Patent ID: 7533267

Claim:
An anti-tampering signature method comprising the steps of: providing a rewriteable medium including (i) an information display area wherein display data is stored in a visually viewable, rewritable and erasable state, (ii) a plurality of display data certifier identification areas wherein display data certifier signature information is stored in a visually viewable, rewritable and erasable state; and (iii) a plurality of certification data areas corresponding respectively to each said certifier identification area for displaying and storing certification data respectively indicates a registration status of an associated certifier signature information in a visually viewable, rewritable and erasable state; determining whether or not said certifier signature information contained in each of said plurality of display data certifier identification areas, or to be added to one or more of said display data certifier identification areas, matches with corresponding registered certifier signature information stored in, or separately added to, a registered certifier signature information database, and, in those cases wherein a match is judged to be present, adding said registration status of said certifier signature information to said certification data areas associated with the certifier identification area displaying said certifier signature information, and in those cases wherein a match is not judged to be present, issuing a warning that signature tampering may have occurred; extracting as a characteristic quantity a general characteristic of image data generated by reading the display data according to an instruction from a certifier who has certified the display data, generating encrypted data by encrypting said characteristic quantity using an encryption key paired with an identifier, appending each said identifier and its associated encrypted data to the rewritable medium in a certification data area corresponding to the certifier who issued the instruction for the extraction of the characteristic information, obtaining the encryption key based on the identifier according to an instruction of a verifier who verifies a certificate, decrypting the obtained characteristic quantity of the display data, and judging whether or not the decrypted characteristic quantity obtained by decrypting the encrypted data and the characteristic quantity of the display data match, and, in those cases wherein a match is not judged to be present, issuing a warning that signature tampering may have occurred.