Extensible Messaging and Presence Protocol (XMPP): Address Format
draft-ietf-xmpp-6122bis-13

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XMPP                                                      P. Saint-Andre
Internet-Draft                                                      &yet
Obsoletes: 6122 (if approved)                         September 10, 2014
Intended status: Standards Track
Expires: March 14, 2015

   Extensible Messaging and Presence Protocol (XMPP): Address Format
                       draft-ietf-xmpp-6122bis-13

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
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   This Internet-Draft will expire on March 14, 2015.

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

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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Preparation, Comparison, and Enforcement  . . . . . . . . . .   3
   4.  Addresses . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Fundamentals  . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Domainpart  . . . . . . . . . . . . . . . . . . . . . . .   6
       4.2.1.  Preparation . . . . . . . . . . . . . . . . . . . . .   7
       4.2.2.  Enforcement . . . . . . . . . . . . . . . . . . . . .   7
       4.2.3.  Comparison  . . . . . . . . . . . . . . . . . . . . .   8
     4.3.  Localpart . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.3.1.  Preparation . . . . . . . . . . . . . . . . . . . . .   8
       4.3.2.  Enforcement . . . . . . . . . . . . . . . . . . . . .   9
       4.3.3.  Comparison  . . . . . . . . . . . . . . . . . . . . .  10
     4.4.  Resourcepart  . . . . . . . . . . . . . . . . . . . . . .  10
       4.4.1.  Preparation . . . . . . . . . . . . . . . . . . . . .  11
       4.4.2.  Enforcement . . . . . . . . . . . . . . . . . . . . .  11
       4.4.3.  Comparison  . . . . . . . . . . . . . . . . . . . . .  12
     4.5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Enforcement in JIDs and JID Parts . . . . . . . . . . . . . .  15
   6.  Internationalization Considerations . . . . . . . . . . . . .  17
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     7.1.  PRECIS Profiles Registry  . . . . . . . . . . . . . . . .  17
       7.1.1.  JIDlocalIdentifierClass . . . . . . . . . . . . . . .  17
       7.1.2.  JIDresourceFreeformClass  . . . . . . . . . . . . . .  18
     7.2.  Stringprep Profiles Registry  . . . . . . . . . . . . . .  19
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
     8.1.  Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . .  19
     8.2.  Reuse of Unicode  . . . . . . . . . . . . . . . . . . . .  19
     8.3.  Address Spoofing  . . . . . . . . . . . . . . . . . . . .  19
       8.3.1.  Address Forging . . . . . . . . . . . . . . . . . . .  20
       8.3.2.  Address Mimicking . . . . . . . . . . . . . . . . . .  20
   9.  Conformance Requirements  . . . . . . . . . . . . . . . . . .  22
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     10.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Appendix A.  Differences from RFC 6122  . . . . . . . . . . . . .  28
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  28
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  29

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,

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   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.  Preparation, Comparison, and Enforcement

   This document distinguishes between three different actions that an
   XMPP entity can take:

   o  Enforcement entails applying all of the rules specified for a
      particular profile (JIDlocalIdentifierClass or
      JIDresourceFreeformClass) to an individual string.  Enforcement is
      the responsibility of an XMPP server (although a server does not
      need to enforce the rules every time it handles a JID or JID part;
      see Section 5 for a detailed discussion).

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   o  Comparison entails applying all of the rules specified for a
      particular profile to two separate strings, for the purpose of
      determining if the two strings are equivalent.

   o  Preparation entails only ensuring that the characters in an
      individual string are allowed by the underlying PRECIS base class
      (IdentifierClass or FreeformClass).  Preparation can the
      responsibility of an XMPP client or (in some circumstances) an
      XMPP server (here again see Section 5 for a detailed discussion).

4.  Addresses

4.1.  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].

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     jid           = [ localpart "@" ] domainpart [ "/" resourcepart ]
     localpart     = 1*1023(localbyte)
                     ;
                     ; a "localbyte" is a byte used to represent a
                     ; UTF-8 encoded Unicode code point that conforms
                     ; to the "JIDlocalIdentifierClass" 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 conforms
                     ; to RFC 5890
                     ;
     resourcepart  = 1*1023(resourcebyte)
                     ;
                     ; a "resourcebyte" is a byte used to represent a
                     ; UTF-8 encoded Unicode code point that conforms
                     ; to the "JIDresourceFreeformClass" 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.

      Implementation Note: The length limits on JIDs and parts of JIDs
      are based on octets (bytes), not characters.  UTF-8 encoding can
      result in more than one octet per character.

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      Implementation Note: When dividing a JID into its component parts,
      an implementation needs to match the separator characters '@' and
      '/' before applying any transformation algorithms, which might
      decompose certain Unicode code points to the separator characters
      (e.g., under Unicode Normalization Form KC U+FE6B SMALL COMMERCIAL
      AT decomposes to U+0040 COMMERCIAL AT, although note that this
      decomposition does not occur under Unicode Normalization C, which
      is used in this specification).

   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.

4.2.  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).

      Informational Note: The term "fully-qualified domain name" is not
      well defined.  In [RFC1034] it is also called an absolute domain
      name, and the two terms are associated in [RFC1535].  The earliest
      use of the term can be found in [RFC1123].  References to those
      older specifications ought not to be construed as limiting the
      characters of a fully-qualified domain name to the ASCII range;
      for example, [RFC5890] mentions that a fully-qualified domain name
      can contain one or more U-labels.

      Interoperability Note: Domainparts that are IP addresses might not
      be accepted by other services for the purpose of server-to-server
      communication, and domainparts that are unqualified hostnames
      cannot be used on public networks because they are resolvable only
      on a local network.

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   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.

4.2.1.  Preparation

   An XMPP entity that prepares a string for inclusion in a 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].

4.2.2.  Enforcement

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

   1.  The string MUST consist only of Unicode code points that conform
       to the rules specified in [RFC5892] (which includes Unicode
       normalization).

   2.  All uppercase and titlecase code points in the string MUST be
       mapped to their lowercase equivalents, preferably using Unicode

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       Default Case Folding as defined in Chapter 3 of the Unicode
       Standard [UNICODE].

   3.  Fullwidth and halfwidth characters in the string MUST be mapped
       to their decomposition mappings.

   These rules MUST be applied in the order shown.  The reader is
   advised that this order is different from the order for localparts
   and resourceparts as described under Section 4.3 and Section 4.4, in
   order to maintain consistency with the IDNA methods in both [RFC5892]
   and [RFC5895].

4.2.3.  Comparison

   An XMPP entity that performs comparison of two strings before or
   after their inclusion in 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").

4.3.  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>).

   A localpart 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.

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

4.3.1.  Preparation

   An XMPP entity that prepares a string for inclusion in a localpart
   slot MUST ensure that the string consists only of Unicode code points
   that conform to the "IdentifierClass" base string class defined in
   [I-D.ietf-precis-framework].  In addition, the string MUST be encoded
   as UTF-8 [RFC3629].

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4.3.2.  Enforcement

   An XMPP entity that performs enforcement in localpart slots MUST
   prepare a string as described in the previous section and MUST also
   apply the width-mapping rules, case-mapping, normalization, and
   exception rules for the JIDlocalIdentifierClass profile described
   below (these rules MUST be applied in the order shown).

   1.  Fullwidth and halfwidth characters MUST be mapped to their
       decomposition mappings.

   2.  Uppercase and titlecase characters MUST be mapped to their
       lowercase equivalents, preferably using Unicode Default Case
       Folding as defined in Chapter 3 of the Unicode Standard
       [UNICODE].

   3.  All characters MUST be normalized using Unicode Normalization
       Form C (NFC).

   The exclusion rule for the The JIDlocalIdentifierClass profile is as
   follows, i.e., the characters listed below are explicitly disallowed
   in XMPP localparts even though they are allowed by the
   IdentifierClass base class:

      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., @

      Implementation Note: An XMPP-specific method for escaping the
      above-listed characters (along with U+0020, i.e., ASCII SPACE) has
      been defined in the JID Escaping specification [XEP-0106].

   With regard to directionality, applications MUST apply the "Bidi
   Rule" defined in [RFC5893] (i.e., each of the six conditions of the
   Bidi Rule must be satisfied).

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4.3.3.  Comparison

   An XMPP entity that performs comparison of two strings before or
   after their inclusion in localpart 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").

4.4.  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:

   o  Use of the '/' character as a separator between the domainpart and
      the resourcepart does not imply that XMPP addresses are
      hierarchical in the way that, say, HTTP URIs are hierarchical (see
      [RFC3986] for general discussion); thus for example an XMPP
      address of the form <localpart@domainpart/foo/bar> does not
      identify a resource "bar" that exists below a resource "foo" in a
      hierarchy of resources associated with the entity
      "localpart@domainpart".

   o  The '@' character is allowed in the resourcepart and is often used
      in the "handle" shown in XMPP chatrooms [XEP-0045].  For example,
      the JID <room@chat.example.com/user@host> describes an entity who
      is an occupant of the room <room@chat.example.com> with a handle
      of <user@host>.  However, chatroom services do not necessarily
      check such an asserted handle against the occupant's real JID.

   A resourcepart 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.

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

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   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.

4.4.1.  Preparation

   An XMPP entity that prepares a string for inclusion in a resourcepart
   slot MUST ensure that the string consists only of Unicode code points
   that conform to the "FreeformClass" base string class defined in
   [I-D.ietf-precis-framework].  In addition, the string MUST be encoded
   as UTF-8 [RFC3629].

4.4.2.  Enforcement

   An XMPP entity that performs enforcement in resourcepart slots MUST
   prepare a string as described in the previous section and MUST also
   apply the width-mapping rules, special mapping, additional mapping,
   case-mapping, and normalization rules for the
   JIDresourceFreeformClass profile described below (these rules MUST be
   applied in the order shown).

   1.  Fullwidth and halfwidth characters MAY be mapped to their
       decomposition mappings.

   2.  Any instances of non-ASCII space MUST be mapped to ASCII space
       (U+0020); such an instance is any Unicode code point that has a
       compatibility mapping of any kind (including but not limited to
       <compat> as for U+0384 GREEK TONOS, <noBreak> as for U+2007
       FIGURE SPACE, and <wide> as for U+3000 IDEOGRAPHIC SPACE) to
       U+0020 SPACE.

   3.  So-called additional mappings MAY be applied, such as mapping of
       characters that are similar to common delimiters (such as '@',
       ':', '/', '+', '-', and '.', e.g., mapping of IDEOGRAPHIC FULL
       STOP (U+3002) to FULL STOP (U+002E)) and special handling of
       certain characters or classes of characters (e.g., mapping of
       non-ASCII spaces to ASCII space); the PRECIS mappings document
       [I-D.ietf-precis-mappings] describes such mappings in more
       detail.

   4.  Uppercase and titlecase characters MAY be mapped to their
       lowercase equivalents, preferably using Unicode Default Case
       Folding as defined in Chapter 3 of the Unicode Standard
       [UNICODE].

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   5.  All characters MUST be normalized using Unicode Normalization
       Form C (NFC).

   Finally, leading and trailing whitespace (i.e., one or more instances
   of the ASCII space character at the beginning or end of a
   resourcepart) MUST be removed (e.g., "stpeter " is mapped to
   "stpeter").

   Note: There is no exclusion rule for the JIDresourceFreeformClass
   profile.

   With regard to directionality, applications MUST apply the "Bidi
   Rule" defined in [RFC5893] (i.e., each of the six conditions of the
   Bidi Rule must be satisfied).

4.4.3.  Comparison

   An XMPP entity that performs comparison of two strings before or
   after their inclusion in resourcepart 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").

4.5.  Examples

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

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   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

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   (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 "\27" 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

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   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.

5.  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 (such that
   JIDs and parts of JIDs are in conformance), 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]).

   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

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   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:

   o  The 'from' and 'to' stream attributes and the 'from' and 'to'
      stanza attributes [RFC6120].

   o  The 'jid' attribute of the roster <item/> element for contact list
      management [RFC6121].

   o  The 'value' attribute of the <item/> element for Privacy Lists
      [RFC3921] [XEP-0016] when the value of the 'type' attribute is
      "jid".

   o  The 'jid' attribute of the <item/> element for Service Discovery
      defined in [XEP-0030].

   o  The <value/> element for Data Forms [XEP-0004], when the 'type'
      attribute is "jid-single" or "jid-multi".

   o  The 'jid' attribute of the <conference/> element for Bookmark
      Storage [XEP-0048].

   o  The <JABBERID/> of the <vCard/> element for vCard 3.0 [XEP-0054]
      and the <uri/> child of the <impp/> element for vCard 4.0

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      [XEP-0292] when the XML character data identifies an XMPP URI
      [RFC5122].

   o  The 'from' attribute of the <delay/> element for Delayed Delivery
      [XEP-0203].

   o  The 'jid' attribute of the <item/> element for the Blocking
      Command [XEP-0191].

   o  The 'from' and 'to' attributes of the <result/> and <verify/>
      elements for Server Dialback [RFC3921], [XEP-0220].

   o  The 'from' and 'to' attributes of the <iq/>, <message/>, and
      <presence/> elements for the Jabber Component Protocol [XEP-0114].

   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].

6.  Internationalization Considerations

   XMPP applications MUST support IDNA2008 for domainparts as described
   under Section 4.2, the "JIDlocalIdentifierClass" profile for
   localparts as described under Section 4.3, and the
   "JIDresourceFreeformClass" profile for resourceparts as described
   under Section 4.4.  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.

      Interoperability Note: For backward compatibility, many existing
      XMPP implementations and deployments support IDNA2003 [RFC3490]
      for domainparts, and the stringprep [RFC3454] profiles Nodeprep
      and Resourceprep [RFC3920] for localparts and resourceparts.

7.  IANA Considerations

7.1.  PRECIS Profiles Registry

7.1.1.  JIDlocalIdentifierClass

   The following completed template provides the information necessary
   for the IANA to add 'JIDlocalIdentifierClass' to the PRECIS Profiles
   Registry.

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   Name:  JIDlocalIdentifierClass.

   Applicability:  Localparts of XMPP addresses.

   Base Class:  IdentifierClass.

   Replaces:  Nodeprep.

   Width Mapping:  Map fullwidth and halfwidth characters to their
      decomposition mappings.

   Additional Mappings:  None required or recommended.

   Case Mapping:  Map uppercase and titlecase characters to lowercase.

   Normalization:  NFC.

   Directionality:  The "Bidi Rule" defined in RFC 5893 applies.

   Exclusions:  Eight legacy characters in the ASCII range: U+0022,
      U+0026, U+0027, U+002F, U+003A, U+003C, U+003E, U+0040.

   Enforcement:  In general, XMPP servers are responsible for enforcing
      the rules (although XMPP clients and components can also be
      responsible for doing so, depending on the JID slots, localpart
      slots, and resourcepart slots where JIDs or parts of JIDs are
      used).

   Specification:  this document.  [Note to RFC Editor: please change
      "this document" to the number issued for this specification.]

7.1.2.  JIDresourceFreeformClass

   The following completed template provides the information necessary
   for the IANA to add 'JIDresourceFreeformClass' to the PRECIS Profiles
   Registry.

   Profile:  JIDresourceFreeformClass.

   Applicability:  Resourceparts of XMPP addresses.

   Base Class:  FreeformClass

   Replaces:  The Resourceprep profile of Stringprep.

   Width Mapping:  Optional.

   Additional Mappings:  Map non-ASCII space to ASCII space.

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   Case Mapping:  Optional.

   Normalization:  NFC.

   Directionality:  The "Bidi Rule" defined in RFC 5893 applies.

   Exclusions:  None.

   Enforcement:  In general, XMPP servers are responsible for enforcing
      the rules (although XMPP clients and components can also be
      resonsible for doing so, depending on the protocol slots where
      JIDs or parts of JIDs are used).

   Specification:  this document.  [Note to RFC Editor: please change
      "this document" to the number issued for this specification.]

7.2.  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, and if
   possible to mark them as a deprecated (with a pointer to this
   document).

8.  Security Considerations

8.1.  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.

8.2.  Reuse of Unicode

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

8.3.  Address Spoofing

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

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8.3.1.  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:

   o  A poorly implemented server ignores the requirement for stamping
      the 'from' address.  This would enable any entity that
      authenticated with the server to send stanzas from any
      localpart@domainpart as long as the domainpart matches the sending
      domain of the server.

   o  An actively malicious server generates stanzas on behalf of any
      registered account at the domain or domains hosted at that server.

   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.

8.3.2.  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).

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   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:

   o  A domainpart is always employed as one part of an entity's address
      in XMPP.  One common usage is as the address of a server or
      server-side service, such as a multi-user chat service [XEP-0045].
      The security of such services could be compromised based on
      different interpretations of the internationalized domainpart; for
      example, a user might authorize a malicious entity at a fake
      server to view the user's presence information, or a user could
      join chatrooms at a fake multi-user chat service.

   o  A localpart can be employed as one part of an entity's address in
      XMPP.  One common usage is as the username of an instant messaging
      user; another is as the name of a multi-user chat room; and many
      other kinds of entities could use localparts as part of their
      addresses.  The security of such services could be compromised
      based on different interpretations of the internationalized
      localpart; for example, a user entering a single internationalized
      localpart could access another user's account information, or a
      user could gain access to a hidden or otherwise restricted chat
      room or service.

   o  A resourcepart can be employed as one part of an entity's address
      in XMPP.  One common usage is as the name for an instant messaging
      user's connected resource; another is as the nickname of a user in
      a multi-user chat room; and many other kinds of entities could use
      resourceparts as part of their addresses.  The security of such
      services could be compromised based on different interpretations
      of the internationalized resourcepart; for example, two or more
      confusable resources could be bound at the same time to the same
      account (resulting in inconsistent authorization decisions in an
      XMPP application that uses full JIDs), or a user could send a
      private message to someone other than the intended recipient in a
      multi-user chat room.

   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].

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9.  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:

   o  A human-readable name

   o  An informational description

   o  A reference to the particular section of this document that
      normatively defines the feature

   o  Whether the feature applies to the Client role, the Server role,
      or both (where "N/A" signifies that the feature is not applicable
      to the specified role)

   o  Whether the feature MUST or SHOULD be implemented, where the
      capitalized terms are to be understood as described in [RFC2119]

   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 4.2

   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 4.2

   Roles:  Server MUST, client SHOULD.

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   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 4.3

   Roles:  Server MUST, client SHOULD.

   Feature:  address-localpart-prep

   Description:  Ensure that the localpart of an XMPP address conforms
      to the "JIDlocalIdentifierClass" profile.

   Section:  Section 4.3

   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 4.4

   Roles:  Server MUST, client SHOULD.

   Feature:  address-resource-prep

   Description:  Ensure that the resourcepart of an XMPP address
      conforms to the "JIDresourceFreeformClass" profile.

   Section:  Section 4.4

   Roles:  Server MUST, client SHOULD.

10.  References

10.1.  Normative References

   [I-D.ietf-precis-framework]
              Saint-Andre, P. and M. Blanchet, "Precis Framework:
              Handling Internationalized Strings in Protocols", draft-
              ietf-precis-framework-18 (work in progress), September
              2014.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

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   [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., Ed. 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.

   [RFC5893]  Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
              Internationalized Domain Names for Applications (IDNA)",
              RFC 5893, 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,
              <http://www.unicode.org/versions/Unicode6.3.0/>.

   [UTR36]    The Unicode Consortium, "Unicode Technical Report #36:
              Unicode Security Considerations", November 2013,
              <http://www.unicode.org/reports/tr36/>.

10.2.  Informative References

   [I-D.ietf-precis-mappings]
              Yoneya, Y. and T. NEMOTO, "Mapping characters for PRECIS
              classes", draft-ietf-precis-mappings-08 (work in
              progress), June 2014.

   [I-D.ietf-precis-nickname]
              Saint-Andre, P., "Preparation and Comparison of
              Nicknames", draft-ietf-precis-nickname-09 (work in
              progress), January 2014.

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   [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., Ed., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, October 2004.

   [RFC3921]  Saint-Andre, P., Ed., "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.

   [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.

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   [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,
              <http://unicode.org/reports/tr39/>.

   [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.

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   [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.

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   [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,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

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.

   o  Changed domainpart preparation to use IDNA2008 (instead of
      IDNA2003).

   o  Changed localpart preparation to use the JIDlocalIdentifierClass
      profile of the PRECIS IdentifierClass (instead of the Nodeprep
      profile of Stringprep).

   o  Changed resourcepart preparation to use the
      JIDresourceFreeformClass profile of the PRECIS FreeformClass
      (instead of the Resourceprep profile of Stringprep).

   o  Specified that internationalized labels within domainparts must be
      U-labels (instead of "should be" U-labels).

   o  Specified that fullwidth and halfwidth characters must be mapped
      to their decomposition mappings (previously handled through the
      use of NFKC).

   o  Specified the use of Unicode Normalization Form C (instead of
      Unicode Normalization Form KC as specified in the Nodeprep and
      Resourceprep profiles of Stringprep).

   o  Specified that servers must enforce the address formatting rules.

Appendix B.  Acknowledgements

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

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

Saint-Andre              Expires March 14, 2015                [Page 28]
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Author's Address

   Peter Saint-Andre
   &yet
   P.O. Box 787
   Parker, CO  80134
   USA

   Email: peter@andyet.net

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