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409 lines
15 KiB
XML
409 lines
15 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE xep SYSTEM 'xep.dtd' [
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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>Instant Stream Resumption</title>
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<abstract>This specification introduces a mechanism for instant
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stream resumption, based on Stream Management (XEP-0198), allowing
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XMPP entities to instantaneously resume an XMPP stream.</abstract>
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<legal>
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<copyright>This XMPP Extension Protocol is copyright (c) 1999 -
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2016 by the XMPP Standards Foundation (XSF).</copyright>
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<permissions>Permission is hereby granted, free of charge, to any
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person obtaining a copy of this specification (the
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"Specification"), to make use of the Specification
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without restriction, including without limitation the rights to
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implement the Specification in a software program, deploy the
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Specification in a network service, and copy, modify, merge,
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publish, translate, distribute, sublicense, or sell copies of the
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Specification, and to permit persons to whom the Specification is
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furnished to do so, subject to the condition that the foregoing
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copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Specification. Unless
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separate permission is granted, modified works that are
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redistributed shall not contain misleading information regarding
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the authors, title, number, or publisher of the Specification, and
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shall not claim endorsement of the modified works by the authors,
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any organization or project to which the authors belong, or the
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XMPP Standards Foundation.</permissions>
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<warranty>## NOTE WELL: This Specification is provided on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, express or implied, including, without limitation, any
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warranties or conditions of TITLE, NON-INFRINGEMENT,
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MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. In no event
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shall the XMPP Standards Foundation or the authors of this
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Specification be liable for any claim, damages, or other
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liability, whether in an action of contract, tort, or otherwise,
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arising from, out of, or in connection with the Specification or
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the implementation, deployment, or other use of the
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Specification. ##</warranty>
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<liability>In no event and under no legal theory, whether in tort
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(including negligence), contract, or otherwise, unless required by
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applicable law (such as deliberate and grossly negligent acts) or
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agreed to in writing, shall the XMPP Standards Foundation or any
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author of this Specification be liable for damages, including any
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direct, indirect, special, incidental, or consequential damages of
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any character arising out of the use or inability to use the
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Specification (including but not limited to damages for loss of
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goodwill, work stoppage, computer failure or malfunction, or any
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and all other commercial damages or losses), even if the XMPP
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Standards Foundation or such author has been advised of the
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possibility of such damages.</liability>
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<conformance>This XMPP Extension Protocol has been contributed in
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full conformance with the XSF's Intellectual Property Rights
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Policy (a copy of which may be found at <<link
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url='http://xmpp.org/extensions/ipr-policy.shtml'>http://xmpp.org/extensions/ipr-policy.shtml</link>>
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or obtained by writing to XSF, P.O. Box 1641, Denver, CO 80201
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USA).</conformance>
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</legal>
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<number>xxxx</number>
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<status>ProtoXEP</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>XMPP Core</spec>
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<spec>XEP-0198</spec>
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<spec>XEP-0300</spec>
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</dependencies>
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<supersedes/>
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<supersededby/>
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<shortname>isr</shortname>
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<author>
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<firstname>Florian</firstname>
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<surname>Schmaus</surname>
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<email>flo@geekplace.eu</email>
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<jid>flo@geekplace.eu</jid>
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</author>
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<revision>
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<version>0.0.2</version>
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<date>2016-03-11</date>
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<initials>fs</initials>
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<remark><p>Second draft.</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>2016-02-12</date>
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<initials>fs</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>This XEP specifies an instant stream resumption mechanism based
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on &xep0198;, allowing XMPP entities to instantaneously resume an
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XMPP stream. This can be seen as the complementary part to &xep0305;
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allowing for fast XMPP session (re-)establishment.</p>
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<p>Compared to the existing stream resumption mechanism of <link
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url='http://xmpp.org/extensions/xep-0198.html#resumption'><cite>XEP-0198</cite>
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§ 5</link>, the approach defined herein reduces the round trips
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required to resume a stream to exactly <em>one</em> (besides the
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round trips required by the TLS handshake). This is achieved by
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using just a secure key to resume the stream.</p>
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</section1>
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<section1 topic='Glossary' anchor='glossary'>
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<dl>
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<di>
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<dt>ISR</dt>
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<dd>Instant Stream Resumption.</dd>
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</di>
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<di>
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<dt>Instant Stream Resumption Key (ISR Key)</dt>
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<dd>A key, represented as string, which contains at least 128
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bits of entropy generated by a cryptographically secure random
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number generator.</dd>
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</di>
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<di>
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<dt>TLS</dt>
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<dd>Transport Layer Security (&rfc5246;).</dd>
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</di>
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</dl>
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</section1>
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<!--
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<section1 topic='Use Cases' anchor='usecases'>
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<p>STRONGLY RECOMMENDED.</p>
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</section1>
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-->
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<section1 topic='Obtaining a Instant Stream Resumption Key' anchor='obtain'>
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<p>If an entity supports ISR, then the <enabled/>
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Nonza<note>XEP-0360: Nonzas (are not Stanzas) <<link
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url='https://xmpp.org/extensions/xep-0360.html'>https://xmpp.org/extensions/xep-0360.html</link>>.</note>,
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which is send as positive reply upon a request to enable Stream
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Management, MUST contain an 'key' attribute qualified by the
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'urn:xmpp:isr:0' namespace containing a ISR Key. The Nonza MAY
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also contain a 'location' attribute qualified by the
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'urn:xmpp:isr:0' namespace which specifies the preferred IP address
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or hostname, and a TCP port number of the host which should be used
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for instant stream resumption.</p>
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<example caption='An <enabled/> Nonza with a ISR key'><![CDATA[
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<enabled
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xmlns='urn:xmpp:sm:3'
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xmlns:isr='urn:xmpp:isr:0'
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isr:key='a0b9162d-0981-4c7d-9174-1f55aedd1f52'/>]]></example>
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<example caption='An <enabled/> Nonza with a ISR key and location'><![CDATA[
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<enabled
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xmlns='urn:xmpp:sm:3'
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xmlns:isr='urn:xmpp:isr:0'
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isr:key='a0b9162d-0981-4c7d-9174-1f55aedd1f52'
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isr:location='isr.example.org:5222'/>]]></example>
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</section1>
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<section1 topic='Instant Stream Resumption' anchor='isr'>
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<p>In order to instantaneously resume an XMPP stream the initiating
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entity, which is either an XMPP client or server, must posses a
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valid ISR key. After it has obtained the ISR key, using the process
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described in the previous section, it first determines the host for
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resumption, and after that, tries to perform the instant stream
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resumption.</p>
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<section2 topic='Determing the Host for Resumption' anchor='host'>
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<p>The lookup mechanism order to determine host candidates for ISR
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resumption is as follows:</p>
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<ol>
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<li>The host provided in the optional 'location' attribute
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qualified by the 'urn:xmpp:isr:0' namespace found in the
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<enabled/> element of <cite>XEP-0198</cite> (the
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"isr:location").
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</li>
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<li>The hosts determined by means of &xep0368;.</li>
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<li>The host announced in the 'location' attribute of the
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<enabled/> Nonza defined in <cite>XEP-0198</cite>.</li>
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<li>Standard host lookup mechanisms.</li>
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</ol>
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<p>The host candidates retrieved by those mechanisms SHOULD be
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tried by the initiating entity in this order.</p>
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<p>Note that the hosts announced by the 'location' attribute
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qualified by the 'urn:xmpp:isr:0' namespace MUST be connected to
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using TLS from the beginning, i.e. <starttls/> MUST NOT be
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used, instead the TLS handshake is performed right after
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establishing the connection.</p>
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<p>This order prefers hosts which allow connections where TLS is
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enabled from the beginning. This is desirable to reduce the
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required round trips by skipping the <starttls/> step.</p>
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</section2>
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<section2 topic='Performing Instant Stream Resumption' anchor='resume'>
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<p>After the remote host on which the instant stream resumption
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should be performed was determined, the initiating entity connects
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to the host, and establishes TLS by either</p>
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<ol>
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<li>establishing a TLS session right away, or</li>
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<li>performing STARTTLS (&rfc6120; § 5).</li>
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</ol>
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<p>Next, the initiating entity sends an XMPP <stream> open
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element followed by a <instant-resume/> Nonza qualified by
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the 'urn:xmpp:isr:0' namespace which MUST contain the previous
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stream identifier, the <cite>XEP-0198</cite> "SM-ID", in the
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'previd' attribute, the sequence number of the last by Stream
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Management handled stanza in the 'h' attribute and the
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initiator-hmac as value of at least one <hash/> element as
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specified by &xep0300;, which are put as child elements under the
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<hmac/> element.</p>
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<p>The initiator-hmac is defined as follows:</p>
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<p class='box'>
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initiator-hamc = Base64(HMAC(key, "Initiator" ||
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tls-server-end-point))
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</p>
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<p>The function defined in &rfc2104; is used to compute the HMAC
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using the hash algorithm specified in the 'algo' attribute of the
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<hash/> element as the cryptographic hash function H. The
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ISR Key is used as key of the HMAC. And the bytewise concatnation
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of the ASCII String "Initiator" and the bytes from
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tls-server-end-point, which a TLS Channel Binding defined in
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&rfc5929; § 4, is used a the HMAC text. The resulting bytes of the
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HMAC function are encoded using Base64 as defined in &rfc4648;
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<link url='https://tools.ietf.org/html/rfc4648#section-4'>§
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4</link> and resulting string is used as text value of the
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<hash/> element.</p>
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<p>Note that the initiating entity SHOULD pipeline the instant
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stream resumption request together with then initial
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<stream> open element. The initiating entity is able to do
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so since it already knows that the service supports ISR because it
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announced an ISR key. Servers MUST nevertheless announce that they
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support ISR by including an <isr/> element qualified by the
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'urn:xmpp:isr:0' namespace in their stream features.</p>
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<example caption='Initiating entity requests instant stream resumption'><![CDATA[
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<stream:stream
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from='juliet@im.example.com'
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to='im.example.com'
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version='1.0'
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xml:lang='en'
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xmlns='jabber:client'
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xmlns:stream='http://etherx.jabber.org/streams'>
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<inst-resume
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xmlns='urn:xmpp:isr:0'
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previd='some-long-sm-id'
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h='42'>
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<hmac>
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<hash xmlns='urn:xmpp:hashes:1' algo='sha256'>
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initator-hmac
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</hash>
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</hmac>
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</inst-resume>]]></example>
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<p>ISR MUST only be performed over TLS secured sessions. What
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follows is that the ISR feature MUST only be announced after
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STARTTLS has been successfully performed or on streams where TLS
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was established from the beginning.</p>
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<section3 topic='Successful Stream Resumption' anchor='isr-success'>
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<p>On success the server replies with <inst-resumed/>
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Nonza which MUST contain a <em>new</em> ISR Key found in the
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'key' attribute, the sequence number of the last by Stream
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Mangement handled stanza in the 'h' attribute and the
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'responder-hmac' as value of the <hash/> element being a
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child of the <hamc/> element.</p>
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<p>The responder-hmac is defined as follows:</p>
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<p class='box'>
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responder-hmac = Base64(HMAC(key, "Responder" ||
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tls-server-end-point))
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</p>
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<p>That is, it is the same as the initiator-hamc, but instead of
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using the ASCII string "Initiator", the ASCII string "Responder"
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is used.</p>
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<p>The initiating entity is required to verify the
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responder-hmac achieve mutual authentication.</p>
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<example caption='Server acknowledges instant stream resumption'><![CDATA[
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<stream:stream
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from='im.example.com'
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id='t7AMCin9zjMNwQKDnplntZPIDEI='
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to='juliet@im.example.com'
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version='1.0'
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xml:lang='en'
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xmlns='jabber:client'
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xmlns:stream='http://etherx.jabber.org/streams'>
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<stream:features>
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<isr xmlns='urn:xmpp:isr:0'/>
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</stream:features>
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<inst-resumed
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xmlns='urn:xmpp:isr:0'
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key='006b1a29-c549-41c7-a12c-2a931822f8c0'
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h='21'>
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<hmac>
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<hash xmlns='urn:xmpp:hashes:1' algo='sha-256'>
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responder-hmac
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</hash>
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</hmac>
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</inst-resumed>]]></example>
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<p>After the <inst-resumed/> was received and has been
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verified both entities MUST consider the resumed stream to be
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re-established. This includes all previously negotiated stream
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features like &xep0138;. It does however not include the
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specific state of the features: For example in case of Stream
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Compression, the dictionary used by the compression mechanism of
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the resumed stream MUST NOT be considered to be restored after
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instant stream resumption.</p>
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</section3>
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<section3 topic='Failed Stream Resumptino' anchor='isr-failed'>
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<p>If the server is unable to resume the stream instantly it
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MUST reply with a <failed/> Nonza qualified by the
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'urn:xmpp:isr:0' namespace.</p>
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<example caption='Server indicates instant stream resumption failure'><![CDATA[
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<failed
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xmlns='urn:xmpp:isr:0'/>]]></example>
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<p>The server MAY also include a 'h' attribute in the
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<failed/> element indicating the number of stanzas it has
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handled so far.</p>
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<example caption='Server indicates failure with handled stanzas count'><![CDATA[
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<failed
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xmlns='urn:xmpp:isr:0'
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h='22'/>]]></example>
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<p>Instant stream resumption errors SHOULD be considered
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recoverable, the initiating entity MAY continue with normal
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session establishment; however, misuse of stream management MAY
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result in termination of the stream.</p>
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</section3>
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</section2>
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</section1>
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<section1 topic='Security Considerations' anchor='security'>
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<p>It is of vital importance that the Instant Stream Resumption Key
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is generated by a cryptographically secure random generator. See
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&rfc4086; for more information about Randomness Requirements for
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Security</p>
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</section1>
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<section1 topic='IANA Considerations' anchor='iana'>
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<p>This document requires no interaction with &IANA;.</p>
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</section1>
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<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
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<p>The ®ISTRAR; includes 'urn:xmpp:isr:0' in its registry of protocol namespaces (see &NAMESPACES;).</p>
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</section1>
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<section1 topic='XML Schema' anchor='schema'>
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<p>TODO: Add after the XEP leaves the 'experimental' state.</p>
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</section1>
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<section1 topic='Acknowledgements' anchor='acknowledgements'>
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<p>Thanks to Jonas Wielicki and Thijs Alkemade for their feedback.</p>
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</section1>
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</xep>
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