ROM Hack Save editing

[deathfisaro]

I use hex editor to edit saves, but can't figure out how to get the checksum right
I usually swap two values (Like 25 01 into 01 25) which worked for earlier consoles but doesn't seem to work for DS.
Is there any way to figure out how to get it correct?

I tried other games save file editors but it seemed to be adding or subtracting to random addresses.

 

[FAST6191]

Checkusms and hashes can be everything from parity to bytesums to md5 grade stuff, figuring out what (usually via disassembly or a decent emulator) is half the fun.

If it turns out to be a BIOS based hash function (normally a crc16 variant) how they are implemented can be found in GBATek:
http://nocash.emubase.de/gbatek.htm#biosfunctions

 

[deathfisaro]

Awww...
I opened up a save and found it wasn't encrypted so I was thinking dude this is piece of cake. But looks like I'm in for a hellota trial and error

 

[FAST6191]

Trial and error should not take up that much time, try getting many (30 or so) saves with very little difference (one step further, 1 second longer or a copy to another "file" is a good one sometimes).

That way you can start to pinpoint the hash and what the save file does.

You could also bypass the save check (crackers trainer for Final Fantasy 3 does if I recall) enabling you to reverse engineer the save first.

 

[deathfisaro]

Meh gave up
Too many things change between saves and i can't figure out the checksum.
I guess I gotta get a real time save enabled flashcart, for real time save/load are not checked

 

[FAST6191]

Try an emulator and a windows debugger before saving back and using the emulator made save.

 

[Pikachu025]

Usually you can just (with the proper Hex-Editor (for example WinHex)) highlight the whole file except header/checksum, tell the prog to calculate checksum (Tools -> Compute Hash in WinHex (the last thing I did used Checksum 32bit)), then either add or substract a certain number to get the correct checksum. Play a little till you get the correct thing, it's not too hard after you've done it once.

At least, that's what has worked for me the few times I tried to hack a save...