mirror of
https://github.com/moparisthebest/xeps
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135 lines
7.0 KiB
XML
135 lines
7.0 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE xep SYSTEM 'xep.dtd' [
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<!ENTITY secret "<secret/>">
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<!ENTITY % ents SYSTEM 'xep.ent'>
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%ents;
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]>
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
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<xep>
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<header>
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<title>Jingle Encrypted Transports - OMEMO</title>
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<abstract>Extension for JET introducing OMEMO End-to-End Encrypted Jingle Transports.</abstract>
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&LEGALNOTICE;
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<number>0396</number>
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<status>Experimental</status>
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<type>Standards Track</type>
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<sig>Standards</sig>
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<approver>Council</approver>
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<dependencies>
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<spec>XEP-0391</spec>
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<spec>XEP-0234</spec>
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<spec>XEP-0384</spec>
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</dependencies>
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<supersedes/>
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<supersededby/>
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<shortname>jet-omemo</shortname>
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<schemaloc>
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<ns>jingle</ns>
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<url>http://xmpp.org/schemas/jingle.xsd</url>
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</schemaloc>
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<schemaloc>
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<ns>jingle:errors</ns>
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<url>http://xmpp.org/schemas/jingle-errors.xsd</url>
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</schemaloc>
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<registry/>
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<discuss>jingle</discuss>
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&paulschaub;
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<revision>
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<version>0.1</version>
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<date>2017-11-29</date>
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<initials>XEP Editor (jwi)</initials>
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<remark><p>Accepted by Council as Expremental XEP</p></remark>
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</revision>
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<revision>
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<version>0.0.1</version>
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<date>2017-10-06</date>
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<initials>vv</initials>
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<remark><p>First draft</p></remark>
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</revision>
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</header>
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<section1 topic='Introduction' anchor='intro'>
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<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>
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</section1>
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<section1 topic='Mappings' anchor='mappings'>
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<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 <key> attribute and initialization vector from the <iv> 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>
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</section1>
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<section1 topic='Limitaions' anchor='limitations'>
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<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>
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<p>Since OMEMO deviceIds are not bound to XMPP resources, the initiator MUST encrypt the Transport Key for every device of the recipient.</p>
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</section1>
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<section1 topic='Key Transport' anchor='transport'>
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<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 <security> 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>
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<p></p>
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<example caption="Romeo initiates an OMEMO encrypted file offer"><![CDATA[
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<iq from='romeo@montague.example/dr4hcr0st3lup4c'
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id='nzu25s8'
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to='juliet@capulet.example/yn0cl4bnw0yr3vym'
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type='set'>
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<jingle xmlns='urn:xmpp:jingle:1'
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action='session-initiate'
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initiator='romeo@montague.example/dr4hcr0st3lup4c'
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sid='851ba2'>
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<content creator='initiator' name='a-file-offer' senders='initiator'>
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<description xmlns='urn:xmpp:jingle:apps:file-transfer:5'>
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<file>
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<date>1969-07-21T02:56:15Z</date>
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<desc>This is a test. If this were a real file...</desc>
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<media-type>text/plain</media-type>
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<name>test.txt</name>
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<range/>
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<size>6144</size>
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<hash xmlns='urn:xmpp:hashes:2'
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algo='sha-1'>w0mcJylzCn+AfvuGdqkty2+KP48=</hash>
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</file>
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</description>
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<transport xmlns='urn:xmpp:jingle:transports:s5b:1'
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mode='tcp'
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sid='vj3hs98y'>
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<candidate cid='hft54dqy'
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host='192.168.4.1'
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jid='romeo@montague.example/dr4hcr0st3lup4c'
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port='5086'
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priority='8257636'
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type='direct'/>
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</transport>
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<security xmlns='urn:xmpp:jingle:jet:0'
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name='a-file-offer'
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cipher='urn:xmpp:ciphers:aes-128-gcm-nopadding'
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type='eu.siacs.conversations.axolotl'>
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<encrypted xmlns='eu.siacs.conversations.axolotl'>
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<header sid='27183'>
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<key rid='31415'>BASE64ENCODED...</key>
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<key prekey="true" rid='12321'>BASE64ENCODED...</key>
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<!-- ... -->
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<iv>BASE64ENCODED...</iv>
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</header>
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</encrypted>
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</security>
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</content>
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</jingle>
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</iq>]]></example>
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<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>
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</section1>
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<section1 topic='Determining Support' anchor='support'>
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<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>
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<example caption="Service discovery information request"><![CDATA[
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<iq from='romeo@montague.example/dr4hcr0st3lup4c'
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id='uw72g176'
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to='juliet@capulet.example/yn0cl4bnw0yr3vym'
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type='get'>
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<query xmlns='http://jabber.org/protocol/disco#info'/>
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</iq>]]></example>
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<example caption="Service discovery information response"><![CDATA[
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<iq from='juliet@capulet.example/yn0cl4bnw0yr3vym'
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id='uw72g176'
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to='romeo@montague.example/dr4hcr0st3lup4c'
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type='result'>
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<query xmlns='http://jabber.org/protocol/disco#info'>
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<feature var='urn:xmpp:jingle:jet:0'/>
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<feature var='urn:xmpp:jingle:jet-omemo:0'/>
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</query>
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</iq>]]></example>
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<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>
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</section1>
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</xep>
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