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Versions: (draft-saintandre-xmpp-address) 00 01 02 03 04 05 06 07 08 09 RFC 6122

XMPP                                                      P. Saint-Andre
Internet-Draft                                                     Cisco
Intended status: Standards Track                       November 17, 2010
Expires: May 21, 2011


   Extensible Messaging and Presence Protocol (XMPP): Address Format
                       draft-ietf-xmpp-address-07

Abstract

   This document defines the format for addresses used in the Extensible
   Messaging and Presence Protocol (XMPP), including support for non-
   ASCII characters.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 May 21, 2011.

Copyright Notice

   Copyright (c) 2010 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
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   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.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Acknowledgements . . . . . . . . . . . . . . . . . . . . .  4
   2.  Addresses  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Fundamentals . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Domainpart . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.3.  Localpart  . . . . . . . . . . . . . . . . . . . . . . . .  7
     2.4.  Resourcepart . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Internationalization Considerations  . . . . . . . . . . . . .  9
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     4.1.  Reuse of Stringprep  . . . . . . . . . . . . . . . . . . .  9
     4.2.  Reuse of Unicode . . . . . . . . . . . . . . . . . . . . .  9
     4.3.  Address Spoofing . . . . . . . . . . . . . . . . . . . . .  9
       4.3.1.  Address Forging  . . . . . . . . . . . . . . . . . . .  9
       4.3.2.  Address Mimicking  . . . . . . . . . . . . . . . . . . 10
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
     5.1.  Nodeprep Profile of Stringprep . . . . . . . . . . . . . . 13
     5.2.  Resourceprep Profile of Stringprep . . . . . . . . . . . . 13
   6.  Conformance Requirements . . . . . . . . . . . . . . . . . . . 13
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix A.  Nodeprep  . . . . . . . . . . . . . . . . . . . . . . 18
     A.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 18
     A.2.  Character Repertoire . . . . . . . . . . . . . . . . . . . 18
     A.3.  Mapping  . . . . . . . . . . . . . . . . . . . . . . . . . 18
     A.4.  Normalization  . . . . . . . . . . . . . . . . . . . . . . 19
     A.5.  Prohibited Output  . . . . . . . . . . . . . . . . . . . . 19
     A.6.  Bidirectional Characters . . . . . . . . . . . . . . . . . 19
     A.7.  Notes  . . . . . . . . . . . . . . . . . . . . . . . . . . 19
   Appendix B.  Resourceprep  . . . . . . . . . . . . . . . . . . . . 20
     B.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 20
     B.2.  Character Repertoire . . . . . . . . . . . . . . . . . . . 21
     B.3.  Mapping  . . . . . . . . . . . . . . . . . . . . . . . . . 21
     B.4.  Normalization  . . . . . . . . . . . . . . . . . . . . . . 21
     B.5.  Prohibited Output  . . . . . . . . . . . . . . . . . . . . 21
     B.6.  Bidirectional Characters . . . . . . . . . . . . . . . . . 21
   Appendix C.  Differences From RFC 3920 . . . . . . . . . . . . . . 21
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22









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1.  Introduction

1.1.  Overview

   The Extensible Messaging and Presence Protocol (XMPP) 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 defined canonically by
   [RFC3920] in 2004.

   As specified in RFC 3920, the XMPP address format re-uses the
   "stringprep" technology for preparation of non-ASCII characters
   [STRINGPREP], including the Nameprep profile for internationalized
   domain names as specified in [NAMEPREP] and [IDNA2003] along with two
   XMPP-specific profiles for the localpart and resourcepart.

   Since the publication of RFC 3920, IDNA2003 has been superseded by
   IDNA2008 (see [IDNA-PROTO] and related documents), which is not based
   on stringprep.  Following the lead of the IDNA community, other
   technology communities that use stringprep have begun discussions
   about migrating away from stringprep toward more "modern" approaches.
   The XMPP community is participating in those discussions in order to
   find a replacement for the Nodeprep and Resourceprep profiles of
   stringprep defined in RFC 3920.  However, work on updated handling of
   internationalized addresses is currently in progress within the
   PRECIS Working Group and at the time of this writing it seems that
   such work might take several years to complete.  Because all other
   aspects of revised documentation for XMPP have been incorporated into
   [XMPP], the XMPP Working Group decided to split the XMPP address
   format into a separate specification so as not to significantly delay
   publication of improved documentation for XMPP while awaiting the
   conclusion of work on updated handling of internationalized
   addresses.

   Therefore, this specification provides corrected documentation of the
   XMPP address format using the internationalization technologies
   available in 2004 (when RFC 3920 was published), with the intent that
   this specification will be superseded as soon as work on a new
   approach to preparation and comparison of internationalized strings
   has been defined by the PRECIS Working Group and applied to the
   specific cases of XMPP localparts and resourceparts.  In the
   meantime, this document normatively references [IDNA2003] and
   [NAMEPREP]; XMPP software implementations are encouraged to begin
   migrating to IDNA2008 (see [IDNA-PROTO] and related documents)
   because it is nearly certain that the specification superseding this
   one will re-use IDNA2008.



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1.2.  Terminology

   Many important terms used in this document are defined in [IDNA2003],
   [STRINGPREP], [UNICODE], and [XMPP].

   The keywords "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
   [KEYWORDS].

1.3.  Acknowledgements

   Thanks to Ben Campbell, Waqas Hussain, Jehan Pages and Florian Zeitz
   for their feedback.  Thanks also to Richard Barnes for his review on
   behalf of the Security Directorate.

   The Working Group chairs were Ben Campbell and Joe Hildebrand.

   The responsible Area Director was Gonzalo Camarillo.

   Some text in this document was borrowed or adapted from [IDNA-DEFS],
   [IDNA-PROTO], [IDNA-RATIONALE], and [XEP-0165].


2.  Addresses

2.1.  Fundamentals

   An XMPP entity is anything that is network-addressable and that can
   communicate using XMPP.  For historical reasons, the native address
   of an XMPP entity is called a Jabber Identifier or JID.  A valid JID
   is a string of [UNICODE] code points, encoded using [UTF-8], 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).

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












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      jid           = [ localpart "@" ] domainpart [ "/" resourcepart ]
      localpart     = 1*(nodepoint)
                      ; a "nodepoint" is a UTF-8 encoded Unicode code
                      ; point that satisfies the Nodeprep profile of
                      ; stringprep
      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 in RFC
                      ; 3986 applies to the matching process
      ifqdn         = 1*(namepoint)
                      ; a "namepoint" is a UTF-8 encoded Unicode
                      ; code point that satisfies the Nameprep
                      ; profile of stringprep
      resourcepart  = 1*(resourcepoint)
                      ; a "resourcepoint" is a UTF-8 encoded Unicode
                      ; code point that satisfies the Resourceprep
                      ; profile of stringprep

   All JIDs are based on the foregoing structure.  One common use of
   this structure is to identify a messaging and presence account, the
   server that hosts the account, and a connected resource (e.g., a
   specific device) in the form of <localpart@domainpart/resourcepart>.
   However, localparts other than clients are possible; for example, a
   specific chat room offered by a multi-user chat service (see
   [XEP-0045]) is addressed as <room@service> (where "room" is the name
   of the chat room and "service" is the hostname of the multi-user chat
   service) and a specific occupant of such a room could be addressed as
   <room@service/nick> (where "nick" is the occupant's room nickname).
   Many other JID types are possible (e.g., <domainpart/resourcepart>
   could be a server-side script or service).

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

   For the purpose of communication over an XMPP network (e.g., in the
   'to' or 'from' address of an XMPP stanza), an entity's address MUST
   be represented as a JID, not as a Uniform Resource Identifier [URI]
   or Internationalized Resource Identifier [IRI].  An XMPP URI or IRI
   [XMPP-URI] is in essence a JID prepended with 'xmpp:', but the native
   addressing format used in XMPP is that of a mere JID without a URI
   scheme.  [XMPP-URI] is provided only for identification and
   interaction outside the context of XMPP itself, for example when
   linking to a JID from a web page.  See [XMPP-URI] for a description
   of the process for securely extracting a JID from an XMPP URI or IRI.




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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., U+FE6B SMALL COMMERCIAL AT might decompose into U+0040
      COMMERCIAL AT).

2.2.  Domainpart

   The DOMAINPART of a JID is that portion after the '@' character (if
   any) and before the '/' 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, a publish-subscribe service, or a user
   directory).

   The domainpart for every XMPP service MUST be a fully qualified
   domain name ("FQDN"; see [DNS]), IPv4 address, IPv6 address, or
   unqualifed hostname (i.e., a text label that is resolvable on a local
   network).

      Interoperability Note: Domainparts that are IP addresses might not
      be accepted by other services for the sake 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.

   A domainpart MUST NOT be zero bytes in length and MUST NOT be more
   than 1023 bytes in length.

   If the domainpart includes a final character considered to be a label
   separator (dot) by [IDNA2003] or [DNS], 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]; in particular, the
   character MUST be stripped before any other canonicalization steps
   are taken, such as application of the [NAMEPREP] profile of
   [STRINGPREP] or completion of the ToASCII operation as described in
   [IDNA2003].

   A domainpart consisting of a fully qualified domain name MUST be an
   "internationalized domain name" as defined in [IDNA2003], that is, it
   MUST be "a domain name in which every label is an internationalized
   label" and MUST follow the rules for construction of



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   internationalized domain names specified in [IDNA2003].  When
   preparing a text label (consisting of a sequence of UTF-8 encoded
   Unicode code points) for representation as an internationalized label
   in the process of constructing an XMPP domainpart or comparing two
   XMPP domainparts, an application MUST ensure that for each text label
   it is possible to apply without failing the ToASCII operation
   specified in [IDNA2003] with the UseSTD3ASCIIRules flag set (thus
   forbidding ASCII code points other than letters, digits, and
   hyphens).  If the ToASCII operation can be applied without failing,
   then the label is an internationalized label.  (Note: The ToASCII
   operation includes application of the [NAMEPREP] profile of
   [STRINGPREP] and encoding using the algorithm specified in
   [PUNYCODE]; for details, see [IDNA2003].)  Although XMPP applications
   do not communicate the output of the ToASCII operation (called an
   "ACE label") over the wire, it MUST be possible to apply that
   operation without failing to each internationalized label.  If an
   XMPP application receives as input an ACE label, it SHOULD convert
   that ACE label to an internationalized label using the ToUnicode
   operation (see [IDNA2003]) before including the label in an XMPP
   domainpart that will be communicated over the wire on an XMPP network
   (however, instead of converting the label, there are legitimate
   reasons why an application might instead refuse the input altogether
   and return an error to the entity that provided the offending data).

   In the terms of IDNA2008 [IDNA-DEFS], the domainpart of a JID is a
   "domain name slot".

2.3.  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).  The entity
   represented by an XMPP localpart is addressed within the context of a
   specific domain.

   A localpart MUST NOT be zero bytes in length and MUST NOT be more
   than 1023 bytes in length.

   A localpart MUST be formatted such that the Nodeprep profile of
   [STRINGPREP] can be applied without failing (see Appendix A).  Before
   comparing two localparts, an application MUST first ensure that the
   Nodeprep profile has been applied to each identifier (the profile
   need not be applied each time a comparison is made, as long as it has
   been applied before comparison).




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2.4.  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) belonging to the
   entity associated with an XMPP localpart at a local domain.

   When an XMPP address does not include a resourcepart (i.e., when it
   is of the form <domainpart> or <localpart@domainpart>), it is
   referred to as a BARE JID.  When an XMPP address includes a
   resourcepart (i.e., when it is of the form <domainpart/resourcepart>
   or <localpart@domainpart/resourcepart>), is referred to as a FULL
   JID.

   A resourcepart MUST NOT be zero bytes in length and MUST NOT be more
   than 1023 bytes in length.

   A resourcepart MUST be formatted such that the Resourceprep profile
   of [STRINGPREP] can be applied without failing (see Appendix B).
   Before comparing two resourceparts, an application MUST first ensure
   that the Resourceprep profile has been applied to each identifier
   (the profile need not be applied each time a comparison is made, as
   long as it has been applied before comparison).

      Informational Note: For historical reasons, the term "resource
      identifier" is often used in XMPP to refer to the optional portion
      of an XMPP address that follows the domainpart and the "/"
      separator character; to help prevent confusion between an XMPP
      "resource identifier" and the meanings of "resource" and
      "identifier" provided in Section 1.1 of [URI], this specification
      uses the term "resourcepart" instead of "resource identifier" (as
      in RFC 3920).

   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 addresses are
      hierarchical; 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@domain".





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   o  The '@' character is allowed in the resourcepart, and is often
      used in the "nick" shown in XMPP chatrooms.  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 an (asserted)
      nick of <user@host>.  However, chatroom services do not
      necessarily check such an asserted nick against the occupant's
      real JID.


3.  Internationalization Considerations

   XMPP servers MUST, and XMPP clients SHOULD, support [IDNA2003] for
   domainparts (including the [NAMEPREP] profile of [STRINGPREP]), the
   Nodeprep (Appendix A) profile of [STRINGPREP] for localparts, and the
   Resourceprep (Appendix B) profile of [STRINGPREP] for resourceparts;
   this enables XMPP addresses to include a wide variety of characters
   outside the US-ASCII range.  Rules for enforcement of the XMPP
   address format are provided in [XMPP].


4.  Security Considerations

4.1.  Reuse of Stringprep

   The security considerations described in [STRINGPREP] apply to the
   Nodeprep (Appendix A) and Resourceprep (Appendix B) profiles defined
   in this document for XMPP localparts and resourceparts.  The security
   considerations described in [STRINGPREP] and [NAMEPREP] apply to the
   Nameprep profile that is re-used here for XMPP domainparts.

4.2.  Reuse of Unicode

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

4.3.  Address Spoofing

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

4.3.1.  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 SASL negotiation).  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".



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   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 [XMPP]).  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.

   Therefore, an entity outside the security perimeter of a particular
   server cannot reliably distinguish between bare 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 such poorly implemented or rogue servers.  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 in addition to modifying 'from' addresses.

   Furthermore, it is possible for an attacker to forge JIDs at other
   domains by means of a DNS poisoning attack if DNS security extensions
   [DNSSEC] are not used.

4.3.2.  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.  For
   example, in some XMPP clients the address "ju1iet@example.org"
   (spelled with the number one as the third character of the localpart)
   might appear to be the same as "juliet@example.org (spelled with the
   lower-case version of the letter "L"), especially on casual visual
   inspection; this phenomenon is sometimes called "typejacking".  A
   more sophisticated example of address mimicking might involve the use
   of characters from outside the familiar Latin extended-A block of
   Unicode code points, such as the characters U+13DA U+13A2 U+13B5
   U+13AC U+13A2 U+13AC U+13D2 from the Cherokee block instead of the
   similar-looking US-ASCII characters "STPETER".

   In some examples of address mimicking, it is unlikely that the
   average user could tell the difference between the real JID and the
   fake JID.  (Indeed, there is no programmatic way to distinguish with
   full certainty which is the fake JID and which is the real JID; in



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   some communication contexts, the JID formed of Cherokee characters
   might be the real JID and the JID formed of US-ASCII characters might
   thus appear to be the fake JID.)  Because JIDs can contain almost any
   properly-encoded Unicode code point, it can be relatively easy to
   mimic some JIDs in XMPP systems.  The possibility of address
   mimicking introduces security vulnerabilities of the kind that have
   also plagued the World Wide Web, specifically the phenomenon known as
   phishing.

   These problems arise because Unicode and ISO/IEC 10646 repertoires
   have many characters that look similar (so-called "confusable
   characters" or "confusables").  In many cases, XMPP users might
   perform visual matching, such as when comparing the JIDs of
   communication partners.  Because it is impossible to map similar-
   looking characters without a great deal of context (such as knowing
   the fonts used), stringprep and stringprep-based technologies such as
   Nameprep, Nodeprep, and Resourceprep do nothing to map similar-
   looking characters together, nor do they prohibit some characters
   because they look like others.  As a result, XMPP localparts and
   resourceparts could contain confusable characters, producing JIDs
   that appear to mimic other JIDs and thus leading to security
   vulnerabilities such as the following:

   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, a user could
      attempt to bind multiple resources with the same name, or a user
      could send a message to someone other than the intended recipient
      in a multi-user chat room.

   Despite the fact that some specific suggestions about identification
   and handling of confusable characters appear in the Unicode Security
   Considerations [UNICODE-SEC], it is also true (as noted in



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   [IDNA-DEFS]) that "there are no comprehensive technical solutions to
   the problems of confusable characters".  Mimicked JIDs that involve
   characters from only one script, or from the script typically
   employed by a particular user or community of language users, are not
   easy to combat (e.g., the simple typejacking attack previously
   described, which relies on a surface similarity between the
   characters "1" and "l" in some presentations).  However, mimicked
   addresses that involve characters from more than one script, or from
   a script not typically employed by a particular user or community of
   language users, can be mitigated somewhat through the application of
   appropriate registration policies at XMPP services and presentation
   policies in XMPP client software.  Therefore the following policies
   are encouraged:

   1.  Because an XMPP service that allows registration of XMPP user
       accounts (localparts) plays a role similar to that of a registry
       for DNS domain names, such a service SHOULD establish a policy
       about the scripts or blocks of characters it will allow in
       localparts at the service.  Such a policy is likely to be
       informed by the languages and scripts that are used to write
       registered account names; in particular, to reduce confusion, the
       service MAY forbid registration of XMPP localparts that contain
       characters from more than one script and to restrict
       registrations to characters drawn from a very small number of
       scripts (e.g., scripts that are well-understood by the
       administrators of the service).  Such policies are also
       appropriate for XMPP services that allow temporary or permanent
       registration of XMPP resourceparts, e.g., during resource binding
       [XMPP] or upon joining an XMPP-based chat room [XEP-0045].  For
       related considerations in the context of domain name
       registration, refer to Section 4.3 of [IDNA-PROTO] and Section
       3.2 of [IDNA-RATIONALE].  Note well that methods for enforcing
       such restrictions are out of scope for this document.

   2.  Because every human user of an XMPP client presumably has a
       preferred language (or, in some cases, a small set of preferred
       languages), an XMPP client SHOULD gather that information either
       explicitly from the user or implicitly via the operating system
       of the user's device.  Furthermore, because most languages are
       typically represented by a single script (or a small set of
       scripts) and most scripts are typically contained in one or more
       blocks of characters, an XMPP client SHOULD warn the user when
       presenting a JID that mixes characters from more than one script
       or block, or that uses characters outside the normal range of the
       user's preferred language(s).  This recommendation is not
       intended to discourage communication across different communities
       of language users; instead, it recognizes the existence of such
       communities and encourages due caution when presenting unfamiliar



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       scripts or characters to human users.


5.  IANA Considerations

   The following sections update the registrations provided in
   [RFC3920].

5.1.  Nodeprep Profile of Stringprep

   The Nodeprep profile of stringprep is defined under Nodeprep
   (Appendix A).  The IANA has registered Nodeprep in the stringprep
   profile registry.

   Name of this profile:

      Nodeprep

   RFC in which the profile is defined:

      XXXX

   Indicator whether or not this is the newest version of the profile:

      This is the first version of Nodeprep

5.2.  Resourceprep Profile of Stringprep

   The Resourceprep profile of stringprep is defined under Resourceprep
   (Appendix B).  The IANA has registered Resourceprep in the stringprep
   profile registry.

   Name of this profile:

      Resourceprep

   RFC in which the profile is defined:

      XXXX

   Indicator whether or not this is the newest version of the profile:

      This is the first version of Resourceprep


6.  Conformance Requirements

   This section describes a protocol feature set that summarizes the



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   conformance requirements of this specification.  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 [KEYWORDS]

   The feature set specified here attempts to adhere to the concepts and
   formats proposed by Larry Masinter within the IETF's NEWTRK Working
   Group in 2005, as captured in [INTEROP].  Although this feature set
   is more detailed than called for by [REPORTS], it provides a suitable
   basis for the generation of implementation reports to be submitted in
   support of advancing this specification from Proposed Standard to
   Draft Standard in accordance with [PROCESS].

   Feature:  address-domain-length
   Description:  Ensure that the domainpart of an XMPP address is at
      least one byte in length and at most 1023 bytes in length.
   Section:  Section 2.2
   Roles:  Both MUST.

   Feature:  address-domain-prep
   Description:  Ensure that the domainpart of an XMPP address conforms
      to the Nameprep profile of Stringprep.
   Section:  Section 2.2
   Roles:  Client SHOULD, Server MUST.

   Feature:  address-localpart-length
   Description:  Ensure that the localpart of an XMPP address is at
      least one byte in length and at most 1023 bytes in length.
   Section:  Section 2.3
   Roles:  Both MUST.







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   Feature:  address-localpart-prep
   Description:  Ensure that the localpart of an XMPP address conforms
      to the Nodeprep profile of Stringprep.
   Section:  Section 2.3
   Roles:  Client SHOULD, Server MUST.

   Feature:  address-resource-length
   Description:  Ensure that the resourcepart of an XMPP address is at
      least one byte in length and at most 1023 bytes in length.
   Section:  Section 2.4
   Roles:  Both MUST.

   Feature:  address-resource-prep
   Description:  Ensure that the resourcepart of an XMPP address
      conforms to the Resourceprep profile of Stringprep.
   Section:  Section 2.2
   Roles:  Client SHOULD, Server MUST.


7.  References

7.1.  Normative References

   [ABNF]     Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [IDNA2003]
              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.

   [KEYWORDS]
              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [NAMEPREP]
              Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
              Profile for Internationalized Domain Names (IDN)",
              RFC 3491, March 2003.

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

   [STRINGPREP]
              Hoffman, P. and M. Blanchet, "Preparation of



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              Internationalized Strings ("stringprep")", RFC 3454,
              December 2002.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard, Version
              3.2.0", 2000.

              The Unicode Standard, Version 3.2.0 is defined by The
              Unicode Standard, Version 3.0 (Reading, MA, Addison-
              Wesley, 2000.  ISBN 0-201-61633-5), as amended by the
              Unicode Standard Annex #27: Unicode 3.1
              (http://www.unicode.org/reports/tr27/) and by the Unicode
              Standard Annex #28: Unicode 3.2
              (http://www.unicode.org/reports/tr28/).

   [UNICODE-SEC]
              The Unicode Consortium, "Unicode Technical Report #36:
              Unicode Security Considerations", 2008.

   [UTF-8]    Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [XMPP]     Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", draft-ietf-xmpp-3920bis-19 (work
              in progress), November 2010.

7.2.  Informative References

   [DNS]      Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [DNSSEC]   Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, March 2005.

   [IDNA-DEFS]
              Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, August 2010.

   [IDNA-PROTO]
              Klensin, J., "Internationalized Domain Names in
              Applications (IDNA): Protocol", RFC 5891, August 2010.

   [IDNA-RATIONALE]
              Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Background, Explanation, and
              Rationale", RFC 5894, August 2010.




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   [INTEROP]  Masinter, L., "Formalizing IETF Interoperability
              Reporting", draft-ietf-newtrk-interop-reports-00 (work in
              progress), October 2005.

   [IRI]      Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [PROCESS]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [PUNYCODE]
              Costello, A., "Punycode: A Bootstring encoding of Unicode
              for Internationalized Domain Names in Applications
              (IDNA)", RFC 3492, March 2003.

   [REPORTS]  Dusseault, L. and R. Sparks, "Guidance on Interoperation
              and Implementation Reports for Advancement to Draft
              Standard", BCP 9, RFC 5657, September 2009.

   [RFC3920]  Saint-Andre, P., Ed., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, October 2004.

   [URI]      Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [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,
              July 2008.

   [XEP-0060]
              Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
              Subscribe", XSF XEP 0060, September 2008.

   [XEP-0165]
              Saint-Andre, P., "Best Practices to Discourage JID
              Mimicking", XSF XEP 0045, December 2007.

   [XML]      Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F.,
              and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth



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              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20060816, August 2006,
              <http://www.w3.org/TR/2006/REC-xml-20060816>.

   [XMPP-URI]
              Saint-Andre, P., "Internationalized Resource Identifiers
              (IRIs) and Uniform Resource Identifiers (URIs) for the
              Extensible Messaging and Presence Protocol (XMPP)",
              RFC 5122, February 2008.


Appendix A.  Nodeprep

A.1.  Introduction

   This appendix defines the "Nodeprep" profile of stringprep.  As such,
   it specifies processing rules that will enable users to enter
   internationalized localparts in the Extensible Messaging and Presence
   Protocol (XMPP) and have the highest chance of getting the content of
   the strings correct.  (An XMPP localpart is the optional portion of
   an XMPP address that precedes an XMPP domainpart and the '@'
   separator; it is often but not exclusively associated with an instant
   messaging username.)  These processing rules are intended only for
   XMPP localparts and are not intended for arbitrary text or any other
   aspect of an XMPP address.

   This profile defines the following, as required by [STRINGPREP]:

   o  The intended applicability of the profile: internationalized
      localparts within XMPP
   o  The character repertoire that is the input and output to
      stringprep: Unicode 3.2, specified in Section 2 of this Appendix
   o  The mappings used: specified in Section 3
   o  The Unicode normalization used: specified in Section 4
   o  The characters that are prohibited as output: specified in Section
      5
   o  Bidirectional character handling: specified in Section 6

A.2.  Character Repertoire

   This profile uses Unicode 3.2 with the list of unassigned code points
   being Table A.1, both defined in Appendix A of [STRINGPREP].

A.3.  Mapping

   This profile specifies mapping using the following tables from
   [STRINGPREP]:




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      Table B.1
      Table B.2

A.4.  Normalization

   This profile specifies the use of Unicode normalization form KC, as
   described in [STRINGPREP].

A.5.  Prohibited Output

   This profile specifies the prohibition of using the following tables
   from [STRINGPREP].

      Table C.1.1
      Table C.1.2
      Table C.2.1
      Table C.2.2
      Table C.3
      Table C.4
      Table C.5
      Table C.6
      Table C.7
      Table C.8
      Table C.9

   In addition, the following additional Unicode characters are also
   prohibited:

      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., @

A.6.  Bidirectional Characters

   This profile specifies checking bidirectional strings, as described
   in Section 6 of [STRINGPREP].

A.7.  Notes

   Because the additional characters prohibited by Nodeprep are
   prohibited after normalization, an implementation MUST NOT enable a
   human user to input any Unicode code point whose decomposition
   includes those characters; such code points include but are not



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   necessarily limited to the following (refer to [UNICODE] for complete
   information).

   o  U+2100 (ACCOUNT OF)
   o  U+2101 (ADDRESSED TO THE SUBJECT)
   o  U+2105 (CARE OF)
   o  U+2106 (CADA UNA)
   o  U+226E (NOT LESS-THAN)
   o  U+226F (NOT GREATER-THAN)
   o  U+2A74 (DOUBLE COLON EQUAL)
   o  U+FE13 (SMALL COLON)
   o  U+FE60 (SMALL AMPERSAND)
   o  U+FE64 (SMALL LESS-THAN SIGN)
   o  U+FE65 (SMALL GREATER-THAN SIGN)
   o  U+FE6B (SMALL COMMERCIAL AT)
   o  U+FF02 (FULLWIDTH QUOTATION MARK)
   o  U+FF06 (FULLWIDTH AMPERSAND)
   o  U+FF07 (FULLWIDTH APOSTROPHE)
   o  U+FF0F (FULLWIDTH SOLIDUS)
   o  U+FF1A (FULLWIDTH COLON)
   o  U+FF1C (FULLWIDTH LESS-THAN SIGN)
   o  U+FF1E (FULLWIDTH GREATER-THAN SIGN)
   o  U+FF20 (FULLWIDTH COMMERCIAL AT)


Appendix B.  Resourceprep

B.1.  Introduction

   This appendix defines the "Resourceprep" profile of stringprep.  As
   such, it specifies processing rules that will enable users to enter
   internationalized resourceparts in the Extensible Messaging and
   Presence Protocol (XMPP) and have the highest chance of getting the
   content of the strings correct.  (An XMPP resourcepart is the
   optional portion of an XMPP address that follows an XMPP domainpart
   and the '/' separator.)  These processing rules are intended only for
   XMPP resourceparts and are not intended for arbitrary text or any
   other aspect of an XMPP address.

   This profile defines the following, as required by [STRINGPREP]:

   o  The intended applicability of the profile: internationalized
      resourceparts within XMPP
   o  The character repertoire that is the input and output to
      stringprep: Unicode 3.2, specified in Section 2 of this Appendix
   o  The mappings used: specified in Section 3





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   o  The Unicode normalization used: specified in Section 4
   o  The characters that are prohibited as output: specified in Section
      5
   o  Bidirectional character handling: specified in Section 6

B.2.  Character Repertoire

   This profile uses Unicode 3.2 with the list of unassigned code points
   being Table A.1, both defined in Appendix A of [STRINGPREP].

B.3.  Mapping

   This profile specifies mapping using the following tables from
   [STRINGPREP]:

      Table B.1

B.4.  Normalization

   This profile specifies the use of Unicode normalization form KC, as
   described in [STRINGPREP].

B.5.  Prohibited Output

   This profile specifies the prohibition of using the following tables
   from [STRINGPREP].

      Table C.1.2
      Table C.2.1
      Table C.2.2
      Table C.3
      Table C.4
      Table C.5
      Table C.6
      Table C.7
      Table C.8
      Table C.9

B.6.  Bidirectional Characters

   This profile specifies checking bidirectional strings, as described
   in Section 6 of [STRINGPREP].


Appendix C.  Differences From RFC 3920

   Based on consensus derived from implementation and deployment
   experience as well as formal interoperability testing, the following



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   substantive modifications were made from RFC 3920.

   o  Corrected the ABNF syntax to (1) ensure consistency with [URI] and
      [IRI], and (2) prevent zero-length localparts, domainparts, and
      resourceparts.
   o  To avoid confusion with the term "node" as used in [XEP-0030] and
      [XEP-0060], changed the term "node identifier" to "localpart" (but
      retained the name "Nodeprep" for backward compatibility).
   o  To avoid confusion with the terms "resource" and "identifier" as
      used in [URI], changed the term "resource identifier" to
      "resourcepart".
   o  Corrected the nameprep processing rules to require use of the
      UseSTD3ASCIIRules flag.


Author's Address

   Peter Saint-Andre
   Cisco
   1899 Wyknoop Street, Suite 600
   Denver, CO  80202
   USA

   Phone: +1-303-308-3282
   Email: psaintan@cisco.com


























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