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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Chris Newman 3 Internet-Draft Sun Microsystems 4 Intended Status: Proposed Standard Arnt Gulbrandsen 5 Oryx Mail Systems GmhH 6 Alexey Melnikov 7 Isode Limited 8 November 14, 2007 10 Internet Message Access Protocol Internationalization 11 draft-ietf-imapext-i18n-13.txt 13 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six 25 months and may be updated, replaced, or obsoleted by other documents 26 at any time. It is inappropriate to use Internet-Drafts as 27 reference material or to cite them other than as "work in progress". 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet- 31 Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft expires in February 2008. 36 Copyright Notice 38 Copyright (C) The IETF Trust (2007). 40 Abstract 42 Internet Message Access Protocol (IMAP) version 4rev1 has basic 43 support for non-ASCII characters in mailbox names and search 44 substrings. It also supports non-ASCII message headers and content 45 encoded as specified by Multipurpose Internet Mail Extensions 46 (MIME). This specification defines a collection of IMAP extensions 48 Internet-draft November 2007 50 which improve international support including comparator negotiation 51 for search, sort and thread, language negotiation for international 52 error text, and translations for namespace prefixes. 54 Table of Contents 56 1. Conventions Used in this Document . . . . . . . . . . . . . . 2 57 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . 3 59 3.1 LANGUAGE Extension Requirements . . . . . . . . . . . . . . . 3 60 3.2 LANGUAGE Command . . . . . . . . . . . . . . . . . . . . . . 4 61 3.3 LANGUAGE Response . . . . . . . . . . . . . . . . . . . . . . 6 62 3.4 TRANSLATION Extension to the NAMESPACE Response . . . . . . . 6 63 3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6 64 4. COMPARATOR Extension . . . . . . . . . . . . . . . . . . . . 7 65 4.1 COMPARATOR Extension Requirements . . . . . . . . . . . . . . 8 66 4.2 Comparators and Charsets . . . . . . . . . . . . . . . . . . 9 67 4.3 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . 9 68 4.4 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10 69 4.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 10 70 5. Other IMAP Internationalization Issues . . . . . . . . . . . 11 71 5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11 72 5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 11 73 5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 11 74 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 75 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 76 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 77 9. Relevant Standards for i18n IMAP Implementations . . . . . . 13 78 Normative References . . . . . . . . . . . . . . . . . . . . 13 79 Informative References . . . . . . . . . . . . . . . . . . . 14 80 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 15 81 Intellectual Property and Copyright Statements . . . . . . . 16 83 Conventions Used in This Document 85 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 86 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 87 document are to be interpreted as described in [RFC2119]. 89 The formal syntax use the Augmented Backus-Naur Form (ABNF) 90 [RFC4234] notation including the core rules defined in Appendix A. 91 The UTF8-related productions are defined in [RFC3629]. 93 In examples, "C:" and "S:" indicate lines sent by the client and 94 server respectively. If a single "C:" or "S:" label applies to 95 multiple lines, then the line breaks between those lines are for 97 Internet-draft November 2007 99 editorial clarity only and are not part of the actual protocol 100 exchange. 102 2. Introduction 104 This specification defines two IMAP4rev1 [RFC3501] extensions to 105 enhance international support. These extensions can be advertised 106 and implemented separately. 108 The LANGUAGE extension allows the client to request a suitable 109 language for protocol error messages and in combination with the 110 NAMESPACE extension [RFC2342] enables namespace translations. 112 The COMPARATOR extension allows the client to request a suitable 113 collation which will modify the behavior of the base specification's 114 SEARCH command as well as the SORT and THREAD extensions [SORT]. 115 This leverages the collation registry [RFC4790]. 117 3. LANGUAGE Extension 119 IMAP allows server responses to include human-readable text that in 120 many cases needs to be presented to the user. But that text is 121 limited to US-ASCII by the IMAP specification [RFC3501] in order to 122 preserve backwards compatibility with deployed IMAP implementations. 123 This section specifies a way for an IMAP client to negotiate which 124 language the server should use when sending human-readable text. 126 The LANGUAGE extension only provides a mechanism for altering fixed 127 server strings such as response text and NAMESPACE folder names. 128 Assigning localized language aliases to shared mailboxes would be 129 done with a separate mechanism such as the proposed METADATA 130 extension (see [METADATA]). 132 3.1 LANGUAGE Extension Requirements 134 IMAP servers that support this extension MUST list the keyword 135 LANGUAGE in their CAPABILITY response as well as in the greeting 136 CAPABILITY data. 138 A server that advertises this extension MUST use the language "i- 139 default" as described in [RFC2277] as its default language until 140 another supported language is negotiated by the client. A server 141 MUST include "i-default" as one of its supported languages. 143 Clients and servers that support this extension MUST also support 145 Internet-draft November 2007 147 the NAMESPACE extension [RFC2342]. 149 The LANGUAGE command is valid in all states. Clients are urged to 150 issue LANGUAGE before authentication, since some servers send 151 valuable user information as part of authentication (e.g. "password 152 is correct, but expired"). 154 3.2 LANGUAGE Command 156 Arguments: Optional language range arguments. 158 Response: A possible LANGUAGE response (see section 3.3). 159 A possible NAMESPACE response (see section 3.4). 161 Result: OK - Command completed 162 NO - Could not complete command 163 BAD - arguments invalid 165 The LANGUAGE command requests that human-readable text emitted by 166 the server be localized to a language matching one of the language 167 range argument as described by section 2 of [RFC4647]. 169 If the command succeeds, the server will return human-readable 170 responses in the first supported language specified. These 171 responses will be in UTF-8 [RFC3629]. The server MUST send a 172 LANGUAGE response specifying the language used, and the change takes 173 effect immediately after the LANGUAGE response. 175 If the command fails, the server continues to return human-readable 176 responses in the language it was previously using. 178 The special "default" language range argument indicates a request to 179 use a language designated as preferred by the server administrator. 180 The preferred language MAY vary based on the currently active user. 182 If a language range does not match a known language tag exactly but 183 does match a language by the rules of [RFC4647], the server MUST 184 send an untagged LANGUAGE response indicating the language selected. 186 If there aren't any arguments, the server SHOULD send an untagged 187 LANGUAGE response listing the languages it supports. If the server 188 is unable to enumerate the list of languages it supports it MAY 189 return a tagged NO response to the enumeration request. 191 < The server defaults to using English i-default responses until 192 the user explicitly changes the language. > 194 Internet-draft November 2007 196 C: A001 LOGIN KAREN PASSWORD 197 S: A001 OK LOGIN completed 199 < Client requested MUL language, which no server supports. > 201 C: A002 LANGUAGE MUL 202 S: A002 NO Unsupported language MUL 204 < A LANGUAGE command with no arguments is a request to enumerate 205 the list of languages the server supports. > 207 C: A003 LANGUAGE 208 S: * LANGUAGE (EN DE IT i-default) 209 S: A003 OK Supported languages have been enumerated 211 C: B001 LANGUAGE 212 S: B001 NO Server is unable to enumerate supported languages 214 < Once the client changes the language, all responses will be in 215 that language starting after the LANGUAGE response. Note that 216 this includes the NAMESPACE response. Because RFCs are in US- 217 ASCII, this document uses an ASCII transcription rather than 218 UTF-8 text, e.g. ue in the word "ausgefuehrt" > 220 C: C001 LANGUAGE DE 221 S: * LANGUAGE (DE) 222 S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" 223 ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" 224 "TRANSLATION" ("Gemeinsame Mailboxen/"))) 225 S: C001 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt 227 < If a server does not support the requested primary language, 228 responses will continue to be returned in the current language 229 the server is using. > 231 C: D001 LANGUAGE FR 232 S: D001 NO Diese Sprache ist nicht unterstuetzt 233 C: D002 LANGUAGE DE-IT 234 S: * LANGUAGE (DE-IT) 235 S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION" 236 ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" 237 "TRANSLATION" ("Gemeinsame Mailboxen/"))) 238 S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt 239 C: D003 LANGUAGE "default" 240 S: * LANGUAGE (DE) 241 S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt 243 < Server does not speak French, but does speak English. User 245 Internet-draft November 2007 247 speaks Canadian French and Canadian English. > 249 C: E001 LANGUAGE FR-CA EN-CA 250 S: * LANGUAGE (EN) 251 S: E001 OK Now speaking English 253 3.3 LANGUAGE Response 255 Contents: A list of one or more language tags. 257 The LANGUAGE response occurs as a result of a LANGUAGE command. A 258 LANGUAGE response with a list containing a single language tag 259 indicates that the server is now using that language. A LANGUAGE 260 response with a list containing multiple language tags indicates the 261 server is communicating a list of available languages to the client, 262 and no change in the active language has been made. 264 3.4 TRANSLATION Extension to the NAMESPACE Response 266 If localized representations of the namespace prefixes are available 267 in the selected language, the server SHOULD include these in the 268 TRANSLATION extension to the NAMESPACE response. 270 The TRANSLATION extension to the NAMESPACE response returns a single 271 string, containing the modified UTF-7 [RFC3501] encoded translation 272 of the namespace prefix. It is the responsibility of the client to 273 convert between the namespace prefix and the translation of the 274 namespace prefix when presenting mailbox names to the user. 276 In this example a server supports the IMAP4 NAMESPACE command. It 277 uses no prefix to the user's Personal Namespace, a prefix of "Other 278 Users" to its Other Users' Namespace and a prefix of "Public 279 Folders" to its only Shared Namespace. Since a client will often 280 display these prefixes to the user, the server includes a 281 translation of them that can be presented to the user. 283 C: A001 LANGUAGE DE-IT 284 S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" 285 ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" 286 "TRANSLATION" ("Gemeinsame Mailboxen/"))) 287 S: A001 OK LANGUAGE-Befehl ausgefuehrt 289 3.5 Formal Syntax 291 Internet-draft November 2007 293 The following syntax specification inherits ABNF [RFC4234] rules 294 from IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the 295 Identifying Languages [RFC4646], UTF-8 [RFC3629] and Collected 296 Extensions to IMAP4 ABNF [RFC4466]. 298 command-any =/ language-cmd 299 ; LANGUAGE command is valid in all states 301 language-cmd = "LANGUAGE" *(SP lang-range-quoted) 303 response-payload =/ language-data 305 language-data = "LANGUAGE" SP "(" lang-tag-quoted *(SP 306 lang-tag-quoted) ")" 308 namespace-trans = SP DQUOTE "TRANSLATION" DQUOTE SP "(" string ")" 309 ; the string is encoded in Modified UTF-7. 310 ; this is a subset of the syntax permitted by 311 ; the Namespace-Response-Extension rule in [RFC4466] 313 lang-range-quoted = astring 314 ; Once any literal wrapper or quoting is removed, this 315 ; follows the language-range rule in [RFC4647] 317 lang-tag-quoted = astring 318 ; Once any literal wrapper or quoting is removed, this follows 319 ; the Language-Tag rule in [RFC4646] 321 resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR 322 *(UTF8-TEXT-CHAR / "[") 323 ; After the server is changed to a language other than 324 ; i-default, this resp-text rule replaces the resp-text 325 ; rule from [RFC3501]. 327 UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4 328 ; UTF-8 excluding 7-bit control characters and "[" 330 4. COMPARATOR Extension 332 IMAP4rev1 [RFC3501] includes the SEARCH command which can be used to 333 locate messages matching criteria including human-readable text. 334 The SORT extension [SORT] to IMAP allows the client to ask the 335 server to determine the order of messages based on criteria 336 including human-readable text. These mechanisms require the ability 337 to support non-English search and sort functions. 339 This section defines an IMAP extension to negotiate use of 341 Internet-draft November 2007 343 comparators [RFC4790] to internationalize IMAP SEARCH, SORT and 344 THREAD. The IMAP extension consists of a new command to determine 345 or change the active comparator and a new response to indicate the 346 active comparator and possibly other available comparators. 348 The term "default comparator" refers to the comparator which is used 349 by SEARCH and SORT absent any negotiation using the COMPARATOR 350 command. The term "active comparator" refers to the comparator 351 which will be used within a session e.g. by SEARCH and SORT. The 352 COMPARATOR command is used to change the active comparator. 354 The active comparator applies to the following SEARCH keys: "BCC", 355 "BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER". If the 356 server also advertises the "SORT" extension, then the active 357 comparator applies to the following SORT keys: "CC", "FROM", 358 "SUBJECT" and "TO". If the server advertises THREAD=ORDEREDSUBJECT, 359 then the active comparator applies to the ORDEREDSUBJECT threading 360 algorithm. If the server advertises THREAD=REFERENCES, then the 361 active comparator applies to the subject field comparisons done by 362 REFERENCES threading algorithm. Future extensions may choose to 363 apply the active comparator to their SEARCH keys. 365 For SORT and THREAD, the pre-processing necessary to extract the 366 base subject text from a Subject header occurs prior to the 367 application of a comparator. 369 4.1 COMPARATOR Extension Requirements 371 IMAP servers that support this extension MUST list the keyword 372 COMPARATOR in their CAPABILITY data once IMAP enters authenticated 373 state, and MAY list that keyword in other states. 375 A server that advertises this extension MUST implement the 376 i;unicode-casemap comparator, as defined in [UCM]. It MAY implement 377 other comparators from the IANA registry established by [RFC4790]. 379 A server that advertises this extension SHOULD use i;unicode-casemap 380 as the default comparator. The selection of the default comparator 381 MAY be adjustable by the server administrator, and MAY be sensitive 382 to the current user. Once the IMAP connection enters authenticated 383 state, the default comparator MUST remain static for the remainder 384 of that connection. 386 A server that advertises this extension MUST support UTF-8 as a 387 SEARCH charset. 389 The COMPARATOR command is valid in authenticated and selected 391 Internet-draft November 2007 393 states. 395 Note that since SEARCH uses the substring operation, IMAP servers 396 can only implement collations that offer the substring operation 397 (see [RFC4790 section 4.2.2). Since SORT uses ordering operation 398 (and by implication equality), IMAP servers which advertise the SORT 399 extension can only implement collations that offer all three 400 operations (see [RFC4790] sections 4.2.2-4). 402 If the active collation does not provide the operations needed by an 403 IMAP command, the server MUST respond with a tagged BAD. 405 4.2 Comparators and Character Encodings 407 RFC 3501, section 6.4.4 says: 409 In all search keys that use strings, a message matches 410 the key if the string is a substring of the field. The 411 matching is case-insensitive. 413 When performing the SEARCH operation, the active comparator is 414 applied instead of the case-insensitive matching specified above. 416 An IMAP server which performs collation operations (e.g., as part of 417 commands such as SEARCH, SORT, THREAD) does so according to the 418 following procedure: 420 (a) MIME encoding (for example see [RFC2047] for headers and 421 [RFC2045] for body parts) MUST be removed in the texts being 422 collated. 424 If MIME encoding removal fails for a message (e.g., a body part 425 of the message has an unsupported Content-Transfer-Encoding, 426 uses characters not allowed by the Content-Transfer-Encoding, 427 etc.), the collation of this message is undefined by this 428 specification, and is handled in an implementation-dependent 429 manner. 431 (b) The decoded text from (a) MUST be converted to the charset 432 expected by the active comparator. 434 (c) For the substring operation: 435 If step (b) failed (e.g., the text is in an unknown charset, 436 contains a sequence which is not valid according in that 437 charset, etc.), the original decoded text from (a) (i.e., 438 before the charset conversion attempt) is collated using the 439 i;octet comparator (see [RFC4790]). 441 Internet-draft November 2007 443 If step (b) was successful, the converted text from (b) is 444 collated according to the active comparator. 446 For the ordering operation: 448 All strings that were successfully converted by step (b) are 449 separated from all strings that failed step (b). Strings in 450 each group are collated independently. All strings that fail 451 step (b) are collated (after applying step (a)) using the 452 i;octet comparator (see [RFC4790]). All strings successfully 453 converted by step (b) are collated using the active comparator. 454 The resulting sorted list is produced by appending all collated 455 "failed" strings after all strings collated using the active 456 comparator. 457 <> 459 If the substring operation (e.g., IMAP SEARCH) of the active 460 comparator returns the "undefined" result (see section 4.2.3 of 461 [RFC4790]) for either the text specified in the SEARCH command or 462 the message text, then the operation is repeated on the result of 463 step (a) using the i;octet comparator. 465 The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate 466 the following together: strings encoded using unknown or invalid 467 character encodings, strings in unrecognized charsets, and invalid 468 input (as defined by the active collation). 470 4.3 COMPARATOR Command 472 Arguments: Optional comparator order arguments. 474 Response: A possible COMPARATOR response (see Section 4.4). 476 Result: OK - Command completed 477 NO - No matching comparator found 478 BAD - arguments invalid 480 The COMPARATOR command is used to determine or change the active 481 comparator. When issued with no arguments, it results in a 482 COMPARATOR response indicating the currently active comparator. 484 When issued with one or more comparator argument, it changes the 485 active comparator as directed. (If more than one installed 486 comparator is matched by an argument, the first argument wins.) The 487 COMPARATOR response lists all matching comparators if more than one 489 Internet-draft November 2007 491 matches the specified patterns. 493 The argument "default" refers to the server's default comparator. 494 Otherwise each argument is an collation specification as defined in 495 the Internet Application Protocol Comparator Registry [RFC4790]. 497 < The client requests activating a Czech comparator if possible, 498 or else a generic international comparator which it considers 499 suitable for Czech. The server picks the first supported 500 comparator. > 502 C: A001 COMPARATOR "cz;*" i;basic 503 S: * COMPARATOR i;basic 504 S: A001 OK Will use i;basic for collation 506 4.4 COMPARATOR Response 508 Contents: The active comparator. 509 An optional list of available matching comparators 511 The COMPARATOR response occurs as a result of a COMPARATOR command. 512 The first argument in the comparator response is the name of the 513 active comparator. The second argument is a list of comparators 514 which matched any of the arguments to the COMPARATOR command and is 515 present only if more than one match is found. 517 4.5 Formal Syntax 519 The following syntax specification inherits ABNF [RFC4234] rules 520 from IMAP4rev1 [RFC3501], and Internet Application Protocol 521 Comparator Registry [RFC4790]. 523 command-auth =/ comparator-cmd 525 resp-text-code =/ "BADCOMPARATOR" / "BADMATCH" 527 comparator-cmd = "COMPARATOR" *(SP comp-order-quoted) 529 response-payload =/ comparator-data 531 comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "(" 532 comp-id-quoted *(SP comp-id-quoted) ")"] 534 comp-id-quoted = astring 535 ; Once any literal wrapper or quoting is removed, this 536 ; follows the collation-id rule from [RFC4790] 538 Internet-draft November 2007 540 comp-order-quoted = astring 541 ; Once any literal wrapper or quoting is removed, this 542 ; follows the collation-order rule from [RFC4790] 544 comp-sel-quoted = astring 545 ; Once any literal wrapper or quoting is removed, this 546 ; follows the collation-selected rule from [RFC4790] 548 4.6 UNICASEMAP Extension Requirements 550 An IMAP server that implements the i;unicode-casemap comparator 551 [UCM] and satisfies all requirements specified in sections 4, 4.1 552 and 4.2 of this document, but doesn't implement the COMPARATOR 553 command and response, SHOULD advertise the UNICASEMAP capability in 554 the CAPABILITY response. 556 5. Other IMAP Internationalization Issues 558 The following sections provide an overview of various other IMAP 559 internationalization issues. These issues are not resolved by this 560 specification, but could be resolved by other standards work, such 561 as that being done by the EAI group (see [IMAP-EAI]). 563 5.1 Unicode Userids and Passwords 565 IMAP4rev1 presently restricts the userid and password fields of the 566 LOGIN command to US-ASCII. The "userid" and "password" fields of the 567 IMAP LOGIN command are restricted to US-ASCII only until a future 568 standards track RFC states otherwise. Servers are encouraged to 569 validate both fields to make sure they conform to the formal syntax 570 of UTF-8 and to reject the LOGIN command if that syntax is violated. 571 Servers MAY reject the use of any 8-bit in the "userid" or 572 "password" field. 574 When AUTHENTICATE is used, some servers may support userids and 575 passwords in Unicode [RFC3490] since SASL (see [RFC4422]) allows 576 that. However, such userids cannot be used as part of email 577 addresses. 579 5.2 UTF-8 Mailbox Names 581 The modified UTF-7 mailbox naming convention described in section 582 5.1.3 of RFC 3501 is best viewed as an transition from the status 583 quo in 1996 when modified UTF-7 was first specified. At that time, 585 Internet-draft November 2007 587 there was widespread unofficial use of local character sets such as 588 ISO-8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant 589 non-interoperability. 591 The requirements in section 5.1 of RFC 3501 are very important if 592 we're ever going to be able to deploy UTF-8 mailbox names. Servers 593 are encouraged to enforce them. 595 5.3 UTF-8 Domains, Addresses and Mail Headers 597 There is now an IETF standard for Internationalizing Domain Names in 598 Applications [RFC3490]. While IMAP clients are free to support this 599 standard, an argument can be made that it would be helpful to simple 600 clients if the IMAP server could perform this conversion (the same 601 argument would apply to MIME header encoding [RFC2047]). However, 602 it would be unwise to move forward with such work until the work in 603 progress to define the format of international email addresses is 604 complete. 606 6. IANA Considerations 608 The IANA is requested to add LANGUAGE, COMPARATOR and UNICASEMAP to 609 the IMAP4 Capabilities Registry. [Note to IANA: 610 http://www.iana.org/assignments/imap4-capabilities] 612 7. Security Considerations 614 The LANGUAGE extension makes a new command available in "Not 615 Authenticated" state in IMAP. Some IMAP implementations run with 616 root privilege when the server is in "Not Authenticated" state and 617 do not revoke that privilege until after authentication is complete. 618 Such implementations are particularly vulnerable to buffer overflow 619 security errors at this stage and need to implement parsing of this 620 command with extra care. 622 A LANGUAGE command issued prior to activation of a security layer is 623 subject to an active attack which suppresses or modifies the 624 negotiation and thus makes STARTTLS or authentication error messages 625 more difficult to interpret. This is not a new attack as the error 626 messages themselves are subject to active attack. Clients MUST re- 627 issue the LANGUAGE command once a security layer is active, so this 628 does not impact subsequent protocol operations. 630 Both the LANGUAGE and COMPARATOR extensions use the UTF-8 charset, 631 thus the security considerations for UTF-8 [RFC3629] are relevent. 633 Internet-draft November 2007 635 However, neither uses UTF-8 for identifiers so the most serious 636 concerns do not apply. 638 8. Acknowledgements 640 The LANGUAGE extension is based on a previous Internet draft by Mike 641 Gahrns and Alexey Melnikov, a substantial portion of the text in 642 that section was written by them. Many people have participated in 643 discussions about an IMAP Language extension in the various fora of 644 the IETF and Internet working groups, so any list of contributors is 645 bound to be incomplete. However, the authors would like to thank 646 Andrew McCown for early work on the original proposal, John Myers 647 for suggestions regarding the namespace issue, along with Jutta 648 Degener, Mark Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo 649 and Martin Duerst for their many suggestions that have been 650 incorporated into this document. 652 Initial discussion of the COMPARATOR extension involved input from 653 Mark Crispin and other participants of the IMAP Extensions WG. 655 9. Relevant Standards for i18n IMAP Implementations 657 This is a non-normative list of standards to consider when 658 implementing i18n aware IMAP software. 660 o The LANGUAGE and COMPARATOR extensions to IMAP (this 661 specification). 662 o The 8-bit rules for mailbox naming in section 5.1 of RFC 3501. 663 o The Mailbox International Naming Convention in section 5.1.3 of 664 RFC 3501. 665 o MIME [RFC2045] for message bodies. 666 o MIME header encoding [RFC2047] for message headers. 667 o The IETF EAI working group. 668 o MIME Parameter Value and Encoded Word Extensions [RFC2231] for 669 filenames. Quality IMAP server implementations will 670 automatically combine multipart parameters when generating the 671 BODYSTRUCTURE. There is also some deployed non-standard use of 672 MIME header encoding inside double-quotes for filenames. 673 o IDNA [RFC3490] and punycode [RFC3492] for domain names 674 (presently only relevant to IMAP clients). 675 o The UTF-8 charset [RFC3629]. 676 o The IETF policy on Character Sets and Languages [RFC2277]. 678 Normative References 680 Internet-draft November 2007 682 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 683 Requirement Levels", BCP 14, RFC 2119, March 1997. 685 [RFC2277] Alvestrand, "IETF Policy on Character Sets and 686 Languages", BCP 18, RFC 2277, January 1998. 688 [RFC2342] Gahrns, Newman, "IMAP4 Namespace", RFC 2342, May 1998. 690 [RFC3501] Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 691 4rev1", RFC 3501, March 2003. 693 [RFC3629] Yergeau, "UTF-8, a transformation format of ISO 10646", 694 STD 63, RFC 3629, November 2003. 696 [RFC4234] Crocker, Overell, "Augmented BNF for Syntax 697 Specifications: ABNF", RFC 4234, Brandenburg 698 Internetworking, Demon Internet Ltd, October 2005. 700 [RFC4422] Melnikov, Zeilenga, "Simple Authentication and Security 701 Layer (SASL)", RFC 4422, June 2006. 703 [RFC4466] Melnikov, Daboo, "Collected Extensions to IMAP4 ABNF", 704 RFC 4466, Isode Ltd., April 2006. 706 [RFC4646] Philips, Davis, "Tags for Identifying Languages", BCP 47, 707 RFC 4646, September 2006. 709 [RFC4647] Philips, Davis, "Matching of Language Tags", BCP 47, RFC 710 4647, September 2006. 712 [RFC4790] Newman, Duerst, Gulbrandsen, "Internet Application 713 Protocol Comparator Registry", RFC 4790, February 2007 715 [SORT] Crispin, M. and K. Murchison, "INTERNET MESSAGE ACCESS 716 PROTOCOL - SORT AND THREAD EXTENSION", draft-ietf- 717 imapext-sort-19 (work in progress), November 2006. 719 [UCM] Crispin, "i;unicode-casemap - Simple Unicode Collation 720 Algorithm", RFC 5051, October 2007. 722 [RFC2045] Freed, Borenstein, "Multipurpose Internet Mail Extensions 723 (MIME) Part One: Format of Internet Message Bodies", RFC 724 2045, November 1996. 726 [RFC2047] Moore, "MIME (Multipurpose Internet Mail Extensions) Part 727 Three: Message Header Extensions for Non-ASCII Text", RFC 728 2047, November 1996. 730 Internet-draft November 2007 732 Informative References 734 [RFC2231] Freed, Moore, "MIME Parameter Value and Encoded Word 735 Extensions: Character Sets, Languages, and 736 Continuations", RFC 2231, November 1997. 738 [RFC3490] Faltstrom, Hoffman, Costello, "Internationalizing Domain 739 Names in Applications (IDNA)", RFC 3490, March 2003. 741 [RFC3492] Costello, "Punycode: A Bootstring encoding of Unicode for 742 Internationalized Domain Names in Applications (IDNA)", 743 RFC 3492, March 2003. 745 [METADATA] Daboo, C., "IMAP METADATA Extension", draft-daboo-imap- 746 annotatemore-11 (work in progress), November 2006. 748 [IMAP-EAI] Resnick, Newman, "IMAP Support for UTF-8", draft-ietf- 749 eai-imap-utf8 (work in progress), May 2006. 751 Authors' Addresses 753 Chris Newman 754 Sun Microsystems 755 3401 Centrelake Dr., Suite 410 756 Ontario, CA 91761 757 US 759 Email: chris.newman@sun.com 761 Arnt Gulbrandsen 762 Oryx Mail Systems GmbH 763 Schweppermannstr. 8 764 D-81671 Muenchen 765 Germany 767 Email: arnt@oryx.com 769 Fax: +49 89 4502 9758 771 Alexey Melnikov 772 Isode Limited 773 5 Castle Business Village, 36 Station Road, 774 Hampton, Middlesex, TW12 2BX, UK 776 Internet-draft November 2007 778 Email: Alexey.Melnikov@isode.com 780 Internet-draft November 2007 782 Intellectual Property Statement 784 The IETF takes no position regarding the validity or scope of any 785 Intellectual Property Rights or other rights that might be claimed 786 to pertain to the implementation or use of the technology described 787 in this document or the extent to which any license under such 788 rights might or might not be available; nor does it represent that 789 it has made any independent effort to identify any such rights. 790 Information on the procedures with respect to rights in RFC 791 documents can be found in BCP 78 and BCP 79. 793 Copies of IPR disclosures made to the IETF Secretariat and any 794 assurances of licenses to be made available, or the result of an 795 attempt made to obtain a general license or permission for the use 796 of such proprietary rights by implementers or users of this 797 specification can be obtained from the IETF on-line IPR repository 798 at http://www.ietf.org/ipr. 800 The IETF invites any interested party to bring to its attention any 801 copyrights, patents or patent applications, or other proprietary 802 rights that may cover technology that may be required to implement 803 this standard. 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