How to encrypt an existing archlinux LVM installation [LVM on LUKS]

Many users need to secure their laptop, workstation or regular PC, this users want to protect their information. In Linux exist many cryptographic techniques to protect a hard disk, directory and partition, one of this techniques is Linux Unified Key Setup (LUKS) which uses the kernel device mapper subsystem via the dm-crypt module which make the encrypted device transparent to the user.

Assumptions

In this tutorial the system drive is called rootDrive and temporally drive is called tmpDrive, the LVM root partition (partition to encrypt) is called rootDriveXY, the temporally partition is called tmpDriveXY both are formatted as Linux LVM.

The entire system are installed in a single volume group, in this tutorial is called “vg-sys”.

You can realize the entire process without umount any partition because of flexibility of LVM, in summary this process can be do on-the-fly.

Warning

The specific case

Steps

# create physical volume
$ pvcreate /dev/tmpDriveXY
# extend "vg-sys" to temporally drive
$ vgextend vg-sys /dev/tmpDriveXY
# move volume group to temporally drive
$ pvmove /dev/rootDriveXY /dev/tmpDriveXY

Once the volume group is moved, reduce the rootDriveXY from volume group “vg-sys” and remove the physical drive to be encrypted /dev/rootDriveXY

# remove physical drive from volume group
$ vgreduce vg-sys /dev/rootDriveXY
# remove physical drive
$ pvremove /dev/rootDriveXY

Change the partition type of root drive, on GPT the code is 8309 for Linux LUKS

# change the code of root drive partition
$ gdisk /dev/rootDrive
# change type with t, choose partition number
# set type 8309 for Linux LUKS
# see changes whit p and write with w
$ gdisk -l /dev/rootDrive

Wipe the partition to prevent cryptographic attacks or unwanted file recovery

# create a temporary encrypted container
$ cryptsetup open --type plain -d /dev/urandom /dev/rootDeviceXY to_be_wiped
# verify
$ lsblk
# wipe with zeros, wait til "No space left on device"
# be patient, this step takes a long time
$ dd if=/dev/zero of=/dev/mapper/to_be_wiped bs=1M status=progress
# close wiped device
$ cryptsetup close to_be_wiped

A this point probably you want to check performance of encrypt algorithms, use the next command to run a benchmark

# check algorithm benchmark
$ cryptsetup benchmark

I choose an aes-xts-plain64 cipher with a key size of 256 and sha256 hash. To encrypt the rootDriveXY use the next command

# encrypt device and set passphrase
$ cryptsetup -v --type luks --cipher aes-xts-plain64 --key-size 256 --hash sha256 --iter-time 2000 --use-urandom --verify-passphrase luksFormat /dev/rootDriveXY

Open encrypted device with passphrase, create a LVM physical volume, extend the “vg-sys” volume to encrypted physical volume and move the temporally drive to encrypted

# open encrypted volume
$ cryptsetup open /dev/rootDriveXY cryptarch
# create a physical LVM device
$ pvcreate /dev/mapper/cryptarch
# extend the "vg-sys" group
$ vgextend vg-sys /dev/mapper/cryptarch
# move volume group to encrypted drive
$ pvmove /dev/tmpDriveXY /dev/mapper/cryptarch

Now remove the temporally drive from LVM

# remove temporally drive from volume group
$ vgreduce vg-sys /dev/tmpDriveXY
# remove physical volume from temporally drive
$ pvremove /dev/tmpDriveXY

Configure mkinitcpio, first edit /etc/mkinitcpio.conf file and change hooks like this

HOOKS=(base udev autodetect keyboard keymap consolefont modconf block encrypt lvm2 filesystems fsck)

Then recreate the initramfs image for linux-lts kernel

$ mkinitcpio -P linux-lts

Configuring the boot loader to unlock the encrypted root partition at boot, the following kernel parameter needs to be set by the boot loader, this can be set in /etc/default/grub

# get UUID of encrypted drive
# in this case /dev/rootDriveXY not /dev/mapper/cryptarch
$ blkid
# add this line in GRUB_CMDLINE_LINUX
cryptdevice=UUID=rootDriveXY-UUID:cryptarch root=/dev/vg-sys/root
# uncoment GRUB_ENABLE_CRYPTODISK="y"
# regenerate grub.cfg file
$ grub-mkconfig -o /boot/grub/grub.cfg

If everything goes fine reboot the system and in boot time the system should ask a password to open the encrypted rootDriveXY as shown in the next image

Finally I recommend to wipe the temporally drive to prevent unwanted data recovery.

Engineer || MSc student || DevOps in progress