[elahieh]

Copying one of my old comments from slashdot... it sounds similar to Sierra's "cpc.com". While I was reading the article I wondered if the equivalent of this process for the 6502 (BRK/COP interrupt table?) would work.

Back in the 1980s Sierra On-Line used to copy protect their adventure games with a copy protection system which involved strangely formatted sectors on the original disk which were impossible to duplicate exactly using standard PC hardware.

The loader "sierra.com" used to call a copy-protection program "cpc.com" which loaded data from the disk to decrypt the main program and run it. cpc.com had some of the most obscure, twisty, awful code ever written to prevent debugging and it constantly used different methods to thwart stepping through the program using INT 3 (these were the days before Soft-Ice).

But the solution (or "crack") was just dead simple. Just fire up debug, step to the beginning of cpc.com, and copy the vector from INT 3 into the INT 13 vector - then cpc.com stops right at the point where the data from the disk is being loaded, so it can be copied.

Despite all the incredibly complex code, cpc.com had to read the data off the disk so there was no way the Sierra programmers could thwart this method.