XMPP P. Saint-Andre
Internet-Draft &yet
Obsoletes: 6122 (if approved) December 2, 2014
Intended status: Standards Track
Expires: June 5, 2015

Extensible Messaging and Presence Protocol (XMPP): Address Format
draft-ietf-xmpp-6122bis-18

Abstract

This document defines the address format for the Extensible Messaging and Presence Protocol (XMPP), including support for code points outside the ASCII range. This document obsoletes RFC 6122.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on June 5, 2015.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.


Table of Contents

1. Introduction

The Extensible Messaging and Presence Protocol (XMPP) [RFC6120] is an application profile of the Extensible Markup Language [XML] for streaming XML data in close to real time between any two or more network-aware entities. The address format for XMPP entities was originally developed in the Jabber open-source community in 1999, first described by [XEP-0029] in 2002, and then defined canonically by [RFC3920] in 2004 and [RFC6122] in 2011.

As specified in RFC 3920 and RFC 6122, the XMPP address format used the "stringprep" technology for preparation and comparison of non-ASCII characters [RFC3454]. Following the migration of internationalized domain names away from stringprep, this document defines the XMPP address format in a way that no longer depends on stringprep (see the PRECIS problem statement [RFC6885]). Instead, this document builds upon the internationalization framework defined by the IETF's PRECIS Working Group [I-D.ietf-precis-framework].

Although every attempt has been made to ensure that the characters allowed in Jabber Identifiers (JIDs) under Stringprep are still allowed and handled in the same way under PRECIS, there is no guarantee of strict backward compatibility because of changes in Unicode and the fact that PRECIS handling is based on Unicode properties, not a hardcoded table of characters. Because it is possible that previously-valid JIDs might no longer be valid (or previously-invalid JIDs might now be valid), operators of XMPP services are advised to perform careful testing before migrating accounts and other data.

This document obsoletes RFC 6122.

2. Terminology

Many important terms used in this document are defined in [I-D.ietf-precis-framework], [RFC5890], [RFC6120], [RFC6365], and [UNICODE].

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Addresses

3.1. Fundamentals

An XMPP entity is anything that can communicate using XMPP. For historical reasons, the network address of an XMPP entity is called a Jabber Identifier ("JID"). A valid JID is a string of Unicode code points [UNICODE], encoded using UTF-8 [RFC3629], and structured as an ordered sequence of localpart, domainpart, and resourcepart, where the first two parts are demarcated by the '@' character used as a separator and the last two parts are similarly demarcated by the '/' character (e.g., <juliet@example.com/balcony>).

The syntax for a JID is defined as follows using the Augmented Backus-Naur Form (ABNF) as specified in [RFC5234].

   jid          = [ localpart "@" ] domainpart [ "/" resourcepart ]
   localpart    = 1*1023(userbyte)
                  ;
                  ; a "userbyte" is a byte used to represent a 
                  ; UTF-8 encoded Unicode code point that can be
                  ; contained in a string that conforms to the 
                  ; "UsernameCaseMapped" profile of the PRECIS 
                  ; IdentifierClass
                  ;
   domainpart   = IP-literal / IPv4address / ifqdn
                  ;
                  ; the "IPv4address" and "IP-literal" rules are 
                  ; defined in RFC 3986, and the first-match-wins 
                  ; (a.k.a. "greedy") algorithm described therein 
                  ; applies to the matching process
                  ;
                  ; note well that reuse of the IP-literal rule from 
                  ; RFC 3986 implies that IPv6 addresses are enclosed 
                  ; in square brackets (i.e., beginning with '[' and
                  ; ending with ']')
                  ;
   ifqdn        = 1*1023(domainbyte)
                  ;
                  ; a "domainbyte" is a byte used to represent a
                  ; UTF-8 encoded Unicode code point that can be 
                  ; contained in a string that conforms to RFC 5890
                  ;
   resourcepart = 1*1023(resourcebyte)
                  ;
                  ; an "opaquebyte" is a byte used to represent a
                  ; UTF-8 encoded Unicode code point that can be
                  ; contained in a string that conforms to the 
                  ; "OpaqueString" profile of the PRECIS 
                  ; FreeformClass
                  ;
        

All JIDs are based on the foregoing structure. However, note that the formal syntax provided above does not capture all of the rules and restrictions that apply to JIDs, which are described below.

Each allowable portion of a JID (localpart, domainpart, and resourcepart) MUST NOT be zero octets in length and MUST NOT be more than 1023 octets in length, resulting in a maximum total size (including the '@' and '/' separators) of 3071 octets.

This document defines the native format for JIDs; see [RFC5122] for information about the representation of a JID as a Uniform Resource Identifier (URI) [RFC3986] or Internationalized Resource Identifier (IRI) [RFC3987] and the extraction of a JID from an XMPP URI or IRI.

3.2. Domainpart

The domainpart of a JID is that portion after the first '@' character (if any) and before the first '/' character (if any); it is the primary identifier and is the only REQUIRED element of a JID (a mere domainpart is a valid JID). Typically a domainpart identifies the "home" server to which clients connect for XML routing and data management functionality. However, it is not necessary for an XMPP domainpart to identify an entity that provides core XMPP server functionality (e.g., a domainpart can identify an entity such as a multi-user chat service [XEP-0045], a publish-subscribe service [XEP-0060], or a user directory).

The domainpart for every XMPP service MUST be a fully-qualified domain name (FQDN), an IPv4 address, an IPv6 address, or an unqualified hostname (i.e., a text label that is resolvable on a local network).

If the domainpart includes a final character considered to be a label separator (dot) by [RFC1034], this character MUST be stripped from the domainpart before the JID of which it is a part is used for the purpose of routing an XML stanza, comparing against another JID, or constructing an XMPP URI or IRI [RFC5122]. In particular, such a character MUST be stripped before any other canonicalization steps are taken.

In general, the content of a domainpart is an Internationalized Domain Name ("IDN") as described in the specifications for Internationalized Domain Names in Applications (commonly called "IDNA2008"), and a domainpart is an "IDNA-aware domain name slot" as defined in [RFC5890].

After any and all normalization, conversion, and mapping of code points as well as encoding of the string as UTF-8, a domainpart MUST NOT be zero octets in length and MUST NOT be more than 1023 octets in length. (Naturally, the length limits of [RFC1034] apply, and nothing in this document is to be interpreted as overriding those more fundamental limits.)

Detailed rules and considerations for preparation, enforcement, and comparison are provided in the following sections.

3.2.1. Preparation

An entity that prepares a string for inclusion in an XMPP domainpart slot MUST ensure that the string consists only of Unicode code points that are allowed in NR-LDH labels or U-labels as defined in [RFC5890]. This implies that the string MUST NOT include A-labels as defined in [RFC5890]; each A-label MUST be converted to a U-label during preparation of a string for inclusion in a domainpart slot. In addition, the string MUST be encoded as UTF-8 [RFC3629].

3.2.2. Enforcement

An entity that performs enforcement in XMPP domainpart slots MUST prepare a string as described in the previous section and MUST also apply the normalization, case-mapping, and width-mapping rules defined in [RFC5892].

3.2.3. Comparison

An entity that performs comparison of two strings before or after their inclusion in XMPP domainpart slots MUST prepare each string and enforce the normalization, case-mapping, and width-mapping rules specified in the previous two sections. The two strings are to be considered equivalent if they are an exact octet-for-octet match (sometimes called "bit-string identity").

3.3. Localpart

The localpart of a JID is an optional identifier placed before the domainpart and separated from the latter by the '@' character. Typically a localpart uniquely identifies the entity requesting and using network access provided by a server (i.e., a local account), although it can also represent other kinds of entities (e.g., a chat room associated with a multi-user chat service [XEP-0045]). The entity represented by an XMPP localpart is addressed within the context of a specific domain (i.e., <localpart@domainpart>).

The localpart of a JID MUST NOT be zero octets in length and MUST NOT be more than 1023 octets in length. This rule is to be enforced after any normalization and mapping of code points as well as encoding of the string as UTF-8.

The localpart of a JID is an instance of the UsernameCaseMapped profile of the PRECIS IdentifierClass, which is specified in [I-D.ietf-precis-saslprepbis]. The rules and considerations provided in that specification MUST be applied to XMPP localparts.

3.3.1. Further Excluded Characters

In XMPP, the following characters are explicitly disallowed in XMPP localparts even though they are allowed by the IdentifierClass base class and the UsernameCaseMapped profile:

U+0022 (QUOTATION MARK), i.e., "
U+0026 (AMPERSAND), i.e., &
U+0027 (APOSTROPHE), i.e., '
U+002F (SOLIDUS), i.e., /
U+003A (COLON), i.e., :
U+003C (LESS-THAN SIGN), i.e., <
U+003E (GREATER-THAN SIGN), i.e., >
U+0040 (COMMERCIAL AT), i.e., @

3.4. Resourcepart

The resourcepart of a JID is an optional identifier placed after the domainpart and separated from the latter by the '/' character. A resourcepart can modify either a <localpart@domainpart> address or a mere <domainpart> address. Typically a resourcepart uniquely identifies a specific connection (e.g., a device or location) or object (e.g., an occupant in a multi-user chat room [XEP-0045]) belonging to the entity associated with an XMPP localpart at a domain (i.e., <localpart@domainpart/resourcepart>).

XMPP entities SHOULD consider resourceparts to be opaque strings and SHOULD NOT impute meaning to any given resourcepart. In particular:

The resourcepart of a JID MUST NOT be zero octets in length and MUST NOT be more than 1023 octets in length. This rule is to be enforced after any normalization and mapping of code points as well as encoding of the string as UTF-8.

The resourcepart of a JID is an instance of the OpaqueString profile of the PRECIS FreeformClass, which is specified in [I-D.ietf-precis-saslprepbis]. The rules and considerations provided in that specification MUST be applied to XMPP resourceparts.

3.4.1. Applicability to XMPP

In some contexts, it might be appropriate to apply more restrictive rules to the preparation, enforcement, and comparison of XMPP resourceparts. For example, in XMPP Multi-User Chat [XEP-0045] it might be appropriate to apply the rules specified in [I-D.ietf-precis-nickname]. However, the application of more restrictive rules is out of scope for resourceparts in general and is properly defined in specifications for the relevant XMPP extensions.

3.5. Examples

The following examples illustrate a small number of JIDs that are consistent with the format defined above.

Table 1: A sample of legal JIDs

+---------------------------------+---------------------------------+
| # | JID                         | Notes                           |
+---------------------------------+---------------------------------+
| 1 | juliet@example.com          | A "bare JID"                    |
+---------------------------------+---------------------------------+
| 2 | juliet@example.com/foo      | A "full JID"                    |
+---------------------------------+---------------------------------+
| 3 | juliet@example.com/foo bar  | Single space in resourcepart    |
+---------------------------------+---------------------------------+
| 4 | foo\20bar@example.com       | Single space in localpart, as   |
|   |                             | optionally escaped using the    |
|   |                             | XMPP "JID Escaping" extension   |
+---------------------------------+---------------------------------+
| 5 | fussball@example.com        | Another bare JID                |
+---------------------------------+---------------------------------+
| 6 | fu&#xDF;ball@example.com    | The third character is LATIN    |
|   |                             | SMALL LETTER SHARP S (U+00DF)   |
+---------------------------------+---------------------------------+
| 7 | &#x3C0;@example.com         | A localpart of GREEK SMALL      |
|   |                             | LETTER PI (U+03C0)              |
+---------------------------------+---------------------------------+
| 8 | &#x3C0;@example.com/&#x3A3; | A resourcepart of GREEK CAPITAL |
|   |                             | LETTER SIGMA (U+03A3)           |
+---------------------------------+---------------------------------+
| 9 | &#x3C0;@example.com/&#x3C3; | A resourcepart of GREEK SMALL   |
|   |                             | LETTER SIGMA (U+03C3)           |
+---------------------------------+---------------------------------+
| 10| &#x3C0;@example.com/&#x3C2; | A resourcepart of GREEK SMALL   |
|   |                             | LETTER FINAL SIGMA (U+03C2)     |
+---------------------------------+---------------------------------+
| 11| henryiv@example.com/&#x265A;| A resourcepart of the Unicode   |
|   |                             | character BLACK CHESS KING      |
|   |                             | (U+265A)                        |
+---------------------------------+---------------------------------+
| 12| example.com                 | A domainpart                    |
+---------------------------------+---------------------------------+
| 13| example.com/foobar          | A domainpart plus resourcepart  |
+---------------------------------+---------------------------------+
        

Several points are worth noting. Regarding examples 5 and 6: although in German the character esszett (LATIN SMALL LETTER SHARP S, U+00DF) can mostly be used interchangeably with the two characters "ss", the localparts in these examples are different and (if desired) a server would need to enforce a registration policy that disallows one of them if the other is registered. Regarding examples 8, 9, and 10: case-mapping of GREEK CAPITAL LETTER SIGMA (U+03A3) to lowercase (i.e., to GREEK SMALL LETTER SIGMA, U+03C3) during comparison would result in matching the JIDs in examples 8 and 9; however, because the PRECIS mapping rules do not account for the special status of GREEK SMALL LETTER FINAL SIGMA (U+03C2), the JIDs in examples 8 and 10 or examples 9 and 10 would not be matched. Regarding example 11: symbol characters such as BLACK CHESS KING (U+265A) are allowed by the PRECIS FreeformClass and thus can be used in resourceparts. Regarding example 13: JIDs consisting of a domainpart and resourcepart are rarely seen in the wild, but are allowed according to the XMPP address format.

The following examples illustrate strings that are not JIDs because they violate the format defined above.

Table 2: A sample of strings that violate the JID rules

+---------------------------------+---------------------------------+
| # | Non-JID string              | Notes                           |
+---------------------------------+---------------------------------+
| 13| "juliet"@example.com        | Quotation marks (U+0022) in     | 
|   |                             | localpart                       |
+---------------------------------+---------------------------------+
| 14| foo bar@example.com         | Space (U+0020) in localpart     |
+---------------------------------+---------------------------------+
| 15| juliet@example.com/ foo     | Leading space in resourcepart   |
+---------------------------------+---------------------------------+
| 16| <@example.com/>             | Zero-length localpart and       |
|   |                             | resourcepart ('<' and '>') are  |
|   |                             | used here to show the start and |
|   |                             | end of the JID in question      |
+---------------------------------+---------------------------------+
| 17| henry&#x2163;@example.com   | The sixth character is ROMAN    |
|   |                             | NUMERAL FOUR (U+2163)           |
+---------------------------------+---------------------------------+
| 18| &#x265A;@example.com        | A localpart of BLACK CHESS KING | 
|   |                             | (U+265A)                        |
+---------------------------------+---------------------------------+
| 19| juliet@                     | A localpart without domainpart  |
+---------------------------------+---------------------------------+
| 20| /foobar                     | A resourcepart without          |
|                                 | domainpart                      |
+---------------------------------+---------------------------------+
        

Here again, several points are worth noting. Regarding example 15, even though ASCII SPACE (U+0020) is disallowed in the PRECIS IdentifierClass, it can be escaped to "\20" in XMPP localparts by using the JID Escaping rules defined in [XEP-0106], as illustrated by example 4 in Table 1. Regarding example 17, the Unicode character ROMAN NUMERAL FOUR (U+2163) has a compatibility equivalent of the string formed of LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL LETTER V (U+0056), but characters with compatibility equivalents are not allowed in the PRECIS IdentiferClass. Regarding example 18: symbol characters such as BLACK CHESS KING (U+265A) are not allowed in the PRECIS IdentifierClass; however, both of the non-ASCII characters in examples 17 and 18 are allowed in the PRECIS Freeform class and therefore in the XMPP resourcepart (as illustrated for U+265A by example 11 in Table 1). Regarding examples 19 and 20: the domainpart is required in a JID.

4. Enforcement in JIDs and JID Parts

Enforcement entails applying all of the rules specified in this document. Enforcement of the XMPP address format rules is the responsibility of XMPP servers. Although XMPP clients SHOULD prepare complete JIDs and parts of JIDs in accordance with this document before including them in protocol slots within XML streams, XMPP servers MUST enforce the rules wherever possible and reject stanzas and other XML elements that violate the rules (for stanzas, by returning a <jid-malformed/> error to the sender as described in Section 8.3.3.8 of [RFC6120]).

Entities that enforce the rules specified in this document are encouraged to be liberal in what they accept by following this procedure:

  1. Where possible, map characters (e.g, through width mapping, additional mapping, special mapping, case mapping, or normalization) and accept the mapped string.
  2. If mapping is not possible (e.g., because a character is disallowed in the FreeformClass), reject the string and return a <jid-malformed/> error.

Enforcement applies to complete JIDs and to parts of JIDs. To facilitate implementation, this document defines the concepts of "JID slot", "localpart slot", and "resourcepart slot" (similar to the concept of a "domain name slot" for IDNA2008 defined in Section 2.3.2.6 of [RFC5890]):

JID Slot:
An XML element or attribute explicitly designated in XMPP or in XMPP extensions for carrying a complete JID.
Localpart Slot:
An XML element or attribute explicitly designated in XMPP or in XMPP extensions for carrying the localpart of a JID.
Resourcepart Slot:
An XML element or attribute explicitly designated in XMPP or in XMPP extensions for carrying the resourcepart of a JID.

A server is responsible for enforcing the address format rules when receiving protocol elements from clients where the server is expected to handle such elements directly or to use them for purposes of routing a stanza to another domain or delivering a stanza to a local entity; two examples from [RFC6120] are the 'to' attribute on XML stanzas (which is a JID slot used by XMPP servers for routing of outbound stanzas) and the <resource/> child of the <bind/> element (which is a resourcepart slot used by XMPP servers for binding of a resource to an account for routing of stanzas between the server and a particular client). An example from [RFC6121] is the 'jid' attribute of the roster <item/> element.

A server is not responsible for enforcing the rules when the protocol elements are intended for communication among other entities, typically within the payload of a stanza that the server is merely routing to another domain or delivering to a local entity. Two examples are the 'initiator' attribute in the Jingle extension [XEP-0166] (which is a JID slot used for client-to-client coordination of multimedia sessions) and the 'nick' attribute in the Multi-User Chat extension [XEP-0045] (which is a resourcepart slot used for administrative purposes in the context of XMPP chatrooms). In such cases, clients SHOULD enforce the rules themselves and not depend on the server to do so, and client implementers need to understand that not enforcing the rules can lead to a degraded user experience or to security vulnerabilities. However, when an add-on service (e.g., a multi-user chat service) handles a stanza directly, it ought to enforce the rules as well, as defined in the relevant specification for that type of service.

This document does not provide an exhaustive list of JID slots, localpart slots, or resourcepart slots. However, implementers of core XMPP servers are advised to consider as JID slots at least the following elements and attributes when they are handled directly or used for purposes of routing to another domain or delivering to a local entity:

Developers of XMPP clients and specialized XMPP add-on services are advised to check the appropriate specifications for JID slots, localpart slots, and resourcepart slots in XMPP protocol extensions such as Service Discovery [XEP-0030], Multi-User Chat [XEP-0045], Publish-Subscribe [XEP-0060], SOCKS5 Bytestreams [XEP-0065], In-Band Registration [XEP-0077], Roster Item Exchange [XEP-0144], and Jingle [XEP-0166].

5. Internationalization Considerations

XMPP applications MUST support IDNA2008 for domainparts as described under Section 3.2, the "UsernameCaseMapped" profile for localparts as described under Section 3.3, and the "OpaqueString" profile for resourceparts as described under Section 3.4. This enables XMPP addresses to include a wide variety of characters outside the ASCII range. Rules for enforcement of the XMPP address format are provided in [RFC6120] and specifications for various XMPP extensions.

6. IANA Considerations

6.1. Stringprep Profiles Registry

The Stringprep specification [RFC3454] did not provide for entries in the Stringprep Profiles registry to be marked as anything except current or not current. Because this document obsoletes RFC 6122, which registered the "Nodeprep" and "Resourceprep" profiles, IANA is requested at the least to mark those profiles as not current (preferably with a pointer to this document).

7. Security Considerations

7.1. Reuse of PRECIS

The security considerations described in [I-D.ietf-precis-framework] apply to the "IdentifierClass" and "FreeformClass" base string classes used in this document for XMPP localparts and resourceparts, respectively. The security considerations described in [RFC5890] apply to internationalized domain names, which are used here for XMPP domainparts.

7.2. Reuse of Unicode

The security considerations described in [UTS39] apply to the use of Unicode characters in XMPP addresses.

7.3. Address Spoofing

There are two forms of address spoofing: forging and mimicking.

7.3.1. Address Forging

In the context of XMPP technologies, address forging occurs when an entity is able to generate an XML stanza whose 'from' address does not correspond to the account credentials with which the entity authenticated onto the network (or an authorization identity provided during negotiation of SASL authentication [RFC4422] as described in [RFC6120]). For example, address forging occurs if an entity that authenticated as "juliet@im.example.com" is able to send XML stanzas from "nurse@im.example.com" or "romeo@example.net".

Address forging is difficult in XMPP systems, given the requirement for sending servers to stamp 'from' addresses and for receiving servers to verify sending domains via server-to-server authentication (see [RFC6120]). However, address forging is possible if:

Therefore, an entity outside the security perimeter of a particular server cannot reliably distinguish between JIDs of the form <localpart@domainpart> at that server and thus can authenticate only the domainpart of such JIDs with any level of assurance. This specification does not define methods for discovering or counteracting the kind of poorly implemented or rogue servers just described. However, the end-to-end authentication or signing of XMPP stanzas could help to mitigate this risk, since it would require the rogue server to generate false credentials for signing or encryption of each stanza, in addition to modifying 'from' addresses.

7.3.2. Address Mimicking

Address mimicking occurs when an entity provides legitimate authentication credentials for and sends XML stanzas from an account whose JID appears to a human user to be the same as another JID. Because many characters are visually similar, it is relatively easy to mimic JIDs in XMPP systems. As one simple example, the localpart "ju1iet" (using the Arabic numeral one as the third character) might appear the same as the localpart "juliet" (using lowercase "L" as the third character).

As explained in [RFC5890], [I-D.ietf-precis-framework], [UTR36], and [UTS39], there is no straightforward solution to the problem of visually similar characters. Furthermore, IDNA and PRECIS technologies do not attempt to define such a solution. As a result, XMPP domainparts, localparts, and resourceparts could contain such characters, leading to security vulnerabilities such as the following:

XMPP services and clients are strongly encouraged to define and implement consistent policies regarding the registration, storage, and presentation of visually similar characters in XMPP systems. In particular, service providers and software implementers are strongly encouraged to apply the policies recommended in [I-D.ietf-precis-framework].

8. Conformance Requirements

This section describes a protocol feature set that summarizes the conformance requirements of this specification (similar feature sets are provided for XMPP in [RFC6120] and [RFC6121]). This feature set is appropriate for use in software certification, interoperability testing, and implementation reports. For each feature, this section provides the following information:

The feature set specified here provides a basis for interoperability testing and follows the spirit of a proposal made by Larry Masinter within the IETF's NEWTRK Working Group in 2005 [INTEROP].

Feature:
address-domain-length
Description:
Ensure that the domainpart of an XMPP address is at least one octet in length and at most 1023 octets in length, and that it conforms to the underlying length limits of the DNS.
Section:
Section 3.2
Roles:
Server MUST, client SHOULD.

Feature:
address-domain-prep
Description:
Ensure that the domainpart of an XMPP address conforms to IDNA2008, that it contains only NR-LDH labels and U-labels (not A-labels), and that all uppercase and titlecase code points are mapped to their lowercase equivalents.
Section:
Section 3.2
Roles:
Server MUST, client SHOULD.

Feature:
address-localpart-length
Description:
Ensure that the localpart of an XMPP address is at least one octet in length and at most 1023 octets in length.
Section:
Section 3.3
Roles:
Server MUST, client SHOULD.

Feature:
address-localpart-prep
Description:
Ensure that the localpart of an XMPP address conforms to the "UsernameCaseMapped" profile of the PRECIS IdentifierClass.
Section:
Section 3.3
Roles:
Server MUST, client SHOULD.

Feature:
address-resource-length
Description:
Ensure that the resourcepart of an XMPP address is at least one octet in length and at most 1023 octets in length.
Section:
Section 3.4
Roles:
Server MUST, client SHOULD.

Feature:
address-resource-prep
Description:
Ensure that the resourcepart of an XMPP address conforms to the "OpaqueString" profile of the PRECIS FreeformClass.
Section:
Section 3.4
Roles:
Server MUST, client SHOULD.

9. References

9.1. Normative References

[I-D.ietf-precis-framework] Saint-Andre, P. and M. Blanchet, "Precis Framework: Handling Internationalized Strings in Protocols", Internet-Draft draft-ietf-precis-framework-20, November 2014.
[I-D.ietf-precis-saslprepbis] Saint-Andre, P. and A. Melnikov, "Username and Password Preparation Algorithms", Internet-Draft draft-ietf-precis-saslprepbis-11, November 2014.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in Applications (IDNA): Protocol", RFC 5891, August 2010.
[RFC5892] Faltstrom, P., "The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)", RFC 5892, August 2010.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 6120, March 2011.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version 6.3", 2013.
[UTR36] The Unicode Consortium, "Unicode Technical Report #36: Unicode Security Considerations", November 2013.

9.2. Informative References

[I-D.ietf-precis-nickname] Saint-Andre, P., "Preparation and Comparison of Nicknames", Internet-Draft draft-ietf-precis-nickname-13, November 2014.
[INTEROP] Masinter, L., "Formalizing IETF Interoperability Reporting", Work in Progress, October 2005.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, October 1989.
[RFC1535] Gavron, E., "A Security Problem and Proposed Correction With Widely Deployed DNS Software", RFC 1535, October 1993.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ("stringprep")", RFC 3454, December 2002.
[RFC3490] Faltstrom, P., Hoffman, P. and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003.

See Section 1 for an explanation of why the normative reference to an obsoleted specification is needed.

[RFC3920] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 3920, October 2004.
[RFC3921] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence", RFC 3921, October 2004.
[RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005.
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names and Passwords", RFC 4013, February 2005.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006.
[RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers (IRIs) and Uniform Resource Identifiers (URIs) for the Extensible Messaging and Presence Protocol (XMPP)", RFC 5122, February 2008.
[RFC5894] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Background, Explanation, and Rationale", RFC 5894, August 2010.
[RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for Internationalized Domain Names in Applications (IDNA) 2008", RFC 5895, September 2010.
[RFC6121] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence", RFC 6121, March 2011.
[RFC6122] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Address Format", RFC 6122, March 2011.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in Internationalization in the IETF", BCP 166, RFC 6365, September 2011.
[RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and Problem Statement for the Preparation and Comparison of Internationalized Strings (PRECIS)", RFC 6885, March 2013.
[UTS39] The Unicode Consortium, "Unicode Technical Standard #39: Unicode Security Mechanisms", July 2012.
[XEP-0004] Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T. and P. Saint-Andre, "Data Forms", XSF XEP 0004, August 2007.
[XEP-0016] Millard, P. and P. Saint-Andre, "Privacy Lists", XSF XEP 0016, February 2007.
[XEP-0029] Kaes, C., "Definition of Jabber Identifiers (JIDs)", XSF XEP 0029, October 2003.
[XEP-0030] Hildebrand, J., Millard, P., Eatmon, R. and P. Saint-Andre, "Service Discovery", XSF XEP 0030, June 2008.
[XEP-0045] Saint-Andre, P., "Multi-User Chat", XSF XEP 0045, February 2012.
[XEP-0048] Blackman, R., Millard, P. and P. Saint-Andre, "Bookmarks", XSF XEP 0048, November 2007.
[XEP-0054] Saint-Andre, P., "vcard-temp", XSF XEP 0054, July 2008.
[XEP-0060] Millard, P., Saint-Andre, P. and R. Meijer, "Publish-Subscribe", XSF XEP 0060, July 2010.
[XEP-0065] Smith, D., Miller, M., Saint-Andre, P. and J. Karneges, "SOCKS5 Bytestreams", XSF XEP 0065, April 2011.
[XEP-0077] Saint-Andre, P., "In-Band Registration", XSF XEP 0077, January 2012.
[XEP-0106] Hildebrand, J. and P. Saint-Andre, "JID Escaping", XSF XEP 0106, June 2007.
[XEP-0114] Saint-Andre, P., "Jabber Component Protocol", XSF XEP 0114, March 2005.
[XEP-0144] Saint-Andre, P., "Roster Item Exchange", XSF XEP 0144, August 2005.
[XEP-0165] Saint-Andre, P., "Best Practices to Discourage JID Mimicking", XSF XEP 0165, December 2007.
[XEP-0166] Ludwig, S., Beda, J., Saint-Andre, P., McQueen, R., Egan, S. and J. Hildebrand, "Jingle", XSF XEP 0166, December 2009.
[XEP-0191] Saint-Andre, P., "Blocking Command", XSF XEP 0191, July 2012.
[XEP-0203] Saint-Andre, P., "Delayed Delivery", XSF XEP 0203, September 2009.
[XEP-0220] Miller, J., Saint-Andre, P. and P. Hancke, "Server Dialback", XSF XEP 0220, August 2012.
[XEP-0292] Saint-Andre, P. and S. Mizzi, "vCard4 Over XMPP", XSF XEP 0292, October 2011.
[XML] Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J. and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC-xml-20081126, November 2008.

Appendix A. Differences from RFC 6122

Based on consensus derived from working group discussion, implementation and deployment experience, and formal interoperability testing, the following substantive modifications were made from RFC 6122.

Appendix B. Acknowledgements

Thanks to Miguel Garcia, Joe Hildebrand, Jonathan Lennox, Matt Miller, and Florian Zeitz for their feedback.

Some text in this document was borrowed or adapted from [RFC5890], [RFC5891], [RFC5894], and [XEP-0165].

Peter Saint-Andre wishes to acknowledge Cisco Systems, Inc., for employing him during his work on earlier versions of this document.

Author's Address

Peter Saint-Andre &yet EMail: peter@andyet.com URI: https://andyet.com/