An optical disc is authenticated by measuring physical attributes of the disc. A challenge is presented to the drive comprising the disc. The challenge includes locations on the disc to be used for authentication. The locations are determined each time the disc is to be authenticated. No restriction is placed on the locations on the medium, and no restriction is placed on the number of locations. Locations on the disc are accessed and an answer to the challenge is calculated in accordance with a physical attribute pertaining to the locations. The answer can include an angle between the locations, the physical separation between the locations, an amount of time elapsed between detection of the locations, an amount of time taken to read data between written between the locations, or a number of rotations occurring between detection of the locations. The answer is analyzed to determine the validity of the disc.