For those users getting the EXPKEYSIG error.
Method 1:
3 steps, in a terminal
1. wget 'https://download.tuxfamily.org/antix/releases/antix-archive-keyring.asc'
or
wget 'http://repo.antixlinux.com/antix-archive-keyring.asc'
2. sudo apt-key add antix-archive-keyring.asc
3. sudo apt-get update
Method 2:
1. Download antix-archive-keyring_20019.3.13_all.deb from here: http://repo.antixlinux.com
In the directory where you downloaded the deb
2. sudo dpkg -i antix-archive-keyring_20019.3.13_all.deb
3. sudo apt-get update