Unless they where build directly into your working kernel, you'll need to load the following modules:
modprobe cryptoloop modprobe crypto_null
You will also need to load the module for the encryption algoritm you want to use: aes, blowfish, twofish, etc. In this example I will use aes, which is said to be a good compromise between performance and security.
Before formating the filesystem, flush the disk with random data, this will make it harder for an attacker to detect patterns in your encrypted partition.
dd if=/dev/urandom of=/dev/sda1 bs=1M
Or create a file in an existing partition:
dd if=/dev/urandom of=~/.crypto bs=1024k count=30000
Next set up a loop device:
losetup -e aes /dev/loop0 /dev/sda1
And next, make the filesystem:
Next mount the filesystem with the following instruction:
mount -t ext3 /dev/loop0 /media/crypto
After trying it out unmount it and detach the loop device:
umount /media/crypto losetup -d /dev/loop0
You can now mount the filesystem with the following instruction:
mount -t ext3 /dev/sda1 /media/crypto/ -oencryption=aes
Or better yet, add the following line to your /etc/fstab file to make life easier:
/dev/sda1 /media/crypto ext3 user,noauto,encryption=aes 0 0
And that's it, more peace of mind,..