Messages in this thread | | | Date | Thu, 27 Nov 2003 07:07:24 +0100 | From | Willy Tarreau <> | Subject | Re: Copy protection of the floppies |
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Hi,
I don't believe in copy protection at all because what your program can read, other programs can read, and what your program can test, others can trick it into not testing it anymore.
However, there was a solution that I found clever : the weak bit. Basically, a floppy was written with a special controller, and one sector had invalid states that could randomly be read either 0 or 1 by the drive. The software then tried to read the same sector 10 times and expected the contents to change due to the controller's inability to identify the data as clear 0 or 1. A copy of the floppy would definitely fix the contents to what was read at the copy time, so the software would not see any more changes during its read test and would conclude that it was a copy.
I'm not certain that this was fully compatible with all drives and/or controllers, because there's always a risk of some hardware always reporting 0's or 1's on this sector, but I found the concept original.
Of course, it took the editor far more time to develop this solution than the crackers to "fix" the software. You know, launch debug, replace the offending JZ with a JMP or with a NOP/NOP...
Sincerely, I don't think you want to spend so much time developping something which can be broken within a few minutes.
Regards, Willy
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