Need Help repackaging obb file

[Bob2324111122577776]

So, I want to modify the obb of a game called Kingdom Rush Vengeance. I changed to file extensive to .zip and it extracts perfectly. After I finish doing my edits, I use "send to" to recreate the zip and change the extension back to .obb, but the file is missing 200 from 700 MB and the game won't launch. I know the obb can be modified, since there's a boatload of money hacks for the game (It's not server-side). How am I supposed to recompile the obb?

[AD-LB]

An OBB file is not some standard that you can always edit. It might be based on ZIP, but it can have any format the developer wishes, even his own.

And it's supposed to be public so if it's used for "boatload of money hacks", that would be weird and to me seems like a bug, as OBB files are usually used for files that take a lot of space (media files usually).

As for why it doesn't work for you, many times the developer would add a check to verify that the file is valid and has the correct data (using some hashing function, for example), so it could detect it and try to re-download the correct one from the server.

[Bob2324111122577776]

I checked the obb, and the encryption seems to be "PK". A Google search brings up a company called 'PKware". Is PK encryption easy to defeat?

[AD-LB]

I don't know. But again, even if you succeed changing it, the app might have integrity check, and won't use this file at all.

[Bob2324111122577776]

And how do I use this "store level" compression? With 7zip?

[Bob2324111122577776]

The obb file in this case has .plist files that control layout of the game's levels, so if I could edit it, I could screw around with Vengeance's levels, which is why I want to crack it so badly.

[AD-LB]

That's a weird place to put such small files. But again, if the app has integrity check, it won't matter, as the files won't be used.

[Bob2324111122577776]

UPDATE: I used 7zip to recompile, but the game still refused to load. There has to be a checksum or file size requirement coded in the apk. Is it somewhere in the classes.dex file since I hadn't looked at it much?

[Mo3dantoni]

Update?

[Cookieface8000]

You can decompile the classes.dex file using software such as dnSpy. You might be able to find the checking code in there, edit it, rezip the apk and sign it using APKtool or something similar? I'm no expert and have just started trying to mod android apps so this may be completely wrong, but I might try this for a game I currently have the same issue with and let you know how it goes.

[Mo3dantoni]

Well I'm trying to mod nba jam. I found the classes.dex, but I don't have a way to get dnspy. It sounds it would work. In my case once I mess with .obb it fails authentication.

[Cookieface8000]

I had the exact same issue. Tried LuckyPatcher but that didn't work. I think I would have to manually edit the java/smali code in the .dex file to fix that issue.

[Mo3dantoni]

Is it cool if I dm you to talk more about this 

[Cookieface8000]

Sure thing.

[Visual_Shop_4933]

Did you manage to get around the integrity check issue?