Allows you to create a different encryption password for booting your device than unlocking your screen. This allows you to have a stronger device encryption password (which you only need to enter once after booting your device) and a simpler pattern/PIN/password for unlocking your screen. If an attacker tries to guess your simple pattern/PIN/password, he has only few tries (default is 3) after which the device is rebooted and he needs to enter your strong device encryption password again. Root privileges required.