LUKS (Linux Unified Key Setup) is one of the various disk encryption formats available for Linux that is platform agnostic. This tutorial will provide you with root and swap partitions inside of a LVM (Linux Volume Manager) volume contained inside of an encrypted LUKS partition. This tutorial also allows for you to unlock the LUKS partition remotely using a simplified SSH server daemon using any compatible SSH client program.
Prerequisites
- A CentOS 7 x64 Minimal ISO Library server instance.
- A sudo user.
- SSH public key(s).
- Dracut-Crypt-SSH.
Step 1: Environment Setup
On the Deploy Servers page, do the following:
- Choose your server location in the
Server Location
section. - Choose
CentOS7
under theISO Library
tab of theServer Type
section. - Choose the hardware specifications you require in the
Server Size
section. - Click the
Deploy Now
button.
Use the View Console
option to access the VPS instance via the noVNC console.
Step 2: Start The CentOS 7 Text Mode Installer
Select the Install CentOS Linux 7
option.
Press the Tab
key.
Enter text
after vmlinuz initrd=initrd.img inst.stage2=hd:LABEL=CentOS/x207/x20/86_64 quiet
so that it looks like this vmlinuz initrd=initrd.img inst.stage2=hd:LABEL=CentOS/x207/x20/86_64 quiet text
and press the Enter
key.
The VPS will now boot into the text mode CentOS installer. You will see a screen in the noVNC console like pictured in the image below.
Step 3: Setup LVM On LUKS Full Disk Encryption
Use the Alt + Right Arrow Key
combination to navigate to the TTY2 console to type commands on the command line.
Type the following commands below to create a partition for containing the GRUB2 boot loader, an unencrypted /boot
partition and a primary partition that will hold the LUKS partition.
parted -a opt -s /dev/vda mklabel gpt
parted -s /dev/vda unit mb
parted -s /dev/vda mkpart primary 1 3
parted -s /dev/vda name 1 grub
parted -s /dev/vda set 1 bios_grub on
parted -s /dev/vda mkpart primary 3 259
parted -s /dev/vda name 2 boot
parted -s /dev/vda mkpart primary 259 100%
parted -s /dev/vda name 3 root
Type the following command to display the partition layout.
parted -s /dev/vda print
Next, fill the named rootfs
partition with pseudo-random data. This will take a little over a half an hour to complete.
dd if=/dev/urandom of=/dev/vda3 bs=1M status=progress
On CentOS 7, the cryptsetup
commands uses the default cipher of aes-xts-plain64
, the default key size of 256 bits and the default hash of SHA1. Instead, the LUKS partition will be created with the more secure Serpent cipher, with a key size of 512 bits and with the Whirlpool hash.
cryptsetup luksFormat /dev/vda3 -c serpent-xts-plain64 -h whirlpool -s 512
Input the answers, when prompted with the following queries, then press the Enter
key:
- Are you sure? (Type uppercase yes):
YES
- Enter passphrase:
strong-password
- Verify passphrase:
strong-password
Optional: Backup The LUKS Partition Header
Warning This will allow root login and copying without a password prompt. Kill this SSH server after you’ve retrieved the /tmp/luks-header-backup.img
file.
For safekeeping, save a copy of the LUKS partition header. This ensures that if the header of your LUKS partition is somehow damaged, it can be restored. If the header is damaged without a working backup, your data is lost forever.
cryptsetup luksHeaderBackup /dev/vda3 --header-backup-file /tmp/luks-header-backup.img
To copy the /tmp/luks-header-backup.img
file from the server, a SSH server must be temporarily started, using the secure copy executable scp
on a client host, to retrieve it.
Type the following command below to generate the SSH host keys.
sshd-keygen
Type the following command below to create the /etc/ssh/sshd_config
file.
cp /etc/ssh/sshd_config.anaconda /etc/ssh/sshd_config
Type the following command below to edit the /etc/ssh/sshd_config
file.
vi /etc/ssh/sshd_config
To edit the file, press the Insert
key and use the arrow keys to navigate to sections of the file that need editing.
In line one, change the number in Port 22
from the default of 22
to a random number of your choice between 1025
and 65535
. (Example: port 25782
)
Scroll down to line number thirteen, press the End
key and press the Enter
key.
On the next line, add HostKey /etc/ssh/ssh_host_ed25519_key
and press the Enter
key.
On the next line, add HostKey /etc/ssh/ssh_host_rsa_key
and press the Enter
key.
Press the Esc
key, type :wq
and press the Enter
key to save the file.
The default network interface eth0
needs an IP address. Type the following command below to assign the IP address listed for your instance to the eth0
network interface.
dhclient
Type the following command to display the assigned IP address. The IP address will be listed immediately after inet
and before netmask
. (Example: inet 192.0.2.1
netmask)
ifconfig eth0
Type the following command to start the SSH server.
/usr/sbin/sshd
If using the scp
command from a command line on a client machine, use the following command below as a template to retrieve the /tmp/luks-header-backup.img
file. Replace 25782
with the actual port number assigned in the /etc/ssh/sshd_config
. Replace 192.0.2.1
with the actual assigned IP address.
scp -P 25782 root@192.0.2.1:/tmp/luks-header-backup.img .
After the retrieval of luks-header-backup.img
file, immediately kill the SSH server by typing the command below in the noVNC console window.
killall sshd
Open the LUKS partition in order to set up the LVM physical volume that will reside inside.
cryptsetup luksOpen /dev/vda3 centos
Input the passphrase created earlier to open the LUKS partition when prompted, then press the Enter
key.
Enter passphrase for /dev/vda3
: strong-password
Type the following command below:
ls /dev/mapper
It will contain the following files named centos
, control
, live-base
and live-rw
. The centos
is the LUKS partition.
Type the following command below to create the LVM physical volume.
pvcreate /dev/mapper/centos
When successful, you will receive the following message:
Physical volume "/dev/mapper/centos" successfully created
Type the following command below to create the LVM volume group.
vgcreate ssd /dev/mapper/centos
When successful, you will receive the following message:
Volume group "ssd" successfully created
Type the following command below to create a LVM logical volume for a swap partition. Use sound judgment to create a swap partition, of the necessary size (-L = size of the volume), based on your VPS instance.
lvcreate -L 1G -n swap ssd
When successful, you will receive the following message:
Logical volume "swap" created
Type the following command below to create a LVM logical volume for the root partition. This will use the remaining free space while reserving five percent (5%) to contain LVM snapshots of your logical volumes if you so choose.
lvcreate -l 95%FREE -n root ssd
When successful, you will receive the following message:
Logical volume "root" created
Display the LVM physical volume.
pvdisplay
You will see text in the noVNC console similar to what is pictured in the image below.
Display the LVM volume group.
vgdisplay
You will see text in the noVNC console similar to what is pictured in the image below.
Display the LVM logical volume(s).
lvdisplay
You will see text in the noVNC console similar to what is pictured in the image below.
Type the following command below to deactivate the LVM volume group. This must be completed in order to allow cryptsetup
to close the LUKS partition in the next step.
vgchange -a n
When successful, you will receive the following message:
0 logical volume(s) in volume group "ssd" now active
Close the LUKS volume.
cryptsetup luksClose centos
Type the following command below:
ls /dev/mapper
It will contain the following files named control
, live-base
and live-rw
. The centos
file, containing the LUKS partition, will be missing to ensure that that it was closed properly.
Type reboot
and press the Enter
key to reboot.
Step 4: Start The CentOS 7 GUI Mode Installer
Select the Install CentOS Linux 7
option and press the Enter
key.
The VPS will now boot into the GUI mode CentOS installer. You will see a screen in the noVNC console like pictured in the image below. Select Install CentOS 7
(1) and press the Enter
key.
On the WELCOME TO CENTOS 7
screen, click the blue Continue
button (1).
Attention If you’re not using the default language of English and the locale of the United States, input your language in the search bar (1). Click on the language (2) and the appropriate locale (3) associated with it. When satisfied, click the blue Continue
button (4).
On the INSTALLATION SUMMARY
screen, click on INSTALLATION DESTINATION (Automatic partitioning selected)
(1) under SYSTEM
.
On the INSTALLATION DESTINATION
screen, select the I will configure partitioning
(1) option under Other Storage Options (Partitioning)
and click the blue Done
button (2) at the top left of the screen.
On the MANUAL PARTITIONING
screen, click on the Unknown
expandable accordion (1). It will reveal three partitions named BIOS Boot (vda1)
, Unknown (vda2)
and Encrypted (LUKS) (vda3)
.
With the BIOS Boot
partition highlighted in blue (1), select the checkbox option of Reformat
(2) next to the File System:
accordion and click the Update Settings
button (3).
Click on the Unknown
partition (1) so that it is highlighted in blue. Select the checkbox option of Reformat
(2) next to the File System:
accordion. Select ext2
in the File System:
accordion (3), enter /boot
in the text field (4) under Mount Point:
, enter boot
in the text field (5) under Label:
and click the Update Settings
button (6).
Click on the Encrypted (LUKS)
partition (1) so that it is highlighted in blue. Enter the passphrase you created for LUKS partition in Step 3: Setup LVM On LUKS Full Disk Encryption
in the Passphrase:
text field (2) and click the Unlock
button (3).
A new Unknown
expandable accordion (1) will appear. It will reveal two partitions named Unknown (ssd-root)
and Unknown (ssd-swap)
.
With the Unknown (ssd-root)
partition (1) highlighted in blue, select the checkbox option of Reformat
(2) next to the File System:
accordion. Select xfs
in the File System:
accordion (3), enter /
in the text field (4) under Mount Point:
, enter root
in the text field (5) under Label:
and click the Update Settings
button (6).
Click on the Unknown (ssd-swap)
(1) partition so that it is highlighted in blue. Select the checkbox option of Reformat
(2) next to the File System:
accordion. Select swap
in the File System:
accordion (3), enter swap
in the text field (4) under Label:
and click the Update Settings
button (5).
Click the blue Done
button (1) at the top left of the screen.
A box named SUMMARY OF CHANGES
will pop up. Click the Accept Changes
button (1). This will bring you back to the WELCOME TO CENTOS 7
screen.
Click on NETWORK & HOST NAME (Not connected)
(1) under SYSTEM
.
On the NETWORK & HOST NAME
screen, move the slider (1), next to the right of Ethernet(eth0)
field, from the OFF
position to the ON
position. If you want to use a custom hostname instead of the default (192.0.2.1.vultr.com) in the Host name:
text box (2), change it. Click the blue Done
button (3) at the top left of the screen. This will bring you back to the WELCOME TO CENTOS 7
screen.
When you are satisfied with the options on the WELCOME TO CENTOS 7
screen, click the blue Begin Installation
button (1).
On the CONFIGURATION
screen, click on ROOT PASSWORD (Root password is not set)
(1) under USER SETTINGS
.
On the ROOT PASSWORD
screen, enter a strong password in both the Root Password:
(1) and Confirm:
(2) text fields. Click the blue Done
button (3) at the top left of the screen. This will bring you back to the CONFIGURATION
screen.
On the CONFIGURATION
screen, click on USER CREATION (No user will be created)
(1) under USER SETTINGS
.
On the CREATE USER
screen, enter your full name in the Full name
text field (1), an username in the User name
text field (2), a strong password in both the Password
(3) and Confirm password
(4) text fields. Click on the Advanced...
button (5).
A box named ADVANCED USER CONFIGURATION
will pop up. In the Add user to the following groups:
text field (1) under Group Membership
, enter wheel
and click the Save Changes
button (2).
Click the blue Done
button (1) at the top left of the screen.
The post-installation process will now commence. It will take a few minutes to complete. When it is finished, click on the blue Reboot
button (1) to reboot your VPS instance.
Navigate back to the VULTR Server Management Screen. Click on the Settings
link at the top. Click on Custom ISO
on the menu on the left side. On the Custom ISO
page, click on the Remove ISO
button to unmount the ISO and reboot into your CentOS 7 VPS instance. Click the OK
button when prompted and the VPS instance will reboot.
Navigate back to the View Console
window to access the VPS instance via the noVNC console. Refresh the window if noVNC has disconnected.
You will be prompted to enter the passphrase (Example: Please enter passphrase for disk primary (luks-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)!:
) you created for LUKS partition in Step 3: Setup LVM On LUKS Full Disk Encryption
. Enter the passphrase and press the Enter
key.
You will then be presented with the console login prompt. You can now close the noVNC console window.
Step 5: Update The System
Log in via SSH with a regular user and update the system as follows.
sudo yum install epel-release -y
sudo yum clean all && sudo yum update -y
Step 6: Install Dracut-Crypt-SSH
While still logged in as a regular user, type the following commands below to install dracut-crypt-ssh
.
sudo yum install wget -y
sudo wget -O /etc/yum.repos.d/rbu-dracut-crypt-ssh-epel-7.repo https://copr.fedorainfracloud.org/coprs/rbu/dracut-crypt-ssh/repo/epel-7/rbu-dracut-crypt-ssh-epel-7.repo
sudo yum install dracut-crypt-ssh -y
Type the following command below to install the nano
editor to ease editing of files.
sudo yum install nano -y
You will need to edit the default grub file located in /etc/default/grub
.
sudo nano /etc/default/grub
Insert rd.neednet=1 ip=dhcp
between GRUB_CMDLINE_LINUX="crashkernel=auto
and rd.luks.uuid=luks-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
.
Save the file by entering the following keyboard combinations. Press the Ctrl
+ x
keys, press the y
key and press the Enter
key.
Regenerate you GRUB configuration file by type the command below.
sudo grub2-mkconfig -o /etc/grub2.cfg
Backup the original /etc/dracut.conf.d/crypt-ssh.conf
by typing the following command below.
sudo mv /etc/dracut.conf.d/crypt-ssh.conf /etc/dracut.conf.d/crypt-ssh.conf.orig
Create a new /etc/dracut.conf.d/crypt-ssh.conf
file by typing the following command below.
sudo nano /etc/dracut.conf.d/crypt-ssh.conf
Copy and paste the following text below into the nano
editor.
dropbear_acl="/etc/dropbear/keys/authorized_keys"
dropbear_ecdsa_key="/etc/dropbear/keys/ssh_ecdsa_key"
dropbear_rsa_key="/etc/dropbear/keys/ssh_rsa_key"
Create the directory keys
under /etc/dropbear/
, with the necessary directory permissions, that will hold the authorized_keys
, ssh_ecdsa_key
and ssh_rsa_key
files.
sudo mkdir /etc/dropbear/keys/; sudo chmod /etc/dropbear/keys/
Generate the ssh_ecdsa_key
and ssh_rsa_key
files with the ssh_keygen
program by typing the following commands below. Press the Enter
key twice, for each command, when prompted for passphrases.
sudo ssh-keygen -t ecdsa -f /etc/dropbear/keys/ssh_ecdsa_key
sudo ssh-keygen -t rsa -f /etc/dropbear/keys/ssh_rsa_key
Change the file permissions on ssh_ecdsa_key
, ssh_ecdsa_key.pub
, ssh_rsa_key
and ssh_rsa_key.pub
by typing the command below.
sudo chmod 400 /etc/dropbear/keys/*_key; sudo chmod 444 /etc/dropbear/keys/*.pub
Generate public keys using the How Do I Generate SSH Keys?
tutorial, found at the beginning of the tutorial under Prerequisites
, for your prospective client operating system.
Copy and paste all the text in the public key into the /etc/dropbear/keys/authorized_keys
file using the nano
program by typing the command below.
sudo nano /etc/dropbear/keys/authorized_keys
You must first build the initramfs and any subsequent update of the dracut-crypt-ssh configuration. Type the following command below for the initial build of the initramfs.
sudo dracut -f
Once that’s complete, your CentOS 7 install is set up to listen for your SSH client to connect and allow you to unlock the LUKS partition using your passphrase. You may now reboot your CentOS 7 instance by typing the command below.
sudo reboot
On your client systems, refer to sections 3.3. Unlocking the volumes interactively
and 3.4. Unlocking using the
unlockcommand
of the Dracut-Crypt-SSH GitHub page to either force a passphrase prompt or use the unlock
command to open your LUKS partition from your SSH client.
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