Copy protection for optical discs

An optical disc carrying a plurality of pits and lands in its surface, each defining a state transition and thereby defining data, the data comprising:

• data patterns, the data patterns being originally such that the data patterns cannot be accurately copied onto another disc by a writer for recordable discs which has a limited ability to look ahead during encoding, wherein the original data patterns have a DSV (digital sum value) which has a rapid rate of change;
• the data patterns making up an authenticating signature;
• wherein the original data patterns having been subjected to an exclusive Or (XOR) scrambling algorithm;
• the scrambled data patterns of the authenticating signature and other data having been applied to the optical disc in a mastering process, wherein the mastering process includes using a laser beam recorder controlled by an encoder which has a larger ability to look ahead than the writer;
• the scrambled data patterns having been encoded using EFM (eight to fourteen modulation) with a second XOR scrambling algorithm having the same pattern of scrambling data as the first XOR scrambling algorithm;
• and
• the twice scrambled data patterns and other data having been applied to the optical disk;
• wherein transitions in the EFM signal from the applied data patterns are shifted from their ideal values, or the ability of disc drives to maintain optimal head positioning is compromised by the twice scrambled data patterns.