Since X.509 has no standard fingerprint mechanisms, the SHA1 value in hex of the certificate is used as name. The public key data is the X.509 certificate in DER encoding. To be included in an XML stream the data is Base64 encoded.

OpenPGP (&rfc4880;) defines how to create fingerprints. This fingerprint is used as unique name. The public key data is the OpenPGP public key using binary output. Like X.509 certificates the data must be Base64 encoded to fit in an XML stream.

Besides the name and 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 certificate for each client for &xep0178; or &xep0250;. 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.

The signature has an issuer and the signature data. The issuer contains the unique name / 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 Public Key Publication via PEP).

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).

The next example contains am X.509 certificate signed by the key defined in the first example.

If the pubkeys PEP node does not exist already then the entity must create it. The node MUST have a NodeID of "urn:xmpp:tmp:pubkey" &NSNOTE;.

The node MUST be configured as follows:

• Items published to the node are persistent (this is done by setting the "persist_items" option to true).
• 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").

If the user wants to control access to his/her identity (see Security Considerations) 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").

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;.

The entity publishes a key by sending a pubsub publish request to the pubsub service. A previously published key can be updated by re-publishing the key using the same ItemID. The value of the ItemID SHOULD be set to the fingerprint of the public key (the name). Therefore subscribers or other interested entities are able to request a single key by specifying its fingerprint (for example, when a subscriber is using C2C Authentication Using TLS).

After the account owner publishes the key, the pubsub service shall send a notification to each subscriber or otherwise authorized and interested entity.