The need to encrypt filesystems is to make ur data more secure and safe.
The whole steps include
1) Creating a partition with the fdisk utility ( pre-requisite :-( )
2) Selecting a cipher.
3) Setting up a loop device using the losetup command.
4) Detaching the loop back device
5) Mouting the parition
alright... lets get started..!
let me assume u have created the partition /dev/hda7
first of all we need to shred the partition
#shred -n 1 /dev/hda7
this command would overwrite /dev/hda7 only once!
we can use the dd command to overwrite the device..
#dd if=/dev/urandom of=/dev/hda7 bs=1M
Now we need to select a cipher for the encyption
u can list the available ciphers by cat /proc/crypto
here i am using the serpent cipher
make sure u have got the serpent cipher modules inbuilt in ur kernel!
#modprobe cryptoloop ( to setup the loop device described in the next step )
the next step is to setup a loop device using the losetup command.
#losetup -e serpent /dev/loop0 /dev/hda7
It prompts u for a passphrase. DONOT forget the passphrase as its not easy to change
the passphrase as it is hashed to create the encryption key.
Now create a filesystem on the loopback device and mount it.
#mke2fs -j /dev/loop0
#mount -t ext3 /dev/loop0 /cryptfs
once we have mounted the partition, we can then detach the
loop back device frm the partition.
#losetup -d /dev/loop0
Now mount the partition,
#mount -o encryption=serpent /dev/hda7 /cryptfs
the passphrase which we have given during the loop device setup will be asked
and u need to enter it correctly to mount the device.