In recent years, as a result of progress in digital information compression techniques and widespread use of global communication infrastructures such as the Internet, copyright works such as music, images, video, and games are distributed via communication lines to households as digital copyright works.
In order to establish a distribution system which protects the rights of copyright holders of digital copyright works and the profits of distributors, it is critical to prevent dishonest acts such as acquisition of a digital copyright work by communication interception, wiretapping, impersonation, and duplication and tampering of data received and stored in a storage medium. Therefore, copyright protection techniques, such as encryption and authentication for authenticating whether a system is authorized and scrambling data, are needed.
A variety of copyright protection techniques have been conventionally used. A representative technique is a challenge-response mutual authentication technique. In this technique, when accessing a confidential data storage area storing confidential data which requires copyright protection, a random number and a response value are exchanged between devices to mutually authenticate whether the other of them is authorized. The access is permitted only when the authentication is successful.
After the mutual authentication has been carried out between the authorized devices, an unauthorized party may impersonate one of the authorized device and dishonestly acquire confidential data by accessing the confidential data storage area.