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xeps/xep-0440.xml
2020-06-14 14:52:16 +02:00

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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY rfc5056 "<span class='ref'><link url='http://tools.ietf.org/html/rfc5056'>RFC 5056</link></span> <note>RFC 5056: On the Use of Channel Bindings to Secure Channels &lt;<link url='http://tools.ietf.org/html/rfc5056'>http://tools.ietf.org/html/rfc5056</link>&gt;.</note>" >
<!ENTITY iana-cb-types "<span class='ref'><link url='https://www.iana.org/assignments/channel-binding-types/channel-binding-types.xhtml'>IANA Channel-Binding Types Registry</link></span> <note>IANA Channel-Binding Types Registry &lt;<link url='https://www.iana.org/assignments/channel-binding-types/channel-binding-types.xhtml'>https://www.iana.org/assignments/channel-binding-types/channel-binding-types.xhtml</link>&gt;.</note>" >
<!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
<title>SASL Channel-Binding Type Capability</title>
<abstract>This specification allows servers to annouce their supported SASL channel-binding types to clients.</abstract>
&LEGALNOTICE;
<number>0440</number>
<status>Experimental</status>
<type>Standards Track</type>
<sig>Standards</sig>
<approver>Council</approver>
<dependencies>
<spec>XMPP Core</spec>
</dependencies>
<supersedes/>
<supersededby/>
<shortname>sasl-cb-types</shortname>
&flow;
<revision>
<version>0.1.0</version>
<date>2020-06-14</date>
<initials>XEP Editor (jsc)</initials>
<remark>Accepted by vote of Council on 2020-05-27.</remark>
</revision>
<revision>
<version>0.0.1</version>
<date>2020-05-20</date>
<initials>fs</initials>
<remark><p>First draft.</p></remark>
</revision>
</header>
<section1 topic='Introduction' anchor='intro'>
<p>SASL channel-binding is a technique to increase the security of
connections (&rfc5056;). Unfortunately, the SASL profile specified
in &rfc6120; lacks a method for the server to announce its supported
channel-binding types. This hinders the adoption of channel-binding,
especially since the error protocol to execute after a client
requested a channel-binding type unsupported by the server is
basically unspecified.</p>
<p>The extension defined herein fills the gap left by &rfc6120;, by
allowing the server the announce its supported channel-binding
types.</p>
</section1>
<section1 topic='Announcing the SASL Channel-Binding Type Capability' anchor='sasl-cb-type'>
<p>This protocol consists of a single optional extension element
named 'sasl-channel-binding' qualified by the 'urn:xmpp:sasl-cb:0'
namespace. The 'sasl-channel-binding' element MUST contain one or
more 'channel-binding' elements, of which each MUST have an
attribute with the name 'type'. The value of the 'type' attribute
SHOULD be the "Channel-binding unique prefix" of a channel-binding
type which was registered with the &iana-cb-types;.</p>
<p>A server declares that it supports particular channel-binding
types by listing the supported types via the 'sasl-channel-binding'
element defined herein. The 'sasl-channel-binding' element could
appear as child element to the SASL &lt;mechanisms/&gt;
stream-feature element, qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace, as specified in
&rfc6120;. Another potential appearance of
&lt;sasl-channel-binding&gt; is as child element of the
&lt;mechanisms/&gt; stream-feature element as specified in the
&xep0388;.</p>
<example caption='Example &lt;mechanisms/&gt; stream feature with SASL Channel-Binding Type Capability.'><![CDATA[
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>EXTERNAL</mechanism>
<mechanism>SCRAM-SHA-1-PLUS</mechanism>
<mechanism>PLAIN</mechanism>
<sasl-channel-binding xmlns='urn:xmpp:sasl-cb:0'>
<channel-binding type='tls-server-end-point'/>
<channel-binding type='tls-exporter'/>
</sasl-channel-binding>
</mechanisms>
</stream:features>]]></example>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<p>The author belives that this document itself does not yield any
new security considerations.<note>Hopefully somebody will correct him, in
case he is wrong.</note></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>This document requires no interaction with the XMPP registrar.</p>
</section1>
<section1 topic='XML Schema' anchor='schema'>
<p>TODO: Add if the XEP is scheduled for the state after 'experimental'.</p>
</section1>
<section1 topic='Acknowledgements' anchor='acknowledgements'>
<p>Thanks to Sam Whited for the discussion about the underlying
issue and incentivizing me to come up with this extension.</p>
</section1>
</xep>