Hex Editing NDS Save Files against CRC32/MD5 (Help!)

So, I've noticed that the DS game Carnival Games has EU AR codes, but not NA. By Googling around, I managed to find the GameID (as it is a rom on my AceKard) and add the EU cheats verbatim. Now, the codes don't work, so I tried hex-editing the save (via Cygnus)... found the value, etc. and... Corrupt Save. I made a backup...so... I tried again and again just to find out that it relies on a checksum for validity reason...

Gee, it sounds like the problem editing the SONG SUMMONER (iPod) saves...

So, what I want to know is how to fix the CRC32/MD5 checksum, to make the file "valid"... I already tried subtracting the 1/2/4/8 byte simple checksums between the original and modified... matched and no-go.
Post Merge: [time]1256592702[/time]
Bumping. Really, I need to know. You know how many games can be cheated out like this, especially if there weren't any AR codes for the games?

 

Maybe you're interested how i solved my BIG problem.
I played a lot to Professor Layton first chapter (Il professor layton ed il paese dei misteri.nds). I launched second chapter (Il professor Layton ed il vaso di pandora.nds) and suddenly coming back to the first chapter sav was damaged and unreadable!!! BIG TROUBLE!!!
The second chapter damaged the first chapter save file partially (because of naming! Use short notation for ROM files! Renamed to Layton-Misteri.nds and Layton-Pandora.nds no problem at all!!!!!!).
Through trying different solutions and hex editing a lot i discovered the solution.
In the sav file (mine of course, see if is the same for you) the CRC check bytes (8 bytes) are the first one.
The CRC isn't calculated all over the save file indeed. It is referred only to bytes until first "FFFFFFFFF etc." section.
So i created a new save file with NDS, i took first section and i copied it to the damaged file.
Even if a lot of bytes (not the dimension and the structure of course!!!) were different it ran fine!

So try to create a new file save of your game.
Compare with the cheated or the damaged one and substitute the first section bytes.

I don't know if every save file structure is the same, but, i confirm that i solved this HUGE ;-) trouble.


I'm sorry but i tried to calculate many checksums and no one was the same as in the header bytes. I think (as we can deduce from "Layton solution") that the checksum isn't calculated all over the sav file.

An easier solution is to ask to R4 team the sav file structure, but this is more difficult than the most difficult Layton's enigma!


Ciao!


GM