systemd-cryptsetup@.service, systemd-cryptsetup — Full disk decryption logic
systemd-cryptsetup@.service
/usr/lib/systemd/systemd-cryptsetup
systemd-cryptsetup@.service
                is a service responsible for setting up encrypted
                block devices. It is instantiated for each device that
                requires decryption for access.
systemd-cryptsetup@.service
                will ask for hard disk passwords via the 
                password agent logic, in order to query the
                user for the password using the right mechanism at
                boot and during runtime.
At early boot and when the system manager
                configuration is reloaded this
                /etc/crypttab is translated into
                systemd-cryptsetup@.service units
                by
                systemd-cryptsetup-generator(8).