<abstract>This document defines an XMPP protocol extension that enables XMPP entities to interact with spim filters by marking unsolicited or suspicious XMPP stanzas.</abstract>
<legal>
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<p>There are various spim protection methods exist in XMPP: &xep0016;, &xep0158;, &xep0191;, &xep0268; and &xep0275;. But they may not be sufficient enough:</p>
<p>Service administrators might want to deploy server-based spim recognition software to fill in the gaps. However, every automated spim recognition suffers from <em>false positives</em> - situations where a stanza incorrectly qualified as spim. To avoid them, a spim filter doesn't block suspicious stanza, but marks it and sends to a client in a regular manner. A client software doesn't need to interrupt a user when processing such marked stanzas: for example, it may put them silently in "SPAM" folder, so a user can look through them at any time later. Furthermore, a spim filter may take user's experience into account. When a user receives an unsolicited stanza, he or she can mark it as spim. In this case a client software sends an automatic complaint to a server-based spim filter. This specification deals with both cases. Thus, in contrast to &xep0159;, it doesn't introduce any spim blocking techniques. Also, the various spim recognition procedures that may be employed by the server are beyond the scope of this document.
<p>An implementation compliant with this document MUST support spim markers as described in <linkurl='#spim-marker'>Spim Marker</link> use case. Support for spim reports, as described in <linkurl='#spim-report'>Spim Report</link> use case, is RECOMMENDED.</p>
</section1>
<section1topic='Glossary'anchor='glossary'>
<p>The following terms are used throughout this document:</p>
<dl>
<di><dt>Filtering Entity</dt><dd>An XMPP entity which performs spim recognitions, blocks or marks suspicious stanzas and accepts spim reports. Example: a server or an external component with built-in spim recognition module.</dd></di>
<di><dt>Receiving Entity</dt><dd>An XMPP entity which directly receives marked stanzas and sends spim reports. Example: a client or a conference (&xep0045;).</dd></di>
</dl>
</section1>
<section1topic='Use Cases'anchor='usecases'>
<section2topic='Spim Marker'anchor='spim-marker'>
<p>The filtering entity marks abusive stanza by adding <mark/> child element qualified by the 'urn:xmpp:spim-marker:0' namespace. The element MUST possess the 'filter' attribute whose value MUST be a full jid of the filtering entity. The <mark/> element MAY contain character data which SHOULD be a human-readable description of the reason to mark. The filtering entity MUST NOT add more than one <mark/> element and MUST delete all other <mark/> elements matching itself before adding a new one. The filtering entity MAY remove any <mark/> elements matching itself even if it doesn't add a new one.</p>
<examplecaption="User's Server Marked Abusive Message"><![CDATA[
<p>Processing rules of marked stanzas taken by the receiving entity are beyond the scope of this document. One possible solution is to put such stanzas silently in so-called "SPAM" folder.</p>
</section2>
<section2topic='Spim Report'anchor='spim-report'>
<p>If the filtering entity wishes to receive abuse report for the stanza, it MUST add <report/> child element qualified by the 'urn:xmpp:spim-report:0' namespace and MUST possess the 'key' and the 'filter' attributes. A value of the 'key' attribute is arbitrary, but SHOULD have at least 128 bits of randomness. The 'key' attribute is needed to match the corresponding complaint (if any) with the sender. The value of the 'filter' attribute MUST be a full jid of the filtering entity. The filtering entity MUST NOT add more than one <report/> element and MUST delete all other <report/> elements matching itself before adding a new one. The filtering entity MAY remove any <report/> elements matching itself even if it doesn't add a new one.</p>
<examplecaption="Multiple Filters Wishes to Receive Abuse Report"><![CDATA[
<presencetype='subscribe'
from='robot@abuser.com'
to='innocent@victim.com'
id='spam2'>
<reportxmlns='urn:xmpp:spim-report:0'
key='571c9641d8442920'
filter='filter.victim.com'/>
<reportxmlns='urn:xmpp:spim-report:0'
key='b258acbcb4bb8e66ac'
filter='victim.com'/>
</presence>
]]></example>
<p>The receiving entity MAY complain by sending an IQ-set containing the <query/> child element qualified by the 'urn:xmpp:spim-report:0' namespace. A value of the 'filter' attribute MUST be copied in the 'to' attribute of the IQ-set stanza. The element MUST possess 'key' attribute copied from the original stanza.</p>
<p>The receiving entity MUST ignore any <report/> elements generated by untrusted filtering entities. If there are more than one <report/> element matching the same filtering entity, all of them MUST be ignored.</p>
<p>The filtering entity MUST respond with an empty IQ-result stanza upon successful completion of the request:</p>
<examplecaption="Complaint Was Accepted"><![CDATA[
<iqtype='result'
from='filter.victim.com'
to='innocent@victim.com/laptop'
id='complaint1'/>
<iqtype='result'
from='victim.com'
to='innocent@victim.com/laptop'
id='complaint2'/>
]]></example>
</section2>
</section1>
<section1topic='Business Rules'anchor='rules'>
<p>A filtering entity SHOULD only add <mark/> or <report/> elements and a receiving entity SHOULD only process those elements if the corresponding stanza envolves an interaction with a human user: subscription requests, messages, conference invites, voice calls, etc. For example, it doesn't make a lot of sense to mark &xep0232; stanzas.</p>
<p>To avoid obvious false positives and user confusions, a filtering entity SHOULD NOT add <mark/> or <report/> elements to a stanza and a receiving entity SHOULD ignore <mark/> and <report/> elements of a stanza if:</p>
<p>If an entity supports the spim markers, it MUST report that by including a service discovery feature of "urn:xmpp:spim-marker:0" in response to a &xep0030; information request. If an entity supports the spim reports, it MUST report that by including a service discovery feature of "urn:xmpp:spim-report:0" in response to a &xep0030; information request:</p>
<examplecaption="Service Discovery Information Request"><