mirror of
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483 lines
20 KiB
XML
483 lines
20 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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&mwild;
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<revision>
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<version>0.2.0</version>
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<date>2021-07-20</date>
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<initials>mw</initials>
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<remark><p>Re-write the flow with a more focused approach.</p></remark>
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</revision>
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<revision>
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<version>0.1.1</version>
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<date>2018-08-06</date>
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<initials>pep</initials>
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<remark><p>Fix trivial typo</p></remark>
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</revision>
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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. Another common reason is that the provider goes
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out of service (with a notice).</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.</p>
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</section1>
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<section1 topic='Requirements' anchor='reqs'>
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<p>This document aims to satisfy the following requirements:</p>
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<ul>
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<li>Users should be able to notify their contacts of a change of address.</li>
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<li>Contacts should be able to verify that such a notification is legitimate, to prevent malicious actors from spoofing notifications.</li>
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<li>It should be possible for a contact's server to automatically update the contact's roster for seamless migrations.</li>
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<li>In the absence of a contact's support for this protocol, it should fall back to a simple manual subscription approval.</li>
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</ul>
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</section1>
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<section1 topic='Glossary' anchor='glossary'>
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<dl>
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<di>
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<dt>Moved notification</dt>
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<dd>An XML <moved/> element sent to a contact to inform them that
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the user is moving to a new address.
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</dd>
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</di>
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<di>
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<dt>Moved statement</dt>
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<dd>An XML <moved/> element published by the user on their old
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account. It is used by contacts to verify that moved notifications
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are genuine.
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</dd>
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</di>
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</dl>
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</section1>
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<section1 topic='Use Cases' anchor='usecases'>
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<p>We start with the situation where the user, let's call them Juliet, has two accounts -
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her original account <tt>juliet@im.example.net</tt> and a shiny new account on her personal
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domain, <tt>juliet@capulet.example</tt>.</p>
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<p>Juliet would like to migrate all her data and contacts to her new account, with minimal
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disruption.</p>
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<section2 topic='User publishes moved statement' anchor='publish-statement'>
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<p>Before notifying contacts of the move, Juliet must connect to her old
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account and publish a "statement" that the account is no longer in
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use. This statement includes the address of her new account.
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</p>
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<p>The statement should be posted to a PEP node with the name 'urn:xmpp:moved:1'. The
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payload should be a <moved/> element in the 'urn:xmpp:moved:1' namespace. This
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element should in turn contain a single <new-jid/> element with the user's new JID
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as its text content.</p>
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<example caption='Juliet's client publishes a moved statement on her old account'><![CDATA[
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<iq from='juliet@im.example.net/VR0sAGae'
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type='set'
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id='pub1'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<publish node='urn:xmpp:moved:1'>
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<item id='current'>
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<moved xmlns='urn:xmpp:moved:1'>
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<new-jid>juliet@capulet.example</new-jid>
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</moved>
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</item>
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</publish>
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</pubsub>
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</iq>
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]]></example>
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</section2>
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<section2 topic='User notifies contacts of move' anchor='publish-notification'>
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<p>After publishing a moved statement on her old account, Juliet proceeds
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to notify her contacts about the move.</p>
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<p>Juliet connects to her new account, and sends a subscription request to
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each of her contacts. These subscription requests MUST contain a <moved/>
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element in the 'urn:xmpp:moved:1' namespace. This element contains a single
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<old-jid/> element with the old JID as its text content.></p>
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<example caption='Juliet sends a subscription request to Romeo from her new account'><![CDATA[
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<presence type='subscribe' to='romeo@montague.example' id='sub1'>
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<moved xmlns='urn:xmpp:moved:1'>
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<old-jid>juliet@im.example.net</old-jid>
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</moved>
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</presence>
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]]></example>
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</section2>
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<section2 topic='Contact receives subscription request with moved notification' anchor='receive-notification-client'>
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<p>Juliet's contact, Romeo, receives the subscription request from Juliet's
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new JID. At this point Romeo has not verified that the new account
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actually belongs to Juliet, and MUST perform such verification before
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acting on the request any differently to usual.</p>
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<p>If the value of <old-jid/> is not in the roster with an approved
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incoming subscription ('from' or 'both'), the <moved/> element
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MUST be ignored entirely.</p>
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<p>To verify the request, Romeo makes a request to the JID specified in
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<old-jid/> (which MUST be a bare JID) to fetch a published move
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statement.</p>
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<example caption='Romeo requests a moved statement from Juliet's old account'><![CDATA[
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<iq type='get'
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from='romeo@capulet.example/laptop'
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to='juliet@im.example.net'
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id='83hKgF'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<items node='urn:xmpp:moved:1'>
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<item id='current'/>
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</items>
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</pubsub>
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</iq>
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]]></example>
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<p>On success, Juliet's server will return the moved statement that Juliet published.</p>
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<example caption='Juliet's old server returns the published moved statement to Romeo'><![CDATA[
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<iq type='result'
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from='juliet@im.example.net'
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to='romeo@capulet.example/laptop'
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id='83hKgF'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<items node='urn:xmpp:moved:1'>
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<item id='current'>
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<moved xmlns='urn:xmpp:moved:1'>
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<new-jid>juliet@capulet.example</new-jid>
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</moved>
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</item>
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</items>
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</pubsub>
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</iq>
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]]></example>
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<p>Romeo MUST now verify that the received subscription request was from
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the same bare JID contained in the <new-jid/> element in the moved
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statement. If the JIDs do not match, or if there was an error fetching
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the moved statement (except for "gone" - see note below), the
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<moved/> element in the incoming subscription request MUST be
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ignored entirely.</p>
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<p class="box">
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<strong>Note:</strong> As a special case, if the attempt to retrieve the
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moved statement results in an error with the <gone/> condition as
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defined in RFC 6120, and that <gone/> element contains a valid
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XMPP URI (e.g. <tt>xmpp:user@example.com</tt>), then the error response
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MUST be handled equivalent to a <moved/> statement containing a
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<new-jid/> element with the JID provided in the URI (e.g.
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<tt>user@example.com</tt>).
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</p>
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<p>Upon successful verification, Romeo's client may present an appropriate
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user interface, informing about Juliet's change of address, and a prompt
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to accept the subscription request from the new address. On the user's
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approval of such a subscription request, the client will typically want
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to also send a subscription request to the contact's new JID to establish
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a mutual subscription.</p>
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<p>Due to the potential for races between multiple clients connected to
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the same account, it is NOT RECOMMENDED for a client to automatically
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act upon migration notifications, but instead await manual interaction
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from the user. As with any inbound subscription request it SHOULD pay
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attention to roster pushes related to the contact, and update the UI
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appropriately if the new contact address is authorized from another
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device.</p>
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</section2>
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<section2 topic='Server-side processing of inbound moved notification' anchor='receive-notification-server'>
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<p>It is not required for Romeo's server to support this specification.
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However if Romeo's server does understand this extension, it SHOULD
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handle the inbound subscription request on behalf of Romeo's clients.
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This improves the user experience for Romeo, especially when he has
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multiple devices.</p>
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<p>Broadly the server should follow exactly the same process as a client
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would. Specifically:
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</p>
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<ol>
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<li>Receive subscription request with 'moved' payload.</li>
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<li>Verify that the old JID has an approved subscription to the user (i.e. a subscription of 'both' or 'from').</li>
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<li>Request moved statement from the old account JID.</li>
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<li>Verify that the new JID in the moved statement matches the 'from' of the subscription request.</li>
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</ol>
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<example caption='Romeo's server requests a moved statement from Juliet's old account'><![CDATA[
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<iq type='get'
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from='romeo@capulet.example'
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to='juliet@im.example.net'
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id='83hKgF'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<items node='urn:xmpp:moved:1'>
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<item id='current'/>
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</items>
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</pubsub>
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</iq>
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]]></example>
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<example caption='Juliet's old server returns the published moved statement to Romeo's server'><![CDATA[
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<iq type='result'
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from='juliet@im.example.net'
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to='romeo@capulet.example/laptop'
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id='83hKgF'>
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<pubsub xmlns='http://jabber.org/protocol/pubsub'>
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<items node='urn:xmpp:moved:1'>
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<item id='current'>
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<moved xmlns='urn:xmpp:moved:1'>
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<new-jid>juliet@capulet.example</new-jid>
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</moved>
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</item>
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</items>
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</pubsub>
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</iq>
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]]></example>
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<p>If verification fails (e.g. due to a missing or incorrect moved
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statement), the server MUST ignore the <moved/> element in the
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subscription request, and process the stanza as a normal subscription
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request. It MUST NOT strip the <moved/> element before forwarding,
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even if verification fails.</p>
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<p>Upon successful verification, the server MUST NOT forward the stanza to
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Romeo's clients, but instead MUST create a roster entry for the new JID
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with a subscription of 'from' (sending out the appropriate roster push),
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and then auto-reply to the subscription request with a presence of type
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'subscribed'.</p>
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<example caption='Romeo's server notifies Romeo about the new roster entry'><![CDATA[
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<iq id='a78b4q6ha463'
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to='romeo@montague.example/orchard'
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type='set'>
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<query xmlns='jabber:iq:roster'>
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<item jid='juliet@capulet.example''
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subscription='from'/>
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</query>
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</iq>
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]]></example>
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<p>After authorizing the new JID, the server should revoke the presence
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subscription of the old account.</p>
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<example caption='Romeo's server notifies Juliet's old account about unsubscription'><![CDATA[
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<presence to='juliet@im.example.net' type='unsubscribed'/>
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]]></example>
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<example caption='Romeo's server notifies Romeo's clients about the old roster entry'><![CDATA[
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<iq id='a78b4q6ha463'
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to='romeo@montague.example/orchard'
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type='set'>
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<query xmlns='jabber:iq:roster'>
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<item jid='juliet@im.example.net''
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subscription='to'/>
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</query>
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</iq>
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]]></example>
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<p>Finally, if the old JID was in the user's roster with a subscription of 'both', the
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server MUST also send a presence of type 'subscribe' to the new JID in
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order to seek establishment of a mutual subscription.</p>
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<example caption='Romeo's server sends subscription request to Juliet's new JID'><![CDATA[
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<presence type='subscribe' id='uc51xs63' from='romeo@montague.example' to='juliet@capulet.example'/>
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]]></example>
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</section2>
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</section1>
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<section1 topic='Implementation Notes' anchor='impl'>
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<section2 topic='Lifetime of moved statement' anchor='impl-lifetime'>
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<p>The moved statement is required for contacts to automatically verify
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the authenticity of moved notifications. After publishing a moved
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statement, the user should keep the statement published and the account
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active for long enough for contacts to switch to the user's new account.</p>
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<p>It is not necessary to remain connected to the old account during the
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transition period. However the account must not be deleted, and the
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server must be available.</p>
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<p>In the event that the move statement is unpublished, the account is deleted,
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or the server becomes unavailable, any contacts that have not yet transitioned
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to the user's new JID will be unable to verify the migration. Those contacts
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will have to manually approve the subscription from the user's new address.</p>
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<p>Migration progress of contacts is obervable through subscription revocations to
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the old account, and subscription approvals to the new account.</p>
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</section2>
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<section2 topic='Alternative verification methods' anchor='impl-alt-verify'>
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<p>Future revisions of this document, or alternative documents, may define
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alternative verification methods. Such methods SHOULD be communicated via
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child elements of <moved/> in an appropriate namespace. As is usual
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throughout XMPP, entities MUST ignore unknown child elements of
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<moved/> in unrecognised namespaces.</p>
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</section2>
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</section1>
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<section1 topic='Security Considerations' anchor='security'>
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<section2 topic='User considerations' anchor='security-user'>
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<p>The following are considerations for the user (exemplified by Juliet in this document):</p>
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<ul>
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<li>A malicious client or other entity with access to the user's account
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can perform a migration, potentially against the user's will and/or
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without their knowledge. Although this is a concern, any malicious
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actor with access to a user's account can abuse that access in many
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ways. Servers that support granting restricted access to accounts
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should consider blocking attempts to publish to the
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'urn:xmpp:moved:1' PEP node from restricted entities.</li>
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<li>To avoid leaking the user's new JID to non-contacts, the PEP node
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containing the moved statement SHOULD be configured to use the
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"presence" access model (this is the default access model defined
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by PEP).</li>
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</ul>
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</section2>
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<section2 topic='Contact considerations' anchor='security-contact'>
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<p>The following are considerations for the contact (exemplified by Romeo in this document), and the contact's server:</p>
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<ul>
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<li>A presence subscription with a <moved/> is trivial for a
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malicious third-party to spoof. The verification methods discussed
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in this document MUST be followed to prevent accepting rogue
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subscription requests.</li>
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<li>It is important to verify that the original JID of the migrating
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user was already authorized to view presence before processing a
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migration.</li>
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<li>After successfully processing a migration, the original account
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should have its presence subscription revoked. This ensures that
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each JID may only be migrated once. Without this precaution the
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migration mechanism can be abused to introduce unlimited arbitrary
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JIDs to contacts' rosters. This precaution also ensures, if the
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old account ends up owned by a new entity, that they will not
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unexpectedly inherit a presence subscription.</li>
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</ul>
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</section2>
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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='registrar'>
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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:1</li>
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</ul>
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</section1>
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<section1 topic='Design Considerations' anchor='design'>
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<section2 topic='Verification methods' anchor='design-verification'>
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<p>There are two general approaches for verification - network-based
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verification, or cryptographic verification. Network-based verification
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(as described in this document) requests a verification statement from
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the user's old account. Cryptographic verification would check a move
|
|
notification against a previously-established cryptographic identify of
|
|
the user.</p>
|
|
<p>Network-based verification:</p>
|
|
<ul>
|
|
<li>Pro: Simple and easy to implement</li>
|
|
<li>Con: depends on the original server being available and supporting PEP</li>
|
|
</ul>
|
|
<p>Cryptographic verification:</p>
|
|
<ul>
|
|
<li>Pro: Can work even if the original server goes offline or begins blocking
|
|
migration attempts.</li>
|
|
<li>Con: More complex implementation.</li>
|
|
<li>Con: Requires user and contacts to manage/track cryptographic keys and
|
|
identies. It may be possible to piggyback on top of an existing cryptographic
|
|
layer, e.g. OMEMO. However this would eliminate the server-side assistance,
|
|
and OMEMO support is not universal among clients.</li>
|
|
</ul>
|
|
|
|
<p>Ultimately this document defines a network-based verification method, but
|
|
leaves an obvious path to extend the protocol with alternative verification
|
|
methods (either in an update to this document, or defined by other
|
|
documents).</p>
|
|
</section2>
|
|
</section1>
|
|
|
|
<section1 topic='XML Schema' anchor='schema'>
|
|
<p>To be done upon advancement to Draft.</p>
|
|
</section1>
|
|
|
|
<section1 topic='Acknowledgements' anchor='ack'>
|
|
<p>This document was formerly driven by Tory Patnoe with the support and feedback provided by Doug Abbink, Mikhail Belov, Peter Saint-Andre, and Peter Sheu.</p>
|
|
<p>It has since been taken over by the current author who thanks Kim Alvefur, Maxime Buquet and Jonas Schäfer for their input and feedback on this specification.</p>
|
|
</section1>
|
|
</xep>
|