Author: Dave Gomboc
Date: 13:56:40 10/10/00
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On October 10, 2000 at 15:41:27, Andrew Dados wrote: >There is one old and clever technique to 100% copy-protect a CD, but expensive. >It would require building custom burners for making original cds. > >The concept is to burn some part of track (lets call it a sector) with very poor >quality, so average read on that sector will give you errors. You'll need some >500 reads and average them to get 'true' content. Statistical analysis over many >reads can be used to proof originality. People used to protect games that were distributed on floppy disks in very similar ways. In fact, the more programmable the disk drive, the wackier things copy protectors would get it to do. I've seen software access track 255 on the floppy drives that were used with the commodore 64. Keep in mind now that on a normally-formatted disk for the 1540/1541 drives there were 35 tracks, and trying to move the head to read track 255 would break your disk drive. Needless to say, the track gap had been altered so that several tracks all partially overlapped each other. This also had the side effect that if a program was dumb enough to try to read and write tracks 1, 2, 3, 4 ... instead of tracks 1, 12, 19, 34 ... that the data would be misread and miscopied. All in all, the bottom line is that the devices are not constructed to be read-only for some portions of the media, so if you can read a disc recorded in some funky format, you can replicate it. Of course, this doesn't even consider that someone will simply write a crack to skip the code that is intended to verify that the copy protection is in place. I still recall with fondness one warez bragg that I read as a kid: "Copy protection in a routine! Dumbest idea yet!" Today, I'd imagine that more people licence or outsource their copy-protection code than ever. >There are other ways to make a custom CD impossible to copy in a burner. (Like >write a replacement driver to understand checksums in a different way. Normal >driver could not read such a CD). Another way is to access small data stub >prewritten on a blank CD in factory. Or write your own iso-9660 replacement :) The same argument applies here. If you can do it, so can somebody else. Okay, maybe nobody would bother just for a chess program, but for something used regularly and consistently (e.g. SDMI for future audio recordings), expect it to not take long! Maybe it won't play on SDMI-compliant devices (due to hardware features), but it will play on everything else! >-Andrew- Dave
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