%ents; ]>
Moved This document defines an XMPP protocol extension that enables a user to inform its contacts about a change in JID. &LEGALNOTICE; xxxx ProtoXEP Standards Track Standards Council XMPP Core moved Tory Patnoe tpatnoe@cisco.com tpatnoe@cisco.com 0.0.7 2010-06-09 tp

Modified syntax to use 'old' and 'new' attributes.

 0.0.6 2010-06-07 tp
  • Update ordering so that it recommends sending the unsubscribe/unsubscribed, before, sending the subscribe
  • Add section documenting what happens when a contact is offline when the unsubscribe/unsubscribed/subscribe stanzas are sent.
  • Added an example about a hacker sending an unsolicited subscribe by guessing a roster entry.
 0.0.5 2010-06-02 tp

Added one-way subscription section

 0.0.4 2010-05-30 tp

Change MUST NOT to SHOULD NOT for clients auto-subscribing back; differentiate between inbound and outbound subscriptions.

 0.0.3 2010-06-02 tp

Add one-way subscription comments.

 0.0.2 2010-05-25 tp

Minor tweaks.

 0.0.1 2010-05-22 tp

First draft.

There are a variety of reasons why a user may wish to change their JID. For example, a surname change because of marriage or simply an easier JID to remember.

This XEP defines an approach for communicating that your JID has moved to a new JID, extending the existing subscription protocol documented in &rfc3921;. The steps outlined here may be done either through a client or automated by a server.

In this scenario user@example.com moves to user2@example2.com. Both the user@example.com and user2@example2.com accounts have been created and still exist. The roster for user@example2.com is empty and the user wants to populate it with their entries from user@example.com.

original JID
user@example.com
new JID
user2@example2.com

Because the original JID is no longer going to be used, the user SHOULD unsubscribe from all the outbound subscriptions user@example.com had. These can be identified as those in the 'to' or 'ask' states as defined in the 'jabber:iq:roster' protocol in &rfc3921;.

To unsubscribe all outbound subscriptions for the original JID send an unsubscribe &PRESENCE; stanza to all the old contacts with a &MOVED; element containing the new JID.

There is the potential for other users to send a malicious unsubscribe containing a spoofed &MOVED; JID. Therefore, clients SHOULD NOT automatically subscribe to the JID contained in the &MOVED; stanza when receiving a subscribe &PRESENCE; stanza without displaying the &MOVED; JID to the user. See the Security Considerations section for details.

I've changed JIDs from user@example.com to user2@example2.com ]]>

Because the original JID is no longer going to be used, the user SHOULD unsubscribe from all contacts the user@example.com had an inbound subscription from. These can be identified as those in the 'from' subscription state as defined in in the 'jabber:iq:roster' protocol in &rfc3921;.

To unsubscribe all inbound subscriptions send an unsubscribed &PRESENCE; stanza to all the old contacts with a &MOVED; element containing the new JID.

There is the potential for other users to send a malicious unsubscribed containing a spoofed &MOVED; JID. Therefore, clients SHOULD NOT automatically subscribe to the JID contained in the &MOVED; stanza without displaying the &MOVED; JID to the user. See the Security Considerations section for details.

I've changed JIDs from user@example.com to user2@example2.com ]]>

Once the new JID has been created on a server it is possible for the new JID to subscribe to the contacts they had on the original JID's roster. This is done by sending a new subscription request with a &MOVED; element containing the new JID.

The new subscription MUST come from the new JID's server.

There is the potential for other users to send a malicious subscribe request and spoof the content of the &MOVED; element identifying an original JID. Therefore, clients SHOULD NOT automatically unsubscribe an existing roster entry if is listed as the target in the &MOVED; element when a subscribe is received. See the Security Consideration section for details.

Clients accepting the moved subscription SHOULD indicate to the user that that this subscription request was the result of a move operation and because of potential malicious behavior SHOULD NOT auto-accept the subscription without displaying the &MOVED; JID to the user.

I've changed JIDs from user@example.com to user2@example2.com ]]>

&rfc3920bis; clarifies that an incoming subscribe &PRESENCE; stanza MUST be preserved by the server and &PRESENCE; stanzas of type unsubscribe and unsubscribed are not preserved on the server. Therefore, for a contact who is offline, their servers MAY have automatically removed the original roster entry when seeing the unsubscribe and unsubscribed stanzas. At the time of writing this XEP, NOT saving and forwarding the presence stanzas will be the default behavior of most servers.

What this means is that a contact coming online after the rename outlined above MAY only see the &PRESENCE; of type 'subscribe' with the &MOVED; element. Clients should be aware of this behavior.

In following the principle of least surprise, it is considered good practice to send the subscribe stanza after the unsubscribe and unsubscribed stanzas.

One of the side effects of this scheme is the potential for a contact to lose the groups to which it had organized the original JID. Clients aware of the &MOVED; element can mitigate this with the following rules.

  • If the contacts client receives an unsubscribed with a &MOVED; element, remove the subscription but initiate a roster push for the original JID with the subscription set to 'none'. When the new subscription is received the new JID MAY be placed into the roster in the same groups as the original JID and the original JID can then be removed from the roster.
  • If a subscribe is received with a &MOVED; element, the client MAY automatically place the new JID into the same groups as the original JID.

As discussed in 'Contacts Offline at the Time the Rename Occurs', a server MAY automatically handle the unsubscribe and unsubscribed stanzas. If this occurs it will be impossible to preserve the original groups.

If the original JID, user@example.com, had only an inbound subscription (from or pending in), then the contact will only receive an unsubscribed &PRESENCE; stanza. The contact's client, knowing the state of the subscription (which is 'to' or 'none' with 'ask='subscribe' from the contact's perspective), at that point MAY choose to prompt the user to subscribe to the new JID listed in the &MOVED; element.

Because of the ability to spoof the &MOVED; element, the client SHOULD NOT automatically subscribe to the &MOVED; element target, but SHOULD present the new JID to the contact before sending out a subscription request.

If the original JID, user@example.com, had only an outbound subscription (to or ask), then the contact SHOULD only receive an unsubscribe &PRESENCE; stanza. The contact's client, knowing the state of the subscription (which is 'from' from the contact's perspective), at that point MAY choose to prompt the user to subscribe to the new JID listed in the &MOVED; element.

Because of the ability to spoof the &MOVED; element, the client SHOULD NOT automatically subscribe to the &MOVED; element target

.
Server state Client state (jabber:iq:roster) Send unsubscribe from original JID Send unsubscribed from original JID Send subscribe from new JID
none none
none + pending out none + ask='subscribe' yes yes
none + pending in n/a yes - server only
none + pending in/out none + ask='subscribe' yes yes - server only yes
to to yes yes
to + pending in to yes yes - server only yes
from from yes
from + pending out from/none + ask='subscribe' yes yes yes
both both yes yes yes

It is not intended for servers to strip any &MOVED; elements from &PRESENCE; stanzas sent in from a client. This allows clients as well as servers to implement these same procedures.

In order to prevent other users from maliciously altering contacts the client SHOULD NOT automatically subscribe to a &MOVED; JID when it receives an unsubscribe and SHOULD NOT automatically unsubscribe to a &MOVED; JID when it receives a subscribe.

The following illustrates an example malicious attack.

  1. userA@example.com subscribes to userB@example.com
  2. The userB@example.com automatically accepts the subscription from userA@example.com. (Automatically done by the client using a simple domain trust).
  3. userA@example.com unsubscribes with the &MOVED; 'new' JID set to companyCEO@example.com.
  4. The previous steps can be repeated and have userB@example.com subscribe to a large number of people.

A similar attack can be done with a new subscribe request causing users by guessing which users are subscribed to a contact.

  1. hacker@example.com subscribes to userB@example.com guessing that userA@example.com is on userB's roster. Subscribe to me! ]]>
  2. If userB's client automatically accepted the subscription without displaying at prompt to userB showing the new JID to be hacker@example.com, then the user has no idea that hacker@example.com was just added to the roster.

This document requires no interaction with &IANA;.

This specification defines the following XML namespace:

  • urn:xmpp:moved:0

Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the foregoing namespace to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.

&NSVER; ]]>

The author wishes to thank Doug Abbink, Mikhail Belov, Peter Saint-Andre, and Peter Sheu for their feedback.