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A method of copy protection for recordable media
Disclosed is a method for preventing illegal copying of copy-righted materials recorded
on media such as optical discs. This method takes advantage of natural defects found
in the recording media. Many approaches exists that make artificial defects by ways
such as punching holes or by simply marking a certain area defected to fool players.
These method can be easily defeated because these defects can be easily reproduced
on new media. The disclosed method is harder to defeat because the defect cannot be
easily reproduced.
The method includes the following steps.
(1) At the time of formatting the disc, locate a small portion of the disc space that
contains natural defects, and format the rest space as usual.
(2) At the time of recording, read the defects to obtain an encryption key by encoding
the "noisy" defects with a well known strong error correction code.
(3) Encode the copy-righted material with the encryption key and record on the disc.
(4) At the time of play back, the encryption key is reconstructed in the same way as
described in step (2). Use this key to decrypt the material.
If the encrypted contents is copied from one disc to another, the contents cannot be
decrypted at the time of play back because the original encryption key cannot be
reconstructed from the new disc.
The construction of the encryption key is only needed each time before play back, so
that a strong error correction code can be used to gua...
