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xeps/inbox/isr.xml
2016-03-15 11:25:06 -05:00

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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
<title>Instant Stream Resumption</title>
<abstract>This specification introduces a mechanism for instant
stream resumption, based on Stream Management (XEP-0198), allowing
XMPP entities to instantaneously resume an XMPP stream.</abstract>
<legal>
<copyright>This XMPP Extension Protocol is copyright (c) 1999 -
2016 by the XMPP Standards Foundation (XSF).</copyright>
<permissions>Permission is hereby granted, free of charge, to any
person obtaining a copy of this specification (the
&quot;Specification&quot;), to make use of the Specification
without restriction, including without limitation the rights to
implement the Specification in a software program, deploy the
Specification in a network service, and copy, modify, merge,
publish, translate, distribute, sublicense, or sell copies of the
Specification, and to permit persons to whom the Specification is
furnished to do so, subject to the condition that the foregoing
copyright notice and this permission notice shall be included in
all copies or substantial portions of the Specification. Unless
separate permission is granted, modified works that are
redistributed shall not contain misleading information regarding
the authors, title, number, or publisher of the Specification, and
shall not claim endorsement of the modified works by the authors,
any organization or project to which the authors belong, or the
XMPP Standards Foundation.</permissions>
<warranty>## NOTE WELL: This Specification is provided on an
&quot;AS IS&quot; BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, express or implied, including, without limitation, any
warranties or conditions of TITLE, NON-INFRINGEMENT,
MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. In no event
shall the XMPP Standards Foundation or the authors of this
Specification be liable for any claim, damages, or other
liability, whether in an action of contract, tort, or otherwise,
arising from, out of, or in connection with the Specification or
the implementation, deployment, or other use of the
Specification. ##</warranty>
<liability>In no event and under no legal theory, whether in tort
(including negligence), contract, or otherwise, unless required by
applicable law (such as deliberate and grossly negligent acts) or
agreed to in writing, shall the XMPP Standards Foundation or any
author of this Specification be liable for damages, including any
direct, indirect, special, incidental, or consequential damages of
any character arising out of the use or inability to use the
Specification (including but not limited to damages for loss of
goodwill, work stoppage, computer failure or malfunction, or any
and all other commercial damages or losses), even if the XMPP
Standards Foundation or such author has been advised of the
possibility of such damages.</liability>
<conformance>This XMPP Extension Protocol has been contributed in
full conformance with the XSF's Intellectual Property Rights
Policy (a copy of which may be found at &lt;<link
url='http://xmpp.org/extensions/ipr-policy.shtml'>http://xmpp.org/extensions/ipr-policy.shtml</link>&gt;
or obtained by writing to XSF, P.O. Box 1641, Denver, CO 80201
USA).</conformance>
</legal>
<number>xxxx</number>
<status>ProtoXEP</status>
<type>Standards Track</type>
<sig>Standards</sig>
<approver>Council</approver>
<dependencies>
<spec>XMPP Core</spec>
<spec>XEP-0198</spec>
<spec>XEP-0300</spec>
</dependencies>
<supersedes/>
<supersededby/>
<shortname>isr</shortname>
<author>
<firstname>Florian</firstname>
<surname>Schmaus</surname>
<email>flo@geekplace.eu</email>
<jid>flo@geekplace.eu</jid>
</author>
<revision>
<version>0.0.2</version>
<date>2016-03-11</date>
<initials>fs</initials>
<remark><p>Second draft.</p></remark>
</revision>
<revision>
<version>0.0.1</version>
<date>2016-02-12</date>
<initials>fs</initials>
<remark><p>First draft.</p></remark>
</revision>
</header>
<section1 topic='Introduction' anchor='intro'>
<p>This XEP specifies an instant stream resumption mechanism based
on &xep0198;, allowing XMPP entities to instantaneously resume an
XMPP stream. This can be seen as the complementary part to &xep0305;
allowing for fast XMPP session (re-)establishment.</p>
<p>Compared to the existing stream resumption mechanism of <link
url='http://xmpp.org/extensions/xep-0198.html#resumption'><cite>XEP-0198</cite>
§ 5</link>, the approach defined herein reduces the round trips
required to resume a stream to exactly <em>one</em> (besides the
round trips required by the TLS handshake). This is achieved by
using just a secure key to resume the stream.</p>
</section1>
<section1 topic='Glossary' anchor='glossary'>
<dl>
<di>
<dt>ISR</dt>
<dd>Instant Stream Resumption.</dd>
</di>
<di>
<dt>Instant Stream Resumption Key (ISR Key)</dt>
<dd>A key, represented as string, which contains at least 128
bits of entropy generated by a cryptographically secure random
number generator.</dd>
</di>
<di>
<dt>TLS</dt>
<dd>Transport Layer Security (&rfc5246;).</dd>
</di>
</dl>
</section1>
<!--
<section1 topic='Use Cases' anchor='usecases'>
<p>STRONGLY RECOMMENDED.</p>
</section1>
-->
<section1 topic='Obtaining a Instant Stream Resumption Key' anchor='obtain'>
<p>If an entity supports ISR, then the &lt;enabled/&gt;
Nonza<note>XEP-0360: Nonzas (are not Stanzas) &lt;<link
url='https://xmpp.org/extensions/xep-0360.html'>https://xmpp.org/extensions/xep-0360.html</link>&gt;.</note>,
which is send as positive reply upon a request to enable Stream
Management, MUST contain an 'key' attribute qualified by the
'urn:xmpp:isr:0' namespace containing a ISR Key. The Nonza MAY
also contain a 'location' attribute qualified by the
'urn:xmpp:isr:0' namespace which specifies the preferred IP address
or hostname, and a TCP port number of the host which should be used
for instant stream resumption.</p>
<example caption='An &lt;enabled/&gt; Nonza with a ISR key'><![CDATA[
<enabled
xmlns='urn:xmpp:sm:3'
xmlns:isr='urn:xmpp:isr:0'
isr:key='a0b9162d-0981-4c7d-9174-1f55aedd1f52'/>]]></example>
<example caption='An &lt;enabled/&gt; Nonza with a ISR key and location'><![CDATA[
<enabled
xmlns='urn:xmpp:sm:3'
xmlns:isr='urn:xmpp:isr:0'
isr:key='a0b9162d-0981-4c7d-9174-1f55aedd1f52'
isr:location='isr.example.org:5222'/>]]></example>
</section1>
<section1 topic='Instant Stream Resumption' anchor='isr'>
<p>In order to instantaneously resume an XMPP stream the initiating
entity, which is either an XMPP client or server, must posses a
valid ISR key. After it has obtained the ISR key, using the process
described in the previous section, it first determines the host for
resumption, and after that, tries to perform the instant stream
resumption.</p>
<section2 topic='Determing the Host for Resumption' anchor='host'>
<p>The lookup mechanism order to determine host candidates for ISR
resumption is as follows:</p>
<ol>
<li>The host provided in the optional 'location' attribute
qualified by the 'urn:xmpp:isr:0' namespace found in the
&lt;enabled/&gt; element of <cite>XEP-0198</cite> (the
"isr:location").
</li>
<li>The hosts determined by means of &xep0368;.</li>
<li>The host announced in the 'location' attribute of the
&lt;enabled/&gt; Nonza defined in <cite>XEP-0198</cite>.</li>
<li>Standard host lookup mechanisms.</li>
</ol>
<p>The host candidates retrieved by those mechanisms SHOULD be
tried by the initiating entity in this order.</p>
<p>Note that the hosts announced by the 'location' attribute
qualified by the 'urn:xmpp:isr:0' namespace MUST be connected to
using TLS from the beginning, i.e. &lt;starttls/&gt; MUST NOT be
used, instead the TLS handshake is performed right after
establishing the connection.</p>
<p>This order prefers hosts which allow connections where TLS is
enabled from the beginning. This is desirable to reduce the
required round trips by skipping the &lt;starttls/&gt; step.</p>
</section2>
<section2 topic='Performing Instant Stream Resumption' anchor='resume'>
<p>After the remote host on which the instant stream resumption
should be performed was determined, the initiating entity connects
to the host, and establishes TLS by either</p>
<ol>
<li>establishing a TLS session right away, or</li>
<li>performing STARTTLS (&rfc6120; § 5).</li>
</ol>
<p>Next, the initiating entity sends an XMPP &lt;stream&gt; open
element followed by a &lt;instant-resume/&gt; Nonza qualified by
the 'urn:xmpp:isr:0' namespace which MUST contain the previous
stream identifier, the <cite>XEP-0198</cite> "SM-ID", in the
'previd' attribute, the sequence number of the last by Stream
Management handled stanza in the 'h' attribute and the
initiator-hmac as value of at least one &lt;hash/&gt; element as
specified by &xep0300;, which are put as child elements under the
&lt;hmac/&gt; element.</p>
<p>The initiator-hmac is defined as follows:</p>
<p class='box'>
initiator-hamc = Base64(HMAC(key, "Initiator" ||
tls-server-end-point))
</p>
<p>The function defined in &rfc2104; is used to compute the HMAC
using the hash algorithm specified in the 'algo' attribute of the
&lt;hash/&gt; element as the cryptographic hash function H. The
ISR Key is used as key of the HMAC. And the bytewise concatnation
of the ASCII String "Initiator" and the bytes from
tls-server-end-point, which a TLS Channel Binding defined in
&rfc5929; § 4, is used a the HMAC text. The resulting bytes of the
HMAC function are encoded using Base64 as defined in &rfc4648;
<link url='https://tools.ietf.org/html/rfc4648#section-4'>§
4</link> and resulting string is used as text value of the
&lt;hash/&gt; element.</p>
<p>Note that the initiating entity SHOULD pipeline the instant
stream resumption request together with then initial
&lt;stream&gt; open element. The initiating entity is able to do
so since it already knows that the service supports ISR because it
announced an ISR key. Servers MUST nevertheless announce that they
support ISR by including an &lt;isr/&gt; element qualified by the
'urn:xmpp:isr:0' namespace in their stream features.</p>
<example caption='Initiating entity requests instant stream resumption'><![CDATA[
<stream:stream
from='juliet@im.example.com'
to='im.example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<inst-resume
xmlns='urn:xmpp:isr:0'
previd='some-long-sm-id'
h='42'>
<hmac>
<hash xmlns='urn:xmpp:hashes:1' algo='sha256'>
initator-hmac
</hash>
</hmac>
</inst-resume>]]></example>
<p>ISR MUST only be performed over TLS secured sessions. What
follows is that the ISR feature MUST only be announced after
STARTTLS has been successfully performed or on streams where TLS
was established from the beginning.</p>
<section3 topic='Successful Stream Resumption' anchor='isr-success'>
<p>On success the server replies with &lt;inst-resumed/&gt;
Nonza which MUST contain a <em>new</em> ISR Key found in the
'key' attribute, the sequence number of the last by Stream
Mangement handled stanza in the 'h' attribute and the
'responder-hmac' as value of the &lt;hash/&gt; element being a
child of the &lt;hamc/&gt; element.</p>
<p>The responder-hmac is defined as follows:</p>
<p class='box'>
responder-hmac = Base64(HMAC(key, "Responder" ||
tls-server-end-point))
</p>
<p>That is, it is the same as the initiator-hamc, but instead of
using the ASCII string "Initiator", the ASCII string "Responder"
is used.</p>
<p>The initiating entity is required to verify the
responder-hmac achieve mutual authentication.</p>
<example caption='Server acknowledges instant stream resumption'><![CDATA[
<stream:stream
from='im.example.com'
id='t7AMCin9zjMNwQKDnplntZPIDEI='
to='juliet@im.example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:features>
<isr xmlns='urn:xmpp:isr:0'/>
</stream:features>
<inst-resumed
xmlns='urn:xmpp:isr:0'
key='006b1a29-c549-41c7-a12c-2a931822f8c0'
h='21'>
<hmac>
<hash xmlns='urn:xmpp:hashes:1' algo='sha-256'>
responder-hmac
</hash>
</hmac>
</inst-resumed>]]></example>
<p>After the &lt;inst-resumed/&gt; was received and has been
verified both entities MUST consider the resumed stream to be
re-established. This includes all previously negotiated stream
features like &xep0138;. It does however not include the
specific state of the features: For example in case of Stream
Compression, the dictionary used by the compression mechanism of
the resumed stream MUST NOT be considered to be restored after
instant stream resumption.</p>
</section3>
<section3 topic='Failed Stream Resumptino' anchor='isr-failed'>
<p>If the server is unable to resume the stream instantly it
MUST reply with a &lt;failed/&gt; Nonza qualified by the
'urn:xmpp:isr:0' namespace.</p>
<example caption='Server indicates instant stream resumption failure'><![CDATA[
<failed
xmlns='urn:xmpp:isr:0'/>]]></example>
<p>The server MAY also include a 'h' attribute in the
&lt;failed/&gt; element indicating the number of stanzas it has
handled so far.</p>
<example caption='Server indicates failure with handled stanzas count'><![CDATA[
<failed
xmlns='urn:xmpp:isr:0'
h='22'/>]]></example>
<p>Instant stream resumption errors SHOULD be considered
recoverable, the initiating entity MAY continue with normal
session establishment; however, misuse of stream management MAY
result in termination of the stream.</p>
</section3>
</section2>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<p>It is of vital importance that the Instant Stream Resumption Key
is generated by a cryptographically secure random generator. See
&rfc4086; for more information about Randomness Requirements for
Security</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
<p>This document requires no interaction with &IANA;.</p>
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
<p>The &REGISTRAR; includes 'urn:xmpp:isr:0' in its registry of protocol namespaces (see &NAMESPACES;).</p>
</section1>
<section1 topic='XML Schema' anchor='schema'>
<p>TODO: Add after the XEP leaves the 'experimental' state.</p>
</section1>
<section1 topic='Acknowledgements' anchor='acknowledgements'>
<p>Thanks to Jonas Wielicki and Thijs Alkemade for their feedback.</p>
</section1>
</xep>