@forrest
Thanks. OK, the following would help
to download the necessary pgp keys whenever they are needed and in the following to handle the “error message” of unknown keys, but in my opinion, you might lose a lot of control here. Or does the download of every key have to be confirmed by the user?
You might also download the necessary key via
gpg --keyserver [NAME OF KEYSERVER] --recv-key 7A029E54DD5DCE7A
(as ssamer writes in SHA256 checksum of FDroid.apk - #7 by r2d2)
but I have hoped to be able to verify the necessary key before I add it to the key-ring.
I thought, the keyserver should be the address of choice to query it for the owner of a given key.