Copy protection for optical discs
Optical discs, such as CDs, have been protected by the use of an authenticating signature which cannot be copied to another disc. A playing device is required to identify the existence of the authenticating signature in order to access the content of the disc. The authenticating signature may comprise bad sectors at known locations. CD writers now available to consumers allow error detection and error correction data to be specified and this has led to circumvention techniques designed to simulate an original disc. During the writing of a copy disc, bad sectors are identified and provided with alternative data together with incorrect error detection and error correction data. When the copy disc is played bad sectors are reported in exactly the same locations as reported by the original disc thereby enabling the disc to be played even though it is a copy. To defeat techniques which use the error detection and error correction data to circumvent the copy protection, it is proposed to store authenticating signatures in sectors in Mode 2 format. Sectors formatted in this way are not subject to error detection and correction.
1 . A copy protected optical disc carrying an authentication signature, the authentication signature being arranged so that it cannot be accurately copied by a writer of recordable discs, and wherein the authenticating signature is located on the optical disc in such a manner which identifies that there is no error detection nor error correction data associated therewith.
2 . A copy protected optical disc according to claim 1 , carrying data in sectors, and wherein the authenticating signature is provided in at least one sector on the optical disc which is in Mode 2 format.
3 . A copy protected optical disc according to claim 1 , carrying data in sectors, wherein the authenticating signature is provided in at least one sector on the optical disc which is in Mode 2 format, and wherein the authenticating signature is accompanied in the or each sector by appropriate error detection and error correction data.
4 . A copy protected optical disc according to claim 1 , carrying a sequence of bits representing data stored on the disc, the sequence of bits being arranged in sectors, and wherein the authenticating signature has been produced by altering selected bits in at least one sector to provide a pattern of erroneous bits which cannot be corrected during playback.
5 . A copy protected optical disc according to claim 4 , wherein the sequence of bits comprises bits representing content and error correction and error detection data, and wherein the bits which have been altered are bits representing content.
6 . A copy protected optical disc according to claim 1 , wherein the authenticating signature is made up of data patterns chosen to cause DSV problems for writers of recordable discs.
7 . A copy protected optical disc according to claim 6 , wherein the data patterns are chosen to ensure that the DSV has a significant absolute value.
8 . A copy protected optical disc according to claim 6 , wherein the data patterns which are chosen to cause DSV problems are arranged to have a DSV which has a rapid rate of change.
9 . A copy protected optical disc carrying a sequence of bits representing the data stored on the disc, the sequence of bits being arranged in sectors, the optical disc having an authentication signature in at least one sector, the authentication signature having been produced by altering selected bits to provide a pattern of erroneous bits which cannot be corrected during playback, and wherein the authenticating signature is located on the optical disc in a manner which identifies that there is no error detection nor error correction data associated therewith.
10 . A copy protected optical disc according to claim 9 , carrying data in sectors and wherein the authenticating signature is provided in at least one sector on the optical disc which is in Mode 2 format.
11 . A copy protected optical disc according to claim 9 , carrying data in sectors, and wherein the authenticating signature is provided in at least one sector on the optical disc which is in Mode 2 format, and wherein the authenticating signature is accompanied in the or each sector by appropriate error detection and error correction data.
12 . A copy protected optical disc according to claim 9 or claim 10 , wherein the sequence of bits comprises bits representing content and error correction and error detection data, and wherein the bits which have been altered are bits representing content.
13 . A copy protected optical disc carrying data arranged in sectors and having an authenticating signature in at least one sector, wherein the authenticating signature is made up of data patterns chosen to cause DSV problems for writers of recordable discs, and wherein the authenticating signature is located on the optical disc in a manner which identifies that there is no error detection nor error correction data associated therewith.
14 . A copy protected optical disc according to claim 13 , carrying data in sectors and wherein the authenticating signature is provided in at least one sector on the optical disc which is in Mode 2 format.
15 . A copy protected optical disc according to claim 13 , carrying data in sectors, and wherein the authenticating signature is provided in at least one sector on the optical disc which is in Mode 2 format, and wherein the authenticating signature is accompanied in the or each sector by appropriate error detection and error correction data.
16 . A copy protected optical disc according to claim 13 or claim 14 , wherein the data patterns are chosen to ensure that the DSV has a significant absolute value.
17 . A copy protected optical disc according to claim 13 or claim 14 , wherein the data patterns which are chosen to cause DSV problems are arranged to have a DSV which has a rapid rate of change.
18 . A method of copy protecting optical discs, the method comprising adding an authenticating signature to an optical disc during its mastering process, the authenticating signature being arranged so that it cannot be accurately copied by a writer for recordable discs, and the method further comprising locating the authenticating signature on the optical disc in a manner which identifies that there is no error detection nor error correction data associated therewith.
19 . A method of copy protecting optical discs according to claim 18 , further comprising arranging data carried by the optical disc in sectors, and providing the authenticating signature in at least one sector on the optical disc which is in Mode 2 format.
20 . A method of copy protecting optical discs according to claim 19 , further comprising accompanying the authenticating signature in the or each sector with appropriate error detection and error correction data.
21 . A method of copy protecting optical discs according to claim 18 or claim 19 , the method comprising representing data on the optical disc by a sequence of bits encoded onto the disc, and arranging the bits of the sequence in sectors, and producing the authenticating signature by altering selected bits to provide a pattern of erroneous bits which cannot be corrected during playback.
22 . A method of copy protecting optical discs according to claim 18 or claim 19 , the method comprising making up the authenticating signature from data patterns chosen to cause DSV problems for writers of recordable discs, arranging data carried by the disc in sectors, and locating the authenticating signature in at least one sector.
23 . A content file for use in manufacturing a copy protected optical disc carrying an authentication signature, the authentication signature being arranged so that it cannot be accurately copied by a writer of recordable discs, the content file comprising data to be stored on the optical disc, the data being arranged in sectors and being provided with appropriate error detection and error correction data, and the data including the authentication signature which is arranged in at least one sector, the or each sector containing the authentication signature being formatted in a manner which identifies that there is no error detection nor error correction data associated with the authenticating signature.
24 . A content file for use in manufacturing a copy protected optical disc carrying an authentication signature according to claim 23 , wherein the or each sector in which the authenticating signature is arranged is in Mode 2 format.
25 . A content file for use in manufacturing a copy protected optical disc carrying an authentication signature according to claim 24 , wherein the or each sector containing the authenticating signature also contains appropriate error detection and error correction data.
26 . A content file for use in manufacturing a copy protected optical disc carrying an authentication signature according to claim 23 , wherein the data is to be encoded to form a sequence of bits to be stored on the optical disc, and wherein the content file includes means for altering selected bits of the sequence of bits during encoding to provide a pattern of erroneous bits defining the authenticating signature.
27 . A content file for use in manufacturing a copy protected optical disc carrying an authentication signature according to claim 23 , wherein the authenticating signature is made up of data patterns chosen to cause DSV problems for writers of recordable discs.
28 . A content file for use in manufacturing a copy protected optical disc carrying an authentication signature according to claim 27 , wherein the data patterns are chosen to ensure that the DSV has a significant absolute value.
29 . A content file for use in manufacturing a copy protected optical disc carrying an authentication signature according to claim 27 , wherein the data patterns which are chosen to cause DSV problems are arranged to have a DSV which has a rapid rate of change.