Let's add a decentralized XMPP proof to your OpenPGP keys.
Add a message to your XMPP vCard
Go to (mov.im)[https://mov.im] and log in using your XMPP credentials. Click on Configuration and append the following message to the About Me section (make sure to replace FINGERPRINT):
This is an OpenPGP proof that connects my OpenPGP key to this XMPP account. For details check out https://keyoxide.org/guides/openpgp-proofs [Verifying my OpenPGP key: openpgp4fpr:FINGERPRINT]
Using native XMPP clients that support editing the vCard data (such as Gajim) should work as well. Unfortunately, this method appears unreliable and does not work for some.
Update the PGP key (basic edition)
First, edit the key (make sure to replace FINGERPRINT):
gpg --edit-key FINGERPRINT
Get a list of user IDs and find the index of the one to assign the notation to:
Select the desired user ID (make sure to replace N):
Add a new notation:
Enter the notation (make sure to replace XMPP-ID):
The XMPP-ID looks something like an email address: firstname.lastname@example.org.
Save the key:
Upload the key to WKD or use the following command to upload the key to keys.openpgp.org (make sure to replace FINGERPRINT):
gpg --keyserver hkps://keys.openpgp.org --send-keys FINGERPRINT
And you're done! Reload your profile page, it should now show a XMPP account.
Update the PGP key (OMEMO edition)
XMPP communication can be end-to-end encrypted with OMEMO. Verifying OMEMO fingerprints is essential to trust your communication and keep it safe from Man-in-the-Middle attacks.
Keyoxide makes the fingerprint verification process easy for all. Add a special identity proof that not only contains your XMPP-ID but also the fingerprints of all your OMEMO keys.
If your XMPP identity proof is verified, a QR code is shown. Anyone can scan this QR code using XMPP apps like Conversations (free on F-Droid) to not only add you as a contact, but also verify your OMEMO keys with the highest level of trust.
Making this identity proof yourself can be a tad difficult when using clients like Gajim, but luckily for us, Conversations can directly generate the proof by going to Manage accounts > Share > Share as XMPP URI. The resulting URI should look something like:
To take advantage of the easy and secure XMPP identity proof including OMEMO fingerprints, follow the basic edition guide above but replace XMPP-ID with the URI obtained through the Conversations app.