Unity asset files missing header, looks like encrypted/compressed with unknown algorithm

Extraction and unpacking of game archives and compression, encryption, obfuscation, decoding of unknown files
jh961202
Posts: 1
Joined: Tue Jul 13, 2021 7:49 am

Unity asset files missing header, looks like encrypted/compressed with unknown algorithm

Post by jh961202 »

Hello, first time posting here, if there's any inproper stuff in my topic please inform me, will fix them asap.

Recently I've been working on a game from Japan built with Unity, and the game's asset files were readable using AssetStudio or similar tools.
However a recent update shows that they've changed Unity version to 2019.4.11f, and some of the asset are missing their UnityFS header, and the content become nonsense garbled stuff.
Image

By using HxD on some of the files, I discovered there are zlib-like header ( which is "78 9C" ), but this only applies to small amount of the files.
Tried extract using offzip on those zlib-like file still gives out garbled data with no UnityFS header on it, also tried others with QuickBMS with no luck.

My best guess is that they used a in-program custom encryption method, and the files will not be decrypted unless they're loaded then decryped and create the asset dynamically in the memory.
This makes me almost hopeless on finding a method to open them, so I guess I need help from you guys.

Attached is a random asset stripped from the game itself which is encrypted/compressed (NOT the same one as the screenshot ones), any help on how to decrypt it back to regular UnityFS will be really appriciated!

P.S. I'm not a native English speaker, sorry if there's any typo on words or influent content.