The latest
Debian Weekly News
has links to solving the GPG problem `apt-get update` displayed
after the first of the year ('The following signatures couldn't be
verified because the public key is not available', etc.):
Re: GPG
error on apt-get update.
wget
http://ftp-master.debian.org/ziyi_key_2005.asc -O - | sudo apt-key
add -
wget http://ftp-master.debian.org/ziyi_key_2006.asc -O - | sudo
apt-key add -