| 摘要 |
PURPOSE:To surely detect the alteration of information recorded in the optical memory of an optical card and to prevent damage by the alteration. CONSTITUTION:At the time of recording the information in the optical memory, the array 1 of pits for expressing the recording information and the array 2 of the pits provided with a pit pattern for which the array 1 is inverted are recorded in the optical memory in a pair. When the recorded information inside the optical memory is altered, since excessive pits are added to the pit array 1 or 2, inversion relation between the pit arrays 1 and 2 is destroyed. At the time of reading the recorded information, whether or not the pit patterns of both are in the inversion relation is checked by calculating the exclusive OR of the pair of the pit arrays 1 and 2 and it is judged that the alteration is not performed when they are in the inversion relation and that the alteration is performed when the inversion relation is destroyed. |
