<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>An entity MAY have multiple public keys with different formats, signatures, algorithms, strengths and expiry dates. Each client used by a user MAY use different keys. Guidelines how to manage different public keys in included in this document.</p>
<p>This document does not use the 'http://www.w3.org/2000/09/xmldsig#' namespace as specified in &w3xmlsig; because it is too complicated and the complexity is not needed for this use case. The <keyinfo/> element defined in the 'urn:xmpp:pubkey:0' namespace &VNOTE; is based on the ASCII output most cryptographic libraries support. It has two parts: the public key data and signatures from other keys (optional). The optional argument 'jid' SHOULD be set if the X.509 certificate or OpenPGP key does not belong to the user providing it to another.</p>
<p>The public key data is the OpenPGP public key (&rfc4880;) using binary output. Like X.509 certificates the data MUST be Base64 encoded to fit in an XML stream.</p>
<p>Besides the data, a key can have one or more signatures. A signature can be used to sign an X.509 certificate with an OpenPGP key or the other way around. This makes it possible to verify a self-signed X.509 certificate with the OpenPGP web-of-trust. A second use case is the concept of user and client keys. A user MAY choose to use a different X.509 certificates for each client for &xtls; or &saslext;. All these client key can be signed by a user key. Once the user key is known, all clients can be verified. This XMPP based approach makes it possible to use self-signed certificates without setting up a CA (see <linkurl='#management'>Key Management Guidelines for Secure End-to-End Communication</link>).</p>
<p>The signature has an issuer and the signature data. The issuer contains the fingerprint of the key that was used to create the signature. An optional argument 'jid' SHOULD be set if the issuer has a different base JID than the key to sign. This makes it possible to find the issuer key using PEP (see <linkurl='#pub'>Public Key Publication via PEP</link>).</p>
<p>While OpenPGP defines how to sign a string, X.509 does not specify the hash algorithm. For X.509 the signature data MUST contain an attribute what hash and sign algorithms were used. This document only defines 'RSA-SHA1' at this time. To make it easier to use standard cryptographic libraries the hash MUST contain the ASN.1 BER SHA1 algorithm designator prefix required in PKCS1. See XML-SIG section 6.4.2 how to hash and sign a string using RSA-SHA1. In most cases the cryptographic library will automatically take care of this. The data to sign is the X.509 certificate in DER encoding or the OpenPGP binary string of the fingerprint (the provided key data without Base64 encoding).</p>
<section1topic='Public Key Publication via PEP'anchor='pub'>
<p>An entity SHOULD follow the best practices defined in &xep0222; to publish its long-term public keys via its own server. Processes for doing so are described in the following sections.</p>
<section2topic='Creating the Node'anchor='pub-create'>
<li>Keys will be pushed to subscribers only when new keys are published, not when subscribers become newly available or when a new subscription is created (this is done by setting the "send_last_published_item" option to "never").</li>
<p>If the user wants to control access to his/her identity (see <linkurl='#security'>Security Considerations</link>) then the node access model SHOULD be something other than "open" (this can be done by setting the "access_model" option to a value of "authorize", "presence", "roster", or "whitelist").</p>
<p>Alternatively, if the entity's pubsub service supports both the "auto-create" and "publish-options" features, then the entity MAY create the node by publishing a key and in the first publish including a <publish-options/> element. However, note that not all pubsub services support this feature, since it is optional in &xep0060;.</p>
<examplecaption='Entity Auto-Creates Node and Publishes an RSA Key'><