Grand Chase Classic - KOM Files encrypted

jef100 · 05/19/2022, 19:57

Anyone figure out how to unencrypt the KOM file output after unpacking with quickbms? After the Edel patch every other byte is changed (attached what that looks like).

Gintoki147 · 05/19/2022, 21:56

I'd like to share some things I've noticed regarding this encryption.
Before the update, there were a bunch of duplicate files (with the same content) inside fan_map.kom. See below.

Spoiler

After the update, even with encryption, those same files should be identical, but somehow they're not. They're still the same size and the unencrypted bytes are still the same, so I'm 100% convinced they just appear to be different because of the encryption.

Spoiler

Also, you can't swap dungeons anymore. Before this update, you could swap, say, dungeon_trialforest_1.stg with dungeon_TowerofExtinction.stg and it would work. This way, you could enter Tower of Extinction through Trial Forest. You wouldn't get any EXP or items, of course, but you could still do trial playthroughs of any dungeon with this method. If you try this now, the game crashes.

What I'm trying to say is that the encryption key is different for every file, even if they were identical prior to the encryption. That's why the game crashes when you swap files. The game simply can't read them, because the key it uses for file 1 is not the same for file 2. It seems to be an in-house encryption method, but they're somehow deriving a key based on each file name (or some other factor I'm not aware of). The KOM header hasn't changed with this update and it would be really stupid to store 1000+ keys inside main.exe.

Unfortunately, even though I'm a programmer, I don't know much about reverse engineering, so I'm also just waiting for someone else to find a solution. Just wanted to share my two cents. Hope it helps, somehow.

Update:

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