Reverse Engineering Unity3D Files

Unity’s been around since 2005, and in that time it’s grown from a OS X only game engine to a cross platform engine for games, software and interfaces. Unity’s an incredibly powerful platform for both seasoned developers and amateurs alike. In this guide I’ll be using files created with Unity 4. Unity 5 beta is still in development, and I’ve no idea if any of these methods will work with version 5.

Reverse Engineering Unity3D Files (Decompiling)

First off you’ll need some tools.

QuickBMS for extracting the .unity3d file.
This script, used with QuickBMS to extract the .unity3d file.
disunity to extract .assets files.
dotPeek to decompile and view .dll files.

Now with all of those downloaded and extracted/installed, you need to get yourself a unity3d file. This procedure is the same for every unity3d file, no matter what platform it’s for. So go grab yourself one of those. In this guide I’ll be using one I downloaded from a game that’s in development. They use Unity as a front end for their login system.

So first things first, you’ll want to put your .unity3d file, and the bms script in the same folder, just for ease of use. Then run quickbms.exe.

quickbms will ask you to select the script you want to use. Select the one you downloaded.

It’ll then ask you to select the unity3d file you want to extract.

And finally it’ll ask for a directory to extract the files to. Select whatever you like, for this, I’ll just go with the quickbms directory.

And there we have it! You can go ahead and use dotPeek to examine the dlls, but I’m more interested in what’s in the .assets files.

Now, there’s two ways to do this, but I find the easiest and quickest way is to select your unity3d file, and move it to the same directory you extracted disunity to. We can use disunity to extract all the assets within a unity3d file. The reason we didn’t just do this first is disunity ignores the dlls, and other directories that might be in there.

Now, shift right click in explorer, and select “Open command window here”.

Now the command used to extract the unity3d file is very simple disunity extract filename.unity3d

disunity will now extract whatever assets are within the unity3d file. Depending on the filesize, this could take anything from a few seconds to a few minutes. Once it’s done, navigate to the folder it created, and enjoy all your wonderful assets. Depending on what you got your unity3d file from, there could be nearly anything in here, including 2D and 3D assets, fonts, shaders, audio, text files, who knows!

Thanks very much for reading through this, and if you’ve any questions or comments, let me know.

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3 thoughts on “Reverse Engineering Unity3D Files”

  1. It worked for an english file, but I when I tried a Japanese file, I got this:

    – signature of 8 bytes at offset 0x00000000 doesn’t match the one
    expected by the script:

    this one: “UnityRaw”
    55 6e 69 74 79 52 61 77 UnityRaw

    expected: “UnityWeb”
    55 6e 69 74 79 57 65 62 UnityWeb

    – 0 files found in 0 seconds
    coverage file 0 0% 8 41954956 . offset 00000008

    When I swapped “UnityRaw” with “UnityWeb” in the script, it came up with this:

    Error: the compressed LZMA input is wrong or incomplete (0)
    Info: algorithm 17
    offset 0000003c
    input size 0x00334658 3360344
    output size 0x00334658 3360344
    result 0xffffff9c -100

    Error: there is an error with the decompression
    the returned output size is negative (-100)

    Last script line before the error or that produced the error:
    31 clog MEMORY_FILE OFFSET ZSIZE SIZE

    Is there something else I need to change? I tried using the Unity script on aluigi’s site, but that gave me a bunch of files with numbers as extensions. The unity web player, of course, had the same error as the script you linked to.

    Is this something you’ve seen before? If you have any idea, I’d be very grateful to hear your input. From my understanding, the main program should work with Japanese characters, but I’m not sure about the individual scripts.

  2. You mentioned there are two ways for extracting the .assets files.

    Let’s say we got those files but there is no .unity3d file.
    What other options do we have left?

  3. my question is and sorry because im new on this reverse engineering i just wanna look on the scripts for some ui that i liked and i couldnt figure out how to do them and some other component my question is is it possible to look to the whole asset in unity and all the components also .

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