DDLC Plus Asset Decrypter

Doki Doki Literature Club Plus Asset Decrypter

Used to decrypt encrypted Streaming Asset Bundle files (*.cy) in DDLC-Plus.

How to use

1. Download and install PHP for your system from the official website.
2. Open the terminal and use PHP interpreter to execute the script with the usage.
3. Wait for the script to run.
4. Use Perfare/AssetStudio or other tools to unpack the decrypted asset file.

Changelog

• v1.1:
  • Split file into 10M cache to speed up the decryption process
• v1.0:
  • First ver

TO-DOs

• v1.3:
  • Use multiple threads to speed up the decryption process (Requires pthread extension)
• v1.2:
  • Iterate through paths to decrypt all files

Workaround

The game has been cleared and I want to get its wallpaper and new music.

When I got the file, I found that its header is the same, but in an unknown format. By consulting the C# code, the game calls the regular AssetBundles load method. Nothing related to decryption was found in the C# code. I started to disassemble the native PE program and also found no code for decryption.

So I seemed to be stuck in a conundrum. I started to guess the encryption method, and the common ones are AES and XOR. But I didn't find any AES decryption method needed, so I ruled it out. Then I turned to XOR, starting by first guessing the key in a loop from 0 to 100.

Fortunately, the UnityFS file header and the Unity3D engine version were successfully decrypted when the XOR key was 40. By comparing it with StreamingAssets from other Unity3D powered games, I was convinced that this was the normally file.

Unpacked it using AssetStudio, everything worked fine and I got the wallpaper and music I wanted.

There is a saying in Chinese called "暴力出奇迹". Great discoveries require bold guesses, and often they work. :)

Why do I use PHP

Simply, I hate Python syntax.

As an interpretive language, PHP has a friendly syntax similar to that of other languages and is easy to use.

In addition, ~~PHP is the best language in the world and does not accept any refutation~~. LMAO

License

The project is open source under Apache License v2.0. All rights reserved for script author MlgmXyysd.