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'IDNA2008-BIDI' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-PropertyValueAliases' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-RegEx' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-Scripts' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-UAX15' -- No information found for draft-ietf-idnabis-mapping - is the name correct? -- Obsolete informational reference (is this intentional?): RFC 2535 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) -- Obsolete informational reference (is this intentional?): RFC 2671 (Obsoleted by RFC 6891) -- Obsolete informational reference (is this intentional?): RFC 3490 (Obsoleted by RFC 5890, RFC 5891) -- Obsolete informational reference (is this intentional?): RFC 3491 (Obsoleted by RFC 5891) -- Obsolete informational reference (is this intentional?): RFC 4952 (Obsoleted by RFC 6530) Summary: 1 error (**), 0 flaws (~~), 9 warnings (==), 15 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Klensin 3 Internet-Draft August 9, 2009 4 Obsoletes: 3490, 3491 5 (if approved) 6 Updates: 3492 (if approved) 7 Intended status: Standards Track 8 Expires: February 10, 2010 10 Internationalized Domain Names in Applications (IDNA): Protocol 11 draft-ietf-idnabis-protocol-14.txt 13 Status of this Memo 15 This Internet-Draft is submitted to IETF in full conformance with the 16 provisions of BCP 78 and BCP 79. This document may contain material 17 from IETF Documents or IETF Contributions published or made publicly 18 available before November 10, 2008. The person(s) controlling the 19 copyright in some of this material may not have granted the IETF 20 Trust the right to allow modifications of such material outside the 21 IETF Standards Process. Without obtaining an adequate license from 22 the person(s) controlling the copyright in such materials, this 23 document may not be modified outside the IETF Standards Process, and 24 derivative works of it may not be created outside the IETF Standards 25 Process, except to format it for publication as an RFC or to 26 translate it into languages other than English. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF), its areas, and its working groups. Note that 30 other groups may also distribute working documents as Internet- 31 Drafts. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 The list of current Internet-Drafts can be accessed at 39 http://www.ietf.org/ietf/1id-abstracts.txt. 41 The list of Internet-Draft Shadow Directories can be accessed at 42 http://www.ietf.org/shadow.html. 44 This Internet-Draft will expire on February 10, 2010. 46 Copyright Notice 48 Copyright (c) 2009 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents in effect on the date of 53 publication of this document (http://trustee.ietf.org/license-info). 54 Please review these documents carefully, as they describe your rights 55 and restrictions with respect to this document. 57 Abstract 59 This document is the revised protocol definition for 60 internationalized domain names (IDNs). The rationale for changes, 61 the relationship to the older specification, and important 62 terminology are provided in other documents. This document specifies 63 the protocol mechanism, called Internationalizing Domain Names in 64 Applications (IDNA), for registering and looking up IDNs in a way 65 that does not require changes to the DNS itself. IDNA is only meant 66 for processing domain names, not free text. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 71 1.1. Discussion Forum . . . . . . . . . . . . . . . . . . . . . 5 72 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 73 3. Requirements and Applicability . . . . . . . . . . . . . . . . 6 74 3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6 75 3.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 6 76 3.2.1. DNS Resource Records . . . . . . . . . . . . . . . . . 7 77 3.2.2. Non-domain-name Data Types Stored in the DNS . . . . . 7 78 4. Registration Protocol . . . . . . . . . . . . . . . . . . . . 7 79 4.1. Input to IDNA Registration Process . . . . . . . . . . . . 8 80 4.2. Permitted Character and Label Validation . . . . . . . . . 8 81 4.2.1. Input Format . . . . . . . . . . . . . . . . . . . . . 8 82 4.2.2. Rejection of Characters that are not Permitted . . . . 8 83 4.2.3. Label Validation . . . . . . . . . . . . . . . . . . . 8 84 4.2.4. Registration Validation Summary . . . . . . . . . . . 9 85 4.3. Registry Restrictions . . . . . . . . . . . . . . . . . . 9 86 4.4. Punycode Conversion . . . . . . . . . . . . . . . . . . . 10 87 4.5. Insertion in the Zone . . . . . . . . . . . . . . . . . . 10 88 5. Domain Name Lookup Protocol . . . . . . . . . . . . . . . . . 10 89 5.1. Label String Input . . . . . . . . . . . . . . . . . . . . 10 90 5.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 11 91 5.3. A-label Input . . . . . . . . . . . . . . . . . . . . . . 11 92 5.4. Validation and Character List Testing . . . . . . . . . . 11 93 5.5. Punycode Conversion . . . . . . . . . . . . . . . . . . . 13 94 5.6. DNS Name Resolution . . . . . . . . . . . . . . . . . . . 13 95 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 96 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 97 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14 98 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 99 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 100 10.1. Normative References . . . . . . . . . . . . . . . . . . . 14 101 10.2. Informative References . . . . . . . . . . . . . . . . . . 16 102 Appendix A. Summary of Major Changes from IDNA2003 . . . . . . . 17 103 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 18 104 B.1. Changes between Version -00 and -01 of 105 draft-ietf-idnabis-protocol . . . . . . . . . . . . . . . 18 106 B.2. Version -02 . . . . . . . . . . . . . . . . . . . . . . . 18 107 B.3. Version -03 . . . . . . . . . . . . . . . . . . . . . . . 18 108 B.4. Version -04 . . . . . . . . . . . . . . . . . . . . . . . 19 109 B.5. Version -05 . . . . . . . . . . . . . . . . . . . . . . . 19 110 B.6. Version -06 . . . . . . . . . . . . . . . . . . . . . . . 19 111 B.7. Version -07 . . . . . . . . . . . . . . . . . . . . . . . 19 112 B.8. Version -08 . . . . . . . . . . . . . . . . . . . . . . . 19 113 B.9. Version -09 . . . . . . . . . . . . . . . . . . . . . . . 20 114 B.10. Version -10 . . . . . . . . . . . . . . . . . . . . . . . 20 115 B.11. Version -11 . . . . . . . . . . . . . . . . . . . . . . . 21 116 B.12. Version -12 . . . . . . . . . . . . . . . . . . . . . . . 21 117 B.13. Version -13 . . . . . . . . . . . . . . . . . . . . . . . 21 118 B.14. Version -14 . . . . . . . . . . . . . . . . . . . . . . . 22 119 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22 121 1. Introduction 123 This document supplies the protocol definition for internationalized 124 domain names. Essential definitions and terminology for 125 understanding this document and a road map of the collection of 126 documents that make up IDNA2008 appear in [IDNA2008-Defs]. 127 Appendix A discusses the relationship between this specification and 128 the earlier version of IDNA (referred to here as "IDNA2003") and the 129 rationale for these changes, along with considerable explanatory 130 material and advice to zone administrators who support IDNs is 131 provided in another document, [IDNA2008-Rationale]. 133 IDNA works by allowing applications to use certain ASCII string 134 labels (beginning with a special prefix) to represent non-ASCII name 135 labels. Lower-layer protocols need not be aware of this; therefore 136 IDNA does not changes any infrastructure. In particular, IDNA does 137 not depend on any changes to DNS servers, resolvers, or protocol 138 elements, because the ASCII name service provided by the existing DNS 139 can be used for IDNA. 141 IDNA applies only to DNS labels. The base DNS standards [RFC1034] 142 [RFC1035] and their various updates specify how to combine labels 143 into fully-qualified domain names and parse labels out of those 144 names. 146 This document describes two separate protocols, one for IDN 147 registration (Section 4) and one for IDN lookup (Section 5), that 148 share some terminology, reference data and operations. [[anchor2: 149 Note in draft: See the note in the introduction to.]]Section 5 151 1.1. Discussion Forum 153 [[anchor4: RFC Editor: please remove this section.]] 155 This work is being discussed in the IETF IDNABIS WG and on the 156 mailing list idna-update@alvestrand.no 158 2. Terminology 160 Terminology used in IDNA, but also in Unicode or other character set 161 standards and the DNS, appears in [IDNA2008-Defs]. Terminology that 162 is required as part of the IDNA definition, including the definitions 163 of "ACE", appears in that document as well. Readers of this document 164 are assumed to be familiar with [IDNA2008-Defs] and with the DNS- 165 specific terminology in RFC 1034 [RFC1034]. 167 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 168 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 169 document are to be interpreted as described in BCP 14, RFC 2119 170 [RFC2119]. 172 3. Requirements and Applicability 174 3.1. Requirements 176 IDNA makes the following requirements: 178 1. Whenever a domain name is put into an IDN-unaware domain name 179 slot (see Section 2 and [IDNA2008-Defs]), it MUST contain only 180 ASCII characters (i.e., must be either an A-label or an NR-LDH- 181 label), unless the DNS application is not subject to historical 182 recommendations for "hostname"-style names (see [RFC1034] and 183 Section 3.2.1). 185 2. Labels MUST be compared using equivalent forms: either both 186 A-Label forms or both U-Label forms. Because A-labels and 187 U-labels can be transformed into each other without loss of 188 information, these comparisons are equivalent. A pair of 189 A-labels MUST be compared as case-insensitive ASCII (as with all 190 comparisons of ASCII DNS labels). U-labels must be compared 191 as-is, without case-folding or other intermediate steps. Note 192 that it is not necessary to validate labels in order to compare 193 them. In many cases, validation may be important for other 194 reasons and SHOULD be performed. 196 3. Labels being registered MUST conform to the requirements of 197 Section 4. Labels being looked up and the lookup process MUST 198 conform to the requirements of Section 5. 200 3.2. Applicability 202 IDNA applies to all domain names in all domain name slots in 203 protocols except where it is explicitly excluded. It does not apply 204 to domain name slots which do not use the Letter/Digit/Hyphen (LDH) 205 syntax rules. 207 Because it uses the DNS, IDNA applies to many protocols that were 208 specified before it was designed. IDNs occupying domain name slots 209 in those older protocols MUST be in A-label form until and unless 210 those protocols and implementations of them are explicitly upgraded 211 to be aware of IDNs in Unicode. IDNs actually appearing in DNS 212 queries or responses MUST be A-labels. 214 IDNA is not defined for extended label types (see RFC 2671, Section 3 216 [RFC2671]). 218 3.2.1. DNS Resource Records 220 IDNA applies only to domain names in the NAME and RDATA fields of DNS 221 resource records whose CLASS is IN. See RFC 1034 [RFC1034] for 222 precise definitions of these terms. 224 The application of IDNA to DNS resource records depends entirely on 225 the CLASS of the record, and not on the TYPE except as noted below. 226 This will remain true, even as new types are defined, unless a new 227 type defines type-specific rules. Special naming conventions for SRV 228 records (and "underscore names" more generally) are incompatible with 229 IDNA coding. The first two labels on a SRV type record (the ones 230 required to start in "_") MUST NOT be A-labels or U-labels, because 231 conversion to an A-label would lose information (since the underscore 232 is not a letter, digit, or hyphen and is consequently DISALLOWED in 233 IDNs). Of course, those labels may be part of a domain that uses IDN 234 labels at higher levels in the tree. 236 3.2.2. Non-domain-name Data Types Stored in the DNS 238 Although IDNA enables the representation of non-ASCII characters in 239 domain names, that does not imply that IDNA enables the 240 representation of non-ASCII characters in other data types that are 241 stored in domain names, specifically in the RDATA field for types 242 that have structured RDATA format. For example, an email address 243 local part is stored in a domain name in the RNAME field as part of 244 the RDATA of an SOA record (hostmaster@example.com would be 245 represented as hostmaster.example.com). IDNA does not update the 246 existing email standards, which allow only ASCII characters in local 247 parts. Even though work is in progress to define 248 internationalization for email addresses [RFC4952], changes to the 249 email address part of the SOA RDATA would require action in, or 250 updates to, other standards, specifically those that specify the 251 format of the SOA RR. 253 4. Registration Protocol 255 This section defines the procedure for registering an IDN. The 256 procedure is implementation independent; any sequence of steps that 257 produces exactly the same result for all labels is considered a valid 258 implementation. 260 Note that, while the registration and lookup protocols (Section 5) 261 are very similar in most respects, they are different and 262 implementers should carefully follow the appropriate steps. 264 4.1. Input to IDNA Registration Process 266 Registration processes, especially processing by entities, such as 267 "registrars" who deal with registrants before the request actually 268 reaches the zone manager ("registry") are outside the scope of these 269 protocols and may differ significantly depending on local needs. By 270 the time a string enters the IDNA registration process as described 271 in this specification, it is expected to be in Unicode and MUST be in 272 Unicode Normalization Form C (NFC [Unicode-UAX15]). Entities 273 responsible for zone files ("registries") are expected to accept only 274 the exact string for which registration is requested, free of any 275 mappings or local adjustments. They SHOULD avoid any possible 276 ambiguity by accepting registrations only for A-labels, possibly 277 paired with the relevant U-labels so that they can verify the 278 correspondence. 280 4.2. Permitted Character and Label Validation 282 4.2.1. Input Format 284 The registry SHOULD permit submission of labels in A-label form and 285 is encouraged to accept both the A-label form and the U-label one. 286 If it does so, it MUST perform a conversion to a U-label, perform the 287 steps and tests described below, and verify that the A-label produced 288 by the step in Section 4.4 matches the one provided as input. In 289 addition, if a U-label was provided, that U-label and the one 290 obtained by conversion of the A-label MUST match exactly. If, for 291 some reason, these tests fail, the registration MUST be rejected. If 292 the conversion to a U-label is not performed, the registry MUST still 293 verify that the A-label is superficially valid, i.e., that it does 294 not violate any of the rules of Punycode [RFC3492] encoding such as 295 the prohibition on trailing hyphen-minus, appearance of non-basic 296 characters before the delimiter, and so on. Fake A-labels, i.e., 297 invalid strings that appear to be A-labels but are not, MUST NOT be 298 placed in DNS zones that support IDNA. 300 4.2.2. Rejection of Characters that are not Permitted 302 The candidate Unicode string MUST NOT contain characters in the 303 "DISALLOWED" and "UNASSIGNED" lists specified in [IDNA2008-Tables]. 305 4.2.3. Label Validation 307 The proposed label (in the form of a Unicode string, i.e., a string 308 that at least superficially appears to be a U-label) is then 309 examined, performing tests that require examination of more than one 310 character. Character order is considered to be the on-the-wire 311 order, not the display order. 313 4.2.3.1. Consecutive Hyphens 315 The Unicode string MUST NOT contain "--" (two consecutive hyphens) in 316 the third and fourth character positions. 318 4.2.3.2. Leading Combining Marks 320 The Unicode string MUST NOT begin with a combining mark or combining 321 character (see The Unicode Standard, Section 2.11 [Unicode] for an 322 exact definition). 324 4.2.3.3. Contextual Rules 326 The Unicode string MUST NOT contain any characters whose validity is 327 context-dependent, unless the validity is positively confirmed by a 328 contextual rule. To check this, each code-point marked as CONTEXTJ 329 and CONTEXTO in [IDNA2008-Tables] MUST have a non-null rule. If such 330 a code-point is missing a rule, it is invalid. If the rule exists 331 but the result of applying the rule is negative or inconclusive, the 332 proposed label is invalid. 334 4.2.3.4. Labels Containing Characters Written Right to Left 336 If the proposed label contains any characters that are written from 337 right to left it MUST meet the "bidi" criteria [IDNA2008-BIDI]. 339 4.2.4. Registration Validation Summary 341 Strings that contain at least one non-ASCII character, have been 342 produced by the steps above, whose contents pass all of the tests in 343 Section 4.2, and are 63 or fewer characters long in ACE form (see 344 Section 4.4), are U-labels. 346 To summarize, tests are made in Section 4.2 for invalid characters, 347 invalid combinations of characters, for labels that are invalid even 348 if the characters they contain are valid individually, and for labels 349 that do not conform to the restrictions for strings containing right 350 to left characters. 352 4.3. Registry Restrictions 354 In addition to the rules and tests above, there are many reasons why 355 a registry could reject a label. Registries at all levels of the 356 DNS, not just the top level, establish policies about label 357 registrations. Policies are likely to be informed by the local 358 languages and may depend on many factors including what characters 359 are in the label (for example, a label may be rejected based on other 360 labels already registered). See [IDNA2008-Rationale] for a 361 discussion and recommendations about registry policies. 363 The string produced by the steps in Section 4.2 is checked and 364 processed as appropriate to local registry restrictions. Application 365 of those registry restrictions may result in the rejection of some 366 labels or the application of special restrictions to others. 368 4.4. Punycode Conversion 370 The resulting U-label is converted to an A-label (defined in 371 [IDNA2008-Defs] [[anchor13: Insert section number]]). The A-label is 372 the encoding of the U-label according to the Punycode algorithm 373 [RFC3492] with the ACE prefix "xn--" added at the beginning of the 374 string. The resulting string must, of course, conform to the length 375 limits imposed by the DNS. This document updates RFC 3492 only to 376 the extent of replacing the reference to the discussion of the ACE 377 prefix. The ACE prefix is now specified in this document rather than 378 as part of RFC 3490 or Nameprep [RFC3491] but is the same in both 379 sets of documents. 381 The failure conditions identified in the Punycode encoding procedure 382 cannot occur if the input is a U-label as determined by the steps 383 above. 385 4.5. Insertion in the Zone 387 The A-label is registered in the DNS by insertion into a zone. 389 5. Domain Name Lookup Protocol 391 Lookup is different from registration and different tests are applied 392 on the client. Although some validity checks are necessary to avoid 393 serious problems with the protocol, the lookup-side tests are more 394 permissive and rely on the assumption that names that are present in 395 the DNS are valid. That assumption is, however, a weak one because 396 the presence of wild cards in the DNS might cause a string that is 397 not actually registered in the DNS to be successfully looked up. 399 The two steps described in Section 5.2 are required. 401 5.1. Label String Input 403 The user supplies a string in the local character set, typically by 404 typing it or clicking on, or copying and pasting, a resource 405 identifier, e.g., a URI [RFC3986] or IRI [RFC3987] from which the 406 domain name is extracted. Alternately, some process not directly 407 involving the user may read the string from a file or obtain it in 408 some other way. Processing in this step and the next two are local 409 matters, to be accomplished prior to actual invocation of IDNA. 411 5.2. Conversion to Unicode 413 The string is converted from the local character set into Unicode, if 414 it is not already Unicode. Depending on local needs, this conversion 415 may involve mapping some characters into other characters as well as 416 coding conversions. Those issues are discussed in [IDNA2008-Mapping] 417 and the mapping-related sections of [IDNA2008-Rationale]. [[anchor14: 418 Supply section number.]] A Unicode string may require normalization 419 as discussed in Section 4.1. The result MUST be a Unicode string in 420 NFC form. 422 5.3. A-label Input 424 If the input to this procedure appears to be an A-label (i.e., it 425 starts in "xn--"), the lookup application MAY attempt to convert it 426 to a U-label and apply the tests of Section 5.4 and the conversion of 427 Section 5.5 to that form. If the label is converted to Unicode 428 (i.e., to U-label form) using the Punycode decoding algorithm, then 429 the processing specified in those two sections MUST be performed, and 430 the label MUST be rejected if the resulting label is not identical to 431 the original. See the Name Server Considerations section of 432 [IDNA2008-Rationale] for additional discussion on this topic. 434 That conversion and testing SHOULD be performed if the domain name 435 will later be presented to the user in native character form (this 436 requires that the lookup application be IDNA-aware). If those steps 437 are not performed, the lookup process SHOULD at least make tests to 438 determine that the string is actually an A-label, examining it for 439 the invalid formats specified in the Punycode decoding specification. 440 Applications that are not IDNA-aware will obviously omit that 441 testing; others MAY treat the string as opaque to avoid the 442 additional processing at the expense of providing less protection and 443 information to users. 445 5.4. Validation and Character List Testing 447 As with the registration procedure described in Section 4, the 448 Unicode string is checked to verify that all characters that appear 449 in it are valid as input to IDNA lookup processing. As discussed 450 above and in [IDNA2008-Rationale], the lookup check is more liberal 451 than the registration one. Labels that have not been fully evaluated 452 for conformance to the applicable rules are referred to as "putative" 453 labels as discussed in [IDNA2008-Defs][[anchor15: ??? Insert section 454 number -- 2.2.3 as of Defs-09]]. Putative labels with any of the 455 following characteristics MUST BE rejected prior to DNS lookup: 457 o Labels containing code points that are unassigned in the version 458 of Unicode being used by the application, i.e.,in the UNASSIGNED 459 category of [IDNA2008-Tables]. 461 o Labels that are not in NFC form as defined in [Unicode-UAX15]. 463 o Labels containing "--" (two consecutive hyphens) in the third and 464 fourth character positions. 466 o Labels containing prohibited code points, i.e., those that are 467 assigned to the "DISALLOWED" category in the permitted character 468 table [IDNA2008-Tables]. 470 o Labels containing code points that are identified in 471 [IDNA2008-Tables] as "CONTEXTJ", i.e., requiring exceptional 472 contextual rule processing on lookup, but that do not conform to 473 that rule. Note that this implies that a rule must be defined, 474 not null: a character that requires a contextual rule but for 475 which the rule is null is treated in this step as having failed to 476 conform to the rule. 478 o Labels containing code points that are identified in 479 [IDNA2008-Tables] as "CONTEXTO", but for which no such rule 480 appears in the table of rules. Applications resolving DNS names 481 or carrying out equivalent operations are not required to test 482 contextual rules for "CONTEXTO" characters, only to verify that a 483 rule is defined (although they MAY make such tests to provide 484 better protection or give better information to the user). 486 o Labels whose first character is a combining mark (see 487 Section 4.2.3.2). 489 In addition, the application SHOULD apply the following test. 491 o Verification that the string is compliant with the requirements 492 for right to left characters, specified in [IDNA2008-BIDI]. 494 This test may be omitted in special circumstances, such as when the 495 lookup application knows that the conditions are enforced elsewhere, 496 because an attempt to look up and resolve such strings will almost 497 certainly lead to a DNS lookup failure except when wildcards are 498 present in the zone. However, applying the test is likely to give 499 much better information about the reason for a lookup failure -- 500 information that may be usefully passed to the user when that is 501 feasible -- than DNS resolution failure information alone. In any 502 event, lookup applications should avoid attempting to resolve labels 503 that are invalid under that test. 505 For all other strings, the lookup application MUST rely on the 506 presence or absence of labels in the DNS to determine the validity of 507 those labels and the validity of the characters they contain. If 508 they are registered, they are presumed to be valid; if they are not, 509 their possible validity is not relevant. While a lookup application 510 may reasonably issue warnings about strings it believes may be 511 problematic, applications that decline to process a string that 512 conforms to the rules above (i.e., does not look it up in the DNS) 513 are not in conformance with this protocol. 515 5.5. Punycode Conversion 517 The string that has now been validated for lookup is converted to ACE 518 form using the Punycode algorithm (with the ACE prefix added). With 519 the understanding that this summary is not normative (the steps above 520 are), the string is either 522 o in Unicode NFC form that contains no leading combining marks, 523 contains no DISALLOWED or UNASSIGNED code points, has rules 524 associated with any code points in CONTEXTJ or CONTEXTO, and, for 525 those in CONTEXTJ, to satisfies the conditions of the rules; or 527 o in A-label form, was supplied under circumstances in which the 528 U-label conversions and tests have not been performed (see 529 Section 5.3). 531 5.6. DNS Name Resolution 533 That resulting validated string is looked up in the DNS, using normal 534 DNS resolver procedures. That lookup can obviously either succeed 535 (returning information) or fail. 537 6. Security Considerations 539 Security Considerations for this version of IDNA, except for the 540 special issues associated with right to left scripts and characters, 541 are described in [IDNA2008-Defs]. Specific issues for labels 542 containing characters associated with scripts written right to left 543 appear in [IDNA2008-BIDI]. 545 7. IANA Considerations 547 IANA actions for this version of IDNA are specified in 548 [IDNA2008-Tables] and discussed informally in [IDNA2008-Rationale]. 549 The components of IDNA described in this document do not require any 550 IANA actions. 552 8. Contributors 554 While the listed editor held the pen, the original versions of this 555 document represent the joint work and conclusions of an ad hoc design 556 team consisting of the editor and, in alphabetic order, Harald 557 Alvestrand, Tina Dam, Patrik Faltstrom, and Cary Karp. This document 558 draws significantly on the original version of IDNA [RFC3490] both 559 conceptually and for specific text. This second-generation version 560 would not have been possible without the work that went into that 561 first version and its authors, Patrik Faltstrom, Paul Hoffman, and 562 Adam Costello. While Faltstrom was actively involved in the creation 563 of this version, Hoffman and Costello were not and should not be held 564 responsible for any errors or omissions. 566 9. Acknowledgments 568 This revision to IDNA would have been impossible without the 569 accumulated experience since RFC 3490 was published and resulting 570 comments and complaints of many people in the IETF, ICANN, and other 571 communities, too many people to list here. Nor would it have been 572 possible without RFC 3490 itself and the efforts of the Working Group 573 that defined it. Those people whose contributions are acknowledged 574 in RFC 3490, [RFC4690], and [IDNA2008-Rationale] were particularly 575 important. 577 Specific textual changes were incorporated into this document after 578 suggestions from the other contributors, Stephane Bortzmeyer, Vint 579 Cerf, Lisa Dusseault, Mark Davis, Paul Hoffman, Kent Karlsson, Erik 580 van der Poel, Marcos Sanz, Andrew Sullivan, Wil Tan, Ken Whistler, 581 and other WG participants. As is usual with IETF specifications, 582 while the document represents rough consensus, it should not be 583 assumed that all participants and contributors agree with all 584 provisions. Special thanks are due to Paul Hoffman for permission to 585 extract material from his Internet-Draft to form the basis for 586 Appendix A. 588 10. References 590 10.1. Normative References 592 [IDNA2008-BIDI] 593 Alvestrand, H. and C. Karp, "An updated IDNA criterion for 594 right-to-left scripts", August 2009, . 597 [IDNA2008-Defs] 598 Klensin, J., "Internationalized Domain Names for 599 Applications (IDNA): Definitions and Document Framework", 600 August 2009, . 603 [IDNA2008-Tables] 604 Faltstrom, P., "The Unicode Codepoints and IDNA", 605 August 2009, . 608 A version of this document is available in HTML format at 609 http://stupid.domain.name/idnabis/ 610 draft-ietf-idnabis-tables-02.html 612 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 613 STD 13, RFC 1034, November 1987. 615 [RFC1035] Mockapetris, P., "Domain names - implementation and 616 specification", STD 13, RFC 1035, November 1987. 618 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application 619 and Support", STD 3, RFC 1123, October 1989. 621 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 622 Requirement Levels", BCP 14, RFC 2119, March 1997. 624 [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode 625 for Internationalized Domain Names in Applications 626 (IDNA)", RFC 3492, March 2003. 628 [Unicode-PropertyValueAliases] 629 The Unicode Consortium, "Unicode Character Database: 630 PropertyValueAliases", March 2008, . 633 [Unicode-RegEx] 634 The Unicode Consortium, "Unicode Technical Standard #18: 635 Unicode Regular Expressions", May 2005, 636 . 638 [Unicode-Scripts] 639 The Unicode Consortium, "Unicode Standard Annex #24: 640 Unicode Script Property", February 2008, 641 . 643 [Unicode-UAX15] 644 The Unicode Consortium, "Unicode Standard Annex #15: 645 Unicode Normalization Forms", 2006, 646 . 648 10.2. Informative References 650 [ASCII] American National Standards Institute (formerly United 651 States of America Standards Institute), "USA Code for 652 Information Interchange", ANSI X3.4-1968, 1968. 654 ANSI X3.4-1968 has been replaced by newer versions with 655 slight modifications, but the 1968 version remains 656 definitive for the Internet. 658 [IDNA2008-Mapping] 659 Resnick, P., "Mapping Characters in IDNA", August 2009, . 663 [IDNA2008-Rationale] 664 Klensin, J., Ed., "Internationalizing Domain Names for 665 Applications (IDNA): Issues, Explanation, and Rationale", 666 February 2009, . 669 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 670 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 671 RFC 2136, April 1997. 673 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 674 Specification", RFC 2181, July 1997. 676 [RFC2535] Eastlake, D., "Domain Name System Security Extensions", 677 RFC 2535, March 1999. 679 [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", 680 RFC 2671, August 1999. 682 [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, 683 "Internationalizing Domain Names in Applications (IDNA)", 684 RFC 3490, March 2003. 686 [RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep 687 Profile for Internationalized Domain Names (IDN)", 688 RFC 3491, March 2003. 690 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 691 Resource Identifier (URI): Generic Syntax", STD 66, 692 RFC 3986, January 2005. 694 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 695 Identifiers (IRIs)", RFC 3987, January 2005. 697 [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and 698 Recommendations for Internationalized Domain Names 699 (IDNs)", RFC 4690, September 2006. 701 [RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for 702 Internationalized Email", RFC 4952, July 2007. 704 [Unicode] The Unicode Consortium, "The Unicode Standard, Version 705 5.0", 2007. 707 Boston, MA, USA: Addison-Wesley. ISBN 0-321-48091-0 709 Appendix A. Summary of Major Changes from IDNA2003 711 1. Update base character set from Unicode 3.2 to Unicode version- 712 agnostic. 714 2. Separate the definitions for the "registration" and "lookup" 715 activities. 717 3. Disallow symbol and punctuation characters except where special 718 exceptions are necessary. 720 4. Remove the mapping and normalization steps from the protocol and 721 have them instead done by the applications themselves, possibly 722 in a local fashion, before invoking the protocol. 724 5. Change the way that the protocol specifies which characters are 725 allowed in labels from "humans decide what the table of 726 codepoints contains" to "decision about codepoints are based on 727 Unicode properties plus a small exclusion list created by 728 humans". 730 6. Introduce the new concept of characters that can be used only in 731 specific contexts. 733 7. Allow typical words and names in languages such as Dhivehi and 734 Yiddish to be expressed. 736 8. Make bidirectional domain names (delimited strings of labels, 737 not just labels standing on their own) display in a less 738 surprising fashion whether they appear in obvious domain name 739 contexts or as part of running text in paragraphs. 741 9. Remove the dot separator from the mandatory part of the 742 protocol. 744 10. Make some currently-valid labels that are not actually IDNA 745 labels invalid. 747 Appendix B. Change Log 749 [[anchor22: RFC Editor: Please remove this appendix.]] 751 B.1. Changes between Version -00 and -01 of draft-ietf-idnabis-protocol 753 o Corrected discussion of SRV records. 755 o Several small corrections for clarity. 757 o Inserted more "open issue" placeholders. 759 B.2. Version -02 761 o Rewrote the "conversion to Unicode" text in Section 5.2 as 762 requested on-list. 764 o Added a comment (and reference) about EDNS0 to the "DNS Server 765 Conventions" section, which was also retitled. 767 o Made several editorial corrections and improvements in response to 768 various comments. 770 o Added several new discussion placeholder anchors and updated some 771 older ones. 773 B.3. Version -03 775 o Trimmed change log, removing information about pre-WG drafts. 777 o Incorporated a number of changes suggested by Marcos Sanz in his 778 note of 2008.07.17 and added several more placeholder anchors. 780 o Several minor editorial corrections and improvements. 782 o "Editor" designation temporarily removed because the automatic 783 posting machinery does not accept it. 785 B.4. Version -04 787 o Removed Contextual Rule appendices for transfer to Tables. 789 o Several changes, including removal of discussion anchors, based on 790 discussions at IETF 72 (Dublin) 792 o Rewrote the preprocessing material (former Section 5.3 -- see 793 Appendix B.14) somewhat. 795 B.5. Version -05 797 o Updated part of the A-label input explanation (Section 5.3) per 798 note from Erik van der Poel. 800 B.6. Version -06 802 o Corrected a few typographical errors. 804 o Incorporated the material (formerly in Rationale) on the 805 relationship between IDNA2003 and IDNA2008 as an appendix and 806 pointed to the new definitions document. 808 o Text modified in several places to recognize the dangers of 809 interaction between DNS wildcards and IDNs. 811 o Text added to be explicit about the handling of edge and failure 812 cases in Punycode encoding and decoding. 814 o Revised for consistency with the new Definitions document and to 815 make the text read more smoothly. 817 B.7. Version -07 819 o Multiple small textual and editorial changes and clarifications. 821 o Requirement for normalization clarified to apply to all cases and 822 conditions for preprocessing further clarified. 824 o Substantive change to Section 4.2.1, turning a SHOULD to a MUST 825 (see note from Mark Davis, 19 November, 2008 18:14 -0800). 827 B.8. Version -08 829 o Added some references and altered text to improve clarity. 831 o Changed the description of CONTEXTJ/CONTEXTO to conform to that in 832 Tables. In other words, these are now treated as distinction 833 categories (again), rather than as specially-flagged subsets of 834 PROTOCOL VALID. 836 o The discussion of label comparisons has been rewritten to make it 837 more precise and to clarify that one does not need to verify that 838 a string is a [valid] A-label or U-label in order to test it for 839 equality with another string. The WG should verify that the 840 current text is what is desired. 842 o Other changes to reflect post-IETF discussions or editorial 843 improvements. 845 B.9. Version -09 847 o Removed Security Considerations material to Defs document. 849 o Removed the Name Server Considerations material to Rationale. 850 That material is not normative and not needed to implement the 851 protocol itself. 853 o Adjusted terminology to match new version of Defs. 855 o Removed all discussion of local mapping and option for it from 856 registration protocol. Such mapping is now completely prohibited 857 on Registration. 859 o Removed some old placeholders and inquiries because no comments 860 have been received. 862 o Small editorial corrections. 864 B.10. Version -10 866 o Rewrote the registration input material slightly to further 867 clarify the "no mapping on registration" principle. 869 o Added placeholder notes about several tasks, notably reorganizing 870 Section 4 and Section 5 so that subsection numbers are parallel. 872 o Cleaned up an incorrect use of the terms "A-label" and "U-label" 873 in the lookup phase that was spotted by Mark Davis. Inserted a 874 note there about alternate ways to deal with the resulting 875 terminology problem. 877 o Added a temporarily appendix (above) to document alternate 878 strategies for possible replacements for former section 5.3 (see 879 Appendix B.14. 881 B.11. Version -11 883 o Removed dangling reference to "C-label" (editing error in prior 884 draft). 886 o Recast the last steps of the Lookup description to eliminate 887 "apparent" (previously "putative") terminology. 889 o Rewrote major portions of the temporary appendix that describes 890 transitional mappings to improve clarity and add context. 892 o Did some fine-tuning of terminology, notably in Section 3.2.1. 894 B.12. Version -12 896 o Extensive editorial improvements, mostly due to suggestions from 897 Lisa Dusseault. 899 o Conformance statements have been made consistent, especially in 900 Section 4.2.1 and subsequent text, which said "SHOULD" in one 901 place and then said "MAY" as the result of incomplete removal of 902 registration-time mapping. Also clarified the definition of 903 "registration processes" in Section 4.1 -- the previous text had 904 confused several people. 906 o A few new "question to the WG notes have been added about 907 appropriateness or placement of text. If there are no comments on 908 the mailing list, the editor will apply his own judgment. 910 o Several of the usual small typos and other editorial errors have 911 been corrected. 913 o Section 5 has still not been reorganized to match Section 4 in 914 structure and subsection numbering -- will be done as soon as the 915 mapping decisions and references are final. 917 B.13. Version -13 919 o Modified the "putative label" text to better explain the term and 920 explicitly point back to Defs. 922 o Slight rewrite of former section 5.3 to clarify the NFC 923 requirement and to start the transition toward having some of the 924 explanation in the Mapping document. That whole section has been 925 removed in -14, see Appendix B.14 for more information. 927 B.14. Version -14 929 o Fixed substantive typographical error caught by Wil Tan. 931 o Added a check for consecutive hyphens in positions 3 and 4 to 932 Lookup. 934 o Reflected several changes suggested by Andrew Sullivan. 936 o Rearranged and rewrote material to reflect the mapping document 937 and its status. 939 o The former Section 5.3 and Appendix A, which discussed mapping 940 alternatives, have been dropped entirely. Such discussion now 941 belongs in the Mapping document, the portion of Rationale that 942 supports it, or not at all. Section 5.2 has been rewritten 943 slightly to point to Mapping for those issues. 945 o Note: With the revised mapping material inserted, I've just about 946 given up on the idea of having the subsections of Sections 4 and 5 947 exactly parallel each other. Anyone who still feels strongly 948 about this should be prepared to make very specific suggestions. 949 --JcK 951 Author's Address 953 John C Klensin 954 1770 Massachusetts Ave, Ste 322 955 Cambridge, MA 02140 956 USA 958 Phone: +1 617 245 1457 959 Email: john+ietf@jck.com