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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Klensin 3 Internet-Draft September 26, 2008 4 Obsoletes: 3490 (if approved) 5 Intended status: Standards Track 6 Expires: March 30, 2009 8 Internationalized Domain Names in Applications (IDNA): Protocol 9 draft-ietf-idnabis-protocol-05.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 March 30, 2009. 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 . . . . . . . . . . . . . . . . . . . . . . 7 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 . . . . . . . . . . . . . . . . . . . 8 64 4.3.3. Registration Validation Summary . . . . . . . . . . . 8 65 4.4. Registry Restrictions . . . . . . . . . . . . . . . . . . 9 66 4.5. Punycode Conversion . . . . . . . . . . . . . . . . . . . 9 67 4.6. Insertion in the Zone . . . . . . . . . . . . . . . . . . 9 68 5. Domain Name Lookup Protocol . . . . . . . . . . . . . . . . . 9 69 5.1. Label String Input . . . . . . . . . . . . . . . . . . . . 10 70 5.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 10 71 5.3. Character Changes in Preprocessing or the User 72 Interface . . . . . . . . . . . . . . . . . . . . . . . . 10 73 5.4. A-label Input . . . . . . . . . . . . . . . . . . . . . . 11 74 5.5. Validation and Character List Testing . . . . . . . . . . 11 75 5.6. Punycode Conversion . . . . . . . . . . . . . . . . . . . 13 76 5.7. DNS Name Resolution . . . . . . . . . . . . . . . . . . . 13 77 6. Name Server Considerations . . . . . . . . . . . . . . . . . . 13 78 6.1. Processing Non-ASCII Strings . . . . . . . . . . . . . . . 13 79 6.2. DNSSEC Authentication of IDN Domain Names . . . . . . . . 13 80 6.3. Root and other DNS Server Considerations . . . . . . . . . 14 81 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 82 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 83 9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 15 84 9.1. Changes between Version -00 and -01 of 85 draft-ietf-idnabis-protocol . . . . . . . . . . . . . . . 15 86 9.2. Version -02 . . . . . . . . . . . . . . . . . . . . . . . 15 87 9.3. Version -03 . . . . . . . . . . . . . . . . . . . . . . . 16 88 9.4. Version -04 . . . . . . . . . . . . . . . . . . . . . . . 16 89 9.5. Version -05 . . . . . . . . . . . . . . . . . . . . . . . 16 90 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16 91 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 92 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 93 12.1. Normative References . . . . . . . . . . . . . . . . . . . 17 94 12.2. Informative References . . . . . . . . . . . . . . . . . . 18 95 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19 96 Intellectual Property and Copyright Statements . . . . . . . . . . 20 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 first two labels (the ones required to start in "_") on a record with 204 TYPE SRV MUST NOT be A-labels or U-labels (while it would be possible 205 to write a non-ASCII string with a leading underscore, conversion to 206 an A-label would be impossible without loss of information because 207 the underscore is not a letter, digit, or hyphen). Of course, those 208 labels may be part of a domain that uses IDN labels at higher levels 209 in the tree. 211 3.2.2. Non-domain-name Data Types Stored in the DNS 213 Although IDNA enables the representation of non-ASCII characters in 214 domain names, that does not imply that IDNA enables the 215 representation of non-ASCII characters in other data types that are 216 stored in domain names, specifically in the RDATA field for types 217 that have structured RDATA format. For example, an email address 218 local part is stored in a domain name in the RNAME field as part of 219 the RDATA of an SOA record (hostmaster@example.com would be 220 represented as hostmaster.example.com). IDNA specifically does not 221 update the existing email standards, which allow only ASCII 222 characters in local parts. Even though work is in progress to define 223 internationalization for email addresses [RFC4952], changes to the 224 email address part of the SOA RDATA would require action in other 225 standards, specifically those that specify the format of the SOA RR. 227 4. Registration Protocol 229 This section defines the procedure for registering an IDN. The 230 procedure is implementation independent; any sequence of steps that 231 produces exactly the same result for all labels is considered a valid 232 implementation. 234 Note that, while the registration and lookup protocols (Section 5) 235 are very similar in most respects, they are different and 236 implementers should carefully follow the steps they are implementing. 238 4.1. Proposed label 240 The registrant submits a request for an IDN. The user typically 241 produces the request string by the keyboard entry of a character 242 sequence in the local native character set (which might, of course, 243 be Unicode). The registry MAY permit submission of labels in A-label 244 form. If it does so, it SHOULD perform a conversion to a U-label, 245 perform the steps and tests described below, and verify that the 246 A-label produced by the step in Section 4.5 matches the one provided 247 as input. If, for some reason, it does not, the registration MUST be 248 rejected. 249 [[anchor9: Editorial: Should the sentences starting with "The 250 registry" be moved to 4.3? I.e., would they be more in sequence 251 there?]] 253 4.2. Conversion to Unicode and Normalization 255 Some system routine, or a localized front-end to the IDNA process, 256 ensures that the proposed label is a Unicode string or converts it to 257 one as appropriate. That string MUST be in Unicode Normalization 258 Form C (NFC [Unicode-UAX15]). 260 As a local implementation choice, the implementation MAY choose to 261 map some forbidden characters to permitted characters (for instance 262 mapping uppercase characters to lowercase ones), displaying the 263 result to the user, and allowing processing to continue. However, it 264 is strongly recommended that, to avoid any possible ambiguity, 265 entities responsible for zone files ("registries") accept 266 registrations only for A-labels (to be converted to U-labels by the 267 registry) or U-labels actually produced from A-labels, not forms 268 expected to be converted by some other process. 270 4.3. Permitted Character and Label Validation 272 4.3.1. Rejection of Characters that are not Permitted 274 The Unicode string is checked to verify that no characters that IDNA 275 does not permit in input appear in it. Those characters are 276 identified in the "DISALLOWED" and "UNASSIGNED" lists that are 277 discussed in [IDNA2008-Rationale]. The normative rules for producing 278 that list and the initial version of it are specified in 279 [IDNA2008-Tables]. Characters that are either DISALLOWED or 280 UNASSIGNED MUST NOT be part of labels being processed for 281 registration in the DNS. 283 4.3.2. Label Validation 285 The proposed label (in the form of a Unicode string, i.e., a putative 286 U-label) is then examined, performing tests that require examination 287 of more than one character. 289 4.3.2.1. Rejection of Confusing or Hostile Sequences in U-labels 291 The Unicode string MUST NOT contain "--" (two consecutive hyphens) in 292 the third and fourth character positions. 294 4.3.2.2. Leading Combining Marks 296 The first character of the string is examined to verify that it is 297 not a combining mark. If it is a combining mark, the string MUST NOT 298 be registered. 300 4.3.2.3. Contextual Rules 302 Each code point is checked for its identification as characters 303 requiring contextual processing for registration (the list of 304 characters appears as the combination of CONTEXTJ and CONTEXTO in 305 [IDNA2008-Tables]). If that indication appears, the table of 306 contextual rules is checked for a rule for that character. If no 307 rule is found, the proposed label is rejected and MUST NOT be 308 installed in a zone file. If one is found, it is applied (typically 309 as a test on the entire label or on adjacent characters). If the 310 application of the rule does not conclude that the character is valid 311 in context, the proposed label MUST BE rejected. (See the IANA 312 Considerations: IDNA Context Registry section of 313 [IDNA2008-Rationale].) 315 4.3.2.4. Labels Containing Characters Written Right to Left 317 Additional special tests for right-to-left strings are applied (See 318 [IDNA2008-BIDI]. Strings that contain right to left characters that 319 do not conform to the rule(s) identified there MUST NOT be inserted 320 as labels in zone files. 322 4.3.3. Registration Validation Summary 324 Strings that have been produced by the steps above, and whose 325 contents pass the above tests, are U-labels. 327 To summarize, tests are made here for invalid characters, invalid 328 combinations of characters, and for labels that are invalid even if 329 the characters they contain are valid individually. For example, 330 labels containing invisible ("zero-width") characters may be 331 permitted in context with characters whose presentation forms are 332 significantly changed by the presence or absence of the zero-width 333 characters, while other labels in which zero-width characters appear 334 may be rejected. 335 [[anchor16: Should the example text be removed or moved? Note that 336 I've been strongly encouraged to supply specific examples to reduce 337 abstraction and questions about the appropriateness of the text. 338 -JcK]] 340 4.4. Registry Restrictions 342 Registries at all levels of the DNS, not just the top level, are 343 expected to establish policies about the labels that may be 344 registered, and for the processes associated with that action. While 345 exact policies are not specified as part of IDNA2008 and it is 346 expected that different registries may specify different policies, 347 there SHOULD be policies. Even a trivial policy (e.g., "anything can 348 be registered in this zone that can be represented as an A-label - 349 U-label pair") has value because it provides notice to users and 350 applications implementers that the registry cannot be relied upon to 351 provide even minimal user-protection restrictions. These per- 352 registry policies and restrictions are an essential element of the 353 IDNA registration protocol even for registries (and corresponding 354 zone files) deep in the DNS hierarchy. As discussed in 355 [IDNA2008-Rationale], such restrictions have always existed in the 356 DNS. 358 The string produced by the above steps is checked and processed as 359 appropriate to local registry restrictions. Application of those 360 registry restrictions may result in the rejection of some labels or 361 the application of special restrictions to others. 363 4.5. Punycode Conversion 365 The resulting U-label is converted to an A-label (i.e., the encoding 366 of that label according to the Punycode algorithm [RFC3492] with the 367 ACE prefix added, i.e., the "xn--..." form). 368 [[anchor17: Explain why 3492 failures cannot occur or explain what to 369 do if they do.]] 371 4.6. Insertion in the Zone 373 The A-label is registered in the DNS by insertion into a zone. 375 5. Domain Name Lookup Protocol 377 Lookup is conceptually different from registration and different 378 tests are applied on the client. Although some validity checks are 379 necessary to avoid serious problems with the protocol (see 380 Section 5.5 ff.), the lookup-side tests are more permissive and rely 381 heavily on the assumption that names that are present in the DNS are 382 valid. 384 5.1. Label String Input 386 The user supplies a string in the local character set, typically by 387 typing it or clicking on, or copying and pasting, a resource 388 identifier, e.g., a URI [RFC3986] or IRI [RFC3987] from which the 389 domain name is extracted. Or some process not directly involving the 390 user may read the string from a file or obtain it in some other way. 391 Processing in this step and the next two are local matters, to be 392 accomplished prior to actual invocation of IDNA, but at least these 393 two steps must be accomplished in some way. 395 5.2. Conversion to Unicode 397 The string is converted from the local character set into Unicode, if 398 it is not already Unicode. The exact nature of this conversion is 399 beyond the scope of this document, but may involve normalization, as 400 described in Section 4.2. 402 5.3. Character Changes in Preprocessing or the User Interface 404 The Unicode string MAY then be processed to prevent confounding of 405 user expectations. For instance, it would be reasonable, at this 406 step, to convert all upper case characters to lower case, if this 407 makes sense in the user's environment. The procedures described in 408 this section are ordinarily useful only for processing direct user 409 input and when needed for backward compatibility with IDNA2003. In 410 general, IDNs appearing in files and those transmitted across the 411 network as part of protocols are expected to be in either ASCII form 412 (including A-labels) or to contain U-labels, not forms requiring 413 mapping or other conversions. 415 Other examples of processing for localization might be applied, 416 especially to direct user input, at this point. They include 417 interpreting various characters as separating domain name components 418 from each other (label separators) because they either look like 419 periods or are used to separate sentences, mapping halfwidth or 420 fullwidth East Asian characters to the common form permitted in 421 labels, or giving special treatment to characters whose presentation 422 forms are dependent only on placement in the label. Such 423 localization changes are also outside the scope of this 424 specification. 426 Recommendations for preprocessing for global contexts (i.e., when 427 local considerations do not apply or cannot be used) and for maximum 428 interoperability with labels that might have been specified under 429 liberal readings of IDNA2003 are given in [IDNA2008-Rationale]. It 430 is important to note that the intent of these specifications is that 431 labels in application protocols, files, or links are intended to be 432 in U-label or A-label form. Preprocessing MUST NOT map a character 433 that is valid in a label (i.e., one that is PROTOCOL-VALID or 434 permitted in any context) into another character. Excessively 435 liberal use of preprocessing, especially to strings stored in files, 436 poses a threat to consistent and predictable behavior for the user 437 even if not to actual interoperability. 439 Because these transformations are local, it is important that domain 440 names that might be passed between systems (e.g., in IRIs) be 441 U-labels or A-labels and not forms that might be accepted locally as 442 a consequence of this step. This step is not standardized as part of 443 IDNA, and is not further specified here. 445 5.4. A-label Input 447 If the input to this procedure appears to be an A-label (i.e., it 448 starts in "xn--"), the lookup application MAY attempt to convert it 449 to a U-label and apply the tests of Section 5.5 and, of course, the 450 conversion of Section 5.6 to that form. If the label is converted to 451 Unicode (i.e., to U-label form) using the Punycode decoding 452 algorithm, then the processing specified in those two sections MUST 453 be performed, and the label MUST be rejected if the resulting label 454 is not identical to the original. See also Section 6.1. 456 In general, that conversion and testing should be performed if the 457 domain name will later be presented to the user in native character 458 form (this requires that the lookup application be IDNA-aware). 459 Applications that are not IDNA-aware will obviously omit that 460 testing; others may treat the string as opaque to avoid the 461 additional processing at the expense of providing less protection and 462 information to users. 464 5.5. Validation and Character List Testing 466 As with the registration procedure, the Unicode string is checked to 467 verify that all characters that appear in it are valid for IDNA 468 lookup processing input. As discussed above and in 469 [IDNA2008-Rationale], the lookup check is more liberal than the 470 registration one. Putative labels with any of the following 471 characteristics MUST BE rejected prior to DNS lookup: 473 o Labels containing code points that are unassigned in the version 474 of Unicode being used by the application, i.e., in the 475 "Unassigned" Unicode category or the UNASSIGNED category of 476 [IDNA2008-Tables]. 478 o Labels that are not in NFC form. 480 o Labels containing prohibited code points, i.e., those that are 481 assigned to the "DISALLOWED" category in the permitted character 482 table [IDNA2008-Tables]. 484 o Labels containing code points that are shown in the permitted 485 character table as requiring a contextual rule and that are 486 flagged as requiring exceptional special processing on lookup 487 ("CONTEXTJ" in the Tables) but do not conform to that rule. 489 o Labels containing other code points that are shown in the 490 permitted character table as requiring a contextual rule 491 ("CONTEXTO" in the tables), but for which no such rule appears in 492 the table of rules. With the exception in the rule immediately 493 above, applications resolving DNS names or carrying out equivalent 494 operations are not required to test contextual rules, only to 495 verify that a rule exists. 497 o Labels whose first character is a combining mark.> 499 In addition, the application SHOULD apply the following test. The 500 test may be omitted in special circumstances, such as when the lookup 501 application knows that the conditions are enforced elsewhere, because 502 an attempt to look up and resolve such strings will almost certainly 503 lead to a DNS lookup failure. However, applying the test is likely 504 to give much better information about the reason for a lookup failure 505 -- information that may be usefully passed to the user when that is 506 feasible -- then DNS resolution failure information alone. In any 507 event, lookup applications should avoid attempting to resolve labels 508 that are invalid under that test. 510 o Verification that the string is compliant with the requirements 511 for right to left characters, specified in [IDNA2008-BIDI]. 513 For all other strings, the lookup application MUST rely on the 514 presence or absence of labels in the DNS to determine the validity of 515 those labels and the validity of the characters they contain. If 516 they are registered, they are presumed to be valid; if they are not, 517 their possible validity is not relevant. A lookup application that 518 declines to process and resolve up a string that conforms to the 519 above rules is not in conformance with this protocol. 521 5.6. Punycode Conversion 523 The validated string, a U-label, is converted to an A-label using the 524 Punycode algorithm with the ACE prefix added. 526 5.7. DNS Name Resolution 528 The A-label is looked up in the DNS, using normal DNS resolver 529 procedures. 531 6. Name Server Considerations 533 6.1. Processing Non-ASCII Strings 535 Existing DNS servers do not know the IDNA rules for handling non- 536 ASCII forms of IDNs, and therefore need to be shielded from them. 537 All existing channels through which names can enter a DNS server 538 database (for example, master files (as described in RFC 1034) and 539 DNS update messages [RFC2136]) are IDN-unaware because they predate 540 IDNA. Other sections of this document provide the needed shielding 541 by ensuring that internationalized domain names entering DNS server 542 databases through such channels have already been converted to their 543 equivalent ASCII A-label forms. 545 Because of the design of the algorithms in Section 4 and Section 5 (a 546 domain name containing only ASCII codepoints can not be converted to 547 an A-label), there can not be more than one A-label form for any 548 given U-label. 550 The current update to the definition of the DNS protocol [RFC2181] 551 explicitly allows domain labels to contain octets beyond the ASCII 552 range (0000..007F), and this document does not change that. Note, 553 however, that there is no defined interpretation of octets 0080..00FF 554 as characters. If labels containing these octets are returned to 555 applications, unpredictable behavior could result. The A-label form, 556 which cannot contain those characters, is the only standard 557 representation for internationalized labels in the current DNS 558 protocol. 560 6.2. DNSSEC Authentication of IDN Domain Names 562 DNS Security [RFC2535] is a method for supplying cryptographic 563 verification information along with DNS messages. Public Key 564 Cryptography is used in conjunction with digital signatures to 565 provide a means for a requester of domain information to authenticate 566 the source of the data. This ensures that it can be traced back to a 567 trusted source, either directly or via a chain of trust linking the 568 source of the information to the top of the DNS hierarchy. 570 IDNA specifies that all internationalized domain names served by DNS 571 servers that cannot be represented directly in ASCII must use the 572 A-label form. Conversion to A-labels must be performed prior to a 573 zone being signed by the private key for that zone. Because of this 574 ordering, it is important to recognize that DNSSEC authenticates a 575 domain name containing A-labels or conventional LDH-labels, not 576 U-labels. In the presence of DNSSEC, no form of a zone file or query 577 response that contains a U-label may be signed or the signature 578 validated. 580 One consequence of this for sites deploying IDNA in the presence of 581 DNSSEC is that any special purpose proxies or forwarders used to 582 transform user input into IDNs must be earlier in the lookup flow 583 than DNSSEC authenticating nameservers for DNSSEC to work. 585 6.3. Root and other DNS Server Considerations 587 IDNs in A-label form will generally be somewhat longer than current 588 domain names, so the bandwidth needed by the root servers is likely 589 to go up by a small amount. Also, queries and responses for IDNs 590 will probably be somewhat longer than typical queries historically, 591 so EDNS0 [RFC2671] support may be more important (otherwise, queries 592 and responses may be forced to go to TCP instead of UDP). 594 7. Security Considerations 596 The general security principles and issues for IDNA appear in 597 [IDNA2008-Rationale]. The comments below are specific to this pair 598 of protocols, but should be read in the context of that material and 599 the definitions and specifications, identified there, on which this 600 one depends. 602 This memo describes procedures for registering and looking up labels 603 that are not compatible with the preferred syntax described in the 604 base DNS specifications (STD13 [RFC1034] [RFC1035] and Host 605 Requirements [RFC1123]) because they contain non-ASCII characters. 606 These procedures depend on the use of a special ASCII-compatible 607 encoding form that contains only characters permitted in host names 608 by those earlier specifications. The encoding is specified in 609 [RFC3492]. No security issues such as string length increases or new 610 allowed values are introduced by the encoding process or the use of 611 these encoded values, apart from those introduced by the ACE encoding 612 itself. 614 Domain names (or portions of them) are sometimes compared against a 615 set domains to be given special treatment if a match occurs, e.g., 616 treated as more privileged than others or blocked in some way. In 617 such situations it is especially important that the comparisons be 618 done properly, as specified in requirement 2 of Section 3.1. For 619 labels already in ASCII form (i.e., are LDH-labels or A-labels), the 620 proper comparison reduces to the same case-insensitive ASCII 621 comparison that has always been used for ASCII labels. 623 The introduction of IDNA means that any existing labels that start 624 with the ACE prefix would be construed as A-labels, at least until 625 they failed one of the relevant tests, whether or not that was the 626 intent of the zone administrator or registrant. There is no evidence 627 that this has caused any practical problems since RFC 3490 was 628 adopted, but the risk still exists in principle. 630 8. IANA Considerations 632 IANA actions for this version of IDNA are specified in 633 [IDNA2008-Rationale]. The component of IDNA described in this 634 document does not require any IANA actions. 636 9. Change Log 638 [[anchor23: RFC Editor: Please remove this section.]] 640 9.1. Changes between Version -00 and -01 of draft-ietf-idnabis-protocol 642 o Corrected discussion of SRV records. 644 o Several small corrections for clarity. 646 o Inserted more "open issue" placeholders. 648 9.2. Version -02 650 o Rewrote the "conversion to Unicode" text in Section 5.2 as 651 requested on-list. 653 o Added a comment (and reference) about EDNS0 to the "DNS Server 654 Conventions" section, which was also retitled. 656 o Made several editorial corrections and improvements in response to 657 various comments. 659 o Added several new discussion placeholder anchors and updated some 660 older ones. 662 9.3. Version -03 664 o Trimmed change log, removing information about pre-WG drafts. 666 o Incorporated a number of changes suggested by Marcos Sanz in his 667 note of 2008.07.17 and added several more placeholder anchors. 669 o Several minor editorial corrections and improvements. 671 o "Editor" designation temporarily removed because the automatic 672 posting machinery does not accept it. 674 9.4. Version -04 676 o Removed Contextual Rule appendices for transfer to Tables. 678 o Several changes, including removal of discussion anchors, based on 679 discussions at IETF 72 (Dublin) 681 o Rewrote the preprocessing material (Section 5.3) somewhat. 683 9.5. Version -05 685 o Updated part of the A-label input explanation (Section 5.4) per 686 note from Erik van der Poel. 688 10. Contributors 690 While the listed editor held the pen, the original versions of this 691 document represent the joint work and conclusions of an ad hoc design 692 team consisting of the editor and, in alphabetic order, Harald 693 Alvestrand, Tina Dam, Patrik Faltstrom, and Cary Karp. This document 694 draws significantly on the original version of IDNA [RFC3490] both 695 conceptually and for specific text. This second-generation version 696 would not have been possible without the work that went into that 697 first version and its authors, Patrik Faltstrom, Paul Hoffman, and 698 Adam Costello. While Faltstrom was actively involved in the creation 699 of this version, Hoffman and Costello were not and should not be held 700 responsible for any errors or omissions. 702 11. Acknowledgements 704 This revision to IDNA would have been impossible without the 705 accumulated experience since RFC 3490 was published and resulting 706 comments and complaints of many people in the IETF, ICANN, and other 707 communities, too many people to list here. Nor would it have been 708 possible without RFC 3490 itself and the efforts of the Working Group 709 that defined it. Those people whose contributions are acknowledged 710 in RFC 3490, [RFC4690], and [IDNA2008-Rationale] were particularly 711 important. 713 Specific textual changes were incorporated into this document after 714 suggestions from Stephane Bortzmeyer, Mark Davis, Paul Hoffman, Erik 715 van der Poel, Marcos Sanz and others. 717 12. References 719 12.1. Normative References 721 [IDNA2008-BIDI] 722 Alvestrand, H. and C. Karp, "An updated IDNA criterion for 723 right-to-left scripts", July 2008, . 726 [IDNA2008-Rationale] 727 Klensin, J., Ed., "Internationalizing Domain Names for 728 Applications (IDNA): Issues, Explanation, and Rationale", 729 July 2008, . 732 [IDNA2008-Tables] 733 Faltstrom, P., "The Unicode Codepoints and IDNA", 734 July 2008, . 737 A version of this document is available in HTML format at 738 http://stupid.domain.name/idnabis/ 739 draft-ietf-idnabis-tables-02.html 741 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 742 STD 13, RFC 1034, November 1987. 744 [RFC1035] Mockapetris, P., "Domain names - implementation and 745 specification", STD 13, RFC 1035, November 1987. 747 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application 748 and Support", STD 3, RFC 1123, October 1989. 750 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 751 Requirement Levels", BCP 14, RFC 2119, March 1997. 753 [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode 754 for Internationalized Domain Names in Applications 755 (IDNA)", RFC 3492, March 2003. 757 [Unicode-PropertyValueAliases] 758 The Unicode Consortium, "Unicode Character Database: 759 PropertyValueAliases", March 2008, . 762 [Unicode-RegEx] 763 The Unicode Consortium, "Unicode Technical Standard #18: 764 Unicode Regular Expressions", May 2005, 765 . 767 [Unicode-Scripts] 768 The Unicode Consortium, "Unicode Standard Annex #24: 769 Unicode Script Property", February 2008, 770 . 772 [Unicode-UAX15] 773 The Unicode Consortium, "Unicode Standard Annex #15: 774 Unicode Normalization Forms", 2006, 775 . 777 12.2. Informative References 779 [ASCII] American National Standards Institute (formerly United 780 States of America Standards Institute), "USA Code for 781 Information Interchange", ANSI X3.4-1968, 1968. 783 ANSI X3.4-1968 has been replaced by newer versions with 784 slight modifications, but the 1968 version remains 785 definitive for the Internet. 787 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 788 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 789 RFC 2136, April 1997. 791 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 792 Specification", RFC 2181, July 1997. 794 [RFC2535] Eastlake, D., "Domain Name System Security Extensions", 795 RFC 2535, March 1999. 797 [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", 798 RFC 2671, August 1999. 800 [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, 801 "Internationalizing Domain Names in Applications (IDNA)", 802 RFC 3490, March 2003. 804 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 805 Resource Identifier (URI): Generic Syntax", STD 66, 806 RFC 3986, January 2005. 808 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 809 Identifiers (IRIs)", RFC 3987, January 2005. 811 [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and 812 Recommendations for Internationalized Domain Names 813 (IDNs)", RFC 4690, September 2006. 815 [RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for 816 Internationalized Email", RFC 4952, July 2007. 818 [Unicode] The Unicode Consortium, "The Unicode Standard, Version 819 5.0", 2007. 821 Boston, MA, USA: Addison-Wesley. ISBN 0-321-48091-0 823 Author's Address 825 John C Klensin 826 1770 Massachusetts Ave, Ste 322 827 Cambridge, MA 02140 828 USA 830 Phone: +1 617 245 1457 831 Email: john+ietf@jck.com 833 Full Copyright Statement 835 Copyright (C) The IETF Trust (2008). 837 This document is subject to the rights, licenses and restrictions 838 contained in BCP 78, and except as set forth therein, the authors 839 retain all their rights. 841 This document and the information contained herein are provided on an 842 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 843 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 844 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 845 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 846 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 847 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 849 Intellectual Property 851 The IETF takes no position regarding the validity or scope of any 852 Intellectual Property Rights or other rights that might be claimed to 853 pertain to the implementation or use of the technology described in 854 this document or the extent to which any license under such rights 855 might or might not be available; nor does it represent that it has 856 made any independent effort to identify any such rights. 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