Encrypting volumes for sensitive data

Reviewed on 03 October 2024 • Published on 04 February 2019

encryption
Cryptsetup

To protect sensitive commercial or client data stored on your Instances, encryption is paramount. The repercussions of such data falling into unauthorized hands can be detrimental to your business. Encrypting the entire volume is the optimal strategy, alleviating concerns about individual folders. By using this method, all sensitive information can reside on an encrypted volume, fortified by an extra layer of security. This tutorial will walk you through the process of encrypting an additional volume using Cryptsetup with LUKS, a universally recognized on-disk format employed in various encryption tools.

Before you start

To complete the actions presented below, you must have:

A Scaleway account logged into the console
Owner status or IAM permissions allowing you to perform actions in the intended Organization
An SSH key
An Instance
A Block Storage volume connected to the Instance
sudo privileges or access to the root user

Installing Cryptsetup

Connect to your Instance via SSH.

Update the apt sources and the software already installed on the Instance:

apt update && apt upgrade -y

Install Cryptsetup on the Instance:

apt install cryptsetup-bin

Enter the command lsblk. This lists your volumes to help you determine which is the additional volume to encrypt:

root@encrypted-disk:~# lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
vda     252:0    0 46.6G  0 disk
|-vda1  252:1    0 46.5G  0 part /
`-vda15 252:15   0  100M  0 part /boot/efi
vdb     252:16   0 46.6G  0 disk

In this example, the space of vdb is not mounted and represents the additional volume of the Instance.

Note

The name of your additional volume may be different, eg sda or other, depending on the Instance type and OS. Replace with the name corresponding to your volume where necessary.

Encrypting the volume

Encrypt the volume vdb with Cryptsetup:

cryptsetup luksFormat /dev/vdb

Tip

On low memory Instances, you may run into out of memory (OOM) errors when running cryptsetup luks{Format,Open} commands on large volumes. To avoid them, add --pbkdf pbkdf2 to your command:

cryptsetup luksFormat --pbkdf pbkdf2 /dev/vdb

A warning appears, reminding you that all data on the volume will be lost.

WARNING!
========
This will overwrite data on /dev/vdb irrevocably.
Are you sure? (Type uppercase yes):

Type YES and press the Enter key, to confirm you want to overwrite the data.

Important
Make sure you have a backup of your data on this volume before you launch Cryptsetup. Your data will be irrevocably overwritten and lost.

A message appears, asking you to configure a passphrase. A passphrase is the key to decrypt the data on the volume.
Type your passphrase and press Enter. For increased security, your passphrase should be a secure and random phrase. If required, you may use a Passphrase generator.

A message appears, asking you to verify your passphrase.
Type your passphrase again to confirm it, then press Enter on your keyboard to encrypt the disk.

Important
If you forget your passphrase, you will not be able to recover your data. Make sure that you store your password securely.

Your volume is now encrypted.

Mapping the encrypted volume

Type the following command to create a mapping (crypthome) of the volume:

cryptsetup luksOpen /dev/vdb crypthome

Enter your passphrase when requested, and press the Enter key on your keyboard:

Enter passphrase for /dev/vdb:

Run the following command to verify the status of the encrypted volume:

cryptsetup -v status crypthome

An output similar to the following appears:

/dev/mapper/crypthome is active.
  type:    LUKS1
  cipher:  aes-xts-plain64
  keysize: 256 bits
  key location: dm-crypt
  device:  /dev/vdb
  sector size:  512
  offset:  4096 sectors
  size:    97652154 sectors
  mode:    read/write
Command successful.

Formatting the encrypted volume

Start by writing zeros to the encrypted volume. This allocates zeros to block data, to ensure that it appears as random data. This provides protection against disclosure of usage patterns:

Install pv (if not already installed) by running the following command:

apt install pv

Launch the following command to run dd:

pv -tpreb /dev/zero | dd of=/dev/mapper/crypthome bs=128M

Important

Depending on the size of your volume this may take some hours to finish.

Once finished, a message similar to the following displays:

dd: error writing '/dev/mapper/crypthome': No space left on device                        <=>                                                 ]
46.6GiB 0:05:29 [ 144MiB/s] [                                                               <=>                                               ]
56+64649 records in
56+64648 records out
49997902848 bytes (50 GB, 47 GiB) copied, 331.56 s, 151 MB/s

Create a file system on the encrypted volume by running the following command:

mkfs.ext4 /dev/mapper/crypthome

An output similar to the following displays once the file system is created:

mke2fs 1.44.1 (24-Mar-2018)
Creating filesystem with 12206519 4k blocks and 3055616 inodes
Filesystem UUID: 80b43994-affd-4687-b7d2-8cfa91303694
Superblock backups stored on blocks:
  32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
  4096000, 7962624, 11239424
Allocating group tables: done
Writing inode tables: done
Creating journal (65536 blocks): done
Writing superblocks and filesystem accounting information: done

Mounting the encrypted volume

Create a folder to mount the volume:

mkdir /mnt/crypthome

Mount the encrypted volume with the following command:

mount /dev/mapper/crypthome /mnt/crypthome/

Verify with lsblk that the volume is mounted:

NAME        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
vda         252:0    0 46.6G  0 disk
|-vda1      252:1    0 46.5G  0 part  /
`-vda15     252:15   0  100M  0 part  /boot/efi
vdb         252:16   0 46.6G  0 disk
`-crypthome 253:0    0 46.6G  0 crypt /mnt/crypthome

The encrypted volume is now mounted at /mnt/crypthome and you can transfer your sensitive data to the volume.

Unmounting the encrypted volume

Unmount the volume from your Instance:

umount /mnt/crypthome

Close the LUKS session with Cryptsetup:

cryptsetup luksClose crypthome

Verify that the volume has been unmounted with lsblk:

NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
vda     252:0    0 46.6G  0 disk
|-vda1  252:1    0 46.5G  0 part /
`-vda15 252:15   0  100M  0 part /boot/efi
vdb     252:16   0 46.6G  0 disk

As you can see, the following lines have disappeared:

vdb         252:16   0 46.6G  0 disk
`-crypthome 253:0    0 46.6G  0 crypt /mnt/crypthome

Remounting the encrypted volume

Use Cryptsetup to open the LUKS session and enter the passphrase when prompted:

cryptsetup luksOpen /dev/vdb crypthome

Mount the volume in the Instance:

mount /dev/mapper/crypthome /mnt/crypthome

Verify that the volume appears with lsblk:

NAME        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
vda         252:0    0 46.6G  0 disk
|-vda1      252:1    0 46.5G  0 part  /
`-vda15     252:15   0  100M  0 part  /boot/efi
vdb         252:16   0 46.6G  0 disk
`-crypthome 253:0    0 46.6G  0 crypt /mnt/crypthome

As you can see, the following lines have reappeared. This means your encrypted volume is mounted again and you can use it to store or access your sensitive data:

vdb         252:16   0 46.6G  0 disk
`-crypthome 253:0    0 46.6G  0 crypt /mnt/crypthome

Changing the LUKS passphrase

LUKS supports up to 8 passphrases for each encrypted volume. You may wish to change the passphrase of your encrypted volume, which you can do as follows:

Check if there is still space available by retrieving the LUKS headers:

cryptsetup luksDump /dev/vdb

The list of available key slots displays:

Key Slot 1: DISABLED
Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED

As you can see 7 slots are available for the volume.

Type the following command and enter any current passphrase:

cryptsetup luksAddKey /dev/vdb

When prompted, enter the new passphrase and its confirmation:

Enter new passphrase for key slot:
Verify passphrase:

Verify that the new passphrase has been taken into account by retrieving the LUKS headers:

cryptsetup luksDump /dev/vdb

Scroll down to the list of available keys, the output should be similar to the following:

Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED

As you can see only 6 slots are available now, meaning that the new key has been configured.

Remove the old passphrase with the following command:

cryptsetup luksRemoveKey /dev/vdb

Enter the passphrase to delete and confirm by pressing Enter.

Verify that the key has been removed by retrieving the LUKS headers:

cryptsetup luksDump /dev/vdb

In the list of available key slots, 7 slots are available again.

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