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

Encryption key information read from an encryption key information storage medium is used to generate an encryption key. Input image data are made into encrypted data using the encryption key. The encrypted data are written into a data storage medium, and first encryption key-related information read from the encryption key information storage medium is written into the data storage medium. The encrypted data and second encryption key-related information are read from the data 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.