Docs:
  https://www.cyberciti.biz/hardware/howto-linux-hard-disk-encryption-with-luks-cryptsetup-command/
  https://www.howtoforge.com/automatically-unlock-luks-encrypted-drives-with-a-keyfile

Assumptions:
  1) We are working on an Ubuntu 18.04 Machine
  2) We want to use /dev/sdX ( USB connected drive ) as the audomounted backup device on /mnt/backups


1) Make sure all components are installed:
  # sudo apt install cryptsetup`
2) Configure the encrypted Luks parition
  # cryptsetup -y -v luksFormat /dev/sdX
3) Initialize the volume and set the inital passphrase:
  # cryptsetup luksOpen /dev/sdX backups
4) Verify it looks right:
  # cryptsetup -v status backups
  # cryptsetup luksDump /dev/sdX
5) Create a blank partition to make sure the mkfs doesn't leave usage patterns
  # pv -tpreb /dev/zero | dd of=/dev/mapper/backups bs=128M
6) Make a Filesystem in the encrypted device:
  # mkfs.ext4 /dev/mapper/backups
7) Mount the Filesystem
  # Mount /dev/mapper/backups /tmp/backups


Automounting:
-------------
1) Put Credentials in a .txt file and lock it down:
  # ls -la /root/.credentials.backup
    -r-------- 1 root root 14 Jul 27 08:33 /root/.credentials.backup
2) Set up luks to use the keyfile by putting this in /etc/crypttab
  sdX_crypt      /dev/disk/by-uuid/61a7bd54-332d-43e8-97bd-e4534b2a67db  /root/.credentials.backup luks

3) Put an entry in /etc/auto/mnt
  backups        -fstype=auto   :/dev/mapper/backups
  * This is ext4, it can't have a uid=,gid= or umask=


FAQ:
----
How do I automatically unlock an encrypted partition?
  # sudo cryptdisks_start <volume_in_crypttab>
    sudo cryptdisks_start backups

How do I mount or remount encrypted partition?
  Type the following command:
  # cryptsetup luksOpen /dev/sdX backups
  # mount /dev/mapper/backups /backups
  # df -H
  # mount

How do I unmount and secure data?
  Type the following commands:
  # umount /backups
  # cryptsetup luksClose backups


Can I run fsck on LUKS based partition / LVM volume?
  Yes, you can use the fsck command On LUKS based systems:
  # umount /backups
  # fsck -vy /dev/mapper/backups
  # mount /dev/mapper/backups /tmp/backups

See how to run fsck On LUKS (dm-crypt) based LVM physical volume for more details.

How do I change LUKS passphrase (password) for encrypted partition?
  Type the following command
  ### see key slots, max -8 i.e. max 8 passwords can be setup for each device ####
  # cryptsetup luksDump /dev/sdX
  # cryptsetup luksAddKey /dev/sdX
  :  Enter any passphrase:
  :  Enter new passphrase for key slot:
  :  Verify passphrase:
  #  Add a keyfile contents to the luks volume
  # cryptsetup luksAddKey /dev/sdX /root/.credentials
  :  Enter any passphrase:
  :  Enter new passphrase for key slot:
  :  Verify passphrase:

Remove or delete the old password:
  # cryptsetup luksRemoveKey /dev/sdX