Method and apparatus for preventing illegal copy or illegal installation of information of optical recording medium

An information reproducing system comprising means (17) for rotationally driving a disc-like optical recording medium (2) wherein information is recorded in a recording layer in the form of pits, an optical head (6) for reading out the recorded information from said optical recording medium, head-moving means (23) for making said optical head movable radially on said optical recording medium, and signal processing means for processing the information read out through said optical head, which system is characterized by including:

• first physical information detecting means (743, 38, 665) for detecting, on the basis of information read out through one of said optical head and a magnetic head, first physical feature information (532) which is representative of at least one of information of a two-dimensional physical arrangement of a pit or low-reflection section and a configuration of said pit or low-reflection section of said recording layer on said optical recording medium and which is enciphered and recorded at manufacture of said optical recording medium;
• decryption means (534) for decoding the first physical feature information into a plain text using disclosed key cipher system cipher function (695b, 698B, 735h);
• means (17a, 6, 38, 703a) for measuring a physical feature of said optical recording medium to detect second physical feature information indicative of at least one of information of a physical arrangement of said pit or low-reflection section and a configuration of said pit or low-reflection section;
• check means (535) for checking said second physical feature information with said first physical feature information already decoded into a plain text to make a decision as to whether or not both are in a specific relation to each other;
• and
• control means (717, 665) for, when the check means decides that said second physical feature information is not in the specific relation to said first physical feature information, stopping one of an operation of a specific program read out from said optical recording medium, a subsequent reading-out of information from said optical recording medium, and a given process of information, read out from the optical recording medium, the given process being practiced by said signal processing means.