<remark><p>Major revision; split into three namespaces and three corresponding PEP nodes, one each for public keys, attestations, and revocations; iterated the version number for public keys to urn:xmpp:pubkey:1; added detailed data to each node payload; removed some use cases to simply the protocol.</p></remark>
<remark><p>Required specification of an algorithm for elements with hashes; removed fingerprint in <keyinfo/>; added sign request; added guidelines for key management; improved examples; changed namespace from urn:xmpp:tmp:pubkey to urn:xmpp:pubkey:0.</p></remark>
<remark><p>Merged node creation and first publish examples; recommended the value of each <KeyName/> element and id attribute is set to the key fingerprint; added fprint element and more examples</p></remark>
<p>End-to-end encryption between XMPP clients and mutual authentication between a client and a server are desirable goals for the XMPP network. To enable these features, typically an XMPP user will need to possess a public key (or multiple keys), along with an associated private key that is not made public. The goal of this document is to provide simple methods for the exchange of public keys among XMPP users -- specifically, data formats that enable an XMPP entity to complete the following use cases:</p>
<p>This document assumes that each user will have a privately-generated key. A user <strong>might</strong> have more than one key (e.g., different keys for different clients) and the user's key <strong>might</strong> be signed by other entities, such as a certification authority (CA) or another user. However, the simplest case is a single key per user.</p>
<p>The data formats defined here are deliberately kept very simple, with the key itself represented as ASCII output (of the kind supported by most cryptographic libraries) and any metadata represented using a few straightforward XML elements and attributes. This document does not use the 'http://www.w3.org/2000/09/xmldsig#' namespace as specified in &w3xmlsig;; although that format is quite powerful, it introduces unnecessary levels of complexity for this use case.</p>
<p>We define three payload elements:</p>
<ol>
<li>The <pubkey/> element (qualified by the 'urn:xmpp:pubkey:1' namespace) specifies a single public key for a user.</li>
<li>The <revoke/> element (qualified by the 'urn:xmpp:revoke:1' namespace) specifies old keys that a user once used but has now revoked.</li>
<li>The <attest/> element (qualified by the 'urn:xmpp:attest:1' namespace) specifies one or more signed copies of a user's public key.</li>
</ol>
<p>An entity MAY support only public key publishing (the 'urn:xmpp:pubkey:1' namespace) and not support revocations and attestations.</p>
<p>A single public key is contained in a <pubkey/> element qualified by the 'urn:xmpp:pubkey:1' namespace &VNOTE;, for which the defined child elements are as follows:</p>
<tablecaption='Children of the <pubkey/> Element'>
<tr>
<th>Element</th>
<th>Description</th>
</tr>
<tr>
<td><begin/></td>
<td>The UTC DateTime before which the key shall not be considered valid, formatted according to &xep0082;.</td>
</tr>
<tr>
<td><end/></td>
<td>The UTC DateTime after which the key shall not be considered valid, formatted according to <cite>XEP-0082</cite>.</td>
</tr>
<tr>
<td><jid/></td>
<td>The XMPP address associated with this key.</td>
</tr>
<tr>
<td><key/></td>
<td>The ASCII output representation of an RSA public key generated in accordance with &rfc3447;.</td>
</tr>
<tr>
<td><print/></td>
<td>The SHA-256 fingerprint for this key.</td>
</tr>
<tr>
<td><uri/></td>
<td>A URI at which the key can be retrieved outside the XMPP network; this element is OPTIONAL.</td>
<p>A user can revoke his own key. The revocation is contained in a <revoke/> element qualified by the 'urn:xmpp:revoke:1' namespace &VNOTE;, for which the defined child elements are as follows:</p>
<tablecaption='Children of the <revoke/> Element'>
<tr>
<th>Element</th>
<th>Description</th>
</tr>
<tr>
<td><key/></td>
<td>The public key that was revoked.</td>
</tr>
<tr>
<td><keyprint/></td>
<td>The SHA-256 fingerprint of the public key that was revoked.</td>
</tr>
<tr>
<td><signature/></td>
<td>A signature for the revocation, as described below.</td>
</tr>
<tr>
<td><revocationprint/></td>
<td>The SHA-256 fingerprint of the key used to sign the revocation.</td>
</tr>
<tr>
<td><revocationtime/></td>
<td>The UTC DateTime at which the key was revoked, formatted according to <cite>XEP-0082</cite>.</td>
</tr>
</table>
<p>The data that is signed MUST be the revoked public key (i.e., the XML character data of the <key/> element), the SHA-256 fingerprint of the revoked public key (i.e., the XML character data of the <keyprint/> element), the SHA-256 fingerprint of the key used to sign the revocation (i.e., the XML character data of the <revocationprint/> element), and the time of the revocation (i.e., the XML character data of the <revocationtime/> element), concatenated together with no spaces or other additional characters.</p>
<p>As an example, consider a revocation of the key from Example 1, where the SHA-256 fingerprint of the revoked key is 13475c8e27399908b4447d7c52ab30822872832eba3a654f0d80e07fb4157673, the SHA-256 fingerprint of the key used to sign the revocation is becb78566783166f4a1a7c64e28dae288fe1a0f2825f6b593b336ce186c6b056, and the time of the revocation is 2009-12-14T20:49:16Z. The string to be signed would be as follows (where line breaks are not significant).</p>
<p>Whether in the context of the public key infrastructure (PKI) or a web of trust, a user might want to publish signed copies of his public key, where the signer might be another user or a trusted third party such as a certification authority (CA). The signing key could even be another key owned by the user (e.g., a primary key used to sign a secondary key associated with a particular device controlled by the user). Furthermore, the signing material might be an RSA key, a DSA key, an X.509 certificate, an OpenPGP key, or any other format.</p>
<p>Each signed copy is contained in an <attest/> element qualified by the 'urn:xmpp:attest:1' namespace &VNOTE;, for which the defined child elements are as follows:</p>
<tablecaption='Children of the <attest/> Element'>
<tr>
<th>Element</th>
<th>Description</th>
</tr>
<tr>
<td><keyprint/></td>
<td>The SHA-256 fingerprint of the public key that was signed.</td>
</tr>
<tr>
<td><signature/></td>
<td>The signature itself, as described below.</td>
</tr>
<tr>
<td><signerjid/></td>
<td>The XMPP address of the signer.</td>
</tr>
<tr>
<td><signerprint/></td>
<td>The SHA-256 fingerprint of the signer's key.</td>
</tr>
<tr>
<td><signtime/></td>
<td>The UTC DateTime at which the key was signed, formatted according to <cite>XEP-0082</cite>.</td>
</tr>
</table>
<p>The data that is signed MUST be the user's public key (i.e., the XML character data of the <key/> element), the SHA-256 fingerprint of the user's public key (i.e., the XML character data of the <keyprint/> element), the signer's JID (i.e., the XML character data of the <signerjid/> element), the SHA-256 fingerprint of the signer's key (i.e., the XML character data of the <signerprint/> element), and the time of the attestation (i.e., the XML character data of the <signtime/> element), concatenated together with no spaces or other additional characters.</p>
<p>As an example, consider an attestation of the key from Example 1, where the signer's JID is stpeter@jabber.org, the fingerprint of the signer's key is "becb78566783166f4a1a7c64e28dae288fe1a0f2825f6b593b336ce186c6b056", and the time of the attestation is 2009-12-14T18:43:00Z. The string to be signed would be as follows (where line breaks are not significant).</p>
<p>A user SHOULD publish public keys, attestations, and revocations via &xep0163;, in particular adhering to the best practices defined in &xep0222;.</p>
<p>Any other authorized entity can then receive notifications related to the user's public keys, and retrieve keys, attestations, and revocations.</p>
<p>If the user has only one public key (the simplest and most common case), then the pubkey PEP node SHOULD have only one item, with an ItemID of "current".</p>
<section1topic='Requesting a Public Key Directly'anchor='request'>
<p>If it is not possible for the user to publish his key via PEP, or for a contact to retrieve the user's key via PEP, the contact MAY request the user's key directly by sending an &IQ; of type 'get' to the user's particular full JID, containing an empty <pubkey/> element qualified by the 'urn:xmpp:pubkey:1' namespace &VNOTE;.</p>
<p>The receiving client then return its public key (which might be different from the overall key for the user, e.g. a key for only a particular device).</p>
<section1topic='Sending a Public Key Directly'anchor='send'>
<p>An entity might need to send its public key to another entity, for example if it has generated a new key but does not have a way to publish the new key (or does not wish to publish the key in a world-readable fashion). In this case the entity MAY include the key directly in a &MESSAGE; stanza.</p>
<examplecaption='Sending a key in a message'><![CDATA[
<p>There are several situations in which it is helpful for an entity to signal that it is currently generating a key. For example, a client that does not have access to permanent storage might generate a key on startup, but key generation might not be complete when the client sends initial presence upon establishing an XMPP session. In this case the client might signal support for the public key format in the entity capabilities data that it includes in its initial presence broadcast, but also include an indication that it is currently generating a key.</p>
<examplecaption='Key generation in progress'><![CDATA[
<presencefrom='peter@jabber.org/foo'>
<generatingxmlns='urn:xmpp:pubkey:1'/>
</presence>
]]></example>
<p>After key generation is complete, the entity could publish the new key to the appropriate PEP node (if available) and signal that key generation is complete so that any interested parties can request the new key.</p>
<p>To advertise its support for public keys, revocations, and attestations, when replying to &xep0030; information requests an entity MUST return features for 'urn:xmpp:pubkey:1', 'urn:xmpp:revoke:1', and 'urn:xmpp:attest:1' respectively.</p>
<p>In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in &xep0115;. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.</p>
<p>The reliable association between a user or entity and its public keys is beyond the scope of this document. However, each client SHOULD maintain its own secure library of the public keys it associates with other users.</p>
<p>Upon advancement of this specification to a status of Draft, the ®ISTRAR; shall add these namespaces to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
