Encryption with dm-crypt and LUKS

Pre-Flight

• Installed on CentOS 6.2 x86_64 running on KVM.
• Decided to use LVM to manage the partition I wanted to encrypt for
  future expansion.

Install the necessary tools

If you did a ‘minimal’ CentOS 6.x install, you’ll need these:

yum install cryptsetup device-mapper util-linux  
modprobe dm_crypt  
lsmod | grep dm_crypt

Prepare the Device

I used LVM. This section could’ve been about making a software RAID. If
you’ve prepared your device or have a standard disk (e.g. /dev/sdb1),
you can skip to the next section.

pvcreate /dev/vda2  
vgcreate volgroups /dev/vda2  
lvcreate -l 100%FREE -n secure volgroups

You now have a block storage device at /dev/mapper/volgroups-secure.
You’ll create an encrypted device using it.

Creating the Encrypted Device

cryptsetup luksFormat /dev/mapper/volgroups-secure  
cryptsetup luksOpen   /dev/mapper/volgroups-secure secure

This creates the device /dev/mapper/secure. The cipher used is
AES-256-CBC. Fill it with junk; will take time, but this will prevent
people from knowing the size of data on your device.

dd if=/dev/urandom of=/dev/mapper/secure

Now create a filesystem

mkfs -t ext4 /dev/mapper/secure

Mount it!

mount -t ext4 /dev/mapper/secure /mnt/secure

Close it when done:

crypsetup luksClose secure

Mounting at boot

• Add this to /etc/crypttab (create with 0644 if it doesn’t exist)

  secure   /dev/mapper/volgroups-secure
  

• Then add this to /etc/fstab

  /dev/mapper/secure  /mnt/secure   ext3    defaults  0 0
  

LVM Resizing

For the example above,

lvextend -L+2048G /dev/mapper/volgroups-secure  
resize2fs /dev/mapper/secure