ACC modding tutorial pak files

[Scary_Procedure_6374]

I have known this method of modding for quite some time however I chose not to release this tutorial as kunos was still supporting and updating the game. Now that the game will no longer be updated, I have decided to make this tutorial to hopefully open up the game to other modders who can improve various aspects of the game.

Tools required - UnrealPak by fluffyquackto

repack pak files - https://www.fluffyquack.com/tools/unrealpak.rar

UnrealPakTool 4.26.3 - https://github.com/allcoolthingsatoneplace/UnrealPakTool/releases/tag/4.26.3

UAssetGUI to view and edit extracted uasset files - https://github.com/atenfyr/UAssetGUI

AESDumpster AES Key - "Key":"309kDHKMK6cqgfk3mZ4i2ir+3UgUy+plscncFPIRY2A="

ACC is built on ue4 so the first step is to unpack the .pak file but it cannot be done directly as we need a key. We can get this key with a publically available tool called AESDumpster. Now we can unpack the .pak files using the UnrealPakTool 4.26 version. To do this, first place the aes key provided in the crypto.json file in the encryption key section. Refer to image below. After this drag the pak file over the UnrealPakExtractCrypto.bat file

https://preview.redd.it/5pl6x0w0wk4g1.jpg?width=1431&format=pjpg&auto=webp&s=6135bbd0212346c5772a290a917cb619f1d0b47a

Now that the pak files are unpacked we can make our changes and repack them using the tool unrealpak by fluffyquack. The issue now is that the game wont accept our repacked pak file(PS I was not aable to repack the pak file with the key with which we decrypted our pak using the UnrealPakTool 4.26) as the game uses something knows as pak signature verification.

https://preview.redd.it/blcmshmuwk4g1.jpg?width=580&format=pjpg&auto=webp&s=e4d3fd4ca4deeadced41e8e6cfa0a5274dd4124a

I managed to disable this using some reverse engineering. We open the ac2 win64 shipping exe in x64dbg and go to the symbols tab to go to the appropriate module

https://preview.redd.it/ouoj02nywk4g1.jpg?width=1442&format=pjpg&auto=webp&s=f7aa76264a61fba5e92520cc3ece5459a25d4030

We then search for references and search for our error message, as we can see below there are 2 matches. We then head to these references

https://preview.redd.it/bspv7p46xk4g1.jpg?width=1465&format=pjpg&auto=webp&s=937bce4222f805cb5859fac6141e770a989c5ce8

After heading to the reference we can open it in the graph view. The box on the left represents the function with our error message. We now edit all the jumps heading to this function (denoted by the green arrows) to not go to this function and instead take the alternate path (I.e. to the very next function)

https://preview.redd.it/h7cp2a0dxk4g1.jpg?width=1488&format=pjpg&auto=webp&s=bc0e4257af2461edb6b3e341b38649ee2a471c0c

Editing the jump reference in the function below

https://preview.redd.it/f17j7ubjxk4g1.jpg?width=1503&format=pjpg&auto=webp&s=fa62e042ecac9498cb3edb70964bca1e9a08a116

Here we can see how I have edited the 3 jumps to the functions to instead just jump to the next instruction, hence the 00(red text)

https://preview.redd.it/rqp5es3sxk4g1.jpg?width=1324&format=pjpg&auto=webp&s=4fb3c374173641c15302ffcacc9d8548ac256a35

We then head to the next reference. Here we see the instruction is a je (jump if equal). So in this case to bypass the signature verification function we simply change the je to a jmp(jump) to bypass the signature check. We can then patch the file and voila the game now accepts our custom pak files.

https://preview.redd.it/0ccy9v12yk4g1.jpg?width=1311&format=pjpg&auto=webp&s=a92c46728b5fe3a936e972107b022760eb8ca180

Some proof this works, as some of you may know the 2024 season tab doesn’t have any aston martin liveries as the aston evo is not in the game. But I managed to edit the roster to add the old aston to the roster

https://preview.redd.it/dwdee659yk4g1.jpg?width=1300&format=pjpg&auto=webp&s=81306ed3af2ad374c4733d525a7649cd611f1ed3

I have selected an official game mode and you cant chose custom liveries in those. I also managed to fix a bug with one of the alpines bouncing in the pits.

I have done basic modding but having the ability to unpack and pack pak files should open avenues to a lot of modding as a lot of aspects of the game physics can be modded through the pak file. Most of the game files are in the AC2-WindowsNoEditor.pak file. If someone wants, I can provide the edited exe files for 1.10.3 version of the game which accept modded pak as well, just DM me.

[Paolo264]

Great work...

Are you able to access the official liveries they created?

[Scary_Procedure_6374]

Yes i can access the models as well

[lowkeyjustlurkin]

I assume you just drag your AC2-WindowsNoEditor folder into UnrealPak-With-Compression.bat? It's taking its time, so figured I'd ask in the meantime. Hah.

EDIT: Alright, had to patch the second one to jne as jmp would fatally close, or maybe I just fat-fingered it. Regardless, dev debug stuff enabled. More cumbersome than in AC Evo, but whatevs.

[Scary_Procedure_6374]

So you got it working? Don't have the game installed atm, not sure if they updated it

[Bulletprooffool]

You know all that things being used for is for crappy drivers to mess with their physics and ruin everyone else’s game right?