mirror of
https://github.com/moparisthebest/xeps
synced 2024-12-21 15:18:51 -05:00
333 lines
16 KiB
XML
333 lines
16 KiB
XML
<?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>Encapsulated Digital Signatures in XMPP</title>
|
|
<abstract>This document provides a technical specification for Encapsulated Digital
|
|
Signatures in the Extensible Messaging and Presence Protocol (XMPP).</abstract>
|
|
&LEGALNOTICE;
|
|
<number>0290</number>
|
|
<status>Deferred</status>
|
|
<type>Standards Track</type>
|
|
<sig>Standards</sig>
|
|
<approver>Council</approver>
|
|
<dependencies>
|
|
<spec>XMPP Core</spec>
|
|
<spec>XEP-0001</spec>
|
|
</dependencies>
|
|
<supersedes/>
|
|
<supersededby/>
|
|
<shortname>N/A</shortname>
|
|
&kdz;
|
|
<revision>
|
|
<version>0.2</version>
|
|
<date>2011-01-28</date>
|
|
<initials>kdz</initials>
|
|
<remark>
|
|
<p>Merge manifest and schema-desc objects.</p>
|
|
</remark>
|
|
</revision>
|
|
<revision>
|
|
<version>0.1</version>
|
|
<date>2011-01-26</date>
|
|
<initials>psa</initials>
|
|
<remark>
|
|
<p>Initial published version.</p>
|
|
</remark>
|
|
</revision>
|
|
<revision>
|
|
<version>0.0.1</version>
|
|
<date>2010-11-29</date>
|
|
<initials>kdz</initials>
|
|
<remark>
|
|
<p>Proto-XEP draft.</p>
|
|
</remark>
|
|
</revision>
|
|
</header>
|
|
|
|
<section1 topic="Introduction" anchor="intro">
|
|
<p class="box"><em>This document is one of two proposals for digital signatures in XMPP. It
|
|
is expected that only one of these proposals be progressed beyond Experimental on
|
|
the Standards Track.</em></p>
|
|
|
|
<p>This document provides a technical specification for Encapsulated Digital Signatures in
|
|
Extensible Messaging and Presence Protocol (&xmpp;).</p>
|
|
<p>XMPP Digital Signatures may be used to provide signer authentication, data integrity,
|
|
non-repudiation, and other security services.</p>
|
|
<p>This extension is intended to be highly flexible, supporting a wide range of
|
|
applications. The extension not only supports signing by the originator, but by other
|
|
entities which handle XMPP stanzas. Multiple entities may independently sign a
|
|
stanza.</p>
|
|
<p>A signed manifest approach is used to allow selective signing (only select elements may
|
|
be included in the manifest) and to allow flexibility in handling verification
|
|
errors.</p>
|
|
<p>This extension is intended to support <em>optimistic signing</em>.</p>
|
|
<p>This document offers an encapsulated signature approach based upon &w3xmlsig; (XMLDSIG).
|
|
Implementations of this extension not required to fully implement the XML DSIG
|
|
specification, they may implement only the minimal subset necessary to support this
|
|
extension.</p>
|
|
<p>It is noted that a number of object-level XMPP digital signature extensions have been
|
|
specified over the years. These include &rfc3923; (XMPP E2E), &xep0116; (XMPP PGP), and
|
|
&xep0285;. The limited applicability of encapsulating signature approaches in XMPP is
|
|
discussed in &xep0274;.</p>
|
|
</section1>
|
|
<section1 topic="Signing XMPP Stanzas" anchor="stanza">
|
|
<p>The process that a sending agent follows for securing stanzas is very similar regardless
|
|
of the form of stanza (i.e., <iq/>, <message/>, or <presence/>).</p>
|
|
|
|
<p>The signer begins with the cleartext version of the <message/> stanza "S":</p>
|
|
<example><![CDATA[
|
|
<message from='juliet@capulet.net/balcony'
|
|
id='183ef129'
|
|
to='romeo@montague.net'>
|
|
<thread>8996aef0-061d-012d-347a-549a200771aa</thread>
|
|
<body>Wherefore art thou, Romeo?</body>
|
|
</message>
|
|
]]></example>
|
|
|
|
<p>This is modified prior to signing as follows:</p>
|
|
<ul>
|
|
<li>Default attribute values are added. (Namespace declarations are not modified.)</li>
|
|
<li>Each child element of the stanza is augmented by a <tt>id</tt> attribute qualified
|
|
in the <tt>urn:xmpp:dsig:0</tt> namespace. As these attributes are used to identify
|
|
the element within a manifest, they must be sufficient unique.</li>
|
|
</ul>
|
|
<example><![CDATA[
|
|
<message from='juliet@capulet.net'
|
|
id='183ef129'
|
|
to='romeo@montague.net'
|
|
type='chat'>
|
|
<thread xmlns:d="urn:xmpp:dsig:0" d:id="xxxx-1">8996aef0-061d-012d-347a-549a200771aa</thread>
|
|
<body xmlns:d="urn:xmpp:dsig:0" d:id="xxxx-2">Wherefore art thou, Romeo?</body>
|
|
</message>
|
|
]]></example>
|
|
|
|
<p>The signer builds a stanza description object containing a signer element, the stanza
|
|
element, and a timestamp element. The signer element value is the bare JID of the
|
|
signing entity. When the signing entity is a service entity, the JID may only contain
|
|
service domain. The stanza-desc element is the stanza prepared above with each of its
|
|
child elements replaced by an reference element. The reference element references the
|
|
child element via a "urn:xmpp:dsig:ref:0" URI with an anchor of the value of child
|
|
element's <tt>d:id</tt>. The value of the reference element is the digest value produced
|
|
by the digest method after the specified transforms are applied.</p>
|
|
<example><![CDATA[
|
|
<stanza-desc id="stanza-desc" xmlns="urn:xmpp:dsig:0">
|
|
<signer>juliet@capulet.net</signer>
|
|
<Transforms><Transform Algorithm="urn:xmpp:dsig:transform:0"/></Transform>
|
|
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
|
|
<message from='juliet@capulet.net'
|
|
id='183ef129'
|
|
to='romeo@montague.net'
|
|
type='chat'>
|
|
<reference URI='urn:xmpp:dsig:ref:0#xxxx-1'>...</reference>
|
|
<reference URI='urn:xmpp:dsig:ref:0#xxxx-2'>...</reference>
|
|
</message>
|
|
<timestamp>2010-11-11T13:33:00.123Z</timestamp>
|
|
</stanza-desc>
|
|
]]></example>
|
|
|
|
<p>The signer then builds a SignedInfo element.</p>
|
|
<example><![CDATA[
|
|
<SignedInfo>
|
|
<CanonicalizationMethod Algorithm="urn:xmpp:dsig:transform:0"/>
|
|
<SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#dsa-sha1"/
|
|
<Reference URI="#stanza-desc">
|
|
<Transforms>
|
|
<Transform Algorithm="http://www.w3.org/2006/12/xml-c14n11"/>
|
|
</Transform>
|
|
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
|
|
<DigestValue>...</DigestValue>
|
|
</Reference>
|
|
</SignedInfo>
|
|
]]></example>
|
|
|
|
<p>And then produces a Signature element:</p>
|
|
<example><![CDATA[
|
|
<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
|
|
<SignedInfo>
|
|
<CanonicalizationMethod Algorithm="http://www.w3.org/2006/12/xml-c14n11"/>
|
|
<SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#dsa-sha1"/
|
|
<Reference URI="#stanza-desc">
|
|
<Transforms>
|
|
<Transform Algorithm="http://www.w3.org/2006/12/xml-c14n11"/>
|
|
</Transform>
|
|
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
|
|
<DigestValue>...</DigestValue>
|
|
</Reference>
|
|
</SignedInfo>
|
|
<SignatureValue/>
|
|
<Object>
|
|
<stanza-desc id="stanza-desc" xmlns="urn:xmpp:dsig:0">
|
|
<signer>juliet@capulet.net</signer>
|
|
<Transforms><Transform Algorithm="urn:xmpp:dsig:transform:0"/></Transform>
|
|
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
|
|
<message from='juliet@capulet.net'
|
|
id='183ef129'
|
|
to='romeo@montague.net'
|
|
type='chat'>
|
|
<reference URI='urn:xmpp:dsig:ref:0#xxxx-1'>...</reference>
|
|
<reference URI='urn:xmpp:dsig:ref:0#xxxx-2'>...</reference>
|
|
</message>
|
|
<timestamp>2010-11-11T13:33:00.123Z</timestamp>
|
|
</stanza-desc>
|
|
</Object>
|
|
</Signature>
|
|
]]></example>
|
|
|
|
<p>The signer than computes the SignatureValue element, processing the Signature element as
|
|
a detached signature, and replaces the empty Signature element with it. Finally, the
|
|
signer inserts the Signature element into stanza and forwards the stanza as it normally
|
|
would.</p>
|
|
<example><![CDATA[
|
|
<message from='juliet@capulet.net'
|
|
id='183ef129'
|
|
to='romeo@montague.net'
|
|
type='chat'>
|
|
<thread xmlns:d="urn:xmpp:dsig:0" d:id="xxxx-1">8996aef0-061d-012d-347a-549a200771aa</thread>
|
|
<body xmlns:d="urn:xmpp:dsig:0" d:id="xxxx-2">Wherefore art thou, Romeo?</body>
|
|
<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
|
|
<SignedInfo>
|
|
<CanonicalizationMethod Algorithm="http://www.w3.org/2006/12/xml-c14n11"/>
|
|
<SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#dsa-sha1"/
|
|
<Reference URI="#stanza-desc">
|
|
<Transforms>
|
|
<Transform Algorithm="http://www.w3.org/2006/12/xml-c14n11"/>
|
|
</Transform>
|
|
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
|
|
<DigestValue>...</DigestValue>
|
|
</Reference>
|
|
</SignedInfo>
|
|
<SignatureValue>...</SignatureValue>
|
|
<Object>
|
|
<stanza-desc id="stanza-desc" xmlns="urn:xmpp:dsig:0">
|
|
<signer>juliet@capulet.net</signer>
|
|
<Transforms><Transform Algorithm="urn:xmpp:dsig:transform:0"/></Transform>
|
|
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
|
|
<message from='juliet@capulet.net'
|
|
id='183ef129'
|
|
to='romeo@montague.net'
|
|
type='chat'>
|
|
<reference URI='urn:xmpp:dsig:ref:0#xxxx-1'>...</reference>
|
|
<reference URI='urn:xmpp:dsig:ref:0#xxxx-2'>...</reference>
|
|
</message>
|
|
<timestamp>2010-11-11T13:33:00.123Z</timestamp>
|
|
</stanza-desc>
|
|
</Object>
|
|
</Signature>
|
|
</message>
|
|
]]></example>
|
|
</section1>
|
|
|
|
<section1 topic="Transformation Algorithm" anchor="transform">
|
|
<p>For referenced elements of a stanza, the referenced element is normalized (omitting
|
|
comments), as detailed in &w3canon;, as a document subset of a document containing a
|
|
stream element containing the appropriate jabber:client stanza element containing the
|
|
stanza with the referenced elements. Note that jabber:client stanzas are used when
|
|
constructing this document even when a server is signing a stanza to be sent to another
|
|
server.</p>
|
|
<p>For the stanza in Example 2, the input document would be:</p>
|
|
<example><![CDATA[
|
|
<stream:stream xmlns='jabber:client" xmlns:stream='http://etherx.jabber.org/streams'>
|
|
<message from='juliet@capulet.net'
|
|
id='183ef129'
|
|
to='romeo@montague.net'
|
|
type='chat'>
|
|
<thread xmlns:d="urn:xmpp:dsig:0" d:id="xxxx-1">8996aef0-061d-012d-347a-549a200771aa</thread>
|
|
<body xmlns:d="urn:xmpp:dsig:0" d:id="xxxx-2">Wherefore art thou, Romeo?</body>
|
|
</message>
|
|
</stream:stream>
|
|
]]></example>
|
|
|
|
<p>The canonical form of element referenced by <tt>urn:xmpp:dsig:ref:0#xxx-1</tt> would
|
|
be:</p>
|
|
<example><![CDATA[<thread xmlns="jabber:client" xmlns:d="urn:xmpp:dsig:0" d:id="xxxx-1">8996aef0-061d-012d-347a-549a200771aa</thread>]]></example>
|
|
</section1>
|
|
|
|
<section1 topic="Stanza Element References" anchor="references">
|
|
<p>The URI 'uri:xmpp:dsig:ref:0#xxxx" refers to the child element of the stanza which
|
|
contains the 'uri:xmpp:dsig:0' 'id' attribute with the value "xxxx".</p>
|
|
</section1>
|
|
|
|
<section1 topic="Inclusion and Checking of Timestamps" anchor="timestamps">
|
|
<p>Timestamps are included to help prevent replay attacks. All timestamps MUST conform to
|
|
&rfc3339; and be presented as UTC with no offset, always including the seconds and
|
|
fractions of a second to three digits (resulting in a datetime 24 characters in length).
|
|
Absent a local adjustment to the sending agent's perceived time or the underlying clock
|
|
time, the sending agent MUST ensure that the timestamps it sends to the receiver
|
|
increase monotonically (if necessary by incrementing the seconds fraction in the
|
|
timestamp if the clock returns the same time for multiple requests). The following rules
|
|
apply to the receiving application:</p>
|
|
|
|
<ul style="symbols">
|
|
<li>It MUST verify that the timestamp received is within five minutes of the current
|
|
time, except as described below for offline messages.</li>
|
|
<li>If the foregoing check fails, the timestamp SHOULD be presented to the receiving
|
|
entity (human or application) marked with descriptive text indicating "old
|
|
timestamp" or "future timestamp" and the receiving entity MAY return a stanza error
|
|
to the sender (except as precluded in the protocol).</li>
|
|
</ul>
|
|
|
|
<p>The foregoing timestamp checks assume that the recipient is online when the message is
|
|
received. However, if the recipient is offline then the server will probably store the
|
|
message for delivery when the recipient is next online (offline storage does not apply
|
|
to <iq/> or <presence/> stanzas, only <message/> stanzas). As
|
|
described in &xep0160;, when sending an offline message to the recipient, the server
|
|
SHOULD include delayed delivery data as specified in &xep0203; so that the recipient
|
|
knows that this is an offline message and also knows the original time of receipt at the
|
|
server. In this case, the recipient SHOULD verify that the timestamp received in the
|
|
encrypted message is within five minutes of the time stamped by the recipient's server
|
|
in the <delay/> element.</p>
|
|
</section1>
|
|
|
|
<section1 topic="Mandatory-to-Implement Cryptographic Algorithms" anchor="mti">
|
|
<p>All implementations MUST support the following algorithms. Implementations MAY support
|
|
other algorithms as well.</p>
|
|
<ul>
|
|
<li>TBD</li>
|
|
</ul>
|
|
</section1>
|
|
|
|
<section1 topic="Certificates" anchor="certs">
|
|
<p>To participate in end-to-end signing using the methods defined in this document, a client
|
|
needs to possess an X.509 certificate. It is expected that many clients will generate
|
|
their own (self-signed) certificates rather than obtain a certificate issued by a
|
|
certification authority (CA). In any case the certificate MUST include an XMPP address
|
|
that is represented using the ASN.1 Object Identifier "id-on-xmppAddr" as specified in
|
|
Section 5.1.1 of RFC 3920bis.</p>
|
|
</section1>
|
|
|
|
<section1 topic="Security Considerations" anchor="security">
|
|
<p>TBD.</p>
|
|
</section1>
|
|
|
|
<section1 topic="XMPP Registrar Considerations" anchor="reg">
|
|
<section2 topic="XML Namespace Name for Signed Data in XMPP" anchor="ns">
|
|
<p>A URN sub-namespace of signed content for the Extensible Messaging and Presence
|
|
Protocol (XMPP) is defined as follows.</p>
|
|
<dl>
|
|
<di>
|
|
<dt>URI:</dt>
|
|
<dd>urn:xmpp:dsig</dd>
|
|
</di>
|
|
<di>
|
|
<dt>Specification:</dt>
|
|
<dd>ProtoXEP</dd>
|
|
</di>
|
|
<di>
|
|
<dt>Description:</dt>
|
|
<dd>This is an XML namespace name of signed content for the Extensible Messaging
|
|
and Presence Protocol as defined by ProtoXEP.</dd>
|
|
</di>
|
|
<di>
|
|
<dt>Registrant Contact:</dt>
|
|
<dd>XSF</dd>
|
|
</di>
|
|
</dl>
|
|
</section2>
|
|
</section1>
|
|
</xep>
|