Full disk decryption logic
/lib/systemd/systemd-cryptsetup
[email protected] is a service responsible for setting up encrypted block devices. It is instantiated for each device that requires decryption for access.
[email protected] will ask for hard disk passwords via the \m[blue]password agent logic\m[]\s-2\u[1]\d\s+2, 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 [email protected] units by systemd-cryptsetup-generator(8).
password agent logic
http://www.freedesktop.org/wiki/Software/systemd/PasswordAgents