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jotd · 01 January 2020, 22:28

Now if you know that there's a checksum, and with WinUAE memory read breakpoints, defeating a checksum isn't very difficult. For instance, if the game has a password check system + a checksum, it's obvious that the password checking code is going to be part of the checksum.

But on a real amiga, you don't really have memory read breakpoints (a friend of mine hacked a real-time disassembly program in trace mode to check for reads, it ran on a A500, I used it for stealthy password reads, but it was slow and difficult to use), so it takes a looong time to find those.

(using checksums has a lot of drawbacks/limitations: game code must be fully relocatable, or relocs trip the checksums. If the code has relocated addresses, then there are probably no checksums: it's hard to implement, and is reserved to high-quality games)

01 January 2020, 22:28	#10
jotd This cat is no more Join Date: Dec 2004 Location: FRANCE Age: 52 Posts: 8,302	Now if you know that there's a checksum, and with WinUAE memory read breakpoints, defeating a checksum isn't very difficult. For instance, if the game has a password check system + a checksum, it's obvious that the password checking code is going to be part of the checksum. But on a real amiga, you don't really have memory read breakpoints (a friend of mine hacked a real-time disassembly program in trace mode to check for reads, it ran on a A500, I used it for stealthy password reads, but it was slow and difficult to use), so it takes a looong time to find those. (using checksums has a lot of drawbacks/limitations: game code must be fully relocatable, or relocs trip the checksums. If the code has relocated addresses, then there are probably no checksums: it's hard to implement, and is reserved to high-quality games)