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'Unicode-RegEx' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-Scripts' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode-UAX15' -- Obsolete informational reference (is this intentional?): RFC 2535 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) -- Obsolete informational reference (is this intentional?): RFC 3490 (Obsoleted by RFC 5890, RFC 5891) -- Obsolete informational reference (is this intentional?): RFC 4952 (Obsoleted by RFC 6530) Summary: 1 error (**), 0 flaws (~~), 6 warnings (==), 17 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Klensin, Ed. 3 Internet-Draft May 21, 2008 4 Obsoletes: 3490 (if approved) 5 Intended status: Standards Track 6 Expires: November 22, 2008 8 Internationalizing Domain Names in Applications (IDNA): Protocol 9 draft-ietf-idnabis-protocol-00.txt 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on November 22, 2008. 36 Abstract 38 This document supplies the protocol definition for a revised and 39 updated specification for internationalized domain names (IDNs). The 40 rationale for these changes, the relationship to the older 41 specification, and important terminology are provided in other 42 documents. This document specifies the protocol mechanism, called 43 Internationalizing Domain Names in Applications (IDNA), for 44 registering and looking up IDNs in a way that does not require 45 changes to the DNS itself. IDNA is only meant for processing domain 46 names, not free text. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 51 1.1. Discussion Forum . . . . . . . . . . . . . . . . . . . . . 4 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 3. Requirements and Applicability . . . . . . . . . . . . . . . . 5 54 3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5 55 3.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 5 56 3.2.1. DNS Resource Records . . . . . . . . . . . . . . . . . 6 57 3.2.2. Non-domain-name Data Types Stored in the DNS . . . . . 6 58 4. Registration Protocol . . . . . . . . . . . . . . . . . . . . 6 59 4.1. Proposed label . . . . . . . . . . . . . . . . . . . . . . 6 60 4.2. Conversion to Unicode and Normalization . . . . . . . . . 7 61 4.3. Permitted Character and Label Validation . . . . . . . . . 7 62 4.3.1. Rejection of Characters that are not Permitted . . . . 7 63 4.3.2. Label Validation . . . . . . . . . . . . . . . . . . . 7 64 4.3.3. Registration Validation Summary . . . . . . . . . . . 8 65 4.4. Registry Restrictions . . . . . . . . . . . . . . . . . . 8 66 4.5. Punycode Conversion . . . . . . . . . . . . . . . . . . . 9 67 4.6. Insertion in the Zone . . . . . . . . . . . . . . . . . . 9 68 5. Domain Name Resolution (Lookup) Protocol . . . . . . . . . . . 9 69 5.1. Label String Input . . . . . . . . . . . . . . . . . . . . 9 70 5.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 9 71 5.3. Character Changes in Preprocessing or the User 72 Interface . . . . . . . . . . . . . . . . . . . . . . . . 10 73 5.4. A-label Input . . . . . . . . . . . . . . . . . . . . . . 10 74 5.5. Validation and Character List Testing . . . . . . . . . . 11 75 5.6. Punycode Conversion . . . . . . . . . . . . . . . . . . . 12 76 5.7. DNS Name Resolution . . . . . . . . . . . . . . . . . . . 12 77 6. Name server Considerations . . . . . . . . . . . . . . . . . . 12 78 6.1. Processing Non-ASCII Strings . . . . . . . . . . . . . . . 12 79 6.2. DNSSEC Authentication of IDN Domain Names . . . . . . . . 13 80 6.3. Root Server Considerations . . . . . . . . . . . . . . . . 13 81 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 82 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 83 9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 14 84 9.1. Version -00 of draft-klensin-idnabis-protocol . . . . . . 14 85 9.2. Versions -01 and -02 of draft-klensin-idnabis-protocol . . 14 86 9.3. Version -03 of draft-klensin-idnabis-protocol . . . . . . 14 87 9.4. Version -04 of draft-klensin-idnabis-protocol . . . . . . 15 88 9.5. Version -00 of draft-ietf-idnabis-protocol . . . . . . . . 15 89 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 15 90 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 91 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 92 12.1. Normative References . . . . . . . . . . . . . . . . . . . 16 93 12.2. Informative References . . . . . . . . . . . . . . . . . . 17 94 Appendix A. The Contextual Rules Registry . . . . . . . . . . . . 18 95 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22 96 Intellectual Property and Copyright Statements . . . . . . . . . . 23 98 1. Introduction 100 This document supplies the protocol definition for a revised and 101 updated specification for internationalized domain names. The 102 rationale for these changes and relationship to the older 103 specification and some new terminology is provided in other 104 documents, notably [IDNA2008-Rationale]. 106 IDNA works by allowing applications to use certain ASCII string 107 labels (beginning with a special prefix) to represent non-ASCII name 108 labels. Lower-layer protocols need not be aware of this; therefore 109 IDNA does not depend on changes to any infrastructure. In 110 particular, IDNA does not depend on any changes to DNS servers, 111 resolvers, or protocol elements, because the ASCII name service 112 provided by the existing DNS is entirely sufficient for IDNA. 114 IDNA is applied only to DNS labels. Standards for combining labels 115 into fully-qualified domain names and parsing labels out of those 116 names are covered in the base DNS standards [RFC1035]. An 117 application may, of course, apply locally-appropriate conventions to 118 the presentation forms of domain names as discussed in 119 [IDNA2008-Rationale]. 121 While they share terminology, reference data, and some operations, 122 this document describes two separate protocols, one for IDN 123 registration (Section 4) and one for IDN lookup (Section 5). 125 A good deal of the background material that appeared in RFC 3490 has 126 been removed from this update. That material is either of historical 127 interest only or has been covered from a more recent perspective in 128 RFC 4690 [RFC4690] and [IDNA2008-Rationale]. 130 [[anchor2: Note in Draft: This document still needs more specifics 131 about how to perform some of the tests in the Registration and Lookup 132 protocols described below. Those details will be supplied in a later 133 revision, but the intent should be clear from the existing text.]] 135 1.1. Discussion Forum 137 [[anchor4: RFC Editor: please remove this section.]] 139 This work is being discussed in the IETF IDNABIS WG and on the 140 mailing list idna-update@alvestrand.no 142 2. Terminology 144 General terminology applicable to IDNA, but with meanings familiar to 145 those who have worked with Unicode or other character set standards 146 and the DNS, appears in [IDNA2008-Rationale]. Terminology that is an 147 integral, normative, part of the IDNA definition, including the 148 definitions of "ACE", appears in that document as well. Familiarity 149 with the terminology materials in that document is assumed for 150 reading this one. The reader of this document is assumed to be 151 familiar with DNS-specific terminology as defined in RFC 1034 152 [RFC1034]. 154 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 155 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 156 document are to be interpreted as described in BCP 14, RFC 2119 157 [RFC2119]. 159 3. Requirements and Applicability 161 3.1. Requirements 163 IDNA conformance means adherence to the following requirements: 165 1. Whenever a domain name is put into an IDN-unaware domain name 166 slot (see Section 2 and [IDNA2008-Rationale]), it MUST contain 167 only ASCII characters (i.e., must be either an A-label or an LDH- 168 label), or must be a label associated with a DNS application that 169 is not subject to either IDNA or the historical recommendations 170 for "hostname"-style names [RFC1034]. 172 2. Comparison of labels MUST be done on the A-label form, using an 173 ASCII case-insensitive comparison as with all comparisons of DNS 174 labels. 176 3. Labels being registered MUST conform to the requirements of 177 Section 4. Labels being looked up and the lookup process MUST 178 conform to the requirements of Section 5. 180 3.2. Applicability 182 IDNA is applicable to all domain names in all domain name slots 183 except where it is explicitly excluded. It is not applicable to 184 domain name slots which do not use the LDH syntax rules. 186 This implies that IDNA is applicable to many protocols that predate 187 IDNA. Note that IDNs occupying domain name slots in those older 188 protocols MUST be in A-label form until and unless those protocols 189 and implementations of them are upgraded. 191 3.2.1. DNS Resource Records 193 IDNA applies only to domain names in the NAME and RDATA fields of DNS 194 resource records whose CLASS is IN. 196 There are currently no other exclusions on the applicability of IDNA 197 to DNS resource records. Applicability depends entirely on the 198 CLASS, and not on the TYPE except as noted below. This will remain 199 true, even as new types are defined, unless there is a compelling 200 reason for a new type that requires type-specific rules. The special 201 naming conventions applicable to SRV records are examples of type- 202 specific rules that are incompatible with IDNA coding. Hence the 203 label on a record with TYPE SRV MUST NOT be an A-label or U-label 204 (while it would be possible to write a non-ASCII string with a 205 leading underscore, conversion to an A-label would be impossible 206 without loss of information and because the underscore is not a 207 letter, digit, or hyphen. 209 3.2.2. Non-domain-name Data Types Stored in the DNS 211 Although IDNA enables the representation of non-ASCII characters in 212 domain names, that does not imply that IDNA enables the 213 representation of non-ASCII characters in other data types that are 214 stored in domain names, specifically in the RDATA field for types 215 that have structured RDATA format. For example, an email address 216 local part is stored in a domain name in the RNAME field as part of 217 the RDATA of an SOA record (hostmaster@example.com would be 218 represented as hostmaster.example.com). IDNA specifically does not 219 update the existing email standards, which allow only ASCII 220 characters in local parts. Even though work is in progress to define 221 internationalization for email addresses [RFC4952], changes to the 222 email address part of the SOA RDATA would require action in other 223 standards, specifically those that specify the format of the SOA RR. 225 4. Registration Protocol 227 This section defines the procedure for registering an IDN. The 228 procedure is implementation independent; any sequence of steps that 229 produces exactly the same result for all labels is considered a valid 230 implementation. 232 4.1. Proposed label 234 The registrant submits a request for an IDN. The user typically 235 produces the request string by the keyboard entry of a character 236 sequence in the local native character set. The registry MAY permit 237 submission of labels in A-label form. If it does so, it SHOULD 238 perform a conversion to a U-label, perform the steps and tests 239 described below, and verify that the A-label produced by the step in 240 Section 4.5 matches the one provided as input. If, for some reason, 241 it does not, the registration MUST be rejected. 243 4.2. Conversion to Unicode and Normalization 245 Some system routine, or a localized front-end to the IDNA process, 246 ensures that the proposed label is a Unicode string. That string 247 MUST be in Unicode Normalization Form C (NFC [Unicode-UAX15]). 249 As a local implementation choice, the implementation MAY choose to 250 map some forbidden characters to permitted characters (for instance 251 mapping uppercase characters to lowercase ones), displaying the 252 result to the user, and allowing processing to continue. However, it 253 is strongly recommended that, to avoid any possible ambiguity, 254 entities responsible for zone files ("registries") accept 255 registrations only for A-labels (to be converted to U-labels by the 256 registry) or U-labels actually produced from A-labels, not forms 257 expected to be converted by some other process. 259 4.3. Permitted Character and Label Validation 261 4.3.1. Rejection of Characters that are not Permitted 263 The Unicode string is examined to prohibit characters that IDNA does 264 not permit in input. Those characters are identified in the 265 "DISALLOWED" and "UNASSIGNED" lists that are discussed in 266 [IDNA2008-Rationale]. The normative rules for producing that list 267 and the initial version of it are specified in [IDNA2008-Tables]. 268 Characters that are either DISALLOWED or UNASSIGNED MUST NOT be part 269 of labels being processed for registration in the DNS. 271 4.3.2. Label Validation 273 The proposed label (in the form of a Unicode string, i.e., a putative 274 U-label) is then examined, performing tests that require examination 275 of more than one character. 277 4.3.2.1. Rejection of Confusing or Hostile Sequences in U-labels 279 The Unicode string MUST NOT contain "--" (two consecutive hyphens) in 280 the third and fourth character positions. 282 4.3.2.2. Leading Combining Marks 284 The first character of the string is examined to verify that it is 285 not a combining mark. If it is a combining mark, the string MUST NOT 286 be registered. 288 4.3.2.3. Contextual Rules 290 Each code point is checked for its identification as characters 291 requiring contextual processign for registration (the list of 292 characters appears as the combination of CONTEXTJ and CONTEXTO in 293 [IDNA2008-Tables]). If that indication appears, the table of 294 contextual rules is checked for a rule for that character. If no 295 rule is found, the proposed label is rejected and MUST NOT be 296 installed in a zone file. If one is found, it is applied (typically 297 as a test on the entire label or on adjacent characters). If the 298 application of the rule does not conclude that the character is valid 299 in context, the proposed label MUST BE rejected. (See the IANA 300 Considerations: IDNA Context Registry section of [IDNA2008-Rationale] 301 and Appendix A of this document.) 303 4.3.2.4. Labels Containing Characters Written Right to Left 305 Additional special tests for right-to-left strings are applied (See 306 [IDNA2008-BIDI]. Strings that contain right to left characters that 307 do not conform to the rule(s) identified there MUST NOT be inserted 308 in zone files. 310 4.3.3. Registration Validation Summary 312 Strings that have been produced by the steps above, and whose 313 contents pass the above tests, are U-labels. 315 To summarize, tests are made here for invalid characters, invalid 316 combinations of characters, and for labels that are invalid even if 317 the characters they contain are valid individually. For example, 318 labels containing invisible ("zero-width") characters may be 319 permitted in context with characters whose presentation forms are 320 significantly changed by the presence or absence of the zero-width 321 characters, while other labels in which zero-width characters appear 322 may be rejected. 324 4.4. Registry Restrictions 326 Registries at all levels of the DNS, not just the top level, are 327 expected to establish policies about the labels that may be 328 registered, and for the processes associated with that action. While 329 exact policies are not specified as part of IDNA2008 and it is 330 expected that different registries may specify different policies, 331 there SHOULD be policies. These per-registry policies and 332 restrictions are an essential element of the IDNA registration 333 protocol even for registries (and corresponding zone files) deep in 334 the DNS hierarchy. As discussed in [IDNA2008-Rationale], such 335 restrictions have always existed in the DNS. 337 The string produced by the above steps is checked and processed as 338 appropriate to local registry restrictions. Application of those 339 registry restrictions may result in the rejection of some labels or 340 the application of special restrictions to others. 342 4.5. Punycode Conversion 344 The resulting U-label is converted to an A-label (i.e., the encoding 345 of that label according to the Punycode algorithm [RFC3492] with the 346 prefix included, i.e., the "xn--..." form). 348 4.6. Insertion in the Zone 350 The A-label is registered in the DNS by insertion into a zone. 352 5. Domain Name Resolution (Lookup) Protocol 354 Resolution is conceptually different from registration and different 355 tests are applied on the client. Although some validity checks are 356 necessary to avoid serious problems with the protocol (see 357 Section 5.5 ff.), the resolution-side tests are more permissive and 358 rely heavily on the assumption that names that are present in the DNS 359 are valid. Among other things, this distinction, applied carefully, 360 facilitates expansion of the permitted character lists to include new 361 scripts and accommodate new versions of Unicode without introducing 362 ambiguity into domain name processing. 364 5.1. Label String Input 366 The user supplies a string in the local character set, typically by 367 typing it or clicking on, or copying and pasting, a resource 368 identifier, e.g., a URI [RFC3986] or IRI [RFC3987] from which the 369 domain name is extracted. Or some process not directly involving the 370 user may read the string from a file or obtain it in some other way. 371 Processing in this step and the next two are local matters, to be 372 accomplished prior to actual invocation of IDNA, but at least these 373 two steps must be accomplished in some way. 375 5.2. Conversion to Unicode 377 The local character set, character coding conventions, and, as 378 necessary, display and presentation conventions, are converted to 379 Unicode (without surrogates), paralleling the process described above 380 in Section 4.2. 382 5.3. Character Changes in Preprocessing or the User Interface 384 The Unicode string MAY then be processed, in a way specific to the 385 local environment, to make the result of the IDNA processing match 386 user expectations. For instance, it would be reasonable, at this 387 step, to convert all upper case characters to lower case, if this 388 makes sense in the user's environment. 390 Other examples of processing for localization might be applied, if 391 appropriate, at this point. They include interpreting the KANA 392 MIDDLE DOT as separating domain name components from each other, 393 mapping different "width" forms of the same character into the one 394 form permitted in labels, or giving special treatment to characters 395 whose presentation forms are dependent only on placement in the 396 label. Such localization changes are even further outside the scope 397 of this specification than the ones mentioned above. 399 Recommendations for preprocessing for global contexts (i.e., when 400 local considerations do not apply or cannot be used) and for maximum 401 interoperability with labels that might have been specified under 402 liberal readings of IDNA2003 are given in [IDNA2008-Rationale]. 404 Because these transformations are local, it is important that domain 405 names that might be passed between systems (e.g., in IRIs) be 406 U-labels or A-labels and not forms that might be accepted locally as 407 a consequence of this step. This step is not standardized as part of 408 IDNA, and is not further specified here. 410 5.4. A-label Input 412 If the input to this procedure appears to be an A-label (i.e., it 413 starts in "xn--"), the lookup application MAY attempt to convert it 414 to a U-label and apply the tests of Section 5.5 and, of course, the 415 conversion of Section 5.6 to that form. If the A-label is converted 416 to a U-label then the processing specified in those two sections MUST 417 yield an A-label identical to the original one. See also 418 Section 6.1. 420 In general, that conversion and testing should be performed if the 421 domain name will later be presented to the user in native character 422 form (this requires that the lookup application be IDNA-aware). 423 Applications that are not IDNA-aware will obviously omit that 424 testing; others may treat the string as opaque to avoid the 425 additional processing at the expense of providing less protection and 426 information to users. 428 5.5. Validation and Character List Testing 430 In parallel with the registration procedure, the Unicode string is 431 checked to verify that all characters that appear in it are valid for 432 IDNA resolution input. As discussed above and in 433 [IDNA2008-Rationale], the resolution check is more liberal than the 434 registration one. Putative labels with any of the following 435 characteristics MUST BE rejected prior to DNS lookup: 437 o Labels containing code points that are unassigned in the version 438 of Unicode being used by the application, i.e., in the 439 "Unassigned" Unicode category or the UNASSIGNED category of 440 [IDNA2008-Tables]. 442 o Labels that are not in NFC form. 444 o Labels containing prohibited code points, i.e., those that are 445 assigned to the "DISALLOWED" category in the permitted character 446 table [IDNA2008-Tables]. 448 o Labels containing code points that are shown in the permitted 449 character table as requiring a contextual rule and that are 450 flagged as requiring exceptional special processing on lookup 451 ("CONTEXTJ" in the Tables) MUST conform to the rule, which MUST be 452 present. 454 o Labels containing other code points that are shown in the 455 permitted character table as requiring a contextual rule 456 ("CONTEXTO" in the tables), but for which no such rule appears in 457 the table of rules. With the exception in the rule immediately 458 above, applications resolving DNS names or carrying out equivalent 459 operations are not required to test contextual rules, only to 460 verify that a rule exists. 462 o Labels whose first character is a combining mark. [[anchor17: Note 463 in Draft: this definition may need to be further tightened.]] 465 In addition, the application SHOULD apply the following test. The 466 test may be omitted in special circumstances, such as when the 467 resolver application knows that the conditions are enforced 468 elsewhere, because an attempt to resolve such strings will almost 469 certainly lead to a DNS lookup failure. However, applying the test 470 is likely to give much better information about the reason for a 471 lookup failure -- information that may be usefully passed to the user 472 when that is feasible -- then DNS resolution failure alone. 474 o Verification that the string is compliant with the requirements 475 for right to left characters, specified in [IDNA2008-BIDI]. 477 For all other strings, the resolver MUST rely on the presence or 478 absence of labels in the DNS to determine the validity of those 479 labels and the validity of the characters they contain. If they are 480 registered, they are presumed to be valid; if they are not, their 481 possible validity is not relevant. A resolver that declines to look 482 up a string that conforms to the above rules is not in conformance 483 with this protocol. 485 5.6. Punycode Conversion 487 The validated string, a U-label, is converted to an A-label using the 488 punycode algorithm. 490 5.7. DNS Name Resolution 492 The A-label is looked up in the DNS, using normal DNS procedures. 494 6. Name server Considerations 496 6.1. Processing Non-ASCII Strings 498 Existing DNS servers do not know the IDNA rules for handling non- 499 ASCII forms of IDNs, and therefore need to be shielded from them. 500 All existing channels through which names can enter a DNS server 501 database (for example, master files (as described in RFC 1034) and 502 DNS update messages [RFC2136]) are IDN-unaware because they predate 503 IDNA. Other sections of this document provide the needed shielding 504 by ensuring that internationalized domain names entering DNS server 505 databases through such channels have already been converted to their 506 equivalent ASCII A-label forms. 508 Because of the design of the algorithms in Section 4 and Section 5 (a 509 domain name containing only ASCII codepoints can not be converted to 510 an A-label), there can not be more than one A-label form for each 511 U-label. 513 The current update to the definition of the DNS protocol [RFC2181] 514 explicitly allows domain labels to contain octets beyond the ASCII 515 range (0000..007F), and this document does not change that. Note, 516 however, that there is no defined interpretation of octets 0080..00FF 517 as characters. If labels containing these octets are returned to 518 applications, unpredictable behavior could result. The A-label form, 519 which cannot contain those characters, is the only standard 520 representation for internationalized labels in the current DNS 521 protocol. 523 6.2. DNSSEC Authentication of IDN Domain Names 525 DNS Security [RFC2535] is a method for supplying cryptographic 526 verification information along with DNS messages. Public Key 527 Cryptography is used in conjunction with digital signatures to 528 provide a means for a requester of domain information to authenticate 529 the source of the data. This ensures that it can be traced back to a 530 trusted source, either directly or via a chain of trust linking the 531 source of the information to the top of the DNS hierarchy. 533 IDNA specifies that all internationalized domain names served by DNS 534 servers that cannot be represented directly in ASCII must use the 535 A-label form. Conversion to A-labels must be performed prior to a 536 zone being signed by the private key for that zone. Because of this 537 ordering, it is important to recognize that DNSSEC authenticates a 538 domain name containing A-labels or conventional LDH-labels, not 539 U-labels. In the presence of DNSSEC, no form of a zone file or query 540 response that contains a U-label may be signed or the signature 541 validated. 543 One consequence of this for sites deploying IDNA in the presence of 544 DNSSEC is that any special purpose proxies or forwarders used to 545 transform user input into IDNs must be earlier in the resolution flow 546 than DNSSEC authenticating nameservers for DNSSEC to work. 548 6.3. Root Server Considerations 550 IDNs in A-label form will generally be somewhat longer than current 551 domain names, so the bandwidth needed by the root servers is likely 552 to go up by a small amount. Also, queries and responses for IDNs 553 will probably be somewhat longer than typical queries today, so more 554 queries and responses may be forced to go to TCP instead of UDP. 556 7. Security Considerations 558 The general security principles and issues for IDNA appear in 559 [IDNA2008-Rationale]. The comments below are specific to this pair 560 of protocols, but should be read in the context of that material and 561 the definitions and specifications, identified there, on which this 562 one depends. 564 This memo describes procedures for registering and looking up labels 565 that are not valid according to the base DNS specifications (STD13 566 [RFC1034] [RFC1035] and Host Requirements [RFC1123]) because they 567 contain non-ASCII characters. These procedures depend on the use of 568 a special ASCII-compatable encoded form that contains only characters 569 permitted in host names by those earlier specifications. The 570 encoding is specified in [RFC3492]. No security issues such as 571 string length increases or new allowed values are introduced by the 572 encoding process or the use of these encoded values, apart from those 573 introduced by the ACE encoding itself. 575 Domain names (or portions of them) are sometimes compared against a 576 set of privileged or anti-privileged domains. In such situations it 577 is especially important that the comparisons be done properly, as 578 specified in requirement 2 of Section 3.1. For labels already in 579 ASCII form (i.e., are LDH-labels or A-labels), the proper comparison 580 reduces to the same case-insensitive ASCII comparison that has always 581 been used for ASCII labels. 583 The introduction of IDNA means that any existing labels that start 584 with the ACE prefix would be construed as A-labels, at least until 585 they failed one of the relevant tests, whether or not that was the 586 intent of the zone administrator or registrant. There is no evidence 587 that this has caused any practical problems since RFC 3490 was 588 adopted, but the risk still exists in principle. 590 8. IANA Considerations 592 IANA actions for this version of IDNA are specified in 593 [IDNA2008-Rationale]. 595 9. Change Log 597 [[anchor23: RFC Editor: Please remove this section.]] 599 9.1. Version -00 of draft-klensin-idnabis-protocol 601 Version -00 of this draft was produced in November 2007 by moving 602 text from draft-klensin-idnabis-issues and by copy considerable text 603 from RFC 3490. The result was then extensively edited. 605 9.2. Versions -01 and -02 of draft-klensin-idnabis-protocol 607 These versions reflected a number of editorial changes, some of them 608 significant, and alignment of terminology with 609 draft-faltstrom-idnabis-tables. 611 9.3. Version -03 of draft-klensin-idnabis-protocol 613 o Abstract rewritten to bring its length within RFC Editor 614 guidelines. 616 o Corrections and revisions in response to extensive comments by 617 Mark Davis and others. 619 o Small modifications to several operations, including moving the 620 Normalization steps to a different place in the sequence. 622 o Many editorial changes. 624 9.4. Version -04 of draft-klensin-idnabis-protocol 626 o Revised terminology and removed the MAYBE category as a 627 consequence of design discussions on 30 January 2003 and followup 628 conversations. Also restructured the various operations to treat 629 CONTEXTUAL RULE REQUIRED as a validation step (paralleling bidi), 630 rather than a category. Those changes required changes elsewhere 631 in the document for consistency. 633 o Changed the requirements for normalization, making this a 634 requirement on the calling application rather than an action of 635 this protocol. This is consistent with the general "mappings 636 belong somewhere else" principle. 638 o Updated references. 640 o More editorial work, some independent of the changes, described 641 immediately above. 643 9.5. Version -00 of draft-ietf-idnabis-protocol 645 o Clarified actions to be taken if an A-label is supplied as input. 647 o Moved the contextual rules appendix into this document from 648 draft-klensin-idnabis-issues and made an initial attempt at 649 defining the actual rules. Synchronized the list of characters in 650 that appendix with tables-01. 652 o Added an explicit discussion of A-label input. 654 o Inserted a test for double-hyphen here. 656 10. Contributors 658 While the listed editor held the pen, the original versions of this 659 document represent the joint work and conclusions of an ad hoc design 660 team consisting of the editor and, in alphabetic order, Harald 661 Alvestrand, Tina Dam, Patrik Faltstrom, and Cary Karp. This document 662 draws significantly on the original version of IDNA [RFC3490] both 663 conceptually and for specific text. This second-generation version 664 would not have been possible without the work that went into that 665 first version and its authors, Patrik Faltstrom, Paul Hoffman, and 666 Adam Costello. While Faltstrom was actively involved in the creation 667 of this version, Hoffman and Costello were not and should not be held 668 responsible for any errors or omissions. 670 11. Acknowledgements 672 This revision to IDNA would have been impossible without the 673 accumulated experience since RFC 3490 was published and resulting 674 comments and complaints of many people in the IETF, ICANN, and other 675 communities, too many people to list here. Nor would it have been 676 possible without RFC 3490 itself and the efforts of the Working Group 677 that defined it. Those people whose contributions are acknowledged 678 in RFC 3490, [RFC4690], and [IDNA2008-Rationale] were particularly 679 important. 681 12. References 683 12.1. Normative References 685 [IDNA2008-BIDI] 686 Alvestrand, H. and C. Karp, "An updated IDNA criterion for 687 right-to-left scripts", January 2008, . 691 [IDNA2008-Rationale] 692 Klensin, J., Ed., "Internationalizing Domain Names for 693 Applications (IDNA): Issues, Explanation, and Rationale", 694 February 2008, . 697 [IDNA2008-Tables] 698 Faltstrom, P., "The Unicode Codepoints and IDN", 699 February 2008, . 702 A version of this document, is available in HTML format at 703 http://stupid.domain.name/idnabis/ 704 draft-faltstrom-idnabis-tables-04.html 706 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 707 STD 13, RFC 1034, November 1987. 709 [RFC1035] Mockapetris, P., "Domain names - implementation and 710 specification", STD 13, RFC 1035, November 1987. 712 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application 713 and Support", STD 3, RFC 1123, October 1989. 715 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 716 Requirement Levels", BCP 14, RFC 2119, March 1997. 718 [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode 719 for Internationalized Domain Names in Applications 720 (IDNA)", RFC 3492, March 2003. 722 [Unicode-PropertyValueAliases] 723 The Unicode Consortium, "Unicode Character Database: 724 PropertyValueAliases", March 2008, . 727 [Unicode-RegEx] 728 The Unicode Consortium, "Unicode Technical Standard #18: 729 Unicode Regular Expressions", May 2005, 730 . 732 [Unicode-Scripts] 733 The Unicode Consortium, "Unicode Standard Annex #24: 734 Unicode Script Property", February 2008, 735 . 737 [Unicode-UAX15] 738 The Unicode Consortium, "Unicode Standard Annex #15: 739 Unicode Normalization Forms", 2006, 740 . 742 12.2. Informative References 744 [ASCII] American National Standards Institute (formerly United 745 States of America Standards Institute), "USA Code for 746 Information Interchange", ANSI X3.4-1968, 1968. 748 ANSI X3.4-1968 has been replaced by newer versions with 749 slight modifications, but the 1968 version remains 750 definitive for the Internet. 752 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 753 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 754 RFC 2136, April 1997. 756 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 757 Specification", RFC 2181, July 1997. 759 [RFC2535] Eastlake, D., "Domain Name System Security Extensions", 760 RFC 2535, March 1999. 762 [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, 763 "Internationalizing Domain Names in Applications (IDNA)", 764 RFC 3490, March 2003. 766 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 767 Resource Identifier (URI): Generic Syntax", STD 66, 768 RFC 3986, January 2005. 770 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 771 Identifiers (IRIs)", RFC 3987, January 2005. 773 [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and 774 Recommendations for Internationalized Domain Names 775 (IDNs)", RFC 4690, September 2006. 777 [RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for 778 Internationalized Email", RFC 4952, July 2007. 780 [Unicode] The Unicode Consortium, "The Unicode Standard, Version 781 5.0", 2007. 783 Boston, MA, USA: Addison-Wesley. ISBN 0-321-48091-0 785 Appendix A. The Contextual Rules Registry 787 [[anchor33: Note in Draft: the WG needs to figure out whether this 788 table stays as part of this document, is moved to a separate one, or 789 is incorporated into "tables". Regardless of where they are placed, 790 the WG will still need to review the specific content of the rules. 791 In this version of the document, the table remains something of a 792 illustrative placeholder, not a final specification.]] 794 As discussed in the IANA Considerations section of 795 [IDNA2008-Rationale], a registry of rules that define the contexts in 796 which particular PROTOCOL-VALID characters, characters associated 797 with a requirement for Contextual Information, are permitted. These 798 rules are expressed as tests on the label in which the characters 799 appear (all, or any part of, the label may be tested). 801 For each character specified as requiring a contextual rule, a rule 802 MAY be established with the following data elements: 804 1. The code point associated with the character. 806 2. The name of the character. 808 3. An indication as to whether the code point requires the rule be 809 processed at lookup time (this indication is equivalent to the 810 difference between "CONTEXTJ" and "CONTEXTO" in the tables 811 document [IDNA2008-Tables]). 813 4. A prose description of the contextual rule. 815 5. A description of the contextual rule using Unicode Regular 816 Expression notation [Unicode-RegEx]. Only a Level 1 817 implementation is needed for the expressions below, which also 818 make reference to the Unicode Script definition [Unicode-Scripts] 819 and the Unicode Property Value Aliases list 820 [Unicode-PropertyValueAliases]. Note that in these regular 821 expressions, the label is taken to be an entire line, i.e., "^" 822 refers to the beginning of the label and "$" refers to the end of 823 the label. 825 These regular expressions are used as tests. The contextual 826 requirement is met if there is a match for the regular expression 827 and not met if there is no match. 829 [[anchor34: Patrik and I (JcK) would like to find a way to state 830 these rules that does not require the reader and implementer to 831 understand what we believe to be a fairly exotic element of the 832 Unicode specification. Suggestions welcome.]] 834 6. An optional comment preceded by "#" 836 Should there be any conflict between the two statements of a rule, 837 the regular expression form MUST be considered normative until the 838 registry can be corrected. 840 The rules for the characters listed in the Tables document as 841 exception cases or Join_Controls and for which rules are being 842 defined at this time appear below. 844 [[anchor35: Note in draft: This table is not complete and the rule 845 entries below are temporarily only examples.]] 847 002D; HYPHEN-MINUS; F; 848 Must not appear at the beginning or end of a label; 849 Regular expression: 850 [^^]\u002D|\u00SD[^$] ; 851 # Note that a prohibition on having two hyphens as the third and 852 fourth characters of anything but a valid A-label appears in the 853 specification. 855 200C; ZERO WIDTH NON-JOINER; T; 856 Between two characters from the same script only. The script must 857 be one in which the use of this character causes significant 858 visual transformation of one or both of the adjacent characters; 859 Regular expression: 860 [\p(Script:Deva)\p(Script:Tamil)]\u200C[\p(Script:Deva)\p(Script: 861 Tamil)] ; 862 [[anchor36: That script list is _not_ complete and, in particular, 863 more Indic scripts certainly need to be listed. It also does not 864 correctly express the "same script" restriction mentioned in the 865 prose, since it only tests adjacent characters. Whether this 866 character is required for Arabic script, and with what 867 restrictions if it is, is under discussion in the WG and in other 868 forums. It is clear that a Unicode derived property for script 869 groups that would permit testing, e.g., "Indic Script", would be 870 very helpful here.]] 872 200D; ZERO WIDTH JOINER; T; 873 Between two characters from the same script only. The script must 874 be one in which the use of this character causes significant 875 visual transformation of one or both of the adjacent characters; 876 Regular expression: 877 [\p(Script:Deva)\p(Script:Tamil)]+ 878 \u200D[\p(Script:Deva)\p(Script:Tamil)]+ ; 879 [[anchor37: That script list is _not_ complete and, in particular, 880 more Indic scripts certainly need to be listed. It also does not 881 correctly express the "same script" restriction mentioned in the 882 prose, since it only tests adjacent characters. Whether this 883 character is required for Arabic script, and with what 884 restrictions if it is, is under discussion in the WG and in other 885 forums.]] 887 00B7; MIDDLE DOT; F; 888 Between two 'l' (U+006C) characters only, used to permit the 889 Catalan character ela geminada to be expressed; 890 Regular expression: 891 \u006C\u00B7\u006c ; 893 0375; GREEK LOWER NUMERAL SIGN (KERAIA); F; 894 Greek script only. Might be further restricted to specific 895 following characters; 896 Regular expression: 897 \0375\(Script:Greek) ; 899 02B9; MODIFIER LETTER PRIME; F;;; 900 # Permitted only in contexts in which GREEK LOWER NUMERAL SIGN, 901 U+0375, is permitted. GREEK NUMERAL SIGN, U+0374, and the Lower 902 Numeral Sign (U+0375) are indicators for numeric use of letters in 903 older Greek writing systems. U+02B9 is relevant because 904 normalization maps U+0374 into it.; 905 Regular expression: 906 \(Script:Greek)\02B9\(Script:Greek) ; 907 [[anchor38: The test is that the adjacent characters be in the 908 Greek script. It is not clear whether this is sufficient. The 909 requirement for a preceding Greek letter may not be necessary. 910 More input needed.]] 912 0483; COMBINING CYRILLIC TITLO; F; 913 Cyrillic script only. Might be further restricted to permit only 914 a preceding list of characters. 915 Regular expression: 916 \p(Script:Cyrillic)\u0483 ; 918 05F3; HEBREW PUNCTUATION GERESH; F; 919 The script of the preceding character and the subsequent 920 character, if any, MUST be Hebrew; 921 Regular expression: 922 \p(Script:Hebrew)\u05F3\p(Script:Hebrew)? ; 924 05F4; HEBREW PUNCTUATION GERSHAYIM; F 925 The script of the preceding character and the subsequent 926 character, if any, MUST be Hebrew; 927 Regular expression: 928 \p(Script:Hebrew)\u05F3\p(Script:Hebrew)? ; 930 3005; IDEOGRAPHIC ITERATION MARK; F; 931 MUST NOT be at the beginning of the label, and the previous 932 character MUST be in Han Script; 933 Regular expression: 934 \p(Script:Hani)\u30FB ; 936 303B; VERTICAL IDEOGRAPHIC ITERATION MARK; F; 937 MUST NOT be at the beginning of the label, and the previous 938 character MUST be in Han Script; 939 Regular expression: 940 \p(Script:Hani)\u303B ; 942 30FB; KATAKANA MIDDLE DOT; F; 943 Adjacent characters MUST be Katakana; 944 Regular expression: 945 \p(Script:Kana)\u30FB\p(Script:Kana) ; 947 While the information above is to be used to initialize the registry, 948 IANA should treat the table format in this Appendix simply as an 949 initial, tentative, suggestion. Subject to review and comment from 950 the IESG and any Expert Reviewers, IANA is responsible for, and 951 should develop, a format for that registry, or a copy of it 952 maintained in parallel, that is convenient for retrieval and machine 953 processing and publish the location of that version. 955 Author's Address 957 John C Klensin (editor) 958 1770 Massachusetts Ave, Ste 322 959 Cambridge, MA 02140 960 USA 962 Phone: +1 617 245 1457 963 Fax: 964 Email: john+ietf@jck.com 965 URI: 967 Full Copyright Statement 969 Copyright (C) The IETF Trust (2008). 971 This document is subject to the rights, licenses and restrictions 972 contained in BCP 78, and except as set forth therein, the authors 973 retain all their rights. 975 This document and the information contained herein are provided on an 976 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 977 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 978 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 979 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 980 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 981 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 983 Intellectual Property 985 The IETF takes no position regarding the validity or scope of any 986 Intellectual Property Rights or other rights that might be claimed to 987 pertain to the implementation or use of the technology described in 988 this document or the extent to which any license under such rights 989 might or might not be available; nor does it represent that it has 990 made any independent effort to identify any such rights. Information 991 on the procedures with respect to rights in RFC documents can be 992 found in BCP 78 and BCP 79. 994 Copies of IPR disclosures made to the IETF Secretariat and any 995 assurances of licenses to be made available, or the result of an 996 attempt made to obtain a general license or permission for the use of 997 such proprietary rights by implementers or users of this 998 specification can be obtained from the IETF on-line IPR repository at 999 http://www.ietf.org/ipr. 1001 The IETF invites any interested party to bring to its attention any 1002 copyrights, patents or patent applications, or other proprietary 1003 rights that may cover technology that may be required to implement 1004 this standard. Please address the information to the IETF at 1005 ietf-ipr@ietf.org.