I have a key in my keyring and I don't know how it got there. Every other key I imported other than this one. How do keys make it into the keyring other than by me importing them?
The key could have been imported for various reasons.
You imported it on your own, by using a CLI call or some graphical user interface.
- You accidentally imported it to your personal keyring when adding some private package archive PPA. The Debian/Ubuntu package management heavily relies on OpenPGP signatures.
- Some application like mail clients automatically try to download keys when you want to send an encrypted mail, or you receive a signed mail. You might have received a signed mail, maybe on a mailing list, and the mail client loaded the key to be able to verify the signature.