Anti-tampering signature method for rewritable media, anti-tampering signature apparatus for executing the method, anti-tampering signature system provided with the apparatus, and computer-readable recording medium storing anti-tampering signature program for achieving the method

An anti-tampering signature apparatus is provided with an extraction portion for extracting a characteristic quantity that represents a characteristic of image data according to an instruction from a certifier who has certified display data, an encryption/decryption portion that generates encrypted data by encrypting the characteristic quantity using an encryption key paired with an identifier and decrypts the encrypted data into the characteristic quantity, a media writing portion that appends the identifier and the encrypted data to a rewritable medium, and a controller that judges whether or not the decrypted characteristic quantity and the characteristic quantity extracted from image data generated by reading the display data match.