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XEP-0421: Incorporate feedback from Last Call #1346

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Jun 3, 2024
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XEP-0421: Incorporate feedback from Last Call #1346

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67 changes: 61 additions & 6 deletions xep-0421.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,17 @@
<email>[email protected]</email>
<jid>[email protected]</jid>
</author>
<revision>
<version>0.2.0</version>
<date>2024-05-28</date>
<initials>mw</initials>
<remark><ul>
<li>Make explicit that one can't just hash the real JID.</li>
<li>Expand security considerations.</li>
<li>Add schema.</li>
<li>Fix some examples captions and casing</li>
</ul></remark>
</revision>
<revision>
<version>0.1.0</version>
<date>2019-08-20</date>
Expand Down Expand Up @@ -97,14 +108,14 @@
attaches an &lt;occupant-id&gt; element to the presence sent to all
occupants in the room.
</p>
<example caption="Client sends a message"><![CDATA[
<example caption="Client joins a room"><![CDATA[
<presence
from='[email protected]/pda'
id='n13mt3l'
to='[email protected]/thirdwitch'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>]]></example>
<example caption="Service Sends New Occupant's Presence to All Occupants"><![CDATA[
<example caption="Service sends new cccupant's presence to all occupants"><![CDATA[
<presence
from='[email protected]/thirdwitch'
id='27C55F89-1C6A-459A-9EB5-77690145D624'
Expand All @@ -121,15 +132,15 @@
&lt;occupant-id&gt; element to the message sent to all occupants in the
room.
</p>
<example caption="Occupant Sends a Message to All Occupants"><![CDATA[
<example caption="Client sends a message to all occupants"><![CDATA[
<message
from='[email protected]/pda'
id='hysf1v37'
to='[email protected]'
type='groupchat'>
<body>Harpier cries: 'tis time, 'tis time.</body>
</message>]]></example>
<example caption="Service Reflects Message to All Occupants"><![CDATA[
<example caption="Service reflects message to all occupants"><![CDATA[
<message
from='[email protected]/thirdwitch'
id='hysf1v37'
Expand Down Expand Up @@ -184,6 +195,9 @@
SHOULD generate the identifier such that the occupant identifier of a user
in one room of the service does not match the occupant identifier of the
same user in another room of the same service.
To guarantee the anonymity property, the server MUST NOT generate an
occupant identifier by only hashing the real bare JID using static,
guessable or discoverable parameters.
</p>
<p>
The occupant identifier MUST have a maximum length of 128 characters. The
Expand All @@ -201,8 +215,25 @@
<section1 topic='Security Considerations' anchor='security'>
<p>
If a MUC uses occupant identifiers, nickname changes will be visible to
all occupants of the room. Clients MAY warn users about this circumstance
before joining the room.
all occupants of the room. Clients may warn users about this circumstance
before joining the room or when changing the nickname.
</p>
<p>
When the MUC service does not support this specification, the server will
likely forward any &lt;occupant-id&gt; included in &lt;message&gt;s sent by
other room occupants and reflected by the MUC service. Receiving clients
must be careful to only process occupant identifiers if the MUC server
advertises support for this specification as described in the
<link url='#disco'>Discovering support</link> section.
</p>
<p>
The anonymity property of occupant identifiers is crucial to not
accidentally reveal an occupant's real bare JID to other room occupants.
Specifically, a simple hash over the occupant's real bare JID is not
sufficient as an occupant identifier, as unsalted hashes can be reversed
easily based on a dictionary of candidate JIDs. Review the
<link url='#id-generation'>Occupant ID generation</link> section for more
details.
</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
Expand All @@ -216,4 +247,28 @@
</ul>
</section2>
</section1>
<section1 topic='XML Schema'>
<code><![CDATA[
<?xml version='1.0' encoding='utf-8'?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="urn:xmpp:occupant-id:0"
xmlns="urn:xmpp:occupant-id:0"
elementFormDefault="qualified">

<xs:element name="occupant-id">
<xs:complexType>
<xs:attribute name="id" type="OccupantIdentifier" use="required" />
</xs:complexType>
</xs:element>

<xs:simpleType name="OccupantIdentifier">
<xs:restriction base="xs:string">
<xs:minLength value="1"/>
<xs:maxLength value="128"/>
</xs:restriction>
</xs:simpleType>

</xs:schema>
]]></code>
</section1>
</xep>