From now on, the Release files for the repositories at debian.dev-zero.nl will be signed with a new GPG key. To install packages from these repositories, you need to add that new key to your apt keyring.
There are two ways to do that. The simplest way:
aptitude install debian-devzero-keyring
The alternative way:
gpg –keyserver hkp://pgp.mit.edu –recv-keys F842EC0F
gpg –export F842EC0F | sudo apt-key add -
