<title>Mediated Information eXchange (MIX): JID Hidden Channels.</title>
<abstract>This document defines an extension to Mediated Information eXchange (MIX) specified in XEP-0369. This specification extends MIX to provide a number of privacy control options and in particular JID Hidden Channels. </abstract>
<p>The Mediated Information eXchange (MIX) protocol framework and core capabilities are specified in &xep0369; (MIX-CORE). This specification provides mechanisms to hide participant JIDs from other participants. This is needed to address privacy concerns and to prevent JID harvesting. It also addresses privacy issues, and gives participants options to control sharing of information.
&xep0369; exposes participant JIDs to other participants, and so messages can always be sent directly. When JIDs are hidden this is no longer possible.
Private messages MAY be sent to channel participants if allowed by channel policy. Private messages are switched through the channel to hide addressing.
<tr><td>'JID Visible'</td><td>In these channels all participant JIDs are visible to all channel participants.</td></tr>
<tr><td>'JID Maybe Visible'</td><td>In these channels, participant JIDs are visible to all channel participants when participant preference allows.</td></tr>
<tr><td>'JID Hidden'</td><td>In these channels, no participant JIDs are visible to channel participants, but they are visible to channel administrators.</td></tr>
</table>
<p>
A channel participant MAY specify a preference for JID visibility for the channel, with one of the following values:
<tr><td>'Prefer Visible'</td><td>The users JID will be visible if the channel is JID Visible or JID Maybe Visible channels and hidden if the channel is JID Hidden. </td></tr>
<tr><td>'Prefer Hidden'</td><td>The user's JID will be hidden if the channel is JID Maybe Visible and shown if the channel is JID Visible .</td></tr>
<tr><td>'Enforce Hidden'</td><td>The user's JID will never be shown and the user will be removed from channel if channel mode is changed to JID Visible.</td></tr>
<tr><td>'Enforce Visible'</td><td>The users JID will always be shown and the user will be removed from channel if mode is changed to 'JID Hidden'.</td></tr>
MUC hides real JIDs by using Nicks to identify room occupants. This has problems with Nick changing and with multiple active clients for the same user. MIX identifies channel participants by Stable Participant ID. In &xep0369;, the users JID is in the participants node and is shared in messages and presence. To hide JIDs, this specification makes three key changes
<li>The requirement to include real JID in the participants list is relaxed for channels that are not "JID Visible". For a "JID Hidden" channel, real JIDs MUST NOT be included in the participants list. For a "JID Maybe Visible" channel, real JIDs will be included in the participants node according to participant preference. </li>
It is important that MUC owners and administrators are able to see the JIDs of participant. For this reason, a MIX channel following this specification MUST hold a JID Map node, which gives a mapping between Stable Participant ID and JID.
Where the JID is not being hidden, the resource is simply the resource of the clients full JID. Where the JID is hidden, the resource is replaced with a generated value. For example, 'hag66@shakespeare.example/UUID-a1j/7533' in the channel coven might have an encoded JID of '123456#coven@mix.shakespeare.example/789'. There is no client visible mapping maintained, as this is not needed. The MIX channel will need to maintain a mapping, to support directly addressing clients, such as for client to client disco#info queries. While an encoded JID is held in the presence node, the mapping to real JID MUST NOT be changed. When adding a client to the presence node, the server MAY add the same anonymized JID as used before by that client, or it MAY create a different anonymized JID.
<tr><td>JID Map</td><td>'urn:xmpp:mix:nodes:jidmap'</td><td>For storing a list of Stable Participant IDs from the participants node with a 1:1 mapping to the corresponding JIDs.</td><td>Automatic</td><td>PubSub</td></tr>
<p>The JID Map node is used to associate a Stable Participant ID to its corresponding bare JID. It is a PubSub node with the 'node' attribute set to 'urn:xmpp:mix:nodes:jidmap'. The JID Map node MUST have one entry for each entry in the Participants node. This value is added when a user joins the channel and is removed when the user leaves the channel.
Each item is identified by Stable Participant ID mapping to the bare JID. This node is used to give administrator access to JIDs. This node MUST NOT be modified directly using pubsub.
Only administrators can subscribe to this node. The JID Map node is a permanent node with one item per participant. Information is stored in a <participant/> element qualified by the 'urn:xmpp:mix:anon:0' namespace. The real JID is stored in a <jid/> child element of the <participant/> element. </p>
<p>A channel MAY store user preferences and parameters with each user. A user JID visibility preference has the following values:
</p>
<ol>
<li>'default'. In this setting, the channel default value will be used. This value is used if another value is not explicitly set. This means JID is visible for a JID Visible channel and JID is hidden for JID Hidden and JID Maybe Visible channels.</li>
<li>'never'. If this is set, JID will never be shared and user will be removed from the channel if its mode changes to JID Visible.</li>
<li>'always'. If this is set, JID will always be shared and users will be removed from the channel if its mode changes to JID Hidden.</li>
<li>'prefer not'. If this is set, JID will only be shared if mode is JID Visible.</li>
</ol>
<p>
The user MAY specify that no Private Messages are to be sent from the channel, and allow vCard retrieval.
</p>
<p>
The user MAY specify that presence is not to be shared, which will prevent the MIX Channel from sending a presence probe for the user on channel start-up. The user will also choose to not include the MIX channel in the user's roster, so that presence will not be updated. Where the channel configuration sets 'Participants Must Provide Presence', this variable MUST be set to 'Share'.
</p>
<p>
The following table sets out the standardized user preference values. A MIX implementation MAY use other values.
<p>When joining a channel, the client MAY specify one or more preference options as a &xep0004; form. In the response, the server MUST specify all of the user preferences supported by the server, with default values if the user has not requested a different value. The following example shows joining a channel and setting a preference. The following example shows the message sent from the user's server to the MIX channel, which will have been preceded by a message from the user's client to the user's server.</p>
<examplecaption="User Joins a Channel and Specifies a preference"><