All you need to do is installing dropbear (a tiny SSH server) and BusyBox (a tiny shell, usually already installed) using apt-get. The initrd will be recreated automatically. Then reboot your computer.
arver is a tool to manage encrypted harddisks. Imagine you are a collective with several admin members. Your servers have diffrent LUKS encrypted devices. Either you would need 1 password for every device which everyone needs to know or you use arver! Arver has 1 password for each device and for each member. This password is stored encrypted with the personal gpg-key in the data directory. The admins only need to know the password to the their own gpg secret key.