How to add trusted keys to apt

The aptitude manual has a little section on how add trusted keys to apt.

The list of keys that apt will trust is stored in the keyring file /etc/apt/trusted.gpg. Once you have the GPG key, you can add it to this file by executing the command gpg --no-default-keyring --keyring /etc/apt/trusted.gpg --import newkey.asc . aptitude will then trust any archive that is signed with the key contained in newkey.asc.