Merge branch 'jet-omemo' of into feature/protoxep-jet-omemo

This commit is contained in:
Jonas Wielicki 2017-10-10 08:28:48 +02:00
commit ed63804444
1 changed files with 133 additions and 0 deletions

inbox/jet-omemo.xml Normal file
View File

@ -0,0 +1,133 @@
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY secret "&lt;secret/&gt;">
<!ENTITY % ents SYSTEM 'xep.ent'>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<title>Jingle Encrypted Transports - OMEMO</title>
<abstract>Extension for JET introducing OMEMO End-to-End Encrypted Jingle Transports.</abstract>
<type>Standards Track</type>
<remark><p>First draft</p></remark>
<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=''>KeyTransportElements</link>.</p>
<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 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 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=''>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>
<example caption="Romeo initiates an OMEMO encrypted file offer"><![CDATA[
<iq from='romeo@montague.example/dr4hcr0st3lup4c'
<jingle xmlns='urn:xmpp:jingle:1'
<content creator='initiator' name='a-file-offer' senders='initiator'>
<description xmlns='urn:xmpp:jingle:apps:file-transfer:5'>
<desc>This is a test. If this were a real file...</desc>
<hash xmlns='urn:xmpp:hashes:2'
<transport xmlns='urn:xmpp:jingle:transports:s5b:1'
<candidate cid='hft54dqy'
<security xmlns='urn:xmpp:jingle:jet:0'
<encrypted xmlns='eu.siacs.conversations.axolotl'>
<header sid='27183'>
<key rid='31415'>BASE64ENCODED...</key>
<key prekey="true" rid='12321'>BASE64ENCODED...</key>
<!-- ... -->
<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 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'
<query xmlns=''/>
<example caption="Service discovery information response"><![CDATA[
<iq from='juliet@capulet.example/yn0cl4bnw0yr3vym'
<query xmlns=''>
<feature var='urn:xmpp:jingle:jet:0'/>
<feature var='urn:xmpp:jingle:jet-omemo:0'/>
<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>