apt and pgp

Here is how to install apt gnupg keys. For Marillat repository:

gpg --keyserver hkp://wwwkeys.eu.pgp.net --recv-keys 1F41B907 && gpg -a --export 1F41B907 | sudo apt-key add -

For official Debian repositories:

gpg --keyserver hkp://wwwkeys.eu.pgp.net --recv-keys 2D230C5F && gpg -a --export 2D230C5F | sudo apt-key add -

or

apt-get install debian-archive-keyring