I found this post (from myself) from some time ago.
It was marked by others as the correct solution - or leading to it.
so:
have a look
Getting invalid or corrupted package (PGP signature) error when updating - #4 by Nachlese
I found this post (from myself) from some time ago.
It was marked by others as the correct solution - or leading to it.
so:
have a look
Getting invalid or corrupted package (PGP signature) error when updating - #4 by Nachlese