Cryptsetup

Encrypting a partition on Ubuntu 7.10 (Gutsy) using cryptsetup (LUKS)

• fdisk your partitions and remember them.

I will use sdb2 in my example.

• $ sudo apt-get install cryptsetup

• $ sudo cryptsetup luksFormat /dev/sdb2 -c aes -s 256 -h sha256

WARNING!
========
This will overwrite data on /dev/sdb2 irrevocably.
Are you sure? (Type uppercase yes): YES
Enter LUKS passphrase: 

This is where you make up a password.

• sudo cryptsetup luksOpen /dev/sdb2 backup

I called it backup, you can call it whatever you want. You can do

$ ls -la /dev/mapper

and you should be able to see it!

• $ sudo mke2fs -j /dev/mapper/backup -L backup

You can label it whatever you want, most people use the same as that in /dev/mapper/ for simplicity. This also assumes you want an ext3 filesystem (the -j option). Make whatever filesystem you prefer. You can now mount /dev/mapper/backup manually, or add it to /etc/fstab and /etc/crypttab if it's a static partition.

From passphrase prompt to a file

Although not recommended unless you're aware of the repercussions, you may wish to store the passphrase in a file on your system instead of being prompted. If this is the case, you can create a file either randomly:

$ sudo dd if=/dev/urandom of=/root/lukssecretkey bs=1024 count=4 

or manually create a file with any passphrase in it you choose. Assuming sdc5 is the partition you want to encrypt, add the new key:

$ sudo cryptsetup luksAddKey /dev/sdc5 /root/lukssecretkey

finally you want to edit your /etc/crypttab entry to use the keyfile:

# <target name>	<source device>		<key file>	<options>
crypto 	 /dev/sdc5	/root/lukssecretkey	luks,check=ext2,retry=5