Initial version of jet-omemo

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+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE xep SYSTEM 'xep.dtd' [
+  <!ENTITY secret "&lt;secret/&gt;">
+  <!ENTITY % ents SYSTEM 'xep.ent'>
+%ents;
+]>
+<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
+<xep>
+<header>
+  <title>Jingle Encrypted Transports - OMEMO</title>
+  <abstract>Extension for JET introducing OMEMO End-to-End Encrypted Jingle Transports.</abstract>
+  &LEGALNOTICE;
+  <number>XXXX</number>
+  <status>ProtoXEP</status>
+  <type>Standards Track</type>
+  <sig>Standards</sig>
+  <approver>Council</approver>
+  <dependencies>
+    <spec>XEP-0391</spec>
+    <spec>XEP-0234</spec>
+    <spec>XEP-0384</spec>
+  </dependencies>
+  <supersedes/>
+  <supersededby/>
+  <shortname>jet-omemo</shortname>
+  <schemaloc>
+    <ns>jingle</ns>
+    <url>http://xmpp.org/schemas/jingle.xsd</url>
+  </schemaloc>
+  <schemaloc>
+    <ns>jingle:errors</ns>
+    <url>http://xmpp.org/schemas/jingle-errors.xsd</url>
+  </schemaloc>
+  <registry/>
+  <discuss>jingle</discuss>
+  <author>
+    <firstname>Paul</firstname>
+    <surname>Schaub</surname>
+    <email>vanitasvitae@riseup.net</email>
+    <jid>vanitasvitae@jabberhead.tk</jid>
+  </author>
+  <revision>
+    <version>0.0.1</version>
+    <date>2017-10-06</date>
+    <initials>vv</initials>
+    <remark><p>First draft</p></remark>
+  </revision>
+</header>
+<section1 topic='Introduction' anchor='intro'>
+  <p>&xep0391; can be used to utilize different end-to-end encryption methods to secure Jingle Transports, eg. in the context of &xep0234;. This document aims to extend &xep0391; to allow the use of OMEMO encryption with Jingle transports. To achieve this goal, this protocol extension makes use of OMEMOs <link url='https://xmpp.org/extensions/xep-0384.html#usecases-keysend'>KeyTransportElements</link>.</p>
+</section1>
+<section1 topic='Mappings' anchor='mappings'>
+  <p>Conveniently the OMEMO protocol already provides a way to transport key material to another entity. So called KeyTransportElements are basically normal OMEMO MessageElements, but without a payload, so the contained key can be used for something else (See Section 4.6 of <cite>XEP-0384</cite>). This extension uses the key encrypted in the KeyTransportMessages &lt;key&gt; attribute and initialization vector from the &lt;iv&gt; attribute to secure Jingle Transports. The key corresponds to the <cite>Transport Key</cite> of <cite>XEP-0391</cite>, while the iv corresponds to the <cite>Initialization Vector</cite>. The KeyTransportMessage is the equivalent to the <cite>Envelope Element</cite>. Note that within the Envelope Element, the Transport Key is encrypted with the OMEMO ratchet.</p>
+</section1>
+<section1 topic='Limitaions' anchor='limitations'>
+  <p>Unfortunately &xep0384; determines the type of the transported key to be AES-128-GCM-NoPadding, so no other configuration can be used in the context of this extension.</p>
+  <p>Since OMEMO deviceIds are not bound to XMPP resources, the initiator MUST encrypt the Transport Key for every device of the recipient.</p>
+</section1>
+<section1 topic='Key Transport' anchor='transport'>
+  <p>In order to transport a key to the responder, the initiator creates a fresh AES-128-GCM-NoPadding Transport Key and Initialization Vector and generates an OMEMO KeyTransportElement from it as described in <cite>XEP-0384</cite>. This is then added as a child of the JET &lt;security&gt; element. The 'cipher' attribute MUST be set to 'aes-128-gcm-nopadding:0' (see the <link url='https://xmpp.org/extensions/xep-0391.html#ciphers'>ciphers</link> section of <cite>XEP-0391</cite>). The value of the 'type' attribute must be set to the namespace of the used version of <cite>XEP-0384</cite> &VNOTE;.</p>
+  <p></p>
+  <example caption="Romeo initiates an OMEMO encrypted file offer"><![CDATA[
+<iq from='romeo@montague.example/dr4hcr0st3lup4c'
+    id='nzu25s8'
+    to='juliet@capulet.example/yn0cl4bnw0yr3vym'
+    type='set'>
+  <jingle xmlns='urn:xmpp:jingle:1'
+          action='session-initiate'
+          initiator='romeo@montague.example/dr4hcr0st3lup4c'
+          sid='851ba2'>
+    <content creator='initiator' name='a-file-offer' senders='initiator'>
+      <description xmlns='urn:xmpp:jingle:apps:file-transfer:5'>
+        <file>
+          <date>1969-07-21T02:56:15Z</date>
+          <desc>This is a test. If this were a real file...</desc>
+          <media-type>text/plain</media-type>
+          <name>test.txt</name>
+          <range/>
+          <size>6144</size>
+          <hash xmlns='urn:xmpp:hashes:2'
+                algo='sha-1'>w0mcJylzCn+AfvuGdqkty2+KP48=</hash>
+        </file>
+      </description>
+      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
+                 mode='tcp'
+                 sid='vj3hs98y'>
+        <candidate cid='hft54dqy'
+                   host='192.168.4.1'
+                   jid='romeo@montague.example/dr4hcr0st3lup4c'
+                   port='5086'
+                   priority='8257636'
+                   type='direct'/>
+      </transport>
+      <security xmlns='urn:xmpp:jingle:jet:0'
+                name='a-file-offer'
+                cipher='urn:xmpp:ciphers:aes-128-gcm-nopadding'
+                type='eu.siacs.conversations.axolotl'>
+        <encrypted xmlns='eu.siacs.conversations.axolotl'>
+          <header sid='27183'>
+            <key rid='31415'>BASE64ENCODED...</key>
+            <key prekey="true" rid='12321'>BASE64ENCODED...</key>
+            <!-- ... -->
+            <iv>BASE64ENCODED...</iv>
+          </header>
+        </encrypted>
+      </security>
+    </content>
+  </jingle>
+</iq>]]></example>
+  <p>The recipient decrypts the OMEMO KeyTransportElement to retrieve the Transport Secret. Transport Key and Initialization Vector are later used to encrypt/decrypt data as described in &xep0391;.</p>
+</section1>
+<section1 topic='Determining Support' anchor='support'>
+  <p>To advertise its support for JET-OMEMO, when replying to service discovery information ("disco#info") requests an entity MUST return URNs for any version of this extension, as well as of the JET extension that the entity supports -- e.g., "urn:xmpp:jingle:jet-omemo:0" for this version, or "urn:xmpp:jingle:jet:0" for &xep0391; &VNOTE;.</p>
+  <example caption="Service discovery information request"><![CDATA[
+<iq from='romeo@montague.example/dr4hcr0st3lup4c'
+    id='uw72g176'
+    to='juliet@capulet.example/yn0cl4bnw0yr3vym'
+    type='get'>
+  <query xmlns='http://jabber.org/protocol/disco#info'/>
+</iq>]]></example>
+  <example caption="Service discovery information response"><![CDATA[
+<iq from='juliet@capulet.example/yn0cl4bnw0yr3vym'
+    id='uw72g176'
+    to='romeo@montague.example/dr4hcr0st3lup4c'
+    type='result'>
+  <query xmlns='http://jabber.org/protocol/disco#info'>
+    <feature var='urn:xmpp:jingle:jet:0'/>
+    <feature var='urn:xmpp:jingle:jet-omemo:0'/>
+  </query>
+</iq>]]></example>
+  <p>In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in &xep0115;. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.</p>
+</section1>
+</xep>