// , Where may I find the GPG key for attic-backup.org to verify the binaries from https://attic-backup.org/downloads/releases/0.16/ ?

I did have a quick look on the databases of our Benevolent Corporate Masters:
https://www.google.com/webhp?q=attic-backup.org%20gpg%20key
http://pgp.mit.edu/pks/lookup?search=attic-backup&op=index