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xep-0374.xml 9.4KB

  1. <?xml version='1.0' encoding='UTF-8'?>
  2. <!DOCTYPE xep SYSTEM 'xep.dtd' [
  3. <!ENTITY signcrypt "&lt;signcrypt/&gt;">
  4. <!ENTITY sign "&lt;sign/&gt;">
  5. <!ENTITY crypt "&lt;crypt/&gt;">
  6. <!ENTITY openpgp "&lt;openpgp/&gt;">
  7. <!ENTITY payload "&lt;payload/&gt;">
  8. <!ENTITY rfc3629 "<span class='ref'><link url=''>RFC 3629</link></span> <note>RFC 3629: UTF-8, a transformation format of ISO 10646 &lt;<link url=''></link>&gt;.</note>" >
  9. <!ENTITY % ents SYSTEM 'xep.ent'>
  10. %ents;
  11. ]>
  12. <?xml-stylesheet type='text/xsl' href='xep.xsl'?>
  13. <xep>
  14. <header>
  15. <title>OpenPGP for XMPP Instant Messaging</title>
  16. <abstract>Specifies a OpenPGP for XMPP (XEP-0373) profile for the Instant
  17. Messaging (IM) use case.</abstract>
  19. <number>0374</number>
  20. <status>Deferred</status>
  21. <type>Standards Track</type>
  22. <sig>Standards</sig>
  23. <approver>Council</approver>
  24. <dependencies>
  25. <spec>XMPP Core</spec>
  26. <spec>XEP-0030</spec>
  27. <spec>XEP-0373</spec>
  28. </dependencies>
  29. <supersedes/>
  30. <supersededby/>
  31. <shortname>oxim</shortname>
  32. &flow;
  33. <author>
  34. <firstname>Dominik</firstname>
  35. <surname>Schürmann</surname>
  36. <email></email>
  37. <jid></jid>
  38. </author>
  39. <author>
  40. <firstname>Vincent</firstname>
  41. <surname>Breitmoser</surname>
  42. <email></email>
  43. <jid></jid>
  44. </author>
  45. <revision>
  46. <version>0.2.0</version>
  47. <date>2018-01-25</date>
  48. <initials>XEP Editor (jwi)</initials>
  49. <remark>Defer due to lack of activity.</remark>
  50. </revision>
  51. <revision>
  52. <version>0.1.2</version>
  53. <date>2017-01-20</date>
  54. <initials>fs</initials>
  55. <remark><p>Make use of XEP-0380: Explicit Message Encryption.</p></remark>
  56. </revision>
  57. <revision>
  58. <version>0.1.1</version>
  59. <date>2016-06-04</date>
  60. <initials>fs</initials>
  61. <remark><p>Minior editorial fixes.</p></remark>
  62. </revision>
  63. <revision>
  64. <version>0.1</version>
  65. <date>2016-05-10</date>
  66. <initials>XEP Editor (ssw)</initials>
  67. <remark><p>Initial published version approved by the XMPP Council.</p></remark>
  68. </revision>
  69. <revision>
  70. <version>0.0.1</version>
  71. <date>2016-03-25</date>
  72. <initials>fs</initials>
  73. <remark><p>First draft.</p></remark>
  74. </revision>
  75. </header>
  76. <section1 topic='Introduction' anchor='intro'>
  77. <p>This XMPP extension protocol specifies a profile of &xep0373; for OpenPGP
  78. secured Instant Messaging (IM).</p>
  79. <p>Unlike similar XEPs, e.g., &xep0384;, this XEP <em>does not</em>
  80. provide Forward Secrecy (FS), but as an advantage in return, allows
  81. users to read their archived conversations (respectively their
  82. encrypted data) later on. Of course, only as long as they still
  83. possess the according secret key. FS and being able to decrypt
  84. archived messages are mutually exclusive, i.e., one can not have
  85. both. The authors therefore consider this XEP complementary to
  86. similar ones which also provide end-to-end encryption but with a
  87. different feature set.</p>
  88. </section1>
  89. <section1 topic='OX Instant Messaging Profile' anchor='ox-im-profile'>
  90. <section2 topic='Discovering Support' anchor='disco'>
  91. <p>If an entity supports exchanging OpenPGP encrypted and signed
  92. instant messages over XMPP, i.e., what is specified herein, it MUST
  93. advertise that fact by announcing a &xep0030; feature of
  94. 'urn:xmpp:openpgp:im:0'. It thus includes this feature in response
  95. to a service discovery request.</p>
  96. <example caption="Service Discovery information request"><![CDATA[
  97. <iq type='get'
  98. from=''
  99. to=''
  100. id='disco1'>
  101. <query xmlns=''/>
  102. </iq>]]></example>
  103. <example caption="Service Discovery information response"><![CDATA[
  104. <iq type='result'
  105. from=''
  106. to=''
  107. id='disco1'>
  108. <query xmlns=''>
  109. ...
  110. <feature var='urn:xmpp:openpgp:im:0'/>
  111. ...
  112. </query>
  113. </iq>]]></example>
  114. <p>Because of possible downgrade attacks, users should be given an
  115. option to force the usage of the protocol defined herein no matter
  116. if the remote announces support or not.</p>
  117. </section2>
  118. <section2 topic='OpenPGP Secured Instant Messaging' anchor='openpgp-secured-im'>
  119. <p>In order to establish an OpenPGP secured IM communication, IM
  120. clients first need to determine the public key of their
  121. interlocutor(s). OpenPGP historically provides public keyservers
  122. which can be used for key retrieval. Additional there are methods
  123. to store OpenPGP key information in the Domain Name
  124. System (DNS). This specification does not restrict the mechanism
  125. of key discovery and retrieval, but compliant clients MUST support
  126. the public key announcement as described in <cite>XEP-0373</cite>
  127. <link url='./xep-0373.html#announcing-discover-pubkey'>§ 4</link>.</p>
  128. <p>After the required public keys have been discovered, XMPP
  129. clients engage in an OpenPGP secured IM
  130. conversation by exchanging &openpgp; extension elements. They MUST
  131. use the &signcrypt; OpenPGP content element specified in
  132. <cite>XEP-0373</cite><link url='./xep-0373.html#exchange'>§ 3.1</link>.</p>
  133. <p>The child elements of the OpenPGP content element's &payload;
  134. can be seen as stanza extension elements which are encrypted and
  135. signed. After the &openpgp; element and the including &signcrypt;,
  136. element was verified, they SHOULD be processed similar as if they
  137. had been direct extension elements of the stanza. For example,
  138. direct child elements found in &payload; in the context of IM
  139. could be:</p>
  140. <ul>
  141. <li>Message bodies (&rfc6121; § 5.2.3): &lt;body xmlns='jabber:client'/&gt; </li>
  142. <li>&xep0085;: &lt;active xmlns=''/&gt;</li>
  143. <li>&xep0071;: &lt;html xmlns=''/&gt;</li>
  144. </ul>
  145. <p>But just as with stanza extension elements, child elements of
  146. &payload; can be any extension element. The example above uses
  147. the &lt;body/&gt; element as defined in RFC 6121. Note that it
  148. uses 'jabber:client' as namespace, but since the same
  149. &lt;body/&gt; element is also defined in the 'jabber:server'
  150. namespace, recipients MUST accept both.</p>
  151. </section2>
  152. <section2 topic='OpenPGP Key Handling' anchor='openpgp-key-handling'>
  153. <section3 topic='Choosing Public Keys' anchor='choose-pubkey'>
  154. <p>Clients MUST expect multiple public keys to be announced for a single remote entity. In this case all keys MUST be used for encryption.</p>
  155. </section3>
  156. <section3 topic='OpenPGP Secret Key Synchronization' anchor='openpgp-secret-key-sync'>
  157. <p>Clients MAY want to use the mechanism in <cite>XEP-0373 § 5</cite> to
  158. synchronize their secret key(s) over multiple devices. Thus, they
  159. should query the user's PEP service for an eventually stored
  160. encrypted secret key.</p>
  161. </section3>
  162. </section2>
  163. </section1>
  164. <section1 topic='Business Rules' anchor='rules'>
  165. <section2 topic='Always Use &signcrypt;' anchor='signcrypt-im-use-case'>
  166. <p>Only &signcrypt; MUST be used for the IM
  167. use case. Encrypted but unsigned messages (&crypt;) do not provide
  168. an advantage over unencrypted ones since the sender can not be
  169. verified. As result of this rule, the user interface of
  170. IM clients implementing the protocol defined herein MUST NOT
  171. provide an option for the user to select between sign+crypt, sign
  172. or crypt. This also increases the usability.</p>
  173. </section2>
  174. <section2 topic='Provide Hints' anchor='hint-im-use-case'>
  175. <p>In the IM use case every &MESSAGE; equipped with &openpgp;
  176. SHOULD include an unencrypted &lt;body/&gt; explaining that the actual
  177. message is encrypted. Furthermore the message SHOULD contain a
  178. 'store' hint as defined in &xep0334; <link
  179. url=''>§
  180. 4.4</link> and a "this message contains an encrypted body text" hint
  181. in form of an &lt;encryption/&gt; extension element as specified by
  182. &xep0380;.</p>
  183. <example caption='An encrypted and signed message with hints.'><![CDATA[
  184. <message to=''>
  185. <body>This message is encrypted using OpenPGP.</body>
  186. <store xmlns='urn:xmpp:hints'/>
  187. <encryption xmlns='urn:xmpp:eme:0' namespace='urn:xmpp:openpgp:0'/>
  188. <openpgp xmlns='urn:xmpp:openpgp:0'>
  190. </openpgp>
  191. </message>]]></example>
  192. </section2>
  193. </section1>
  194. <section1 topic='IANA Considerations' anchor='iana'>
  195. <p>This document requires no interaction with &IANA;.</p>
  196. </section1>
  197. <section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  198. <section2 topic='Protocol Namespaces' anchor='registrar-ns'>
  199. <p>The &REGISTRAR; includes 'urn:xmpp:openpgp:0' in its registry of protocol namespaces (see &NAMESPACES;).</p>
  200. </section2>
  201. </section1>
  202. <section1 topic='XML Schema' anchor='schema'>
  203. <p>This XEP does not define a Schema, since it exclusively uses elements from
  204. <cite>XEP-0373</cite> and other XEPs.</p>
  205. </section1>
  206. <section1 topic='Acknowledgements' anchor='acknowledgements'>
  207. <p>
  208. Please refer to the
  209. <link url='./xep-0373.html#acknowledgements'>Acknowledgements section</link>
  210. of <cite>XEP-0373</cite> since the two XEPs where designed together.
  211. </p>
  212. </section1>
  213. </xep>