Encrypted partition on an external hard disk in Ubuntu Linux

Here are short instructions how to create and use encrypted hard disk on Ubuntu Linux. These instructions are tested on Ubuntu 10.10 Maverick Meekat.

We are going to use the following strategy

Use cryptoloop kernel module. This is 100% open source software and the part of mainstream Linux (as opposite to TrueCrypt)
No additional software installations needed – stock Ubuntu is fine
These instructions work also on a server – no GUI needed
We will create an encrypted file on the target hard-drive partition. The target partition can be even NTFS, so the hard disk acts normally in Windows, though you still need Linux to read encrypted files
The encrypted file system will be Ext4 and mounted through a loop device

1. Prerequisites

Plug-in the hard disk to Ubuntu Desktop – it will automount it over USB.

Install cryptoloop driver

    sudo modprobe cryptoloop

Check what mount point the new disk has – in your case it is /media/Elements:

ls /media
cdrom  cdrom0  Elements

Check how much space the disk contains

df -h
/dev/sdc1             932G   94M  932G   1% /media/Elements

Create a loopback file – don’t use the whole disk. In our case, allocate just 500 GB for the encrypted file system. Note that this may take time:

dd if=/dev/zero bs=1G count=500 of=/media/Elements/encrypted-fs

Now mount this file as a crypted loopback device. Note that need you to give separate password for sudo and the encryption. We use SHA-1 encryption. Don’t use password, use passphrase. SHA-1 has 160 bit key and to produce enough entropy, you need a latin sentence of at least 27 case-sensitive alphanumeric characters. We do this using losetup command.

sudo losetup -e sha1 /dev/loop0 /media/Elements/encrypted-fs

Then format this encrypted partition as ext4 file system.

mkfs.ext4 /dev/loop0

And now start using it

mkdir /media/encrypted
mount /dev/loop0 /media/encrypted

Later when you remount the encrypted partition you can simply do

sudo losetup -e sha1 /dev/loop0 /media/Elements/encrypted-fs
mount /dev/loop0 /media/encrypted

After usage always cleanly unmount the encrypted partition before unplugging the external hard-drive

umount /media/encrypted