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Accept inbox/client-key.xml as XEP-0399

Jonas Wielicki 1 year ago
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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY namespace "urn:xmpp:client-key:0">
<!ENTITY draft "draft-cridland-kitten-clientkey-00.txt">
<!ENTITY % ents SYSTEM 'xep.ent'>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<title>Client Key Support</title>
<abstract>This specification defines an XMPP binding of the supporting functions for the CLIENT-KEY SASL mechanism.</abstract>
<type>Standards Track</type>
<initials>XEP Editor (jwi)</initials>
<remark>Accepted by vote of Council on 2018-01-10.</remark>
<remark><p>First draft</p></remark>
<section1 topic='Introduction' anchor='intro'>
<p>The CLIENT-KEY SASL mechanism defined in &draft; suggests supporting protocol messages to be present in the application protocol. This specification defines these for XMPP.</p>

<section1 topic="Typical Flow">
<p>A typical client might use this protocol alongside that of TOTP, &xep0388;, and &draft; as follows.</p>
<p>On first use, a client will use a traditional SASL mechanism using SASL2, such as SCRAM. The server will then prompt using &lt;next-authenticate/> to initiate, or perform, TOTP.</p>
<p>The client will then request a Client Key to reauthenticate later. This may be one or both of a short-term Client Key intended for in-memory storage, perhaps for use with ISR, and a longer-term Client Key used for a "remember this client" to suppress 2FA for a period.</p>
<p>Later authentications will use CLIENT-KEY or CLIENT-KEY-PLUS, and the server SHOULD suppress TOTP in such cases.</p>

<section1 topic="Client Key Support Operations">
<section2 topic="Client Registration">
<p>Client registration requests a Client Key from the server. It is typically used to speed reauthentication during a session, and to elide a full reauthentication at the start of a subsequent session.</p>
<p>In order to register and obtain a Client Key, a client sends an &IQ; of type "set" containing an XML representation of the data required, within a &lt;register/&gt; element qualified by the '&namespace;' namespace, containing four elements in any order. Descriptions of values are here informative; the canonical definition is in &draft;.</p>
<p>&lt;id/> has a text value of the ClientID, a suitable identifier for the client instance, unique within the scope of the authenticated &BAREJID;.</p>
<p>&lt;name/> has a text value of the Client Name, a human-readable name for the client instance.</p>
<p>&lt;key/> has a text value of the ValidationKey, encoded using Base 64. Implementors are strongly advised to take careful note of the requirements of the ValidationKey as discussed in &draft;.</p>
<p>&lt;ttl/> has a text value containing a integer string representation of the number of seconds the Client Key is requested to last for.</p>
<p>In the following example, the ValidationKey is H("Random"), and the TTL is for 30 days - a reasonable "Remember this client" option.</p>
<iq type='set' id='123456'>
<register xmlns=']]>&namespace;<![CDATA['>
<name>SuperChatBiscuit on Honest Pete's Mobile OS</name>
<p>The server responds with two items of information in a &lt;registered/> element qualified by the '&namespace;' namespace. The EncryptedSecret is contained within a &lt;encrypted-secret/> element as a base64-encoded value, and the &lt;expiry/> element contains a timestamp for expiry.</p>
<iq type='result' id='123456'>
<registered xmlns=']]>&namespace;<![CDATA['>
<p>Note that the expiry time might not be 30 days simply because the client has requested it - the server is free to shorten expiry times.</p>
<section2 topic="Key Revocation">
<p>Any authenticated client may revoke a key belonging to the same user by sending an &IQ; of type "set" containing a &lt;revoke/> element qualified by the '&namespace;' namespace, containing a &lt;key/> element whose text value is the ClientID corresponding to the key to be revoked.</p>
<iq type='set' id='123456'>
<revoke xmlns=']]>&namespace;<![CDATA['>
<section2 topic="Key Enumeration">
<p>Any authenticated client may enumerate keys belonging to the same user by sending an &IQ; of type "get" containing a &lt;list/> element qualified by the '&namespace;' namespace.</p>
<iq type='get' id='123456'>
<list xmlns=']]>&namespace;<![CDATA['/>
<p>The server responds with an &IQ; of type 'result', containing the &lt;list/> element qualified by the '&namespace;' namespace. This element contains a sequence of &lt;key/> elements each containing (in any order) the &lt;id/>, &lt;name/> and &lt;expiry/> elements as in registration.</p>
<iq type='result' id='123456'>
<list xmlns=']]>&namespace;<![CDATA['>
<name>SuperChatBiscuit on Honest Pete's Mobile OS</name>
<name>SuperChatChocolate on Honest Bob's Mobile OS</name>

<section1 topic='Determining Support' anchor='support'>
<p>Support for this protocol is advertised as the Disco feature '&namespace;'; however clients MAY infer support if the CLIENT-KEY or CLIENT-KEY-PLUS SASL mechanism is supported.</p>

<section1 topic='Security Considerations' anchor='security'>
<p>Security considerations for this specification are covered within the Internet-Draft &draft; - this specification introduces no further considerations by design, but relies heavily on the guidance given there.</p>