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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 September 1, 2009 4 Obsoletes: 3490, 3491 5 (if approved) 6 Updates: 3492 (if approved) 7 Intended status: Standards Track 8 Expires: March 5, 2010 10 Internationalized Domain Names in Applications (IDNA): Protocol 11 draft-ietf-idnabis-protocol-15.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 March 5, 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 Internationalized 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 . . . . . . . . . . . . . . . . . . . . 11 90 5.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 11 91 5.3. A-label Input . . . . . . . . . . . . . . . . . . . . . . 11 92 5.4. Validation and Character List Testing . . . . . . . . . . 12 93 5.5. Punycode Conversion . . . . . . . . . . . . . . . . . . . 13 94 5.6. DNS Name Resolution . . . . . . . . . . . . . . . . . . . 13 95 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 96 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 97 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14 98 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 99 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 100 10.1. Normative References . . . . . . . . . . . . . . . . . . . 15 101 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 . . . . . . . . . . . . . . . . . . . . . . . 19 108 B.4. Version -04 . . . . . . . . . . . . . . . . . . . . . . . 19 109 B.5. Version -05 . . . . . . . . . . . . . . . . . . . . . . . 19 110 B.6. Version -06 . . . . . . . . . . . . . . . . . . . . . . . 19 111 B.7. Version -07 . . . . . . . . . . . . . . . . . . . . . . . 20 112 B.8. Version -08 . . . . . . . . . . . . . . . . . . . . . . . 20 113 B.9. Version -09 . . . . . . . . . . . . . . . . . . . . . . . 20 114 B.10. Version -10 . . . . . . . . . . . . . . . . . . . . . . . 21 115 B.11. Version -11 . . . . . . . . . . . . . . . . . . . . . . . 21 116 B.12. Version -12 . . . . . . . . . . . . . . . . . . . . . . . 21 117 B.13. Version -13 . . . . . . . . . . . . . . . . . . . . . . . 22 118 B.14. Version -14 . . . . . . . . . . . . . . . . . . . . . . . 22 119 B.15. Version -15 . . . . . . . . . . . . . . . . . . . . . . . 22 120 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23 122 1. Introduction 124 This document supplies the protocol definition for internationalized 125 domain names. Essential definitions and terminology for 126 understanding this document and a road map of the collection of 127 documents that make up IDNA2008 appear in [IDNA2008-Defs]. 128 Appendix A discusses the relationship between this specification and 129 the earlier version of IDNA (referred to here as "IDNA2003"). The 130 rationale for these changes, along with considerable explanatory 131 material and advice to zone administrators who support IDNs is 132 provided in another document, [IDNA2008-Rationale]. 134 IDNA works by allowing applications to use certain ASCII string 135 labels (beginning with a special prefix) to represent non-ASCII name 136 labels. Lower-layer protocols need not be aware of this; therefore 137 IDNA does not change any infrastructure. In particular, IDNA does 138 not depend on any changes to DNS servers, resolvers, or protocol 139 elements, because the ASCII name service provided by the existing DNS 140 can be used for IDNA. 142 IDNA applies only to DNS labels. The base DNS standards [RFC1034] 143 [RFC1035] and their various updates specify how to combine labels 144 into fully-qualified domain names and parse labels out of those 145 names. 147 This document describes two separate protocols, one for IDN 148 registration (Section 4) and one for IDN lookup (Section 5), that 149 share some terminology, reference data and operations. [[anchor2: 150 Note in draft: See the note in the introduction to.]]Section 5 152 1.1. Discussion Forum 154 [[anchor4: RFC Editor: please remove this section.]] 156 This work is being discussed in the IETF IDNABIS WG and on the 157 mailing list idna-update@alvestrand.no 159 2. Terminology 161 Terminology used in IDNA, but also in Unicode or other character set 162 standards and the DNS, appears in [IDNA2008-Defs]. Terminology that 163 is required as part of the IDNA definition, including the definitions 164 of "ACE", appears in that document as well. Readers of this document 165 are assumed to be familiar with [IDNA2008-Defs] and with the DNS- 166 specific terminology in RFC 1034 [RFC1034]. 168 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 169 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 170 document are to be interpreted as described in BCP 14, RFC 2119 171 [RFC2119]. 173 3. Requirements and Applicability 175 3.1. Requirements 177 IDNA makes the following requirements: 179 1. Whenever a domain name is put into an IDN-unaware domain name 180 slot (see Section 2 and [IDNA2008-Defs]), it MUST contain only 181 ASCII characters (i.e., must be either an A-label or an NR-LDH- 182 label), unless the DNS application is not subject to historical 183 recommendations for "hostname"-style names (see [RFC1034] and 184 Section 3.2.1). 186 2. Labels MUST be compared using equivalent forms: either both 187 A-Label forms or both U-Label forms. Because A-labels and 188 U-labels can be transformed into each other without loss of 189 information, these comparisons are equivalent. A pair of 190 A-labels MUST be compared as case-insensitive ASCII (as with all 191 comparisons of ASCII DNS labels). U-labels must be compared 192 as-is, without case-folding or other intermediate steps. Note 193 that it is not necessary to validate labels in order to compare 194 them and that successful comparison does not imply validity. In 195 many cases, validation may be important for other reasons and 196 SHOULD be performed. 198 3. Labels being registered MUST conform to the requirements of 199 Section 4. Labels being looked up and the lookup process MUST 200 conform to the requirements of Section 5. 202 3.2. Applicability 204 IDNA applies to all domain names in all domain name slots in 205 protocols except where it is explicitly excluded. It does not apply 206 to domain name slots which do not use the Letter/Digit/Hyphen (LDH) 207 syntax rules. 209 Because it uses the DNS, IDNA applies to many protocols that were 210 specified before it was designed. IDNs occupying domain name slots 211 in those older protocols MUST be in A-label form until and unless 212 those protocols and implementations of them are explicitly upgraded 213 to be aware of IDNs in Unicode. IDNs actually appearing in DNS 214 queries or responses MUST be A-labels. 216 IDNA is not defined for extended label types (see RFC 2671, Section 3 217 [RFC2671]). 219 3.2.1. DNS Resource Records 221 IDNA applies only to domain names in the NAME and RDATA fields of DNS 222 resource records whose CLASS is IN. See RFC 1034 [RFC1034] for 223 precise definitions of these terms. 225 The application of IDNA to DNS resource records depends entirely on 226 the CLASS of the record, and not on the TYPE except as noted below. 227 This will remain true, even as new types are defined, unless a new 228 type defines type-specific rules. Special naming conventions for SRV 229 records (and "underscore names" more generally) are incompatible with 230 IDNA coding. The first two labels on a SRV type record (the ones 231 required to start in "_") MUST NOT be A-labels or U-labels, because 232 conversion to an A-label would lose information (since the underscore 233 is not a letter, digit, or hyphen and is consequently DISALLOWED in 234 IDNs). Of course, those labels may be part of a domain that uses IDN 235 labels at higher levels in the tree. 237 3.2.2. Non-domain-name Data Types Stored in the DNS 239 Although IDNA enables the representation of non-ASCII characters in 240 domain names, that does not imply that IDNA enables the 241 representation of non-ASCII characters in other data types that are 242 stored in domain names, specifically in the RDATA field for types 243 that have structured RDATA format. For example, an email address 244 local part is stored in a domain name in the RNAME field as part of 245 the RDATA of an SOA record (hostmaster@example.com would be 246 represented as hostmaster.example.com). IDNA does not update the 247 existing email standards, which allow only ASCII characters in local 248 parts. Even though work is in progress to define 249 internationalization for email addresses [RFC4952], changes to the 250 email address part of the SOA RDATA would require action in, or 251 updates to, other standards, specifically those that specify the 252 format of the SOA RR. 254 4. Registration Protocol 256 This section defines the procedure for registering an IDN. The 257 procedure is implementation independent; any sequence of steps that 258 produces exactly the same result for all labels is considered a valid 259 implementation. 261 Note that, while the registration and lookup protocols (Section 5) 262 are very similar in most respects, they are different and 263 implementers should carefully follow the appropriate steps. 265 4.1. Input to IDNA Registration Process 267 Registration processes, especially processing by entities, such as 268 "registrars" who deal with registrants before the request actually 269 reaches the zone manager ("registry") are outside the scope of these 270 protocols and may differ significantly depending on local needs. By 271 the time a string enters the IDNA registration process as described 272 in this specification, it MUST be in Unicode and in Normalization 273 Form C (NFC [Unicode-UAX15]). Entities responsible for zone files 274 ("registries") are expected to accept only the exact string for which 275 registration is requested, free of any mappings or local adjustments. 276 They SHOULD avoid any possible ambiguity by accepting registrations 277 only for A-labels, possibly paired with the relevant U-labels so that 278 they can verify the 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 both label forms are available, it MUST ensure that the A-label 287 form is in lower case, perform a conversion to a U-label, perform the 288 steps and tests described below on that U-label, and then verify that 289 the A-label produced by the step in Section 4.4 matches the one 290 provided as input. In addition, if a U-label was provided, that 291 U-label and the one obtained by conversion of the A-label MUST match 292 exactly. If, for some reason, these tests fail, the registration 293 MUST be rejected. If the conversion to a U-label is not performed, 294 the registry MUST still verify that the A-label is superficially 295 valid, i.e., that it does not violate any of the rules of Punycode 296 [RFC3492] encoding such as the prohibition on trailing hyphen-minus, 297 appearance of non-basic characters before the delimiter, and so on. 298 Fake A-labels, i.e., invalid strings that appear to be A-labels but 299 are not, MUST NOT be placed in DNS zones that support IDNA. 301 4.2.2. Rejection of Characters that are not Permitted 303 The candidate Unicode string MUST NOT contain characters that appear 304 in the "DISALLOWED" and "UNASSIGNED" lists specified in 305 [IDNA2008-Tables]. 307 4.2.3. Label Validation 309 The proposed label (in the form of a Unicode string, i.e., a string 310 that at least superficially appears to be a U-label) is then 311 examined, performing tests that require examination of more than one 312 character. Character order is considered to be the on-the-wire 313 order, not the display order. 315 4.2.3.1. Hyphen Restrictions 317 The Unicode string MUST NOT contain "--" (two consecutive hyphens) in 318 the third and fourth character positions and MUST NOT start or end 319 with a "-" (hyphen). 321 4.2.3.2. Leading Combining Marks 323 The Unicode string MUST NOT begin with a combining mark or combining 324 character (see The Unicode Standard, Section 2.11 [Unicode] for an 325 exact definition). 327 4.2.3.3. Contextual Rules 329 The Unicode string MUST NOT contain any characters whose validity is 330 context-dependent, unless the validity is positively confirmed by a 331 contextual rule. To check this, each code-point marked as CONTEXTJ 332 and CONTEXTO in [IDNA2008-Tables] MUST have a non-null rule. If such 333 a code-point is missing a rule, it is invalid. If the rule exists 334 but the result of applying the rule is negative or inconclusive, the 335 proposed label is invalid. 337 4.2.3.4. Labels Containing Characters Written Right to Left 339 If the proposed label contains any characters that are written from 340 right to left it MUST meet the BIDI criteria [IDNA2008-BIDI]. 342 4.2.4. Registration Validation Summary 344 Strings that contain at least one non-ASCII character, have been 345 produced by the steps above, whose contents pass all of the tests in 346 Section 4.2, and are 63 or fewer characters long in ACE form (see 347 Section 4.4), are U-labels. 349 To summarize, tests are made in Section 4.2 for invalid characters, 350 invalid combinations of characters, for labels that are invalid even 351 if the characters they contain are valid individually, and for labels 352 that do not conform to the restrictions for strings containing right 353 to left characters. 355 4.3. Registry Restrictions 357 In addition to the rules and tests above, there are many reasons why 358 a registry could reject a label. Registries at all levels of the 359 DNS, not just the top level, are expected to establish policies about 360 label registrations. Policies are likely to be informed by the local 361 languages and may depend on many factors including what characters 362 are in the label (for example, a label may be rejected based on other 363 labels already registered). See [IDNA2008-Rationale] for a 364 discussion and recommendations about registry policies. 366 The string produced by the steps in Section 4.2 is checked and 367 processed as appropriate to local registry restrictions. Application 368 of those registry restrictions may result in the rejection of some 369 labels or the application of special restrictions to others. 371 4.4. Punycode Conversion 373 The resulting U-label is converted to an A-label (defined in 374 [IDNA2008-Defs] [[anchor12: ?? Insert section number]]). The 375 A-label is the encoding of the U-label according to the Punycode 376 algorithm [RFC3492] with the ACE prefix "xn--" added at the beginning 377 of the string. The resulting string must, of course, conform to the 378 length limits imposed by the DNS. This document updates RFC 3492 379 only to the extent of replacing the reference to the discussion of 380 the ACE prefix. The ACE prefix is now specified in this document 381 rather than as part of RFC 3490 or Nameprep [RFC3491] but is the same 382 in both sets of documents. 384 The failure conditions identified in the Punycode encoding procedure 385 cannot occur if the input is a U-label as determined by the steps 386 above. 388 4.5. Insertion in the Zone 390 The A-label is registered in the DNS by insertion into a zone. 392 5. Domain Name Lookup Protocol 394 Lookup is different from registration and different tests are applied 395 on the client. Although some validity checks are necessary to avoid 396 serious problems with the protocol, the lookup-side tests are more 397 permissive and rely on the assumption that names that are present in 398 the DNS are valid. That assumption is, however, a weak one because 399 the presence of wild cards in the DNS might cause a string that is 400 not actually registered in the DNS to be successfully looked up. 402 The two steps described in Section 5.2 are required. 404 5.1. Label String Input 406 The user supplies a string in the local character set, typically by 407 typing it or clicking on, or copying and pasting, a resource 408 identifier, e.g., a URI [RFC3986] or IRI [RFC3987] from which the 409 domain name is extracted. Alternately, some process not directly 410 involving the user may read the string from a file or obtain it in 411 some other way. Processing in this step and the next two are local 412 matters, to be accomplished prior to actual invocation of IDNA. 414 5.2. Conversion to Unicode 416 The string is converted from the local character set into Unicode, if 417 it is not already Unicode. Depending on local needs, this conversion 418 may involve mapping some characters into other characters as well as 419 coding conversions. Those issues are discussed in [IDNA2008-Mapping] 420 and the mapping-related sections of [IDNA2008-Rationale].[[anchor13: 421 ?? Supply section number.]] A Unicode string may require 422 normalization as discussed in Section 4.1. The result MUST be a 423 Unicode string in NFC form. 425 5.3. A-label Input 427 If the input to this procedure appears to be an A-label (i.e., it 428 starts in "xn--"), the lookup application MAY attempt to convert it 429 to a U-label, first ensuring that the A-label is entirely in lower 430 case, and apply the tests of Section 5.4 and the conversion of 431 Section 5.5 to that form. If the label is converted to Unicode 432 (i.e., to U-label form) using the Punycode decoding algorithm, then 433 the processing specified in those two sections MUST be performed, and 434 the label MUST be rejected if the resulting label is not identical to 435 the original. See the Name Server Considerations section of 436 [IDNA2008-Rationale] for additional discussion on this topic. 438 That conversion and testing SHOULD be performed if the domain name 439 will later be presented to the user in native character form (this 440 requires that the lookup application be IDNA-aware). If those steps 441 are not performed, the lookup process SHOULD at least make tests to 442 determine that the string is actually an A-label, examining it for 443 the invalid formats specified in the Punycode decoding specification. 444 Applications that are not IDNA-aware will obviously omit that 445 testing; others MAY treat the string as opaque to avoid the 446 additional processing at the expense of providing less protection and 447 information to users. 449 5.4. Validation and Character List Testing 451 As with the registration procedure described in Section 4, the 452 Unicode string is checked to verify that all characters that appear 453 in it are valid as input to IDNA lookup processing. As discussed 454 above and in [IDNA2008-Rationale], the lookup check is more liberal 455 than the registration one. Labels that have not been fully evaluated 456 for conformance to the applicable rules are referred to as "putative" 457 labels as discussed in [IDNA2008-Defs][[anchor14: ??? Insert section 458 number -- 2.2.3 as of Defs-09]]. Putative labels with any of the 459 following characteristics MUST be rejected prior to DNS lookup: 461 o Labels containing code points that are unassigned in the version 462 of Unicode being used by the application, i.e.,in the UNASSIGNED 463 category of [IDNA2008-Tables]. 465 o Labels that are not in NFC form as defined in [Unicode-UAX15]. 467 o Labels containing "--" (two consecutive hyphens) in the third and 468 fourth character positions. 470 o Labels containing prohibited code points, i.e., those that are 471 assigned to the "DISALLOWED" category in the permitted character 472 table [IDNA2008-Tables]. 474 o Labels containing code points that are identified in 475 [IDNA2008-Tables] as "CONTEXTJ", i.e., requiring exceptional 476 contextual rule processing on lookup, but that do not conform to 477 those rules. Note that this implies that a rule must be defined, 478 not null: a character that requires a contextual rule but for 479 which the rule is null is treated in this step as having failed to 480 conform to the rule. 482 o Labels containing code points that are identified in 483 [IDNA2008-Tables] as "CONTEXTO", but for which no such rule 484 appears in the table of rules. Applications resolving DNS names 485 or carrying out equivalent operations are not required to test 486 contextual rules for "CONTEXTO" characters, only to verify that a 487 rule is defined (although they MAY make such tests to provide 488 better protection or give better information to the user). 490 o Labels whose first character is a combining mark (see 491 Section 4.2.3.2). 493 In addition, the application SHOULD apply the following test. 495 o Verification that the string is compliant with the requirements 496 for right to left characters, specified in [IDNA2008-BIDI]. 498 This test may be omitted in special circumstances, such as when the 499 lookup application knows that the conditions are enforced elsewhere, 500 because an attempt to look up and resolve such strings will almost 501 certainly lead to a DNS lookup failure except when wild cards are 502 present in the zone. However, applying the test is likely to give 503 much better information about the reason for a lookup failure -- 504 information that may be usefully passed to the user when that is 505 feasible -- than DNS resolution failure information alone. In any 506 event, lookup applications should avoid attempting to resolve labels 507 that are invalid under that test. 509 For all other strings, the lookup application MUST rely on the 510 presence or absence of labels in the DNS to determine the validity of 511 those labels and the validity of the characters they contain. If 512 they are registered, they are presumed to be valid; if they are not, 513 their possible validity is not relevant. While a lookup application 514 may reasonably issue warnings about strings it believes may be 515 problematic, applications that decline to process a string that 516 conforms to the rules above (i.e., does not look it up in the DNS) 517 are not in conformance with this protocol. 519 5.5. Punycode Conversion 521 The string that has now been validated for lookup is converted to ACE 522 form using the Punycode algorithm (with the ACE prefix added). With 523 the understanding that this summary is not normative (the steps above 524 are), the string is either 526 o in Unicode NFC form that contains no leading combining marks, 527 contains no DISALLOWED or UNASSIGNED code points, has rules 528 associated with any code points in CONTEXTJ or CONTEXTO, and, for 529 those in CONTEXTJ, to satisfy the conditions of the rules; or 531 o in A-label form, was supplied under circumstances in which the 532 U-label conversions and tests have not been performed (see 533 Section 5.3). 535 5.6. DNS Name Resolution 537 That resulting validated string is looked up in the DNS, using normal 538 DNS resolver procedures. That lookup can obviously either succeed 539 (returning information) or fail. 541 6. Security Considerations 543 Security Considerations for this version of IDNA, except for the 544 special issues associated with right to left scripts and characters, 545 are described in [IDNA2008-Defs]. Specific issues for labels 546 containing characters associated with scripts written right to left 547 appear in [IDNA2008-BIDI]. 549 7. IANA Considerations 551 IANA actions for this version of IDNA are specified in 552 [IDNA2008-Tables] and discussed informally in [IDNA2008-Rationale]. 553 The components of IDNA described in this document do not require any 554 IANA actions. 556 8. Contributors 558 While the listed editor held the pen, the original versions of this 559 document represent the joint work and conclusions of an ad hoc design 560 team consisting of the editor and, in alphabetic order, Harald 561 Alvestrand, Tina Dam, Patrik Faltstrom, and Cary Karp. This document 562 draws significantly on the original version of IDNA [RFC3490] both 563 conceptually and for specific text. This second-generation version 564 would not have been possible without the work that went into that 565 first version and especially the contributions of its authors Patrik 566 Faltstrom, Paul Hoffman, and Adam Costello. While Faltstrom was 567 actively involved in the creation of this version, Hoffman and 568 Costello were not and should not be held responsible for any errors 569 or omissions. 571 9. Acknowledgments 573 This revision to IDNA would have been impossible without the 574 accumulated experience since RFC 3490 was published and resulting 575 comments and complaints of many people in the IETF, ICANN, and other 576 communities, too many people to list here. Nor would it have been 577 possible without RFC 3490 itself and the efforts of the Working Group 578 that defined it. Those people whose contributions are acknowledged 579 in RFC 3490, [RFC4690], and [IDNA2008-Rationale] were particularly 580 important. 582 Specific textual changes were incorporated into this document after 583 suggestions from the other contributors, Stephane Bortzmeyer, Vint 584 Cerf, Lisa Dusseault, Paul Hoffman, Kent Karlsson, James Mitchell, 585 Erik van der Poel, Marcos Sanz, Andrew Sullivan, Wil Tan, Ken 586 Whistler, Chris Wright, and other WG participants. Special thanks 587 are due to Paul Hoffman for permission to extract material from his 588 Internet-Draft to form the basis for Appendix A. 590 10. References 592 10.1. Normative References 594 [IDNA2008-BIDI] 595 Alvestrand, H. and C. Karp, "An updated IDNA criterion for 596 right-to-left scripts", August 2009, . 599 [IDNA2008-Defs] 600 Klensin, J., "Internationalized Domain Names for 601 Applications (IDNA): Definitions and Document Framework", 602 August 2009, . 605 [IDNA2008-Tables] 606 Faltstrom, P., "The Unicode Codepoints and IDNA", 607 August 2009, . 610 A version of this document is available in HTML format at 611 http://stupid.domain.name/idnabis/ 612 draft-ietf-idnabis-tables-06.html 614 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 615 STD 13, RFC 1034, November 1987. 617 [RFC1035] Mockapetris, P., "Domain names - implementation and 618 specification", STD 13, RFC 1035, November 1987. 620 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application 621 and Support", STD 3, RFC 1123, October 1989. 623 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 624 Requirement Levels", BCP 14, RFC 2119, March 1997. 626 [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode 627 for Internationalized Domain Names in Applications 628 (IDNA)", RFC 3492, March 2003. 630 [Unicode-PropertyValueAliases] 631 The Unicode Consortium, "Unicode Character Database: 632 PropertyValueAliases", March 2008, . 635 [Unicode-RegEx] 636 The Unicode Consortium, "Unicode Technical Standard #18: 637 Unicode Regular Expressions", May 2005, 638 . 640 [Unicode-Scripts] 641 The Unicode Consortium, "Unicode Standard Annex #24: 642 Unicode Script Property", February 2008, 643 . 645 [Unicode-UAX15] 646 The Unicode Consortium, "Unicode Standard Annex #15: 647 Unicode Normalization Forms", 2006, 648 . 650 10.2. Informative References 652 [ASCII] American National Standards Institute (formerly United 653 States of America Standards Institute), "USA Code for 654 Information Interchange", ANSI X3.4-1968, 1968. 656 ANSI X3.4-1968 has been replaced by newer versions with 657 slight modifications, but the 1968 version remains 658 definitive for the Internet. 660 [IDNA2008-Mapping] 661 Resnick, P., "Mapping Characters in IDNA", August 2009, . 665 [IDNA2008-Rationale] 666 Klensin, J., Ed., "Internationalized Domain Names for 667 Applications (IDNA): Issues, Explanation, and Rationale", 668 February 2009, . 671 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 672 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 673 RFC 2136, April 1997. 675 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 676 Specification", RFC 2181, July 1997. 678 [RFC2535] Eastlake, D., "Domain Name System Security Extensions", 679 RFC 2535, March 1999. 681 [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", 682 RFC 2671, August 1999. 684 [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, 685 "Internationalizing Domain Names in Applications (IDNA)", 686 RFC 3490, March 2003. 688 [RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep 689 Profile for Internationalized Domain Names (IDN)", 690 RFC 3491, March 2003. 692 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 693 Resource Identifier (URI): Generic Syntax", STD 66, 694 RFC 3986, January 2005. 696 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 697 Identifiers (IRIs)", RFC 3987, January 2005. 699 [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and 700 Recommendations for Internationalized Domain Names 701 (IDNs)", RFC 4690, September 2006. 703 [RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for 704 Internationalized Email", RFC 4952, July 2007. 706 [Unicode] The Unicode Consortium, "The Unicode Standard, Version 707 5.0", 2007. 709 Boston, MA, USA: Addison-Wesley. ISBN 0-321-48091-0 711 Appendix A. Summary of Major Changes from IDNA2003 713 1. Update base character set from Unicode 3.2 to Unicode version- 714 agnostic. 716 2. Separate the definitions for the "registration" and "lookup" 717 activities. 719 3. Disallow symbol and punctuation characters except where special 720 exceptions are necessary. 722 4. Remove the mapping and normalization steps from the protocol and 723 have them instead done by the applications themselves, possibly 724 in a local fashion, before invoking the protocol. 726 5. Change the way that the protocol specifies which characters are 727 allowed in labels from "humans decide what the table of 728 codepoints contains" to "decision about codepoints are based on 729 Unicode properties plus a small exclusion list created by 730 humans". 732 6. Introduce the new concept of characters that can be used only in 733 specific contexts. 735 7. Allow typical words and names in languages such as Dhivehi and 736 Yiddish to be expressed. 738 8. Make bidirectional domain names (delimited strings of labels, 739 not just labels standing on their own) display in a less 740 surprising fashion whether they appear in obvious domain name 741 contexts or as part of running text in paragraphs. 743 9. Remove the dot separator from the mandatory part of the 744 protocol. 746 10. Make some currently-valid labels that are not actually IDNA 747 labels invalid. 749 Appendix B. Change Log 751 [[anchor21: RFC Editor: Please remove this appendix.]] 753 B.1. Changes between Version -00 and -01 of draft-ietf-idnabis-protocol 755 o Corrected discussion of SRV records. 757 o Several small corrections for clarity. 759 o Inserted more "open issue" placeholders. 761 B.2. Version -02 763 o Rewrote the "conversion to Unicode" text in Section 5.2 as 764 requested on-list. 766 o Added a comment (and reference) about EDNS0 to the "DNS Server 767 Conventions" section, which was also retitled. 769 o Made several editorial corrections and improvements in response to 770 various comments. 772 o Added several new discussion placeholder anchors and updated some 773 older ones. 775 B.3. Version -03 777 o Trimmed change log, removing information about pre-WG drafts. 779 o Incorporated a number of changes suggested by Marcos Sanz in his 780 note of 2008.07.17 and added several more placeholder anchors. 782 o Several minor editorial corrections and improvements. 784 o "Editor" designation temporarily removed because the automatic 785 posting machinery does not accept it. 787 B.4. Version -04 789 o Removed Contextual Rule appendices for transfer to Tables. 791 o Several changes, including removal of discussion anchors, based on 792 discussions at IETF 72 (Dublin) 794 o Rewrote the preprocessing material (former Section 5.3) somewhat 795 -- see Appendix B.14. 797 B.5. Version -05 799 o Updated part of the A-label input explanation (Section 5.3) per 800 note from Erik van der Poel. 802 B.6. Version -06 804 o Corrected a few typographical errors. 806 o Incorporated the material (formerly in Rationale) on the 807 relationship between IDNA2003 and IDNA2008 as an appendix and 808 pointed to the new definitions document. 810 o Text modified in several places to recognize the dangers of 811 interaction between DNS wild cards and IDNs. 813 o Text added to be explicit about the handling of edge and failure 814 cases in Punycode encoding and decoding. 816 o Revised for consistency with the new Definitions document and to 817 make the text read more smoothly. 819 B.7. Version -07 821 o Multiple small textual and editorial changes and clarifications. 823 o Requirement for normalization clarified to apply to all cases and 824 conditions for preprocessing further clarified. 826 o Substantive change to Section 4.2.1, turning a SHOULD to a MUST 827 (see note from Mark Davis, 19 November, 2008 18:14 -0800). 829 B.8. Version -08 831 o Added some references and altered text to improve clarity. 833 o Changed the description of CONTEXTJ/CONTEXTO to conform to that in 834 Tables. In other words, these are now treated as distinction 835 categories (again), rather than as specially-flagged subsets of 836 PROTOCOL VALID. 838 o The discussion of label comparisons has been rewritten to make it 839 more precise and to clarify that one does not need to verify that 840 a string is a [valid] A-label or U-label in order to test it for 841 equality with another string. The WG should verify that the 842 current text is what is desired. 844 o Other changes to reflect post-IETF discussions or editorial 845 improvements. 847 B.9. Version -09 849 o Removed Security Considerations material to Defs document. 851 o Removed the Name Server Considerations material to Rationale. 852 That material is not normative and not needed to implement the 853 protocol itself. 855 o Adjusted terminology to match new version of Defs. 857 o Removed all discussion of local mapping and option for it from 858 registration protocol. Such mapping is now completely prohibited 859 on Registration. 861 o Removed some old placeholders and inquiries because no comments 862 have been received. 864 o Small editorial corrections. 866 B.10. Version -10 868 o Rewrote the registration input material slightly to further 869 clarify the "no mapping on registration" principle. 871 o Added placeholder notes about several tasks, notably reorganizing 872 Section 4 and Section 5 so that subsection numbers are parallel. 874 o Cleaned up an incorrect use of the terms "A-label" and "U-label" 875 in the lookup phase that was spotted by Mark Davis. Inserted a 876 note there about alternate ways to deal with the resulting 877 terminology problem. 879 o Added a temporarily appendix (above) to document alternate 880 strategies for possible replacements for the former Section 5.3 881 (see Appendix B.14). 883 B.11. Version -11 885 o Removed dangling reference to "C-label" (editing error in prior 886 draft). 888 o Recast the last steps of the Lookup description to eliminate 889 "apparent" (previously "putative") terminology. 891 o Rewrote major portions of the temporary appendix that describes 892 transitional mappings to improve clarity and add context. 894 o Did some fine-tuning of terminology, notably in Section 3.2.1. 896 B.12. Version -12 898 o Extensive editorial improvements, mostly due to suggestions from 899 Lisa Dusseault. 901 o Conformance statements have been made consistent, especially in 902 Section 4.2.1 and subsequent text, which said "SHOULD" in one 903 place and then said "MAY" as the result of incomplete removal of 904 registration-time mapping. Also clarified the definition of 905 "registration processes" in Section 4.1 -- the previous text had 906 confused several people. 908 o A few new "question to the WG notes have been added about 909 appropriateness or placement of text. If there are no comments on 910 the mailing list, the editor will apply his own judgment. 912 o Several of the usual small typos and other editorial errors have 913 been corrected. 915 o Section 5 has still not been reorganized to match Section 4 in 916 structure and subsection numbering -- will be done as soon as the 917 mapping decisions and references are final. 919 B.13. Version -13 921 o Modified the "putative label" text to better explain the term and 922 explicitly point back to Defs. 924 o Slight rewrite of former section 5.3 to clarify the NFC 925 requirement and to start the transition toward having some of the 926 explanation in the Mapping document. That whole section has been 927 removed in -14, see Appendix B.14 for more information. 929 B.14. Version -14 931 o Fixed substantive typographical error caught by Wil Tan. 933 o Added a check for consecutive hyphens in positions 3 and 4 to 934 Lookup. 936 o Reflected several changes suggested by Andrew Sullivan. 938 o Rearranged and rewrote material to reflect the mapping document 939 and its status. 941 o The former Section 5.3 and Appendix A, which discussed mapping 942 alternatives, have been dropped entirely. Such discussion now 943 belongs in the Mapping document, the portion of Rationale that 944 supports it, or not at all. Section 5.2 has been rewritten 945 slightly to point to Mapping for those issues. 947 o Note: With the revised mapping material inserted, I've just about 948 given up on the idea of having the subsections of Sections 4 and 5 949 exactly parallel each other. Anyone who still feels strongly 950 about this should be prepared to make very specific suggestions. 951 --JcK 953 B.15. Version -15 955 o Corrected name of protocol in the abstract ("Internationalization" 956 to "Internationalized") and a few other instances of that error. 958 o Corrected the hyphen test (Section 4.2.3.1). 960 o Added text to deal with the "upper case in A-labels" problem. 962 o Adjusted Acknowledgments to remove Mark Davis's name, per his 963 request and advice from IETF Trust Counsel. 965 o Incorporated other changes from WG Last Call. 967 o Small typographical and editorial corrections. 969 Author's Address 971 John C Klensin 972 1770 Massachusetts Ave, Ste 322 973 Cambridge, MA 02140 974 USA 976 Phone: +1 617 245 1457 977 Email: john+ietf@jck.com