In a recordable data storage medium on which property data was recorded after having been modulated and on which data that is decodable by a cryptographic key to be generated from the property data was recorded, the property data was preferably modulated by a different method from that applied to a read-only data storage medium. Then, an optical disc drive, having no ability to distinguish the recordable data storage medium from the read-only data storage medium, cannot read the recordable data storage medium. Consequently, a greater number of drives should be equipped with the function of recognizing the type of a given data storage medium and the copyright protection function should be consolidated.