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girv · 11 January 2007, 17:45

@joejoe:

Have you examined the code in the areas around the copylock or the call to the copylock to see if there is anything like a checksum? Lazy programmers are a cracker's best weapon

Have you searched for instructions referencing the start (even +- some amounts) of the copylock code? That address has got to get loaded somehow! (aside: was the blitter ever used for a checksum routine? ISTR one or two...)

You could maybe narrow down the search area if you can determine when in the run path the copylock is checksummed. eg: leave the copylock unchanged, set a breakpoint at some point after the copylock return and run the game. When that fires, modify the copylock code (randomly!) and continue. If the game works you know either (a) you don't have a checksum or (b) it's calculated before your breakpoint.

Are you sure its a checksum you're looking for anyway? How are you cracking the copylock? Have you disassembled it to make sure its not doing anything tricky in the encrypted part, or are you just bypassing it and setting the magic number afterwards? Might not be a checksum after all

Sometimes a quick disassembly scroll-by will do the trick ... checksum routines can stand out a mile!

11 January 2007, 17:45	#5
girv Mostly Harmless Join Date: Aug 2004 Location: Northern Ireland Posts: 1,114	@joejoe: Have you examined the code in the areas around the copylock or the call to the copylock to see if there is anything like a checksum? Lazy programmers are a cracker's best weapon Have you searched for instructions referencing the start (even +- some amounts) of the copylock code? That address has got to get loaded somehow! (aside: was the blitter ever used for a checksum routine? ISTR one or two...) You could maybe narrow down the search area if you can determine when in the run path the copylock is checksummed. eg: leave the copylock unchanged, set a breakpoint at some point after the copylock return and run the game. When that fires, modify the copylock code (randomly!) and continue. If the game works you know either (a) you don't have a checksum or (b) it's calculated before your breakpoint. Are you sure its a checksum you're looking for anyway? How are you cracking the copylock? Have you disassembled it to make sure its not doing anything tricky in the encrypted part, or are you just bypassing it and setting the magic number afterwards? Might not be a checksum after all Sometimes a quick disassembly scroll-by will do the trick ... checksum routines can stand out a mile!