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'UTR36' == Outdated reference: A later version (-12) exists of draft-ietf-precis-mappings-07 == Outdated reference: A later version (-19) exists of draft-ietf-precis-nickname-09 -- Obsolete informational reference (is this intentional?): RFC 3454 (Obsoleted by RFC 7564) -- Obsolete informational reference (is this intentional?): RFC 3490 (Obsoleted by RFC 5890, RFC 5891) -- Obsolete informational reference (is this intentional?): RFC 3920 (Obsoleted by RFC 6120) -- Obsolete informational reference (is this intentional?): RFC 3921 (Obsoleted by RFC 6121) -- Obsolete informational reference (is this intentional?): RFC 6122 (Obsoleted by RFC 7622) Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 XMPP P. Saint-Andre 3 Internet-Draft &yet 4 Obsoletes: 6122 (if approved) March 31, 2014 5 Intended status: Standards Track 6 Expires: October 2, 2014 8 Extensible Messaging and Presence Protocol (XMPP): Address Format 9 draft-ietf-xmpp-6122bis-12 11 Abstract 13 This document defines the address format for the Extensible Messaging 14 and Presence Protocol (XMPP), including support for code points 15 outside the ASCII range. This document obsoletes RFC 6122. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on October 2, 2014. 34 Copyright Notice 36 Copyright (c) 2014 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 3. Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 3.1. Fundamentals . . . . . . . . . . . . . . . . . . . . . . 3 55 3.2. Domainpart . . . . . . . . . . . . . . . . . . . . . . . 5 56 3.3. Localpart . . . . . . . . . . . . . . . . . . . . . . . . 6 57 3.4. Resourcepart . . . . . . . . . . . . . . . . . . . . . . 8 58 3.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9 59 4. Enforcement in JIDs and JID Parts . . . . . . . . . . . . . . 12 60 5. Internationalization Considerations . . . . . . . . . . . . . 14 61 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 62 6.1. JIDlocalIdentifierClass . . . . . . . . . . . . . . . . . 14 63 6.2. JIDresourceFreeformClass . . . . . . . . . . . . . . . . 15 64 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 65 7.1. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 16 66 7.2. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 16 67 7.3. Address Spoofing . . . . . . . . . . . . . . . . . . . . 16 68 7.3.1. Address Forging . . . . . . . . . . . . . . . . . . . 16 69 7.3.2. Address Mimicking . . . . . . . . . . . . . . . . . . 17 70 8. Conformance Requirements . . . . . . . . . . . . . . . . . . 18 71 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 72 9.1. Normative References . . . . . . . . . . . . . . . . . . 20 73 9.2. Informative References . . . . . . . . . . . . . . . . . 21 74 Appendix A. Differences from RFC 6122 . . . . . . . . . . . . . 24 75 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 25 76 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 25 78 1. Introduction 80 The Extensible Messaging and Presence Protocol (XMPP) [RFC6120] is an 81 application profile of the Extensible Markup Language [XML] for 82 streaming XML data in close to real time between any two or more 83 network-aware entities. The address format for XMPP entities was 84 originally developed in the Jabber open-source community in 1999, 85 first described by [XEP-0029] in 2002, and then defined canonically 86 by [RFC3920] in 2004 and [RFC6122] in 2011. 88 As specified in RFC 3920 and RFC 6122, the XMPP address format used 89 the "stringprep" technology for preparation of non-ASCII characters 90 [RFC3454]. Following the migration of internationalized domain names 91 away from stringprep, this document defines the XMPP address format 92 in a way that no longer depends on stringprep (see the PRECIS problem 93 statement [RFC6885]). Instead, this document builds upon the 94 internationalization framework defined by the IETF's PRECIS Working 95 Group [I-D.ietf-precis-framework], while attempting to ensure that 96 the characters allowed in Jabber IDs under stringprep are still 97 allowed and handled in the same way under PRECIS. 99 This document obsoletes RFC 6122. 101 2. Terminology 103 Many important terms used in this document are defined in 104 [I-D.ietf-precis-framework], [RFC5890], [RFC6120], [RFC6365], and 105 [UNICODE]. 107 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 108 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 109 "OPTIONAL" in this document are to be interpreted as described in 110 [RFC2119]. 112 3. Addresses 114 3.1. Fundamentals 116 An XMPP entity is anything that can communicate using XMPP. For 117 historical reasons, the network address of an XMPP entity is called a 118 Jabber ID ("JID"). A valid JID is a string of Unicode code points 119 [UNICODE], encoded using UTF-8 [RFC3629], and structured as an 120 ordered sequence of localpart, domainpart, and resourcepart, where 121 the first two parts are demarcated by the '@' character used as a 122 separator and the last two parts are similarly demarcated by the '/' 123 character (e.g., ). 125 The syntax for a JID is defined as follows using the Augmented 126 Backus-Naur Form (ABNF) as specified in [RFC5234]. 128 jid = [ localpart "@" ] domainpart [ "/" resourcepart ] 129 localpart = 1*1023(localpoint) 130 ; 131 ; a "localpoint" is a UTF-8 encoded 132 ; Unicode code point that conforms to 133 ; the "JIDlocalIdentifierClass" profile 134 ; of the PRECIS IdentifierClass 135 ; 136 domainpart = IP-literal / IPv4address / ifqdn 137 ; 138 ; the "IPv4address" and "IP-literal" 139 ; rules are defined in RFC 3986, and 140 ; the first-match-wins (a.k.a. "greedy") 141 ; algorithm described in RFC 3986 142 ; applies to the matching process 143 ; 144 ; note well that reuse of the IP-literal 145 ; rule from RFC 3986 implies that IPv6 146 ; addresses are enclosed in square 147 ; brackets (i.e., beginning with '[' 148 ; and ending with ']') 149 ; 150 ifqdn = 1*1023(domainpoint) 151 ; 152 ; a "domainpoint" is a UTF-8 encoded 153 ; Unicode code point that conforms to 154 ; RFC 5890 155 ; 156 resourcepart = 1*1023(resourcepoint) 157 ; 158 ; a "resourcepoint" is a UTF-8 encoded 159 ; Unicode code point that conforms to 160 ; the "JIDresourceFreeformClass" profile 161 ; of the PRECIS FreeformClass 162 ; 164 All JIDs are based on the foregoing structure. However, note that 165 the formal syntax provided above does not capture all of the rules 166 and restrictions that apply to JIDs, which are described below. 168 Each allowable portion of a JID (localpart, domainpart, and 169 resourcepart) MUST NOT be zero octets in length and MUST NOT be more 170 than 1023 octets in length, resulting in a maximum total size 171 (including the '@' and '/' separators) of 3071 octets. 173 Implementation Note: The length limits on JIDs and parts of JIDs 174 are based on octets (bytes), not characters. UTF-8 encoding can 175 result in more than one octet per character. 177 Implementation Note: When dividing a JID into its component parts, 178 an implementation needs to match the separator characters '@' and 179 '/' before applying any transformation algorithms, which might 180 decompose certain Unicode code points to the separator characters 181 (e.g., under Unicode Normalization Form KC U+FE6B SMALL COMMERCIAL 182 AT decomposes to U+0040 COMMERCIAL AT, although note that this 183 decomposition does not occur under Unicode Normalization C, which 184 is used in this specification). 186 This document defines the native format for JIDs; see [RFC5122] for 187 information about the representation of a JID as a Uniform Resource 188 Identifier (URI) [RFC3986] or Internationalized Resource Identifier 189 (IRI) [RFC3987] and the extraction of a JID from an XMPP URI or IRI. 191 3.2. Domainpart 193 The domainpart of a JID is that portion after the '@' character (if 194 any) and before the '/' character (if any); it is the primary 195 identifier and is the only REQUIRED element of a JID (a mere 196 domainpart is a valid JID). Typically a domainpart identifies the 197 "home" server to which clients connect for XML routing and data 198 management functionality. However, it is not necessary for an XMPP 199 domainpart to identify an entity that provides core XMPP server 200 functionality (e.g., a domainpart can identify an entity such as a 201 multi-user chat service [XEP-0045], a publish-subscribe service 202 [XEP-0060], or a user directory). 204 The domainpart for every XMPP service MUST be a fully-qualified 205 domain name (FQDN), an IPv4 address, an IPv6 address, or an 206 unqualified hostname (i.e., a text label that is resolvable on a 207 local network). 209 Informational Note: The term "fully-qualified domain name" is not 210 well defined. In [RFC1034] it is also called an absolute domain 211 name, and the two terms are associated in [RFC1535]. The earliest 212 use of the term can be found in [RFC1123]. References to those 213 older specifications ought not to be construed as limiting the 214 characters of a fully-qualified domain name to the ASCII range; 215 for example, [RFC5890] mentions that a fully-qualified domain name 216 can contain one or more U-labels. 218 Interoperability Note: Domainparts that are IP addresses might not 219 be accepted by other services for the purpose of server-to-server 220 communication, and domainparts that are unqualified hostnames 221 cannot be used on public networks because they are resolvable only 222 on a local network. 224 If the domainpart includes a final character considered to be a label 225 separator (dot) by [RFC1034], this character MUST be stripped from 226 the domainpart before the JID of which it is a part is used for the 227 purpose of routing an XML stanza, comparing against another JID, or 228 constructing an XMPP URI or IRI [RFC5122]. In particular, such a 229 character MUST be stripped before any other canonicalization steps 230 are taken. 232 In general, the content of a domainpart is an Internationalized 233 Domain Name ("IDN") as described in the specifications for 234 Internationalized Domain Names in Applications (commonly called 235 "IDNA2008"), and a domainpart is an "IDNA-aware domain name slot" as 236 defined in [RFC5890]. The following rules apply to a domainpart that 237 consists of a fully-qualified domain name and MUST be applied in the 238 following order: 240 1. The domainpart MUST contain only NR-LDH labels and U-labels as 241 defined in [RFC5890] and MUST consist only of Unicode code points 242 that conform to the rules specified in [RFC5892] (which includes 243 Unicode normalization). This implies that the domainpart MUST 244 NOT include A-labels as defined in [RFC5890]; each A-label MUST 245 be converted to a U-label during preparation of a domainpart, and 246 comparison MUST be performed using U-labels, not A-labels. 248 2. All uppercase and titlecase code points within the domainpart 249 MUST be mapped to their lowercase equivalents, preferably using 250 Unicode Default Case Folding as defined in Chapter 3 of the 251 Unicode Standard [UNICODE]. 253 3. Fullwidth and halfwidth characters within the domainpart MUST be 254 mapped to their decomposition mappings. 256 Implementation Note: The foregoing order is different from the 257 order for localparts and resourceparts as described below, to 258 maintain consistency with the IDNA methods in both [RFC5892] and 259 [RFC5895]. 261 After any and all normalization, conversion, and mapping of code 262 points, a domainpart MUST NOT be zero octets in length and MUST NOT 263 be more than 1023 octets in length. (Naturally, the length limits of 264 [RFC1034] apply, and nothing in this document is to be interpreted as 265 overriding those more fundamental limits.) 267 3.3. Localpart 269 The localpart of a JID is an optional identifier placed before the 270 domainpart and separated from the latter by the '@' character. 271 Typically a localpart uniquely identifies the entity requesting and 272 using network access provided by a server (i.e., a local account), 273 although it can also represent other kinds of entities (e.g., a chat 274 room associated with a multi-user chat service [XEP-0045]). The 275 entity represented by an XMPP localpart is addressed within the 276 context of a specific domain (i.e., ). 278 A localpart MUST NOT be zero octets in length and MUST NOT be more 279 than 1023 octets in length. This rule is to be enforced after any 280 normalization and mapping of code points. 282 A localpart MUST consist only of Unicode code points that conform to 283 the "JIDlocalIdentifierClass" profile of the "IdentifierClass" base 284 string class defined in [I-D.ietf-precis-framework]. The 285 JIDlocalIdentifierClass profile includes all code points allowed by 286 the IdentifierClass base class, with the exception of the following 287 characters that are explicitly disallowed in XMPP localparts: 289 U+0022 (QUOTATION MARK), i.e., " 291 U+0026 (AMPERSAND), i.e., & 293 U+0027 (APOSTROPHE), i.e., ' 295 U+002F (SOLIDUS), i.e., / 297 U+003A (COLON), i.e., : 299 U+003C (LESS-THAN SIGN), i.e., < 301 U+003E (GREATER-THAN SIGN), i.e., > 303 U+0040 (COMMERCIAL AT), i.e., @ 305 Implementation Note: An XMPP-specific method for escaping the 306 above-listed characters (along with U+0020, i.e., ASCII SPACE) has 307 been defined in the JID Escaping specification [XEP-0106]. 309 The normalization and mapping rules for the JIDlocalIdentifierClass 310 are as follows, where the operations specified MUST be completed in 311 the order shown: 313 1. Fullwidth and halfwidth characters MUST be mapped to their 314 decomposition mappings. 316 2. Uppercase and titlecase characters MUST be mapped to their 317 lowercase equivalents, preferably using Unicode Default Case 318 Folding as defined in Chapter 3 of the Unicode Standard 319 [UNICODE]. 321 3. All characters MUST be mapped using Unicode Normalization Form C 322 (NFC). 324 With regard to directionality, applications MUST apply the "Bidi 325 Rule" defined in [RFC5893] (i.e., each of the six conditions of the 326 Bidi Rule must be satisfied). 328 3.4. Resourcepart 330 The resourcepart of a JID is an optional identifier placed after the 331 domainpart and separated from the latter by the '/' character. A 332 resourcepart can modify either a address or a 333 mere address. Typically a resourcepart uniquely 334 identifies a specific connection (e.g., a device or location) or 335 object (e.g., an occupant in a multi-user chat room [XEP-0045]) 336 belonging to the entity associated with an XMPP localpart at a domain 337 (i.e., ). 339 A resourcepart MUST NOT be zero octets in length and MUST NOT be more 340 than 1023 octets in length. This rule is to be enforced after any 341 normalization and mapping of code points. 343 A resourcepart MUST consist only of Unicode code points that conform 344 to the "JIDresourceFreeformClass" profile of the "FreeformClass" base 345 string class defined in [I-D.ietf-precis-framework]. 347 The normalization and mapping rules for the resourcepart of a JID are 348 as follows, where the operations specified MUST be completed in the 349 order shown: 351 1. Fullwidth and halfwidth characters MAY be mapped to their 352 decomposition mappings. 354 2. Map any instances of non-ASCII space to ASCII space (U+0020). 356 3. So-called additional mappings MAY be applied, such as mapping of 357 characters that are similar to common delimiters (such as '@', 358 ':', '/', '+', '-', and '.', e.g., mapping of IDEOGRAPHIC FULL 359 STOP (U+3002) to FULL STOP (U+002E)) and special handling of 360 certain characters or classes of characters (e.g., mapping of 361 non-ASCII spaces to ASCII space); the PRECIS mappings document 362 [I-D.ietf-precis-mappings] describes such mappings in more 363 detail. 365 4. Uppercase and titlecase characters MAY be mapped to their 366 lowercase equivalents, preferably using Unicode Default Case 367 Folding as defined in Chapter 3 of the Unicode Standard 368 [UNICODE]. 370 5. All characters MUST be mapped using Unicode Normalization Form C 371 (NFC). 373 6. Leading and trailing whitespace (i.e., one or more instances of 374 the ASCII space character at the beginning or end of a 375 resourcepart) MUST be removed (e.g., "stpeter " is mapped to 376 "stpeter"). 378 With regard to directionality, applications MUST apply the "Bidi 379 Rule" defined in [RFC5893] (i.e., each of the six conditions of the 380 Bidi Rule must be satisfied). 382 XMPP entities SHOULD consider resourceparts to be opaque strings and 383 SHOULD NOT impute meaning to any given resourcepart. In particular: 385 o Use of the '/' character as a separator between the domainpart and 386 the resourcepart does not imply that XMPP addresses are 387 hierarchical in the way that, say, HTTP URIs are hierarchical (see 388 [RFC3986] for general discussion); thus for example an XMPP 389 address of the form does not 390 identify a resource "bar" that exists below a resource "foo" in a 391 hierarchy of resources associated with the entity 392 "localpart@domainpart". 394 o The '@' character is allowed in the resourcepart and is often used 395 in the "handle" shown in XMPP chatrooms [XEP-0045]. For example, 396 the JID describes an entity who 397 is an occupant of the room with a handle 398 of . However, chatroom services do not necessarily 399 check such an asserted handle against the occupant's real JID. 401 In some contexts, it might be appropriate to apply more restrictive 402 rules to the preparation and comparison of XMPP resourceparts. For 403 example, in XMPP Multi-User Chat [XEP-0045] it might be appropriate 404 to apply the rules specified in [I-D.ietf-precis-nickname]. However, 405 the application of more restrictive rules is out of scope for 406 resourceparts in general and is properly defined in specifications 407 for the relevant XMPP extensions. 409 3.5. Examples 411 The following examples illustrate a small number of JIDs that are 412 consistent with the format defined above. 414 Table 1: A sample of legal JIDs 416 +---------------------------------+---------------------------------+ 417 | # | JID | Notes | 418 +---------------------------------+---------------------------------+ 419 | 1 | juliet@example.com | A "bare JID" | 420 +---------------------------------+---------------------------------+ 421 | 2 | juliet@example.com/foo | A "full JID" | 422 +---------------------------------+---------------------------------+ 423 | 3 | juliet@example.com/foo bar | Single space in resourcepart | 424 +---------------------------------+---------------------------------+ 425 | 4 | foo\20bar@example.com | Single space in localpart, as | 426 | | | optionally escaped using the | 427 | | | XMPP "JID Escaping" extension | 428 +---------------------------------+---------------------------------+ 429 | 5 | fussball@example.com | Another bare JID | 430 +---------------------------------+---------------------------------+ 431 | 6 | fußball@example.com | The third character is LATIN | 432 | | | SMALL LETTER SHARP S (U+00DF) | 433 +---------------------------------+---------------------------------+ 434 | 7 | π@example.com | A localpart of GREEK SMALL | 435 | | | LETTER PI (U+03C0) | 436 +---------------------------------+---------------------------------+ 437 | 8 | π@example.com/Σ | A resourcepart of GREEK CAPITAL | 438 | | | LETTER SIGMA (U+03A3) | 439 +---------------------------------+---------------------------------+ 440 | 9 | π@example.com/σ | A resourcepart of GREEK SMALL | 441 | | | LETTER SIGMA (U+03C3) | 442 +---------------------------------+---------------------------------+ 443 | 10| π@example.com/ς | A resourcepart of GREEK SMALL | 444 | | | LETTER FINAL SIGMA (U+03C2) | 445 +---------------------------------+---------------------------------+ 446 | 11| henryiv@example.com/♚| A resourcepart of the Unicode | 447 | | | character BLACK CHESS KING | 448 | | | (U+265A) | 449 +---------------------------------+---------------------------------+ 451 Several points are worth noting. Regarding examples 5 and 6: 452 although in German the character esszett (LATIN SMALL LETTER SHARP S, 453 U+00DF) can mostly be used interchangeably with the two characters 454 "ss", the localparts in these examples are different and (if desired) 455 a server would need to enforce a registration policy that disallows 456 one of them if the other is registered. Regarding examples 8, 9, and 457 10: case-mapping of GREEK CAPITAL LETTER SIGMA (U+03A3) to lowercase 458 (i.e., to GREEK SMALL LETTER SIGMA, U+03C3) during comparison would 459 result in matching the JIDs in examples 8 and 9; however, because the 460 PRECIS mapping rules do not account for the special status of GREEK 461 SMALL LETTER FINAL SIGMA (U+03C2), the JIDs in examples 8 and 10 or 462 examples 9 and 10 would not be matched. Regarding example 11: symbol 463 characters such as BLACK CHESS KING (U+265A) are allowed by the 464 PRECIS FreeformClass and thus can be used in resourceparts. 466 The following examples illustrate strings that are not JIDs because 467 they violate the format defined above. 469 Table 2: A sample of strings that violate the JID rules 471 +---------------------------------+---------------------------------+ 472 | # | Non-JID string | Notes | 473 +---------------------------------+---------------------------------+ 474 | 12| "juliet"@example.com | Quotation marks (U+0022) in | 475 | | | localpart | 476 +---------------------------------+---------------------------------+ 477 | 13| foo bar@example.com | Space (U+0020) in localpart | 478 +---------------------------------+---------------------------------+ 479 | 14| juliet@example.com/ foo | Leading space in resourcepart | 480 +---------------------------------+---------------------------------+ 481 | 15| <@example.com/> | Zero-length localpart and | 482 | | | resourcepart ('<' and '>' are | 483 | | | used here to show the start and | 484 | | | end of the JID in question) | 485 +---------------------------------+---------------------------------+ 486 | 16| henryⅣ@example.com | The sixth character is ROMAN | 487 | | | NUMERAL FOUR (U+2163) | 488 +---------------------------------+---------------------------------+ 489 | 17| ♚@example.com | A localpart of BLACK CHESS KING | 490 | | | (U+265A) | 491 +---------------------------------+---------------------------------+ 493 Here again, several points are worth noting. Regarding example 13, 494 even though ASCII SPACE (U+0020) is disallowed in the PRECIS 495 IdentifierClass, it can be escaped to "\27" in XMPP localparts by 496 using the JID Escaping rules defined in [XEP-0106], as illustrated by 497 example 4 in Table 1. Regarding example 16, the Unicode character 498 ROMAN NUMERAL FOUR (U+2163) has a compatibility equivalent of the 499 string formed of LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL 500 LETTER V (U+0056), but characters with compatibility equivalents are 501 not allowed in the PRECIS IdentiferClass. Regarding example 17: 502 symbol characters such as BLACK CHESS KING (U+265A) are not allowed 503 in the PRECIS IdentifierClass; however, both of the non-ASCII 504 characters in examples 16 and 17 are allowed in the PRECIS Freeform 505 class and therefore in the XMPP resourcepart (as illustrated for 506 U+265A by example 11 in Table 1). 508 4. Enforcement in JIDs and JID Parts 510 Enforcement of the XMPP address format rules is the responsibility of 511 XMPP servers. Although XMPP clients SHOULD prepare complete JIDs and 512 parts of JIDs in accordance with this document before including them 513 in protocol slots within XML streams (such that JIDs and parts of 514 JIDs are in conformance), XMPP servers MUST enforce the rules 515 wherever possible and reject stanzas and other XML elements that 516 violate the rules (for stanzas, by returning a error 517 to the sender as described in Section 8.3.3.8 of [RFC6120]). 519 Enforcement applies to complete JIDs and to parts of JIDs. To 520 facilitate implementation, this document defines the concepts of "JID 521 slot", "localpart slot", and "resourcepart slot" (similar to the 522 concept of a "domain name slot" for IDNA2008 defined in 523 Section 2.3.2.6 of [RFC5890]): 525 JID Slot: An XML element or attribute explicitly designated in XMPP 526 or in XMPP extensions for carrying a complete JID. 528 Localpart Slot: An XML element or attribute explicitly designated in 529 XMPP or in XMPP extensions for carrying the localpart of a JID. 531 Resourcepart Slot: An XML element or attribute explicitly designated 532 in XMPP or in XMPP extensions for carrying the resourcepart of a 533 JID. 535 A server is responsible for enforcing the address format rules when 536 receiving protocol elements from clients where the server is expected 537 to handle such elements directly or to use them for purposes of 538 routing a stanza to another domain or delivering a stanza to a local 539 entity; two examples from [RFC6120] are the 'to' attribute on XML 540 stanzas (which is a JID slot used by XMPP servers for routing of 541 outbound stanzas) and the child of the element 542 (which is a resourcepart slot used by XMPP servers for binding of a 543 resource to an account for routing of stanzas between the server and 544 a particular client). An example from [RFC6121] is the 'jid' 545 attribute of the roster element. 547 A server is not responsible for enforcing the rules when the protocol 548 elements are intended for communication among other entities, 549 typically within the payload of a stanza that the server is merely 550 routing to another domain or delivering to a local entity. Two 551 examples are the 'initiator' attribute in the Jingle extension 552 [XEP-0166] (which is a JID slot used for client-to-client 553 coordination of multimedia sessions) and the 'nick' attribute in the 554 Multi-User Chat extension [XEP-0045] (which is a resourcepart slot 555 used for administrative purposes in the context of XMPP chatrooms). 557 In such cases, clients SHOULD enforce the rules themselves and not 558 depend on the server to do so, and client implementers need to 559 understand that not enforcing the rules can lead to a degraded user 560 experience or to security vulnerabilities. However, when an add-on 561 service (e.g., a multi-user chat service) handles a stanza directly, 562 it ought to enforce the rules as well, as defined in the relevant 563 specification for that type of service. 565 This document does not provide an exhaustive list of JID slots, 566 localpart slots, or resourcepart slots. However, implementers of 567 core XMPP servers are advised to consider as JID slots at least the 568 following elements and attributes when they are handled directly or 569 used for purposes of routing to another domain or delivering to a 570 local entity: 572 o The 'from' and 'to' stream attributes and the 'from' and 'to' 573 stanza attributes [RFC6120]. 575 o The 'jid' attribute of the roster element for contact list 576 management [RFC6121]. 578 o The 'value' attribute of the element for Privacy Lists 579 [RFC3921] [XEP-0016] when the value of the 'type' attribute is 580 "jid". 582 o The 'jid' attribute of the element for Service Discovery 583 defined in [XEP-0030]. 585 o The element for Data Forms [XEP-0004], when the 'type' 586 attribute is "jid-single" or "jid-multi". 588 o The 'jid' attribute of the element for Bookmark 589 Storage [XEP-0048]. 591 o The of the element for vCard 3.0 [XEP-0054] 592 and the child of the element for vCard 4.0 593 [XEP-0292] when the XML character data identifies an XMPP URI 594 [RFC5122]. 596 o The 'from' attribute of the element for Delayed Delivery 597 [XEP-0203]. 599 o The 'jid' attribute of the element for the Blocking 600 Command [XEP-0191]. 602 o The 'from' and 'to' attributes of the and 603 elements for Server Dialback [RFC3921], [XEP-0220]. 605 o The 'from' and 'to' attributes of the , , and 606 elements for the Jabber Component Protocol [XEP-0114]. 608 Developers of XMPP clients and specialized XMPP add-on services are 609 advised to check the appropriate specifications for JID slots, 610 localpart slots, and resourcepart slots in XMPP protocol extensions 611 such as Service Discovery [XEP-0030], Multi-User Chat [XEP-0045], 612 Publish-Subscribe [XEP-0060], SOCKS5 Bytestreams [XEP-0065], In-Band 613 Registration [XEP-0077], Roster Item Exchange [XEP-0144], and Jingle 614 [XEP-0166]. 616 5. Internationalization Considerations 618 XMPP applications MUST support IDNA2008 for domainparts as described 619 under Section 3.2, the "JIDlocalIdentifierClass" profile for 620 localparts as described under Section 3.3, and the 621 "JIDresourceFreeformClass" profile for resourceparts as described 622 under Section 3.4. This enables XMPP addresses to include a wide 623 variety of characters outside the ASCII range. Rules for enforcement 624 of the XMPP address format are provided in [RFC6120] and 625 specifications for various XMPP extensions. 627 Interoperability Note: For backward compatibility, many existing 628 XMPP implementations and deployments support IDNA2003 [RFC3490] 629 for domainparts, and the stringprep [RFC3454] profiles Nodeprep 630 and Resourceprep [RFC3920] for localparts and resourceparts. 632 6. IANA Considerations 634 The following completed templates provide the information necessary 635 for the IANA to add 'JIDlocalIdentifierClass' and 636 'JIDresourceFreeformClass' to the PRECIS Profiles Registry. 638 6.1. JIDlocalIdentifierClass 640 Name: JIDlocalIdentifierClass. 642 Applicability: Localparts of XMPP addresses. 644 Base Class: IdentifierClass. 646 Replaces: Nodeprep. 648 Width Mapping: Map fullwidth and halfwidth characters to their 649 decomposition mappings. 651 Additional Mappings: None required or recommended. 653 Case Mapping: Map uppercase and titlecase characters to lowercase. 655 Normalization: NFC. 657 Directionality: The "Bidi Rule" defined in RFC 5893 applies. 659 Exclusions: Eight legacy characters in the ASCII range: U+0022, 660 U+0026, U+0027, U+002F, U+003A, U+003C, U+003E, U+0040. 662 Enforcement: In general, XMPP servers are responsible for enforcing 663 the rules (although XMPP clients and components can also be 664 responsible for doing so, depending on the JID slots, localpart 665 slots, and resourcepart slots where JIDs or parts of JIDs are 666 used). 668 Specification: this document. [Note to RFC Editor: please change 669 "this document" to the number issued for this specification.] 671 6.2. JIDresourceFreeformClass 673 Profile: JIDresourceFreeformClass. 675 Applicability: Resourceparts of XMPP addresses. 677 Base Class: FreeformClass 679 Replaces: The Resourceprep profile of Stringprep. 681 Width Mapping: Optional. 683 Additional Mappings: Map non-ASCII space to ASCII space. 685 Case Mapping: Optional. 687 Normalization: NFC. 689 Directionality: The "Bidi Rule" defined in RFC 5893 applies. 691 Exclusions: None. 693 Enforcement: In general, XMPP servers are responsible for enforcing 694 the rules (although XMPP clients and components can also be 695 resonsible for doing so, depending on the JID slots, localpart 696 slots, and resourcepart slots where JIDs or parts of JIDs are 697 used). 699 Specification: this document. [Note to RFC Editor: please change 700 "this document" to the number issued for this specification.] 702 7. Security Considerations 704 7.1. Reuse of PRECIS 706 The security considerations described in [I-D.ietf-precis-framework] 707 apply to the "IdentifierClass" and "FreeformClass" base string 708 classes used in this document for XMPP localparts and resourceparts, 709 respectively. The security considerations described in [RFC5890] 710 apply to internationalized domain names, which are used here for XMPP 711 domainparts. 713 7.2. Reuse of Unicode 715 The security considerations described in [UTS39] apply to the use of 716 Unicode characters in XMPP addresses. 718 7.3. Address Spoofing 720 There are two forms of address spoofing: forging and mimicking. 722 7.3.1. Address Forging 724 In the context of XMPP technologies, address forging occurs when an 725 entity is able to generate an XML stanza whose 'from' address does 726 not correspond to the account credentials with which the entity 727 authenticated onto the network (or an authorization identity provided 728 during negotiation of SASL authentication [RFC4422] as described in 729 [RFC6120]). For example, address forging occurs if an entity that 730 authenticated as "juliet@im.example.com" is able to send XML stanzas 731 from "nurse@im.example.com" or "romeo@example.net". 733 Address forging is difficult in XMPP systems, given the requirement 734 for sending servers to stamp 'from' addresses and for receiving 735 servers to verify sending domains via server-to-server authentication 736 (see [RFC6120]). However, address forging is possible if: 738 o A poorly implemented server ignores the requirement for stamping 739 the 'from' address. This would enable any entity that 740 authenticated with the server to send stanzas from any 741 localpart@domainpart as long as the domainpart matches the sending 742 domain of the server. 744 o An actively malicious server generates stanzas on behalf of any 745 registered account at the domain or domains hosted at that server. 747 Therefore, an entity outside the security perimeter of a particular 748 server cannot reliably distinguish between JIDs of the form 749 at that server and thus can authenticate only 750 the domainpart of such JIDs with any level of assurance. This 751 specification does not define methods for discovering or 752 counteracting the kind of poorly implemented or rogue servers just 753 described. However, the end-to-end authentication or signing of XMPP 754 stanzas could help to mitigate this risk, since it would require the 755 rogue server to generate false credentials for signing or encryption 756 of each stanza, in addition to modifying 'from' addresses. 758 7.3.2. Address Mimicking 760 Address mimicking occurs when an entity provides legitimate 761 authentication credentials for and sends XML stanzas from an account 762 whose JID appears to a human user to be the same as another JID. 763 Because many characters are visually similar, it is relatively easy 764 to mimic JIDs in XMPP systems. As one simple example, the localpart 765 "ju1iet" (using the Arabic numeral one as the third character) might 766 appear the same as the localpart "juliet" (using lowercase "L" as the 767 third character). 769 As explained in [RFC5890], [I-D.ietf-precis-framework], [UTR36], and 770 [UTS39], there is no straightforward solution to the problem of 771 visually similar characters. Furthermore, IDNA and PRECIS 772 technologies do not attempt to define such a solution. As a result, 773 XMPP domainparts, localparts, and resourceparts could contain such 774 characters, leading to security vulnerabilities such as the 775 following: 777 o A domainpart is always employed as one part of an entity's address 778 in XMPP. One common usage is as the address of a server or 779 server-side service, such as a multi-user chat service [XEP-0045]. 780 The security of such services could be compromised based on 781 different interpretations of the internationalized domainpart; for 782 example, a user might authorize a malicious entity at a fake 783 server to view the user's presence information, or a user could 784 join chatrooms at a fake multi-user chat service. 786 o A localpart can be employed as one part of an entity's address in 787 XMPP. One common usage is as the username of an instant messaging 788 user; another is as the name of a multi-user chat room; and many 789 other kinds of entities could use localparts as part of their 790 addresses. The security of such services could be compromised 791 based on different interpretations of the internationalized 792 localpart; for example, a user entering a single internationalized 793 localpart could access another user's account information, or a 794 user could gain access to a hidden or otherwise restricted chat 795 room or service. 797 o A resourcepart can be employed as one part of an entity's address 798 in XMPP. One common usage is as the name for an instant messaging 799 user's connected resource; another is as the nickname of a user in 800 a multi-user chat room; and many other kinds of entities could use 801 resourceparts as part of their addresses. The security of such 802 services could be compromised based on different interpretations 803 of the internationalized resourcepart; for example, two or more 804 confusable resources could be bound at the same time to the same 805 account (resulting in inconsistent authorization decisions in an 806 XMPP application that uses full JIDs), or a user could send a 807 private message to someone other than the intended recipient in a 808 multi-user chat room. 810 XMPP services and clients are strongly encouraged to define and 811 implement consistent policies regarding the registration, storage, 812 and presentation of visually similar characters in XMPP systems. In 813 particular, service providers and software implementers are strongly 814 encouraged to apply the policies recommended in 815 [I-D.ietf-precis-framework]. 817 8. Conformance Requirements 819 This section describes a protocol feature set that summarizes the 820 conformance requirements of this specification (similar feature sets 821 are provided for XMPP in [RFC6120] and [RFC6121]). This feature set 822 is appropriate for use in software certification, interoperability 823 testing, and implementation reports. For each feature, this section 824 provides the following information: 826 o A human-readable name 828 o An informational description 830 o A reference to the particular section of this document that 831 normatively defines the feature 833 o Whether the feature applies to the Client role, the Server role, 834 or both (where "N/A" signifies that the feature is not applicable 835 to the specified role) 837 o Whether the feature MUST or SHOULD be implemented, where the 838 capitalized terms are to be understood as described in [RFC2119] 840 The feature set specified here provides a basis for interoperability 841 testing and follows the spirit of a proposal made by Larry Masinter 842 within the IETF's NEWTRK Working Group in 2005 [INTEROP]. 844 Feature: address-domain-length 845 Description: Ensure that the domainpart of an XMPP address is at 846 least one octet in length and at most 1023 octets in length, and 847 that it conforms to the underlying length limits of the DNS. 849 Section: Section 3.2 851 Roles: Server MUST, client SHOULD. 853 Feature: address-domain-prep 855 Description: Ensure that the domainpart of an XMPP address conforms 856 to IDNA2008, that it contains only NR-LDH labels and U-labels (not 857 A-labels), and that all uppercase and titlecase code points are 858 mapped to their lowercase equivalents. 860 Section: Section 3.2 862 Roles: Server MUST, client SHOULD. 864 Feature: address-localpart-length 866 Description: Ensure that the localpart of an XMPP address is at 867 least one octet in length and at most 1023 octets in length. 869 Section: Section 3.3 871 Roles: Server MUST, client SHOULD. 873 Feature: address-localpart-prep 875 Description: Ensure that the localpart of an XMPP address conforms 876 to the "JIDlocalIdentifierClass" profile. 878 Section: Section 3.3 880 Roles: Server MUST, client SHOULD. 882 Feature: address-resource-length 884 Description: Ensure that the resourcepart of an XMPP address is at 885 least one octet in length and at most 1023 octets in length. 887 Section: Section 3.4 889 Roles: Server MUST, client SHOULD. 891 Feature: address-resource-prep 892 Description: Ensure that the resourcepart of an XMPP address 893 conforms to the "JIDresourceFreeformClass" profile. 895 Section: Section 3.4 897 Roles: Server MUST, client SHOULD. 899 9. References 901 9.1. Normative References 903 [I-D.ietf-precis-framework] 904 Saint-Andre, P. and M. Blanchet, "Precis Framework: 905 Handling Internationalized Strings in Protocols", draft- 906 ietf-precis-framework-15 (work in progress), March 2014. 908 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 909 STD 13, RFC 1034, November 1987. 911 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 912 Requirement Levels", BCP 14, RFC 2119, March 1997. 914 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 915 10646", STD 63, RFC 3629, November 2003. 917 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 918 Specifications: ABNF", STD 68, RFC 5234, January 2008. 920 [RFC5890] Klensin, J., "Internationalized Domain Names for 921 Applications (IDNA): Definitions and Document Framework", 922 RFC 5890, August 2010. 924 [RFC5891] Klensin, J., "Internationalized Domain Names in 925 Applications (IDNA): Protocol", RFC 5891, August 2010. 927 [RFC5892] Faltstrom, P., "The Unicode Code Points and 928 Internationalized Domain Names for Applications (IDNA)", 929 RFC 5892, August 2010. 931 [RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for 932 Internationalized Domain Names for Applications (IDNA)", 933 RFC 5893, August 2010. 935 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 936 Protocol (XMPP): Core", RFC 6120, March 2011. 938 [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 939 6.3", 2013, 940 . 942 [UTR36] The Unicode Consortium, "Unicode Technical Report #36: 943 Unicode Security Considerations", November 2013, 944 . 946 9.2. Informative References 948 [I-D.ietf-precis-mappings] 949 Yoneya, Y. and T. NEMOTO, "Mapping characters for PRECIS 950 classes", draft-ietf-precis-mappings-07 (work in 951 progress), February 2014. 953 [I-D.ietf-precis-nickname] 954 Saint-Andre, P., "Preparation and Comparison of 955 Nicknames", draft-ietf-precis-nickname-09 (work in 956 progress), January 2014. 958 [INTEROP] Masinter, L., "Formalizing IETF Interoperability 959 Reporting", Work in Progress, October 2005. 961 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application 962 and Support", STD 3, RFC 1123, October 1989. 964 [RFC1535] Gavron, E., "A Security Problem and Proposed Correction 965 With Widely Deployed DNS Software", RFC 1535, October 966 1993. 968 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 969 Internationalized Strings ("stringprep")", RFC 3454, 970 December 2002. 972 [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, 973 "Internationalizing Domain Names in Applications (IDNA)", 974 RFC 3490, March 2003. 976 See Section 1 for an explanation of why the normative 977 reference to an obsoleted specification is needed. 979 [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence 980 Protocol (XMPP): Core", RFC 3920, October 2004. 982 [RFC3921] Saint-Andre, P., Ed., "Extensible Messaging and Presence 983 Protocol (XMPP): Instant Messaging and Presence", RFC 984 3921, October 2004. 986 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 987 Resource Identifier (URI): Generic Syntax", STD 66, RFC 988 3986, January 2005. 990 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 991 Identifiers (IRIs)", RFC 3987, January 2005. 993 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 994 Security Layer (SASL)", RFC 4422, June 2006. 996 [RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers 997 (IRIs) and Uniform Resource Identifiers (URIs) for the 998 Extensible Messaging and Presence Protocol (XMPP)", RFC 999 5122, February 2008. 1001 [RFC5894] Klensin, J., "Internationalized Domain Names for 1002 Applications (IDNA): Background, Explanation, and 1003 Rationale", RFC 5894, August 2010. 1005 [RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for 1006 Internationalized Domain Names in Applications (IDNA) 1007 2008", RFC 5895, September 2010. 1009 [RFC6121] Saint-Andre, P., "Extensible Messaging and Presence 1010 Protocol (XMPP): Instant Messaging and Presence", RFC 1011 6121, March 2011. 1013 [RFC6122] Saint-Andre, P., "Extensible Messaging and Presence 1014 Protocol (XMPP): Address Format", RFC 6122, March 2011. 1016 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 1017 Internationalization in the IETF", BCP 166, RFC 6365, 1018 September 2011. 1020 [RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and 1021 Problem Statement for the Preparation and Comparison of 1022 Internationalized Strings (PRECIS)", RFC 6885, March 2013. 1024 [UTS39] The Unicode Consortium, "Unicode Technical Standard #39: 1025 Unicode Security Mechanisms", July 2012, 1026 . 1028 [XEP-0004] 1029 Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T., and 1030 P. Saint-Andre, "Data Forms", XSF XEP 0004, August 2007. 1032 [XEP-0016] 1033 Millard, P. and P. Saint-Andre, "Privacy Lists", XSF XEP 1034 0016, February 2007. 1036 [XEP-0029] 1037 Kaes, C., "Definition of Jabber Identifiers (JIDs)", XSF 1038 XEP 0029, October 2003. 1040 [XEP-0030] 1041 Hildebrand, J., Millard, P., Eatmon, R., and P. Saint- 1042 Andre, "Service Discovery", XSF XEP 0030, June 2008. 1044 [XEP-0045] 1045 Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February 1046 2012. 1048 [XEP-0048] 1049 Blackman, R., Millard, P., and P. Saint-Andre, 1050 "Bookmarks", XSF XEP 0048, November 2007. 1052 [XEP-0054] 1053 Saint-Andre, P., "vcard-temp", XSF XEP 0054, July 2008. 1055 [XEP-0060] 1056 Millard, P., Saint-Andre, P., and R. Meijer, "Publish- 1057 Subscribe", XSF XEP 0060, July 2010. 1059 [XEP-0065] 1060 Smith, D., Miller, M., Saint-Andre, P., and J. Karneges, 1061 "SOCKS5 Bytestreams", XSF XEP 0065, April 2011. 1063 [XEP-0077] 1064 Saint-Andre, P., "In-Band Registration", XSF XEP 0077, 1065 January 2012. 1067 [XEP-0106] 1068 Hildebrand, J. and P. Saint-Andre, "JID Escaping", XSF XEP 1069 0106, June 2007. 1071 [XEP-0114] 1072 Saint-Andre, P., "Jabber Component Protocol", XSF XEP 1073 0114, March 2005. 1075 [XEP-0144] 1076 Saint-Andre, P., "Roster Item Exchange", XSF XEP 0144, 1077 August 2005. 1079 [XEP-0165] 1080 Saint-Andre, P., "Best Practices to Discourage JID 1081 Mimicking", XSF XEP 0165, December 2007. 1083 [XEP-0166] 1084 Ludwig, S., Beda, J., Saint-Andre, P., McQueen, R., Egan, 1085 S., and J. Hildebrand, "Jingle", XSF XEP 0166, December 1086 2009. 1088 [XEP-0191] 1089 Saint-Andre, P., "Blocking Command", XSF XEP 0191, July 1090 2012. 1092 [XEP-0203] 1093 Saint-Andre, P., "Delayed Delivery", XSF XEP 0203, 1094 September 2009. 1096 [XEP-0220] 1097 Miller, J., Saint-Andre, P., and P. Hancke, "Server 1098 Dialback", XSF XEP 0220, August 2012. 1100 [XEP-0292] 1101 Saint-Andre, P. and S. Mizzi, "vCard4 Over XMPP", XSF XEP 1102 0292, October 2011. 1104 [XML] Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., 1105 and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth 1106 Edition)", World Wide Web Consortium Recommendation REC- 1107 xml-20081126, November 2008, 1108 . 1110 Appendix A. Differences from RFC 6122 1112 Based on consensus derived from working group discussion, 1113 implementation and deployment experience, and formal interoperability 1114 testing, the following substantive modifications were made from RFC 1115 6122. 1117 o Changed domainpart preparation to use IDNA2008 (instead of 1118 IDNA2003). 1120 o Changed localpart preparation to use the JIDlocalIdentifierClass 1121 profile of the PRECIS IdentifierClass (instead of the Nodeprep 1122 profile of Stringprep). 1124 o Changed resourcepart preparation to use the 1125 JIDresourceFreeformClass profile of the PRECIS FreeformClass 1126 (instead of the Resourceprep profile of Stringprep). 1128 o Specified that internationalized labels within domainparts must be 1129 U-labels (instead of "should be" U-labels). 1131 o Specified that fullwidth and halfwidth characters must be mapped 1132 to their decomposition mappings (previously handled through the 1133 use of NFKC). 1135 o Specified the use of Unicode Normalization Form C (instead of 1136 Unicode Normalization Form KC as specified in the Nodeprep and 1137 Resourceprep profiles of Stringprep). 1139 o Specified that servers must enforce the address formatting rules. 1141 Appendix B. Acknowledgements 1143 Thanks to Miguel Garcia, Joe Hildebrand, Matt Miller, and Florian 1144 Zeitz for their feedback. 1146 Some text in this document was borrowed or adapted from [RFC5890], 1147 [RFC5891], [RFC5894], and [XEP-0165]. 1149 Author's Address 1151 Peter Saint-Andre 1152 &yet 1154 Email: ietf@stpeter.im