Prerequisites
- an external hdd or usb key already partitioned
- cryptsetup
Initializing
First format the partition:
cryptsetup luksFormat /dev/<partition>
Now we have a fresh new luks volume. Let’s open it:
cryptsetup luksOpen /dev/<partition> <my_alias>
The volume should be available under /dev/mapper/<my_alias>
Create a filesystem inside the volume:
mkfs.ext4 /dev/mapper/<my_alias>
Perfect. Now close the lurks volume:
cryptsetup luksClose <my_alias>
Initialization is done. Next time you will connect your device your file manager should prompt a pop-up asking the passphrase of your key.
Further Reading and sources