When you add to your distribution depots to benefit from higher version of some software, you are probably often faced with a kind of error message:
W: GPG error: http://ppa.launchpad.net jaunty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY votre_n°_de_clé
To overcome this problem you simply enter in a terminal the following command:
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com votre_n°_de_clé
or :
sudo apt-get install add-apt-key && sudo add-apt-key votre_n°_de_clé