A method to protect data of a drive from illegal accessing without
increasing the load of processing on the drive side and to prevent not
only illegal copying on the drive side but also an illegal action on the
host unit side. Authentication of the drive is executed by the host unit.
If the drive is authenticated, then a contents key is encrypted using a
host ID registered in advance in a storage area of the host unit and a
session key and first identification information read out from a storage
area of the drive. Then, the encrypted contents key is transferred to the
drive while contents data to be recorded and stored into the drive are
encrypted with the contents key by the host unit. Thereafter, the
encrypted contents data is transferred to the drive.
