ja osobne pouzivam takmer vylucne PPA repozitare z launchpad.net a na pridavanie klucov nasledovne. pri kazdom repozitari, napriklad https://launchpad.net/~do-core/+archive/ppa je link ku klucu, URL napriklad:
http://keyserver.ubuntu.com:11371/pks/lookup?search=0xA5D19FDCAA6ABB440CD3464628A8205077558DD0&op=index
...vykopirujem si fingerprint (teda A5D19FDCAA6ABB440CD3464628A8205077558DD0) pastnem do prikazu:
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com A5D19FDCAA6ABB440CD3464628A8205077558DD0

