How to Mount an Encrypted LUKS Partition without Password using Keyfile

Setup the keyfile

• Create the keyfile with which we’re gonna decrypt the encrypted partition.

dd if=/dev/random of=/secure/keyfile.bin bs=512 count=8

• The default location for cryptsetup key files is /etc/cryptsetup-keys.d/cryptdevicename.key. If no kefile is mention in the crypttab file then systemd will look into that default location.

• Add the key to the disk header.

sudo cryptsetup -v luksAddKey /dev/sda4 /secure/keyfile.bin

• Check if the keyfile was added successfully. If you see another key slot is enabled (In this case the second key or Key slot 1), then it was successful.

$ sudo cryptsetup luksDump /dev/sdb1 | grep "Key Slot"
Key Slot 0: ENABLED
Key Slot 1: ENABLED
Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED

Or,

$ sudo cryptsetup luksDump /dev/sdb1 | grep "KeySlots"

• Check if the encrypted partition unlockes with that keyfile.

$ sudo cryptsetup -v luksOpen /dev/sdb1 sdb1_crypt --key-file=/etc/luks-keys/disk_secret_key
Key slot 1 unlocked.
Command successful.

• Close the encrypted partition.

$ sudo cryptsetup -v luksClose sdb1_crypt
Command successful.

Auto mount on boot time

• Get the UUID of the encrypted partition.

$ sudo cryptsetup luksDump /dev/sdb1 | grep "UUID"
UUID:          	2a2375bf-2262-413c-a6a8-fbeb14659c85

• The /etc/crypttab config file to decrypt and mount the encrypted partition on /dev/mapper/.

# /etc/crypttab configuration file 

Data UUID=2a2375bf-2262-413c-a6a8-fbeb14659c85 /secure/keyfile.bin luks,nofail

The nofail option is to be used for secondary non-root partitions on which the boot does not rely. The nofail option allows the system to continue boot without waiting for this partition to decrypt. Otherwise, the system will wait for it to decryp which will slow down boot time.

• On systemd systems perform:

sudo systemctl daemon-reload

• Check if the config is working.

$ sudo cryptdisks_start sdb1_crypt
 * Starting crypto disk...
 * sdb1_crypt (starting)..
 * sdb1_crypt (started)...                 [ OK ] 

Or,

$ sudo systemctl start systemd-cryptsetup@cryptssd.service
$ sudo cryptsetup status cryptssd
/dev/mapper/cryptssd is active.
  type:    LUKS2
......
......

• Then configure the /etc/fstab config file to mount the mapped device.

# /etc/fstab file

/dev/mapper/Data /media/Data ext4    defaults   0       0

• It’s better to limit the permission on the keyfile.

sudo chmod 000 /secure/keyfile.bin

Done!