Encrypt disk:
cryptsetup luksFormat /dev/sdb
Create mapper device and file system:
cryptsetup luksOpen /dev/sdb testdisk
mkfs.ext3 /dev/mapper/testdisk
Create and add to disk password key-file:
dd if=/dev/random of=/root/keyfile-for-disk bs=1 count=256
cryptsetup luksAddKey /dev/sdb test/root/keyfile-for-disk
Automount:
According /etc/crypttab mapper device will be created:
$ cat /etc/crypttab
testdisk /dev/sdb /root/keyfile-for-disk
$ cat /etc/fstab
. . .
/dev/mapper/testdisk /mnt ext3 defaults 0 0