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Old 12 January 2023, 23:08   #1
LittleSandra88
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Big grin Why not complete MFM decoder in boot block?

Dear all =)

I have just read how to crack Street Fighter 2 at
https://securityimpact.files.wordpre...protection.pdf

where I don't understand why the boot block doesn't contain the complete MFM decoder.

Given X-Copy only can read the boot block, then I would expect that the MFM loader and decoder is in the boot block?

But on page 14 he explains how he let's the game decode the data, where I would have expected this decoder must be in the boot block, because how could the boot block other read those tracks?

Can someone explain what I am missing?

Hugs,
Sandra =)
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Old 12 January 2023, 23:17   #2
StingRay
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Just had a (very) quick look, the MFM decoder is in the bootblock at offset $28c.
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Old 12 January 2023, 23:23   #3
LittleSandra88
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Quote:
Originally Posted by StingRay View Post
Just had a (very) quick look, the MFM decoder is in the bootblock at offset $28c.
Ok, that good. =)

Why doesn't he then just use that to decode all the disks?

Wouldn't that be much easier than having the game loaded, where scripting is harder?
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Old 12 January 2023, 23:24   #4
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I did not check the tutorial, I would have simply used the MFM decoder from the bootblock to rip the disks and then worked with the images.
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Old 12 January 2023, 23:26   #5
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Quote:
Originally Posted by StingRay View Post
I did not check the tutorial, I would have simply used the MFM decoder from the bootblock to rip the disks and then worked with the images.
Ok, I am glad to hear that! =)

Thanks for clearing that out =)
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Old 12 January 2023, 23:29   #6
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My pleasure.
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Old 13 January 2023, 00:52   #7
Photon
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Why questions tend to get speculative answers.

On Amiga, a complete MFM loader fits in the bootblock.

Copy protection ideas are a reason why a game wouldn't hand a cracker a complete loader in the bootblock.

Not all MFM loaders released fit in a bootblock. Some coders optimize better/worse than others.
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Old 13 January 2023, 00:57   #8
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Big grin

Quote:
Originally Posted by Photon View Post
Why questions tend to get speculative answers.

On Amiga, a complete MFM loader fits in the bootblock.

Copy protection ideas are a reason why a game wouldn't hand a cracker a complete loader in the bootblock.

Not all MFM loaders released fit in a bootblock. Some coders optimize better/worse than others.
I have been wondering, if there were games that used multiple MFM decoders, so the one in the boot block could only decode the next loader and so forth.

Would that be possible?
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Old 13 January 2023, 01:08   #9
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Yes, such games exist. Multiple SYNCs, completely different track formats (different track length/encoding and more) etc. pp.
Edit: Yogi's Big Clean Up is such a game for example: http://www.whdload.de/games/YogisBigCleanUp.html

Last edited by StingRay; 13 January 2023 at 01:15. Reason: Added example game
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Old 13 January 2023, 01:57   #10
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Big grin

Quote:
Originally Posted by StingRay View Post
Yes, such games exist. Multiple SYNCs, completely different track formats (different track length/encoding and more) etc. pp.
Edit: Yogi's Big Clean Up is such a game for example: http://www.whdload.de/games/YogisBigCleanUp.html
Wow! I would never have guessed a low budget game to do that. Impressive!
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Old 25 January 2023, 06:14   #11
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Ironically X-Copy was used to crack and copy disks but it was commercial software. I have a disk with X-Copy that also includes other tools for disk cracking. Some allowed to map the whole disk with different MFM codes. That way disks could be copied. This would circumvent a static copier that only knew DOS format.

Aside from adding extra drive support I would have thought using a tool to map MFM codes would be easier. Then just duplicate it at will once the MFM codes are known. Of course if the disk has specific corruption on sectors that can break.

In any case no amount of copy protection can ignore the obvious back door in all bootable disks. The boot block. The boot block cannot be encrypted and so makes every boot block a back door. The code is plain. Just read through it and see how it sets up disk registers. Then follow it to the next routine. Having a live debugger like Action Replay helps. But anything thing where boot code can be loaded in will do. Can even execute it. Keeping in mind it tends to run in supervisor mode.
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Old 25 January 2023, 09:13   #12
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Quote:
Originally Posted by Hypex View Post
Ironically X-Copy was used to crack and copy disks but it was commercial software.
Commercial software designed to make piracy easy gets pirated - who would have thunk it!

Quote:
In any case no amount of copy protection can ignore the obvious back door in all bootable disks. The boot block.
That's right. All you can do is make it difficult...

Problem is some people had more fun cracking games than playing them, then were 'obliged' to distribute pirate copies to increase their 'street cred'. If they just cracked disks for their own use it wouldn't have been so bad, and software developers wouldn't have had to apply more and more sophisticated protection schemes.

The real damage wasn't done by the crackers, but by the unscrupulous pirates who were just in it for the money (including users who didn't want to pay for genuine software - not understanding that they were part of the reason it was so expensive).
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Old 25 January 2023, 10:00   #13
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Quote:
Originally Posted by Bruce Abbott View Post
Commercial software designed to make piracy easy gets pirated - who would have thunk it!

That's right. All you can do is make it difficult...

Problem is some people had more fun cracking games than playing them, then were 'obliged' to distribute pirate copies to increase their 'street cred'. If they just cracked disks for their own use it wouldn't have been so bad, and software developers wouldn't have had to apply more and more sophisticated protection schemes.

The real damage wasn't done by the crackers, but by the unscrupulous pirates who were just in it for the money (including users who didn't want to pay for genuine software - not understanding that they were part of the reason it was so expensive).
Piracy never changed anything. Softwares always been expensive.

Look when the CDROM appeared 'we will make the prices lower'.
Bullshit ! They rised up the prices even higher !
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Old 25 January 2023, 15:31   #14
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Quote:
Originally Posted by Bruce Abbott View Post
Commercial software designed to make piracy easy gets pirated - who would have thunk it!

LOL. I had it given to me on disk years ago. I only found out it was commercial a few years back.


Quote:
That's right. All you can do is make it difficult...

Problem is some people had more fun cracking games than playing them, then were 'obliged' to distribute pirate copies to increase their 'street cred'. If they just cracked disks for their own use it wouldn't have been so bad, and software developers wouldn't have had to apply more and more sophisticated protection schemes.

I used to spend time cracking games for my own use. Or hacking as I called it. If I found it too difficult to play I spent time looking for cheat codes in code, analysing keyboard routines and looking for life counters as a last resort. I had a selectable 512KB expansion I used as a poor mans Action replay. Load a game, reboot and disable, examine code locked in the 512KB,




Quote:
The real damage wasn't done by the crackers, but by the unscrupulous pirates who were just in it for the money (including users who didn't want to pay for genuine software - not understanding that they were part of the reason it was so expensive).


I had a few games shared to me. I also loaned my Test Drive II to a school friend I didn't see again. Cost me $50 so I rather angry at that one. Later I found another at a local computer shop in my local shopping centre for $10 bucks and must have bought 5 boxes of games that day. Or was it ten? TD II was different somehow. The shop is gone years ago, but I still know where it used to be.
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