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465 lines
16 KiB
XML
465 lines
16 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE xep SYSTEM 'xep.dtd' [
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<!ENTITY % ents SYSTEM 'xep.ent'>
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<!ENTITY MOVED "<moved/>">
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%ents;
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]>
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
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<xep>
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<header>
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<title>Moved</title>
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<abstract>This document defines an XMPP protocol extension that enables a user to inform its contacts about a change in JID.</abstract>
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&LEGALNOTICE;
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<number>0283</number>
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<status>Experimental</status>
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<type>Standards Track</type>
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<sig>Standards</sig>
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<approver>Council</approver>
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<dependencies>
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<spec>XMPP Core</spec>
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</dependencies>
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<supersedes>
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</supersedes>
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<supersededby/>
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<shortname>moved</shortname>
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<author>
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<firstname>Tory</firstname>
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<surname>Patnoe</surname>
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<email>tpatnoe@cisco.com</email>
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<jid>tpatnoe@cisco.com</jid>
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</author>
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<revision>
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<version>0.1</version>
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<date>2010-06-16</date>
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<initials>psa</initials>
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<remark><p>Initial published version.</p></remark>
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</revision>
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<revision>
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<version>0.0.7</version>
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<date>2010-06-09</date>
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<initials>tp</initials>
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<remark>
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<p>Modified syntax to use 'old' and 'new' attributes.</p>
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</remark>
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</revision>
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<revision>
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<version>0.0.6</version>
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<date>2010-06-07</date>
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<initials>tp</initials>
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<remark>
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<ul>
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<li>Update ordering so that it recommends sending the unsubscribe/unsubscribed, before, sending the subscribe</li>
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<li>Add section documenting what happens when a contact is offline when the unsubscribe/unsubscribed/subscribe stanzas are sent.</li>
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<li>Added an example about a hacker sending an unsolicited subscribe by guessing a roster entry.</li>
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</ul>
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</remark>
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</revision>
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<revision>
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<version>0.0.5</version>
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<date>2010-06-02</date>
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<initials>tp</initials>
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<remark>
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<p>Added one-way subscription section</p>
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</remark>
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</revision>
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<revision>
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<version>0.0.4</version>
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<date>2010-05-30</date>
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<initials>tp</initials>
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<remark>
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<p>Change MUST NOT to SHOULD NOT for clients auto-subscribing back; differentiate between inbound and outbound subscriptions.</p>
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</remark>
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</revision>
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<revision>
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<version>0.0.3</version>
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<date>2010-06-02</date>
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<initials>tp</initials>
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<remark><p>Add one-way subscription comments.</p></remark>
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</revision>
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<revision>
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<version>0.0.2</version>
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<date>2010-05-25</date>
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<initials>tp</initials>
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<remark><p>Minor tweaks.</p></remark>
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</revision>
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<revision>
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<version>0.0.1</version>
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<date>2010-05-22</date>
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<initials>tp</initials>
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<remark><p>First draft.</p></remark>
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</revision>
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</header>
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<section1 topic='Introduction' anchor='intro'>
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<p>There are a variety of reasons why a user may wish to change
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their JID. For example, a surname change because of marriage or simply
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an easier JID to remember.
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</p>
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<p>This XEP defines an approach for communicating that your JID has
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moved to a new JID, extending the existing subscription protocol documented
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in &xmppim;. The steps outlined here may be done either through a client
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or automated by a server.
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</p>
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</section1>
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<section1 topic='Requirements' anchor='reqs'>
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<ul>
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<li>The methods described here maintain compatibility with &xmppcore; and <cite>RFC 6121</cite>.</li>
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</ul>
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</section1>
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<section1 topic='The Move'>
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<p>In this scenario user@example.com moves to user2@example2.com.
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Both the user@example.com and user2@example2.com accounts have been
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created and still exist. The roster for user@example2.com is empty
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and the user wants to populate it with their entries from
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user@example.com.</p>
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<dl>
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<dt><strong>original JID</strong></dt>
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<dd>user@example.com</dd>
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<dt><strong>new JID</strong></dt>
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<dd>user2@example2.com</dd>
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</dl>
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<section2 topic='Unsubscribing the original JID from outbound subscriptions'
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anchor='unsubscribe'>
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<p>Because the original JID is no longer going to be used, the user SHOULD
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unsubscribe from all the outbound subscriptions user@example.com had.
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These can be identified as those in the 'to' or 'ask' states as
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defined in the 'jabber:iq:roster' protocol in &rfc3921;.</p>
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<p>To unsubscribe all outbound subscriptions for the original JID send an
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unsubscribe &PRESENCE; stanza to all the old contacts with a &MOVED;
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element containing the new JID.</p>
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<p>There is the potential for other users to send a malicious unsubscribe
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containing a spoofed &MOVED; JID. Therefore, clients SHOULD NOT
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automatically subscribe to the JID contained in the &MOVED; stanza when
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receiving a subscribe &PRESENCE; stanza without displaying the &MOVED;
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JID to the user. See the Security Considerations section for
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details.</p>
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<example caption='Client unsubscribes outbound subscriptions from original JID'>
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<![CDATA[
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<presence from='user@example.com' to='contact@example.com' type='unsubscribe'>
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<status>I've changed JIDs from user@example.com to user2@example2.com</status>
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<moved xmlns='urn:xmpp:moved:0' new='user2@example2.com'/>
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</presence>
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]]>
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</example>
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</section2>
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<section2 topic='Unsubscribing the original JID from inbound subscriptions'
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anchor='unsubscribed'>
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<p>Because the original JID is no longer going to be used, the user SHOULD
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unsubscribe from all contacts the user@example.com had an inbound
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subscription from. These can be identified as those in the 'from'
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subscription state as defined in in the 'jabber:iq:roster' protocol
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in &rfc3921;.</p>
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<p>To unsubscribe all inbound subscriptions send an unsubscribed
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&PRESENCE; stanza to all the old contacts with a &MOVED; element
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containing the new JID.</p>
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<p>There is the potential for other users to send a malicious unsubscribed
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containing a spoofed &MOVED; JID. Therefore, clients SHOULD NOT
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automatically subscribe to the JID contained in the &MOVED; stanza
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without displaying the &MOVED; JID to the user. See the Security
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Considerations section for details.</p>
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<example caption='Client unsubscribes inbound subscriptions from original JID'>
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<![CDATA[
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<presence from='user@example.com' to='contact@example.com' type='unsubscribed'>
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<status>I've changed JIDs from user@example.com to user2@example2.com</status>
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<moved xmlns='urn:xmpp:moved:0' new='user2@example2.com'/>
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</presence>
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]]>
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</example>
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</section2>
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<section2 topic='Subscribing the new JID to all your existing contacts'
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anchor='subscribe'>
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<p>Once the new JID has been created on a server it is possible for the
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new JID to subscribe to the contacts they had on the original JID's
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roster. This is done by sending a new subscription request with a
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&MOVED; element containing the new JID.
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</p>
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<p>The new subscription MUST come from the new JID's server.</p>
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<p>There is the potential for other users to send a malicious subscribe
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request and spoof the content of the &MOVED; element identifying an
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original JID. Therefore, clients SHOULD NOT automatically unsubscribe
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an existing roster entry if is listed as the target in the &MOVED;
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element when a subscribe is received. See the Security
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Consideration section for details.</p>
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<p>Clients accepting the moved subscription SHOULD indicate to the
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user that that this subscription request was the result of a move
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operation and because of potential malicious behavior SHOULD NOT
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auto-accept the subscription without displaying the &MOVED; JID to the
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user.</p>
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<example caption='Client requests subscription from new JID'>
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<![CDATA[
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<presence from='user2@example2.com' to='contact@example.com' type='subscribe'>
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<status>I've changed JIDs from user@example.com to user2@example2.com</status>
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<moved xmlns='urn:xmpp:moved:0' old='user@example.com'/>
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</presence>
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]]>
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</example>
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</section2>
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<section2 topic='Contacts Offline at the Time the Rename Occurs'
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anchor='offline'>
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<p>&rfc6120; clarifies that an incoming subscribe &PRESENCE; stanza
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MUST be preserved by the server and &PRESENCE; stanzas of type
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unsubscribe and unsubscribed are not preserved on the server.
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Therefore, for a contact who is offline, their servers MAY have
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automatically removed the original roster entry when seeing the
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unsubscribe and unsubscribed stanzas. At the time of writing this XEP,
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NOT saving and forwarding the presence stanzas will be the default
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behavior of most servers.
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</p>
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<p>What this means is that a contact coming online after the rename
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outlined above MAY only see the &PRESENCE; of type 'subscribe' with
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the &MOVED; element. Clients should be aware of this behavior.
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</p>
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</section2>
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<section2 topic='Presence Ordering' anchor='ordering'>
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<p>In following the principle of least surprise, it is considered good
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practice to send the subscribe stanza after the unsubscribe and unsubscribed
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stanzas.
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</p>
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</section2>
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<section2 topic='Preservation of Groups' anchor='grouping'>
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<p>One of the side effects of this scheme is the potential for a contact
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to lose the groups to which it had organized the original JID. Clients
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aware of the &MOVED; element can mitigate this with the following rules.
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</p>
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<ul>
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<li>If the contacts client receives an unsubscribed with a &MOVED;
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element, remove the subscription but initiate a roster push for the
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original JID with the subscription set to 'none'. When the new
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subscription is received the new JID MAY be placed into the roster
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in the same groups as the original JID and the original JID can then be
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removed from the roster.
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</li>
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<li>If a subscribe is received with a &MOVED; element, the client MAY
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automatically place the new JID into the same groups as the original JID.
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</li>
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</ul>
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<p>As discussed in 'Contacts Offline at the Time the Rename Occurs', a
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server MAY automatically handle the unsubscribe and unsubscribed stanzas.
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If this occurs it will be impossible to preserve the original groups.
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</p>
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</section2>
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<section2 topic='One-way subcriptions and full roster state' anchor='one-way'>
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<section3 topic='One-way Inbound subscription' anchor='from_subs'>
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<p>If the original JID, user@example.com, had only an inbound subscription
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(from or pending in), then the contact will only receive an
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unsubscribed &PRESENCE; stanza. The contact's client, knowing the
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state of the subscription (which is 'to' or 'none' with 'ask='subscribe'
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from the contact's perspective), at that point MAY choose to prompt the
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user to subscribe to the new JID listed in the &MOVED; element.</p>
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<p>Because of the ability to spoof the &MOVED; element, the client SHOULD
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NOT automatically subscribe to the &MOVED; element target, but SHOULD
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present the new JID to the contact before sending out a subscription
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request.</p>
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</section3>
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<section3 topic='One-way Outbound subscription' anchor='to_subs'>
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<p>If the original JID, user@example.com, had only an outbound
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subscription (to or ask), then the contact SHOULD only receive an
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unsubscribe &PRESENCE; stanza. The contact's client, knowing the
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state of the subscription (which is 'from' from the contact's perspective),
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at that point MAY choose to prompt
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the user to subscribe to the new JID listed in the &MOVED; element.</p>
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<p>Because of the ability to spoof the &MOVED; element, the client SHOULD
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NOT automatically subscribe to the &MOVED; element target</p>.
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</section3>
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<section3 topic='Roster state and action table' anchor='actions'>
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<table caption="Roster states and actios from the renamed user's perspective">
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<tr>
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<td>Server state</td>
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<td>Client state (jabber:iq:roster)</td>
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<td>Send unsubscribe from original JID</td>
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<td>Send unsubscribed from original JID</td>
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<td>Send subscribe from new JID</td>
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</tr>
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<tr>
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<td>none</td>
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<td>none</td>
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<td></td>
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<td></td>
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<td></td>
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</tr>
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<tr>
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<td>none + pending out</td>
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<td>none + ask='subscribe'</td>
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<td>yes</td>
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<td></td>
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<td>yes</td>
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</tr>
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<tr>
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<td>none + pending in</td>
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<td>n/a</td>
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<td></td>
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<td>yes - server only</td>
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<td></td>
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</tr>
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<tr>
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<td>none + pending in/out</td>
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<td>none + ask='subscribe'</td>
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<td>yes</td>
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<td>yes - server only</td>
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<td>yes</td>
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</tr>
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<tr>
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<td>to</td>
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<td>to</td>
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<td>yes</td>
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<td></td>
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<td>yes</td>
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</tr>
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<tr>
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<td>to + pending in</td>
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<td>to</td>
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<td>yes</td>
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<td>yes - server only</td>
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<td>yes</td>
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</tr>
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<tr>
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<td>from</td>
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<td>from</td>
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<td></td>
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<td>yes</td>
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<td></td>
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</tr>
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<tr>
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<td>from + pending out</td>
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<td>from/none + ask='subscribe'</td>
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<td>yes</td>
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<td>yes</td>
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<td>yes</td>
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</tr>
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<tr>
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<td>both</td>
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<td>both</td>
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<td>yes</td>
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<td>yes</td>
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<td>yes</td>
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</tr>
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</table>
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</section3>
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</section2>
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</section1>
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<section1 topic='Security Considerations' anchor='security'>
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<p>It is not intended for servers to strip any &MOVED; elements from
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&PRESENCE; stanzas sent in from a client. This allows clients as well as
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servers to implement these same procedures.</p>
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<p>In order to prevent other users from maliciously altering contacts
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the client SHOULD NOT automatically subscribe to a &MOVED; JID when it
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receives an unsubscribe and SHOULD NOT automatically unsubscribe to
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a &MOVED; JID when it receives a subscribe.</p>
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<p>The following illustrates an example malicious attack.</p>
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<ol>
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<li>userA@example.com subscribes to userB@example.com</li>
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<li>The userB@example.com automatically accepts the subscription from
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userA@example.com. (Automatically done by the client using a simple
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domain trust).</li>
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<li>userA@example.com unsubscribes with the &MOVED; 'new' JID set to
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companyCEO@example.com.</li>
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<li>The previous steps can be repeated and have userB@example.com subscribe
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to a large number of people.</li>
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</ol>
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<p>A similar attack can be done with a new subscribe request causing users
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by guessing which users are subscribed to a contact.</p>
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<ol>
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<li>hacker@example.com subscribes to userB@example.com guessing that
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userA@example.com is on userB's roster.
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<![CDATA[
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<presence from='hacker@example.com' to='userB@example.com' type='subscribe'>
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<status>Subscribe to me!</status>
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<moved xmlns='urn:xmpp:moved:0' old='userA@example.com'/>
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</presence>
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]]>
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</li>
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<li>If userB's client automatically accepted the subscription without
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displaying at prompt to userB showing the new JID to be hacker@example.com,
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then the user has no idea that hacker@example.com was just added to
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the roster.
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</li>
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</ol>
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</section1>
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<section1 topic='IANA Considerations' anchor='iana'>
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<p>This document requires no interaction with &IANA;.</p>
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</section1>
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<section1 topic='XMPP Registrar Considerations' anchor='reg'>
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<section2 topic='Protocol Namespaces' anchor='registrar-ns'>
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<p>This specification defines the following XML namespace:</p>
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<ul>
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<li>urn:xmpp:moved:0</li>
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</ul>
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<p>Upon advancement of this specification from a status of Experimental
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to a status of Draft, the ®ISTRAR; shall add the foregoing namespace
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to the registry located at &NAMESPACES;, as described in Section 4 of
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&xep0053;.
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</p>
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</section2>
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<section2 topic='Protocol Versioning' anchor='registrar-versioning'>
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&NSVER;
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</section2>
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</section1>
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<section1 topic='XML Schema' anchor='schema'>
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<code><![CDATA[
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<?xml version='1.0' encoding='UTF-8'?>
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<xs:schema
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xmlns:xs='http://www.w3.org/2001/XMLSchema'
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targetNamespace='urn:xmpp:moved:0'
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xmlns='urn:xmpp:moved:0'
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elementFormDefault='qualified'>
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<xs:element name='moved'>
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<xs:complexType>
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<xs:simpleContent>
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<xs:extension base='xs:string'>
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<xs:attribute name='new' type='xs:string' use='optional'/>
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<xs:attribute name='old' type='xs:string' use='optional'/>
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</xs:extension>
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</xs:simpleContent>
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</xs:complexType>
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</xs:element>
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</xs:schema>
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]]></code>
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</section1>
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<section1 topic='Acknowledgements' anchor='ack'>
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<p>The author wishes to thank Doug Abbink, Mikhail Belov, Peter Saint-Andre, and Peter Sheu for their feedback.</p>
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</section1>
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</xep>
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