman & Blanchet Standards Track [Page 1] 59 60RFC 3491 IDN Nameprep March 2003 61 62 63 - The mappings used: specified in section 3. 64 65 - The Unicode normalization used: specified in section 4. 66 67 - The characters that are prohibited as output: specified in section 68 5. 69 70 - Bidirectional character handling: specified in section 6. 71 721.1 Interaction of protocol parts 73 74 Nameprep is used by the IDNA [IDNA] protocol for preparing domain 75 names; it is not designed for any other purpose. It is explicitly 76 not designed for processing arbitrary free text and SHOULD NOT be 77 used for that purpose. Nameprep is a profile of Stringprep 78 [STRINGPREP]. Implementations of Nameprep MUST fully implement 79 Stringprep. 80 81 Nameprep is used to process domain name labels, not domain names. 82 IDNA calls nameprep for each label in a domain name, not for the 83 whole domain name. 84 851.2 Terminology 86 87 The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" 88 in this document are to be interpreted as described in BCP 14, RFC 89 2119 [RFC2119]. 90 912. Character Repertoire 92 93 This profile uses Unicode 3.2, as defined in [STRINGPREP] Appendix A. 94 953. Mapping 96 97 This profile specifies mapping using the following tables from 98 [STRINGPREP]: 99 100 Table B.1 101 Table B.2 102 1034. Normalization 104 105 This profile specifies using Unicode normalization form KC, as 106 described in [STRINGPREP]. 107 108 109 110 111 112 113 114Hoffman & Blanchet Standards Track [Page 2] 115 116RFC 3491 IDN Nameprep March 2003 117 118 1195. Prohibited Output 120 121 This profile specifies prohibiting using the following tables from 122 [STRINGPREP]: 123 124 Table C.1.2 125 Table C.2.2 126 Table C.3 127 Table C.4 128 Table C.5 129 Table C.6 130 Table C.7 131 Table C.8 132 Table C.9 133 134 IMPORTANT NOTE: This profile MUST be used with the IDNA protocol. 135 The IDNA protocol has additional prohibitions that are checked 136 outside of this profile. 137 1386. Bidirectional characters 139 140 This profile specifies checking bidirectional strings as described in 141 [STRINGPREP] section 6. 142 1437. Unassigned Code Points in Internationalized Domain Names 144 145 If the processing in [IDNA] specifies that a list of unassigned code 146 points be used, the system uses table A.1 from [STRINGPREP] as its 147 list of unassigned code points. 148 1498. References 150 1518.1 Normative References 152 153 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 154 Requirement Levels", BCP 14, RFC 2119, March 1997. 155 156 [STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of 157 Internationalized Strings ("stringprep")", RFC 3454, 158 December 2002. 159 160 [IDNA] Faltstrom, P., Hoffman, P. and A. Costello, 161 "Internationalizing Domain Names in Applications 162 (IDNA)", RFC 3490, March 2003. 163 164 165 166 167 168 169 170Hoffman & Blanchet Standards Track [Page 3] 171 172RFC 3491 IDN Nameprep March 2003 173 174 1758.2 Informative references 176 177 [STD13] Mockapetris, P., "Domain names - concepts and 178 facilities", STD 13, RFC 1034, and "Domain names - 179 implementation and specification", STD 13, RFC 1035, 180 November 1987. 181 1829. Security Considerations 183 184 The Unicode and ISO/IEC 10646 repertoires have many characters that 185 look similar. In many cases, users of security protocols might do 186 visual matching, such as when comparing the names of trusted third 187 parties. Because it is impossible to map similar-looking characters 188 without a great deal of context such as knowing the fonts used, 189 stringprep does nothing to map similar-looking characters together 190 nor to prohibit some characters because they look like others. 191 192 Security on the Internet partly relies on the DNS. Thus, any change 193 to the characteristics of the DNS can change the security of much of 194 the Internet. 195 196 Domain names are used by users to connect to Internet servers. The 197 security of the Internet would be compromised if a user entering a 198 single internationalized name could be connected to different servers 199 based on different interpretations of the internationalized domain 200 name. 201 202 Current applications might assume that the characters allowed in 203 domain names will always be the same as they are in [STD13]. This 204 document vastly increases the number of characters available in 205 domain names. Every program that uses "special" characters in 206 conjunction with domain names may be vulnerable to attack based on 207 the new characters allowed by this specification. 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226Hoffman & Blanchet Standards Track [Page 4] 227 228RFC 3491 IDN Nameprep March 2003 229 230 23110. IANA Considerations 232 233 This is a profile of stringprep. It has been registered by the IANA 234 in the stringprep profile registry 235 (www.iana.org/assignments/stringprep-profiles). 236 237 Name of this profile: 238 Nameprep 239 240 RFC in which the profile is defined: 241 This document. 242 243 Indicator whether or not this is the newest version of the 244 profile: 245 This is the first version of Nameprep. 246 24711. Acknowledgements 248 249 Many people from the IETF IDN Working Group and the Unicode Technical 250 Committee contributed ideas that went into this document. 251 252 The IDN Nameprep design team made many useful changes to the 253 document. That team and its advisors include: 254 255 Asmus Freytag 256 Cathy Wissink 257 Francois Yergeau 258 James Seng 259 Marc Blanchet 260 Mark Davis 261 Martin Duerst 262 Patrik Faltstrom 263 Paul Hoffman 264 265 Additional significant improvements were proposed by: 266 267 Jonathan Rosenne 268 Kent Karlsson 269 Scott Hollenbeck 270 Dave Crocker 271 Erik Nordmark 272 Matitiahu Allouche 273 274 275 276 277 278 279 280 281 282Hoffman & Blanchet Standards Track [Page 5] 283 284RFC 3491 IDN Nameprep March 2003 285 286 28712. Authors' Addresses 288 289 Paul Hoffman 290 Internet Mail Consortium and VPN Consortium 291 127 Segre Place 292 Santa Cruz, CA 95060 USA 293 294 EMail: paul.hoffman@imc.org and paul.hoffman@vpnc.org 295 296 297 Marc Blanchet 298 Viagenie inc. 299 2875 boul. Laurier, bur. 300 300 Ste-Foy, Quebec, Canada, G1V 2M2 301 302 EMail: Marc.Blanchet@viagenie.qc.ca 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338Hoffman & Blanchet Standards Track [Page 6] 339 340RFC 3491 IDN Nameprep March 2003 341 342 34313. Full Copyright Statement 344 345 Copyright (C) The Internet Society (2003). All Rights Reserved. 346 347 This document and translations of it may be copied and furnished to 348 others, and derivative works that comment on or otherwise explain it 349 or assist in its implementation may be prepared, copied, published 350 and distributed, in whole or in part, without restriction of any 351 kind, provided that the above copyright notice and this paragraph are 352 included on all such copies and derivative works. However, this 353 document itself may not be modified in any way, such as by removing 354 the copyright notice or references to the Internet Society or other 355 Internet organizations, except as needed for the purpose of 356 developing Internet standards in which case the procedures for 357 copyrights defined in the Internet Standards process must be 358 followed, or as required to translate it into languages other than 359 English. 360 361 The limited permissions granted above are perpetual and will not be 362 revoked by the Internet Society or its successors or assigns. 363 364 This document and the information contained herein is provided on an 365 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 366 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 367 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 368 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 369 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 370 371Acknowledgement 372 373 Funding for the RFC Editor function is currently provided by the 374 Internet Society. 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394Hoffman & Blanchet Standards Track [Page 7] 395 396