To permit only the specific device to reproduce digital data such as video images and sounds.

First encryption key-related information having four items of information, i.e. registration date/time information, and medium unique information, issuing time information and creating date/time information which are read by the authentication reading means are written into an encryption key information storage medium. Encrypted data and encryption key-related information are read from a data storage medium storing the encrypted data encrypted using an encryption key based on encryption key information owned by an authentication storage medium used in a device side executing encryption, and second encryption key-related information obtained based on information owned by the authentication storage medium. The encryption key information read from the encryption key information storage medium is used to generate a decryption key, and the decryption key is used to decrypt the encrypted data read from the data storage medium. Decryption is controlled by the first and second encryption key-related information.