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Author Topic: Disk Nibbling  (Read 4191 times)

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Offline Piru

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Re: Disk Nibbling
« on: November 03, 2005, 07:14:09 PM »
@Zac67
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That's the art of coping with protection schemes. If you can't analyse several 'identical' disks, you're much left to guessing.

Actually you're not. All the custom disk format protected disks must somehow decode the tracks themselves, and thus you can easily find the loader routine: It's normally located either in the bootblock itself, or the blocks loaded by the bootblock. Just save this code instead of executing it, and then disassemble it (by using ReSource or similar tool).

Naturally it takes lot of analysis skills and practice to figure out what the assembly code is doing and why, but in the end you will be able to figure out the disk format. It gets really interesting when the loader code has been obfuscated with some code scrambler, and some decoy code/loaders are inserted to fool the analyser. Also, later some anti-singlestep, anti-breakpoint and anti-resource methods were used aswell.

Often it was race against time: If the game could be sold for few days/weeks without a working crack, it would be making some profit. If the protection was trivial to crack, the illegal copies would seriously hurt the sales.

In a semi-related note: By just talking about these things I'll be commiting a crime in about month when the new finnish copyright law gets in effect.
 

Offline Piru

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Re: Disk Nibbling
« Reply #1 on: November 06, 2005, 09:40:30 PM »
@MarkAshley
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I don't understand why disk copy protection works. I understand that the disk may use a custom bootblock, custom loader, custom format etc. But at the lowest level, the data on that disk is still made up of 1s and 0s, right?

Correct so far.

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So surely if the exact same pattern of 1s and 0s is duplicated on another disk, the bootblock, loader, disk format etc would all be preserved?

Sure, if it was possible, but it isn't. You can't make bit exact copy of a disk with normal computers at least. Something like Catweasel might allow it, but in worst cases you need some really expensive hardware for this.

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So why does the copy protection have to be cracked before the disk can be copied?

See above.