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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 7564 (Obsoleted by RFC 8264) -- Possible downref: Non-RFC (?) normative reference: ref. 'UTR36' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode' == Outdated reference: A later version (-19) exists of draft-ietf-precis-nickname-17 -- Obsolete informational reference (is this intentional?): RFC 3454 (Obsoleted by RFC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 4013 (Obsoleted by RFC 7613) -- Obsolete informational reference (is this intentional?): RFC 6122 (Obsoleted by RFC 7622) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 9 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) June 11, 2015 5 Intended status: Standards Track 6 Expires: December 13, 2015 8 Extensible Messaging and Presence Protocol (XMPP): Address Format 9 draft-ietf-xmpp-6122bis-24 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 December 13, 2015. 34 Copyright Notice 36 Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . . . . . . . 7 57 3.4. Resourcepart . . . . . . . . . . . . . . . . . . . . . . 8 58 3.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9 59 4. Enforcement in JIDs and JID Parts . . . . . . . . . . . . . . 13 60 5. Internationalization Considerations . . . . . . . . . . . . . 15 61 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 62 6.1. Stringprep Profiles Registry . . . . . . . . . . . . . . 15 63 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 64 7.1. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 16 65 7.2. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 16 66 7.3. Address Spoofing . . . . . . . . . . . . . . . . . . . . 16 67 8. Conformance Requirements . . . . . . . . . . . . . . . . . . 18 68 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 69 9.1. Normative References . . . . . . . . . . . . . . . . . . 20 70 9.2. Informative References . . . . . . . . . . . . . . . . . 21 71 Appendix A. Differences from RFC 6122 . . . . . . . . . . . . . 24 72 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 25 73 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 25 75 1. Introduction 77 The Extensible Messaging and Presence Protocol (XMPP) [RFC6120] is an 78 application profile of the Extensible Markup Language [XML] for 79 streaming XML data in close to real time between any two or more 80 network-aware entities. The address format for XMPP entities was 81 originally developed in the Jabber open-source community in 1999, 82 first described by [XEP-0029] in 2002, and then defined canonically 83 by [RFC3920] in 2004 and [RFC6122] in 2011. 85 As specified in RFC 3920 and RFC 6122, the XMPP address format used 86 the "stringprep" technology for preparation and comparison of non- 87 ASCII characters [RFC3454]. Following the movement of 88 internationalized domain names away from stringprep, this document 89 defines the XMPP address format in a way that no longer depends on 90 stringprep (see the PRECIS problem statement [RFC6885]). Instead, 91 this document builds upon the internationalization framework defined 92 by the IETF's PRECIS Working Group [RFC7564]. 94 Although every attempt has been made to ensure that the characters 95 allowed in Jabber Identifiers (JIDs) under Stringprep are still 96 allowed and handled in the same way under PRECIS, there is no 97 guarantee of strict backward compatibility because of changes in 98 Unicode and the fact that PRECIS handling is based on Unicode 99 properties, not a hardcoded table of characters. Because it is 100 possible that previously-valid JIDs might no longer be valid (or 101 previously-invalid JIDs might now be valid), operators of XMPP 102 services are advised to perform careful testing before migrating 103 accounts and other data (see Section 6.1 of 104 [I-D.ietf-precis-saslprepbis] for guidance). 106 This document obsoletes RFC 6122. 108 2. Terminology 110 Many important terms used in this document are defined in [RFC7564], 111 [RFC5890], [RFC6120], [RFC6365], and [Unicode]. 113 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 114 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 115 "OPTIONAL" in this document are to be interpreted as described in 116 [RFC2119]. 118 3. Addresses 120 3.1. Fundamentals 122 An XMPP entity is anything that can communicate using XMPP. For 123 historical reasons, the network address of an XMPP entity is called a 124 Jabber Identifier ("JID"). A valid JID is a string of Unicode code 125 points [Unicode], encoded using UTF-8 [RFC3629], and structured as an 126 ordered sequence of localpart, domainpart, and resourcepart, where 127 the first two parts are demarcated by the '@' character used as a 128 separator and the last two parts are similarly demarcated by the '/' 129 character (e.g., ). 131 The syntax for a JID is defined as follows using the Augmented 132 Backus-Naur Form (ABNF) as specified in [RFC5234]. 134 jid = [ localpart "@" ] domainpart [ "/" resourcepart ] 135 localpart = 1*1023(userbyte) 136 ; 137 ; a "userbyte" is a byte used to represent a 138 ; UTF-8 encoded Unicode code point that can be 139 ; contained in a string that conforms to the 140 ; UsernameCaseMapped profile of the PRECIS 141 ; IdentifierClass defined in 142 ; draft-ietf-precis-saslprepbis 143 ; 144 domainpart = IP-literal / IPv4address / ifqdn 145 ; 146 ; the "IPv4address" and "IP-literal" rules are 147 ; defined in RFC 3986 and RFC 6874 respectively, 148 ; and the first-match-wins (a.k.a. "greedy") 149 ; algorithm described in Appendix B of RFC 3986 150 ; applies to the matching process 151 ; 152 ifqdn = 1*1023(domainbyte) 153 ; 154 ; a "domainbyte" is a byte used to represent a 155 ; UTF-8 encoded Unicode code point that can be 156 ; contained in a string that conforms to RFC 5890 157 ; 158 resourcepart = 1*1023(opaquebyte) 159 ; 160 ; an "opaquebyte" is a byte used to represent a 161 ; UTF-8 encoded Unicode code point that can be 162 ; contained in a string that conforms to the 163 ; OpaqueString profile of the PRECIS 164 ; FreeformClass defined in 165 ; draft-ietf-precis-saslprepbis 166 ; 168 All JIDs are based on the foregoing structure. However, note that 169 the formal syntax provided above does not capture all of the rules 170 and restrictions that apply to JIDs, which are described below. 172 Each allowable portion of a JID (localpart, domainpart, and 173 resourcepart) is 1 to 1023 octets in length, resulting in a maximum 174 total size (including the '@' and '/' separators) of 3071 octets. 176 Implementation Note: The length limits on JIDs and parts of JIDs 177 are based on octets (bytes), not characters. UTF-8 encoding can 178 result in more than one octet per character. 180 Implementation Note: When dividing a JID into its component parts, 181 an implementation needs to match the separator characters '@' and 182 '/' before applying any transformation algorithms, which might 183 decompose certain Unicode code points to the separator characters. 185 Implementation Note: Reuse of the IP-literal rule from [RFC6874] 186 implies that IPv6 addresses are enclosed within square brackets 187 (i.e., beginning with '[' and ; ending with ']'), which was not 188 the case with the definition of the XMPP address format in 189 [RFC3920] but which was changed in [RFC6122]. Also note that the 190 IP-literal rule was updated between [RFC3986] and [RFC6874] to 191 optionally add a zone identifier to any literal address. 193 This document defines the native format for JIDs; see [RFC5122] for 194 information about the representation of a JID as a Uniform Resource 195 Identifier (URI) [RFC3986] or Internationalized Resource Identifier 196 (IRI) [RFC3987] and the extraction of a JID from an XMPP URI or IRI. 198 3.2. Domainpart 200 The domainpart of a JID is that portion which remains once the 201 following parsing steps are taken: 203 1. Remove any portion from the first '/' character to the end of the 204 string (if there is a '/' character present). 206 2. Remove any portion from the beginning of the string to the first 207 '@' character (if there is a '@' character present). 209 This parsing order is important, as illustrated by example 15 in 210 Section 3.5. 212 The domainpart is the primary identifier and is the only REQUIRED 213 element of a JID (a mere domainpart is a valid JID). Typically a 214 domainpart identifies the "home" server to which clients connect for 215 XML routing and data management functionality. However, it is not 216 necessary for an XMPP domainpart to identify an entity that provides 217 core XMPP server functionality (e.g., a domainpart can identify an 218 entity such as a multi-user chat service [XEP-0045], a publish- 219 subscribe service [XEP-0060], or a user directory). 221 The domainpart for every XMPP service MUST be a fully-qualified 222 domain name (FQDN), an IPv4 address, an IPv6 address, or an 223 unqualified hostname (i.e., a text label that is resolvable on a 224 local network). 226 Informational Note: The term "fully-qualified domain name" is not 227 well defined. In [RFC1034] it is also called an absolute domain 228 name, and the two terms are associated in [RFC1535]. The earliest 229 use of the term can be found in [RFC1123]. References to those 230 older specifications ought not to be construed as limiting the 231 characters of a fully-qualified domain name to the ASCII range; 232 for example, [RFC5890] mentions that a fully-qualified domain name 233 can contain one or more U-labels. 235 Interoperability Note: Domainparts that are IP addresses might not 236 be accepted by other services for the purpose of server-to-server 237 communication, and domainparts that are unqualified hostnames 238 cannot be used on public networks because they are resolvable only 239 on a local network. 241 If the domainpart includes a final character considered to be a label 242 separator (dot) by [RFC1034], this character MUST be stripped from 243 the domainpart before the JID of which it is a part is used for the 244 purpose of routing an XML stanza, comparing against another JID, or 245 constructing an XMPP URI or IRI [RFC5122]. In particular, such a 246 character MUST be stripped before any other canonicalization steps 247 are taken. 249 In general, the content of a domainpart is an Internationalized 250 Domain Name ("IDN") as described in the specifications for 251 Internationalized Domain Names in Applications (commonly called 252 "IDNA2008"), and a domainpart is an "IDNA-aware domain name slot" as 253 defined in [RFC5890]. 255 After any and all normalization, conversion, and mapping of code 256 points as well as encoding of the string as UTF-8, a domainpart MUST 257 NOT be zero octets in length and MUST NOT be more than 1023 octets in 258 length. (Naturally, the length limits of [RFC1034] apply, and 259 nothing in this document is to be interpreted as overriding those 260 more fundamental limits.) 262 Detailed rules and considerations for preparation, enforcement, and 263 comparison are provided in the following sections. 265 3.2.1. Preparation 267 An entity that prepares a string for inclusion in an XMPP domainpart 268 slot MUST ensure that the string consists only of Unicode code points 269 that are allowed in NR-LDH labels or U-labels as defined in 270 [RFC5890]. This implies that the string MUST NOT include A-labels as 271 defined in [RFC5890]; each A-label MUST be converted to a U-label 272 during preparation of a string for inclusion in a domainpart slot. 273 In addition, the string MUST be encoded as UTF-8 [RFC3629]. 275 3.2.2. Enforcement 277 An entity that performs enforcement in XMPP domainpart slots MUST 278 prepare a string as described in the previous section and MUST also 279 apply the normalization, case-mapping, and width-mapping rules 280 defined in [RFC5892]. 282 The order in which the rules are applied for IDNA2008 (see 283 [RFC5892] and [RFC5895]) is different from the order for 284 localparts and resourceparts as described under Section 3.3 and 285 Section 3.4. 287 3.2.3. Comparison 289 An entity that performs comparison of two strings before or after 290 their inclusion in XMPP domainpart slots MUST prepare each string and 291 enforce the normalization, case-mapping, and width-mapping rules 292 specified in the previous two sections. The two strings are to be 293 considered equivalent if they are an exact octet-for-octet match 294 (sometimes called "bit-string identity"). 296 3.3. Localpart 298 The localpart of a JID is an optional identifier placed before the 299 domainpart and separated from the latter by the '@' character. 300 Typically a localpart uniquely identifies the entity requesting and 301 using network access provided by a server (i.e., a local account), 302 although it can also represent other kinds of entities (e.g., a chat 303 room associated with a multi-user chat service [XEP-0045]). The 304 entity represented by an XMPP localpart is addressed within the 305 context of a specific domain (i.e., ). 307 The localpart of a JID MUST NOT be zero octets in length and MUST NOT 308 be more than 1023 octets in length. This rule is to be enforced 309 after any normalization and mapping of code points as well as 310 encoding of the string as UTF-8. 312 The localpart of a JID is an instance of the UsernameCaseMapped 313 profile of the PRECIS IdentifierClass, which is specified in 314 [I-D.ietf-precis-saslprepbis]. The rules and considerations provided 315 in that specification MUST be applied to XMPP localparts. 317 Implementation Note: XMPP uses the Simple Authentication and 318 Security Layer (SASL) [RFC4422] for authentication. At the time 319 of this writing, some SASL mechanisms use SASLprep [RFC4013] for 320 handling of usernames and passwords; in the future these SASL 321 mechanisms will likely transition to the use of PRECIS-based 322 handling rules as specified in [I-D.ietf-precis-saslprepbis]. For 323 a detailed discussion about the implications of that transition 324 (including the potential need to modify or remove certain 325 characters in the underlying account database), see both 326 Section 6.1 and Appendix A of [I-D.ietf-precis-saslprepbis]. 328 3.3.1. Further Excluded Characters 330 In XMPP, the following characters are explicitly disallowed in XMPP 331 localparts even though they are allowed by the IdentifierClass base 332 class and the UsernameCaseMapped profile: 334 " U+0022 (QUOTATION MARK) 336 & U+0026 (AMPERSAND) 338 ' U+0027 (APOSTROPHE) 340 / U+002F (SOLIDUS) 342 : U+003A (COLON) 344 < U+003C (LESS-THAN SIGN) 346 > U+003E (GREATER-THAN SIGN) 348 @ U+0040 (COMMERCIAL AT) 350 Implementation Note: An XMPP-specific method for escaping the 351 foregoing characters (along with U+0020, i.e., ASCII SPACE) has 352 been defined in the JID Escaping specification [XEP-0106]. 354 3.4. Resourcepart 356 The resourcepart of a JID is an optional identifier placed after the 357 domainpart and separated from the latter by the '/' character. A 358 resourcepart can modify either a address or a 359 mere address. Typically a resourcepart uniquely 360 identifies a specific connection (e.g., a device or location) or 361 object (e.g., an occupant in a multi-user chat room [XEP-0045]) 362 belonging to the entity associated with an XMPP localpart at a domain 363 (i.e., ). 365 XMPP entities SHOULD consider resourceparts to be opaque strings and 366 SHOULD NOT impute meaning to any given resourcepart. In particular: 368 o Use of the '/' character as a separator between the domainpart and 369 the resourcepart does not imply that XMPP addresses are 370 hierarchical in the way that, say, HTTP URIs are hierarchical (see 372 [RFC3986] for general discussion); thus for example an XMPP 373 address of the form does not 374 identify a resource "bar" that exists below a resource "foo" in a 375 hierarchy of resources associated with the entity 376 "localpart@domainpart". 378 o The '@' character is allowed in the resourcepart and is often used 379 in the "handle" shown in XMPP chatrooms [XEP-0045]. For example, 380 the JID describes an entity who 381 is an occupant of the room with a handle 382 of . However, chatroom services do not necessarily 383 check such an asserted handle against the occupant's real JID. 385 The resourcepart of a JID MUST NOT be zero octets in length and MUST 386 NOT be more than 1023 octets in length. This rule is to be enforced 387 after any normalization and mapping of code points as well as 388 encoding of the string as UTF-8. 390 The resourcepart of a JID is an instance of the OpaqueString profile 391 of the PRECIS FreeformClass, which is specified in 392 [I-D.ietf-precis-saslprepbis]. The rules and considerations provided 393 in that specification MUST be applied to XMPP resourceparts. 395 3.4.1. Applicability to XMPP Extensions 397 In some contexts, it might be appropriate to apply more restrictive 398 rules to the preparation, enforcement, and comparison of XMPP 399 resourceparts. For example, in XMPP Multi-User Chat [XEP-0045] it 400 might be appropriate to apply the rules specified in 401 [I-D.ietf-precis-nickname]. However, the application of more 402 restrictive rules is out of scope for resourceparts in general and is 403 properly defined in specifications for the relevant XMPP extensions. 405 3.5. Examples 407 The following examples illustrate a small number of JIDs that are 408 consistent with the format defined above (note that the characters < 409 and > are used to delineate the actual JIDs and are not part of the 410 JIDs themselves). 412 Table 1: A sample of legal JIDs 414 +----------------------------------+-------------------------------+ 415 | # | JID | Notes | 416 +----------------------------------+-------------------------------+ 417 | 1 | | A "bare JID" | 418 +----------------------------------+-------------------------------+ 419 | 2 | | A "full JID" | 420 +----------------------------------+-------------------------------+ 421 | 3 | | Single space in resourcepart | 422 +----------------------------------+-------------------------------+ 423 | 4 | | At sign in resourcepart | 424 +----------------------------------+-------------------------------+ 425 | 5 | | Single space in localpart, as | 426 | | | optionally escaped using the | 427 | | | XMPP "JID Escaping" extension | 428 +----------------------------------+-------------------------------+ 429 | 6 | | Another bare JID | 430 +----------------------------------+-------------------------------+ 431 | 7 | | The third character is LATIN | 432 | | | SMALL LETTER SHARP S (U+00DF) | 433 +----------------------------------+-------------------------------+ 434 | 8 | <π@example.com> | A localpart of GREEK SMALL | 435 | | | LETTER PI (U+03C0) | 436 +----------------------------------+-------------------------------+ 437 | 9 | <Σ@example.com/foo> | A localpart of GREEK CAPITAL | 438 | | | LETTER SIGMA (U+03A3) | 439 +----------------------------------+-------------------------------+ 440 | 10| <σ@example.com/foo> | A localpart of GREEK SMALL | 441 | | | LETTER SIGMA (U+03C3) | 442 +----------------------------------+-------------------------------+ 443 | 11| <ς@example.com/foo> | A localpart of GREEK SMALL | 444 | | | LETTER FINAL SIGMA (U+03C2) | 445 +----------------------------------+-------------------------------+ 446 | 12| ; | A resourcepart of the Unicode | 447 | | | character BLACK CHESS KING | 448 | | | (U+265A) | 449 +----------------------------------+-------------------------------+ 450 | 13| | A domainpart | 451 +----------------------------------+-------------------------------+ 452 | 14| | A domainpart and resourcepart | 453 +----------------------------------+-------------------------------+ 454 | 15| | A domainpart followed by a | 455 | | | resourcepart that contains an | 456 | | | at sign | 457 +----------------------------------+-------------------------------+ 458 Several points are worth noting. Regarding examples 6 and 7: 459 although in German the character esszett (LATIN SMALL LETTER SHARP S, 460 U+00DF) can mostly be used interchangeably with the two characters 461 "ss", the localparts in these examples are different and (if desired) 462 a server would need to enforce a registration policy that disallows 463 one of them if the other is registered. Regarding examples 9, 10, 464 and 11: case-mapping of GREEK CAPITAL LETTER SIGMA (U+03A3) to 465 lowercase (i.e., to GREEK SMALL LETTER SIGMA, U+03C3) during 466 comparison would result in matching the JIDs in examples 9 and 10; 467 however, because the PRECIS mapping rules do not account for the 468 special status of GREEK SMALL LETTER FINAL SIGMA (U+03C2), the JIDs 469 in examples 9 and 11 or examples 10 and 11 would not be matched. 470 Regarding example 12: symbol characters such as BLACK CHESS KING 471 (U+265A) are allowed by the PRECIS FreeformClass and thus can be used 472 in resourceparts. Regarding examples 14 and 15: JIDs consisting of a 473 domainpart and resourcepart are rarely seen in the wild, but are 474 allowed according to the XMPP address format. Example 15 illustrates 475 the need for careful extraction of the domainpart as described in the 476 first paragraph of Section 3.2. 478 The following examples illustrate strings that are not JIDs because 479 they violate the format defined above. 481 Table 2: A sample of strings that violate the JID rules 483 +----------------------------------+-------------------------------+ 484 | # | Non-JID string | Notes | 485 +----------------------------------+-------------------------------+ 486 | 16| <"juliet"@example.com> | Quotation marks (U+0022) in | 487 | | | localpart | 488 +----------------------------------+-------------------------------+ 489 | 17| | Space (U+0020) in localpart | 490 +----------------------------------+-------------------------------+ 491 | 18| | Leading space in resourcepart | 492 +----------------------------------+-------------------------------+ 493 | 19| <@example.com/> | Zero-length localpart and | 494 | | | resourcepart | 495 +----------------------------------+-------------------------------+ 496 | 20| | The sixth character is ROMAN | 497 | | | NUMERAL FOUR (U+2163) | 498 +----------------------------------+-------------------------------+ 499 | 21| <♚@example.com> | A localpart of BLACK CHESS | 500 | | | KING (U+265A) | 501 +----------------------------------+-------------------------------+ 502 | 22| | A localpart without a | 503 | | | domainpart | 504 +----------------------------------+-------------------------------+ 505 | 23| | A resourcepart without a | 506 | | | domainpart | 507 +----------------------------------+-------------------------------+ 509 Here again, several points are worth noting. Regarding example 17, 510 even though ASCII SPACE (U+0020) is disallowed in the PRECIS 511 IdentifierClass, it can be escaped to "\20" in XMPP localparts by 512 using the JID Escaping rules defined in [XEP-0106], as illustrated by 513 example 4 in Table 1. Regarding example 20, the Unicode character 514 ROMAN NUMERAL FOUR (U+2163) has a compatibility equivalent of the 515 string formed of LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL 516 LETTER V (U+0056), but characters with compatibility equivalents are 517 not allowed in the PRECIS IdentiferClass. Regarding example 21: 518 symbol characters such as BLACK CHESS KING (U+265A) are not allowed 519 in the PRECIS IdentifierClass; however, both of the non-ASCII 520 characters in examples 20 and 21 are allowed in the PRECIS Freeform 521 class and therefore in the XMPP resourcepart (as illustrated for 522 U+265A by example 12 in Table 1). Regarding examples 22 and 23: the 523 domainpart is required in a JID. 525 4. Enforcement in JIDs and JID Parts 527 Enforcement entails applying all of the rules specified in this 528 document. Enforcement of the XMPP address format rules is the 529 responsibility of XMPP servers. Although XMPP clients SHOULD prepare 530 complete JIDs and parts of JIDs in accordance with this document 531 before including them in protocol slots within XML streams, XMPP 532 servers MUST enforce the rules wherever possible and reject stanzas 533 and other XML elements that violate the rules (for stanzas, by 534 returning a error to the sender as described in 535 Section 8.3.3.8 of [RFC6120]). 537 Entities that enforce the rules specified in this document are 538 encouraged to be liberal in what they accept by following this 539 procedure: 541 1. Where possible, map characters (e.g, through width mapping, 542 additional mapping, special mapping, case mapping, or 543 normalization) and accept the mapped string. 545 2. If mapping is not possible (e.g., because a character is 546 disallowed in the FreeformClass), reject the string and return a 547 error. 549 Enforcement applies to complete JIDs and to parts of JIDs. To 550 facilitate implementation, this document defines the concepts of "JID 551 slot", "localpart slot", and "resourcepart slot" (similar to the 552 concept of a "domain name slot" for IDNA2008 defined in 553 Section 2.3.2.6 of [RFC5890]): 555 JID Slot: An XML element or attribute explicitly designated in XMPP 556 or in XMPP extensions for carrying a complete JID. 558 Localpart Slot: An XML element or attribute explicitly designated in 559 XMPP or in XMPP extensions for carrying the localpart of a JID. 561 Resourcepart Slot: An XML element or attribute explicitly designated 562 in XMPP or in XMPP extensions for carrying the resourcepart of a 563 JID. 565 A server is responsible for enforcing the address format rules when 566 receiving protocol elements from clients where the server is expected 567 to handle such elements directly or to use them for purposes of 568 routing a stanza to another domain or delivering a stanza to a local 569 entity; two examples from [RFC6120] are the 'to' attribute on XML 570 stanzas (which is a JID slot used by XMPP servers for routing of 571 outbound stanzas) and the child of the element 572 (which is a resourcepart slot used by XMPP servers for binding of a 573 resource to an account for routing of stanzas between the server and 574 a particular client). An example from [RFC6121] is the 'jid' 575 attribute of the roster element. 577 A server is not responsible for enforcing the rules when the protocol 578 elements are intended for communication among other entities, 579 typically within the payload of a stanza that the server is merely 580 routing to another domain or delivering to a local entity. Two 581 examples are the 'initiator' attribute in the Jingle extension 582 [XEP-0166] (which is a JID slot used for client-to-client 583 coordination of multimedia sessions) and the 'nick' attribute in the 584 Multi-User Chat extension [XEP-0045] (which is a resourcepart slot 585 used for administrative purposes in the context of XMPP chatrooms). 586 In such cases, the entities involved SHOULD enforce the rules 587 themselves and not depend on the server to do so, and client 588 implementers need to understand that not enforcing the rules can lead 589 to a degraded user experience or to security vulnerabilities. 590 However, when an add-on service (e.g., a multi-user chat service) 591 handles a stanza directly, it ought to enforce the rules as well, as 592 defined in the relevant specification for that type of service. 594 This document does not provide an exhaustive list of JID slots, 595 localpart slots, or resourcepart slots. However, implementers of 596 core XMPP servers are advised to consider as JID slots at least the 597 following elements and attributes when they are handled directly or 598 used for purposes of routing to another domain or delivering to a 599 local entity: 601 o The 'from' and 'to' stream attributes and the 'from' and 'to' 602 stanza attributes [RFC6120]. 604 o The 'jid' attribute of the roster element for contact list 605 management [RFC6121]. 607 o The 'value' attribute of the element for Privacy Lists 608 [RFC3921] [XEP-0016] when the value of the 'type' attribute is 609 "jid". 611 o The 'jid' attribute of the element for Service Discovery 612 defined in [XEP-0030]. 614 o The element for Data Forms [XEP-0004], when the 'type' 615 attribute is "jid-single" or "jid-multi". 617 o The 'jid' attribute of the element for Bookmark 618 Storage [XEP-0048]. 620 o The of the element for vCard 3.0 [XEP-0054] 621 and the child of the element for vCard 4.0 622 [XEP-0292] when the XML character data identifies an XMPP URI 623 [RFC5122]. 625 o The 'from' attribute of the element for Delayed Delivery 626 [XEP-0203]. 628 o The 'jid' attribute of the element for the Blocking 629 Command [XEP-0191]. 631 o The 'from' and 'to' attributes of the and 632 elements for Server Dialback [RFC3921], [XEP-0220]. 634 o The 'from' and 'to' attributes of the , , and 635 elements for the Jabber Component Protocol [XEP-0114]. 637 Developers of XMPP clients and specialized XMPP add-on services are 638 advised to check the appropriate specifications for JID slots, 639 localpart slots, and resourcepart slots in XMPP protocol extensions 640 such as Service Discovery [XEP-0030], Multi-User Chat [XEP-0045], 641 Publish-Subscribe [XEP-0060], SOCKS5 Bytestreams [XEP-0065], In-Band 642 Registration [XEP-0077], Roster Item Exchange [XEP-0144], and Jingle 643 [XEP-0166]. 645 5. Internationalization Considerations 647 XMPP applications MUST support IDNA2008 for domainparts as described 648 under Section 3.2, the "UsernameCaseMapped" profile for localparts as 649 described under Section 3.3, and the "OpaqueString" profile for 650 resourceparts as described under Section 3.4. This enables XMPP 651 addresses to include a wide variety of characters outside the ASCII 652 range. Rules for enforcement of the XMPP address format are provided 653 in [RFC6120] and specifications for various XMPP extensions. 655 Interoperability Note: For backward compatibility, many existing 656 XMPP implementations and deployments support IDNA2003 [RFC3490] 657 for domainparts, and the stringprep [RFC3454] profiles Nodeprep 658 and Resourceprep [RFC3920] for localparts and resourceparts. 660 6. IANA Considerations 662 6.1. Stringprep Profiles Registry 664 The Stringprep specification [RFC3454] did not provide for entries in 665 the Stringprep Profiles registry to have any state anything except 666 current or not current. Because this document obsoletes RFC 6122, 667 which registered the "Nodeprep" and "Resourceprep" profiles of 668 Stringprep, IANA is requested to mark those profiles as not current 669 and to cite this document as an additional reference. 671 7. Security Considerations 673 7.1. Reuse of PRECIS 675 The security considerations described in [RFC7564] apply to the 676 "IdentifierClass" and "FreeformClass" base string classes used in 677 this document for XMPP localparts and resourceparts, respectively. 678 The security considerations described in [RFC5890] apply to 679 internationalized domain names, which are used here for XMPP 680 domainparts. 682 7.2. Reuse of Unicode 684 The security considerations described in [UTS39] apply to the use of 685 Unicode characters in XMPP addresses. 687 7.3. Address Spoofing 689 There are two forms of address spoofing: forging and mimicking. 691 7.3.1. Address Forging 693 In the context of XMPP technologies, address forging occurs when an 694 entity is able to generate an XML stanza whose 'from' address does 695 not correspond to the account credentials with which the entity 696 authenticated onto the network (or an authorization identity provided 697 during negotiation of SASL authentication [RFC4422] as described in 698 [RFC6120]). For example, address forging occurs if an entity that 699 authenticated as "juliet@im.example.com" is able to send XML stanzas 700 from "nurse@im.example.com" or "romeo@example.net". 702 Address forging is difficult in XMPP systems, given the requirement 703 for sending servers to stamp 'from' addresses and for receiving 704 servers to verify sending domains via server-to-server authentication 705 (see [RFC6120]). However, address forging is possible if: 707 o A poorly implemented server ignores the requirement for stamping 708 the 'from' address. This would enable any entity that 709 authenticated with the server to send stanzas from any 710 localpart@domainpart as long as the domainpart matches the sending 711 domain of the server. 713 o An actively malicious server generates stanzas on behalf of any 714 registered account at the domain or domains hosted at that server. 716 Therefore, an entity outside the security perimeter of a particular 717 server cannot reliably distinguish between JIDs of the form 718 at that server and thus can authenticate only 719 the domainpart of such JIDs with any level of assurance. This 720 specification does not define methods for discovering or 721 counteracting the kind of poorly implemented or rogue servers just 722 described. However, the end-to-end authentication or signing of XMPP 723 stanzas could help to mitigate this risk, since it would require the 724 rogue server to generate false credentials for signing or encryption 725 of each stanza, in addition to modifying 'from' addresses. 727 7.3.2. Address Mimicking 729 Address mimicking occurs when an entity provides legitimate 730 authentication credentials for and sends XML stanzas from an account 731 whose JID appears to a human user to be the same as another JID. 732 Because many characters are visually similar, it is relatively easy 733 to mimic JIDs in XMPP systems. As one simple example, the localpart 734 "ju1iet" (using the Arabic numeral one as the third character) might 735 appear the same as the localpart "juliet" (using lowercase "L" as the 736 third character). 738 As explained in [RFC5890], [RFC7564], [UTR36], and [UTS39], there is 739 no straightforward solution to the problem of visually similar 740 characters. Furthermore, IDNA and PRECIS technologies do not attempt 741 to define such a solution. As a result, XMPP domainparts, 742 localparts, and resourceparts could contain such characters, leading 743 to security vulnerabilities such as the following: 745 o A domainpart is always employed as one part of an entity's address 746 in XMPP. One common usage is as the address of a server or 747 server-side service, such as a multi-user chat service [XEP-0045]. 748 The security of such services could be compromised based on 749 different interpretations of the internationalized domainpart; for 750 example, a user might authorize a malicious entity at a fake 751 server to view the user's presence information, or a user could 752 join chatrooms at a fake multi-user chat service. 754 o A localpart can be employed as one part of an entity's address in 755 XMPP. One common usage is as the username of an instant messaging 756 user; another is as the name of a multi-user chat room; and many 757 other kinds of entities could use localparts as part of their 758 addresses. The security of such services could be compromised 759 based on different interpretations of the internationalized 760 localpart; for example, a user entering a single internationalized 761 localpart could access another user's account information, or a 762 user could gain access to a hidden or otherwise restricted chat 763 room or service. 765 o A resourcepart can be employed as one part of an entity's address 766 in XMPP. One common usage is as the name for an instant messaging 767 user's connected resource; another is as the nickname of a user in 768 a multi-user chat room; and many other kinds of entities could use 769 resourceparts as part of their addresses. The security of such 770 services could be compromised based on different interpretations 771 of the internationalized resourcepart; for example, two or more 772 confusable resources could be bound at the same time to the same 773 account (resulting in inconsistent authorization decisions in an 774 XMPP application that uses full JIDs), or a user could send a 775 private message to someone other than the intended recipient in a 776 multi-user chat room. 778 XMPP services and clients are strongly encouraged to define and 779 implement consistent policies regarding the registration, storage, 780 and presentation of visually similar characters in XMPP systems. In 781 particular, service providers and software implementers are strongly 782 encouraged to apply the policies recommended in [RFC7564]. 784 8. Conformance Requirements 786 This section describes a protocol feature set that summarizes the 787 conformance requirements of this specification (similar feature sets 788 are provided for XMPP in [RFC6120] and [RFC6121]). The summary is 789 purely informational and the conformance keywords of [RFC2119] as 790 used here are intended only to briefly describe the referenced 791 normative text from the body of this specification. This feature set 792 is appropriate for use in software certification, interoperability 793 testing, and implementation reports. For each feature, this section 794 provides the following information: 796 o A human-readable name 798 o An informational description 800 o A reference to the particular section of this document that 801 normatively defines the feature 803 o Whether the feature applies to the Client role, the Server role, 804 or both (where "N/A" signifies that the feature is not applicable 805 to the specified role) 807 o Whether the feature MUST or SHOULD be implemented, where the 808 capitalized terms are to be understood as described in [RFC2119] 810 The feature set specified here provides a basis for interoperability 811 testing and follows the spirit of a proposal made by Larry Masinter 812 within the IETF's NEWTRK Working Group in 2005 [INTEROP]. 814 Feature: address-domain-length 816 Description: Ensure that the domainpart of an XMPP address is at 817 least one octet in length and at most 1023 octets in length, and 818 that it conforms to the underlying length limits of the DNS. 820 Section: Section 3.2 822 Roles: Server MUST, client SHOULD. 824 Feature: address-domain-prep 826 Description: Ensure that the domainpart of an XMPP address conforms 827 to IDNA2008, that it contains only NR-LDH labels and U-labels (not 828 A-labels), and that all uppercase and titlecase code points are 829 mapped to their lowercase equivalents. 831 Section: Section 3.2 833 Roles: Server MUST, client SHOULD. 835 Feature: address-localpart-length 837 Description: Ensure that the localpart of an XMPP address is at 838 least one octet in length and at most 1023 octets in length. 840 Section: Section 3.3 842 Roles: Server MUST, client SHOULD. 844 Feature: address-localpart-prep 846 Description: Ensure that the localpart of an XMPP address conforms 847 to the "UsernameCaseMapped" profile of the PRECIS IdentifierClass. 849 Section: Section 3.3 851 Roles: Server MUST, client SHOULD. 853 Feature: address-resource-length 855 Description: Ensure that the resourcepart of an XMPP address is at 856 least one octet in length and at most 1023 octets in length. 858 Section: Section 3.4 860 Roles: Server MUST, client SHOULD. 862 Feature: address-resource-prep 864 Description: Ensure that the resourcepart of an XMPP address 865 conforms to the "OpaqueString" profile of the PRECIS 866 FreeformClass. 868 Section: Section 3.4 870 Roles: Server MUST, client SHOULD. 872 9. References 874 9.1. Normative References 876 [I-D.ietf-precis-saslprepbis] 877 Saint-Andre, P. and A. Melnikov, "Username and Password 878 Preparation Algorithms", draft-ietf-precis-saslprepbis-18 879 (work in progress), May 2015. 881 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 882 STD 13, RFC 1034, November 1987. 884 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 885 Requirement Levels", BCP 14, RFC 2119, March 1997. 887 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 888 10646", STD 63, RFC 3629, November 2003. 890 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 891 Resource Identifier (URI): Generic Syntax", STD 66, RFC 892 3986, January 2005. 894 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 895 Specifications: ABNF", STD 68, RFC 5234, January 2008. 897 [RFC5890] Klensin, J., "Internationalized Domain Names for 898 Applications (IDNA): Definitions and Document Framework", 899 RFC 5890, August 2010. 901 [RFC5892] Faltstrom, P., "The Unicode Code Points and 902 Internationalized Domain Names for Applications (IDNA)", 903 RFC 5892, August 2010. 905 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 906 Protocol (XMPP): Core", RFC 6120, March 2011. 908 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 909 Internationalization in the IETF", BCP 166, RFC 6365, 910 September 2011. 912 [RFC6874] Carpenter, B., Cheshire, S., and R. Hinden, "Representing 913 IPv6 Zone Identifiers in Address Literals and Uniform 914 Resource Identifiers", RFC 6874, February 2013. 916 [RFC7564] Saint-Andre, P. and M. Blanchet, "PRECIS Framework: 917 Preparation, Enforcement, and Comparison of 918 Internationalized Strings in Application Protocols", RFC 919 7564, May 2015. 921 [UTR36] The Unicode Consortium, "Unicode Technical Report #36: 922 Unicode Security Considerations", November 2013, 923 . 925 [Unicode] The Unicode Consortium, "The Unicode Standard", 926 2015-present, . 928 9.2. Informative References 930 [I-D.ietf-precis-nickname] 931 Saint-Andre, P., "Preparation and Comparison of 932 Nicknames", draft-ietf-precis-nickname-17 (work in 933 progress), April 2015. 935 [INTEROP] Masinter, L., "Formalizing IETF Interoperability 936 Reporting", Work in Progress, October 2005. 938 [RFC1123] Braden, R., "Requirements for Internet Hosts - Application 939 and Support", STD 3, RFC 1123, October 1989. 941 [RFC1535] Gavron, E., "A Security Problem and Proposed Correction 942 With Widely Deployed DNS Software", RFC 1535, October 943 1993. 945 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 946 Internationalized Strings ("stringprep")", RFC 3454, 947 December 2002. 949 [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, 950 "Internationalizing Domain Names in Applications (IDNA)", 951 RFC 3490, March 2003. 953 See Section 1 for an explanation of why the normative 954 reference to an obsoleted specification is needed. 956 [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence 957 Protocol (XMPP): Core", RFC 3920, October 2004. 959 [RFC3921] Saint-Andre, P., Ed., "Extensible Messaging and Presence 960 Protocol (XMPP): Instant Messaging and Presence", RFC 961 3921, October 2004. 963 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource 964 Identifiers (IRIs)", RFC 3987, January 2005. 966 [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names 967 and Passwords", RFC 4013, February 2005. 969 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 970 Security Layer (SASL)", RFC 4422, June 2006. 972 [RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers 973 (IRIs) and Uniform Resource Identifiers (URIs) for the 974 Extensible Messaging and Presence Protocol (XMPP)", RFC 975 5122, February 2008. 977 [RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for 978 Internationalized Domain Names in Applications (IDNA) 979 2008", RFC 5895, September 2010. 981 [RFC6121] Saint-Andre, P., "Extensible Messaging and Presence 982 Protocol (XMPP): Instant Messaging and Presence", RFC 983 6121, March 2011. 985 [RFC6122] Saint-Andre, P., "Extensible Messaging and Presence 986 Protocol (XMPP): Address Format", RFC 6122, March 2011. 988 [RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and 989 Problem Statement for the Preparation and Comparison of 990 Internationalized Strings (PRECIS)", RFC 6885, March 2013. 992 [UTS39] The Unicode Consortium, "Unicode Technical Standard #39: 993 Unicode Security Mechanisms", July 2012, 994 . 996 [XEP-0004] 997 Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T., and 998 P. Saint-Andre, "Data Forms", XSF XEP 0004, August 2007. 1000 [XEP-0016] 1001 Millard, P. and P. Saint-Andre, "Privacy Lists", XSF XEP 1002 0016, February 2007. 1004 [XEP-0029] 1005 Kaes, C., "Definition of Jabber Identifiers (JIDs)", XSF 1006 XEP 0029, October 2003. 1008 [XEP-0030] 1009 Hildebrand, J., Millard, P., Eatmon, R., and P. Saint- 1010 Andre, "Service Discovery", XSF XEP 0030, June 2008. 1012 [XEP-0045] 1013 Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February 1014 2012. 1016 [XEP-0048] 1017 Blackman, R., Millard, P., and P. Saint-Andre, 1018 "Bookmarks", XSF XEP 0048, November 2007. 1020 [XEP-0054] 1021 Saint-Andre, P., "vcard-temp", XSF XEP 0054, July 2008. 1023 [XEP-0060] 1024 Millard, P., Saint-Andre, P., and R. Meijer, "Publish- 1025 Subscribe", XSF XEP 0060, July 2010. 1027 [XEP-0065] 1028 Smith, D., Miller, M., Saint-Andre, P., and J. Karneges, 1029 "SOCKS5 Bytestreams", XSF XEP 0065, April 2011. 1031 [XEP-0077] 1032 Saint-Andre, P., "In-Band Registration", XSF XEP 0077, 1033 January 2012. 1035 [XEP-0106] 1036 Hildebrand, J. and P. Saint-Andre, "JID Escaping", XSF XEP 1037 0106, June 2007. 1039 [XEP-0114] 1040 Saint-Andre, P., "Jabber Component Protocol", XSF XEP 1041 0114, March 2005. 1043 [XEP-0144] 1044 Saint-Andre, P., "Roster Item Exchange", XSF XEP 0144, 1045 August 2005. 1047 [XEP-0166] 1048 Ludwig, S., Beda, J., Saint-Andre, P., McQueen, R., Egan, 1049 S., and J. Hildebrand, "Jingle", XSF XEP 0166, December 1050 2009. 1052 [XEP-0191] 1053 Saint-Andre, P., "Blocking Command", XSF XEP 0191, July 1054 2012. 1056 [XEP-0203] 1057 Saint-Andre, P., "Delayed Delivery", XSF XEP 0203, 1058 September 2009. 1060 [XEP-0220] 1061 Miller, J., Saint-Andre, P., and P. Hancke, "Server 1062 Dialback", XSF XEP 0220, August 2012. 1064 [XEP-0292] 1065 Saint-Andre, P. and S. Mizzi, "vCard4 Over XMPP", XSF XEP 1066 0292, October 2011. 1068 [XML] Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., 1069 and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth 1070 Edition)", World Wide Web Consortium Recommendation REC- 1071 xml-20081126, November 2008, 1072 . 1074 Appendix A. Differences from RFC 6122 1076 Based on consensus derived from working group discussion, 1077 implementation and deployment experience, and formal interoperability 1078 testing, the following substantive modifications were made from RFC 1079 6122. 1081 o Changed domainpart preparation to use IDNA2008 (instead of 1082 IDNA2003). 1084 o Changed localpart preparation to use the UsernameCaseMapped 1085 profile of the PRECIS IdentifierClass (instead of the Nodeprep 1086 profile of Stringprep). 1088 o Changed resourcepart preparation to use the OpaqueString profile 1089 of the PRECIS FreeformClass (instead of the Resourceprep profile 1090 of Stringprep). 1092 o Specified that internationalized labels within domainparts must be 1093 U-labels (instead of "should be" U-labels). 1095 o Specified that fullwidth and halfwidth characters must be mapped 1096 to their decomposition mappings (previously handled through the 1097 use of NFKC). 1099 o Specified the use of Unicode Normalization Form C (instead of 1100 Unicode Normalization Form KC as specified in the Nodeprep and 1101 Resourceprep profiles of Stringprep). 1103 o Specified that servers must enforce the address formatting rules. 1105 Appendix B. Acknowledgements 1107 Thanks to Ben Campbell, Dave Cridland, Miguel Garcia, Joe Hildebrand, 1108 Jonathan Lennox, Matt Miller, Florian Schmaus, Sam Whited, and 1109 Florian Zeitz for their input during working group discussion. 1111 Dan Romascanu completed a helpful review on behalf of the General 1112 Area Review Team. 1114 During IESG review, Alissa Cooper, Brian Haberman, and Barry Leiba 1115 provided comments that led to improvements in the document. 1117 Thanks also to Matt Miller in his role as document shepherd, Joe 1118 Hildebrand in his role as working group chair, and Ben Campbell in 1119 his role as sponsoring Area Director. 1121 The author wishes to acknowledge Cisco Systems, Inc., for employing 1122 him during his work on earlier draft versions of this document. 1124 Author's Address 1126 Peter Saint-Andre 1127 &yet 1129 Email: peter@andyet.com 1130 URI: https://andyet.com/