Genesis Earthion encryption

[cloudsets]

Users keep complaining that they purchased a copy of the latest aftermarket Genesis craze on Steam and cannot run it in their emulator of choice or off their EverDrive, MegaSD, or Open-ED flash cartridge.

The reason behind this is simple: game.bin is 7 different versions of the game encrypted using a relatively simple cipher, compressed using the LZMA algorithm, and concatenated into a single file. The 7 versions are the English, Japanese, and Portuguese localized releases as well as four prototype builds. The emulator application bundled with the Steam release extracts and decrypts the ROM image for each version of the game when you select it from the options menu.

You can use this anonymously published Python script to extract the ROMs from game.bin:

# Earthion game.bin file unpacker
# v2.0.1
# Please support Ancient and buy the official release:
# https://store.steampowered.com/app/3597580/Earthion/

import lzma
import sys

with open('game.bin', 'rb') as f:
    b = bytearray(f.read())

print('Decrypting game.bin')

fnv_seed = 0xdeafcafe
fnv_prime = 0x1000193

fnv_hash = fnv_seed
for i in range(len(b)):
    b[i] ^= (fnv_hash >> 9) & 0xff
    fnv_hash = ((fnv_hash ^ b[i]) * fnv_prime) & 0xffffffff

if fnv_hash == 0x2bbe2a9f:  # 2025-07-31
    roms = [
        ('Earthion English.md', 0x43, 0x4bbeb8, 0x780000),
        ('Earthion Japanese.md', 0x4bbefb, 0x4b8836, 0x780000),
        ('Earthion Portuguese.md', 0x974731, 0x4bc5a8, 0x780000),
        ('Earthion Summer 2024 Demo.md', 0xe30cd9, 0x259279, 0x6a0000),
        ('Earthion Fall 2024 Demo.md', 0x1089f52, 0x35e3f6, 0x6a0000),
        ('Earthion Winter 2024 Demo.md', 0x13e8348, 0x40e7e8, 0x740000),
        ('Earthion Early Prototype.md', 0x17f6b30, 0x1894a, 0xa0000),
    ]
    confusion = bytes.fromhex('bff058108a26d4775754e507f3e8c999312536c914bb23ca72aef391d93580eda4a3c33babee30b317d6d11ee2478ac9d1b0a623c361aa45424901da8dd439bb939c89bf087976de88669e0fcc7d8995b267fd9ddc2da7c2a959e84f7007cf4680eb4d0a558b4616277c8104494e48e09ecfd00c854a9da4ff7a698f9081b524bb41a32606a6542c878b9968b4969296e0ec78defb5e1881564bf5bc71df72330612b9da175f1ad7a63e1030b30ff8b0198f409ae0a584694b7458d02cdd54a56d41d8c98cb3052a5548e0bd1fb753098767cfc2eebc68f15ef41810423ca0808a1ae108009a14f851add52a0ce04b24243de53325f015f0ac352dd2e77ded3a')
elif fnv_hash == 0x4a3d1a69:  # 2025-08-04
    roms = [
        ('Earthion English.md', 0x43, 0x4c5f44, 0x780000),
        ('Earthion Japanese.md', 0x4c5f87, 0x4c15ae, 0x780000),
        ('Earthion Portuguese.md', 0x987535, 0x4c639d, 0x780000),
        ('Earthion Summer 2024 Demo.md', 0xe4d8d2, 0x2591ca, 0x6a0000),
        ('Earthion Fall 2024 Demo.md', 0x10a6a9c, 0x35e304, 0x6a0000),
        ('Earthion Winter 2024 Demo.md', 0x1404da0, 0x40dc1d, 0x740000),
        ('Earthion Early Prototype.md', 0x18129bd, 0x188d3, 0xa0000),
    ]
    confusion = bytes.fromhex('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')
else:
    print('Unsupported version')
    sys.exit(1)

for filename, offset, size, usize in roms:
    print(f'Uncompressing {filename}')
    packed = b[offset:offset + size]
    # Workaround for https://github.com/python/cpython/issues/92018
    packed[5:13] = b'\xff' * 8
    unpacked = lzma.decompress(packed, format=lzma.FORMAT_ALONE)
    assert len(unpacked) == usize

    print(f'Decrypting {filename}')
    decrypted = bytearray(usize)
    for i in range(usize):
        #x = (active_banks[(i >> 19) & 7] << 19) | (i & 0x7ffff)
        x = i
        y = x ^ ((i >> 6) & 0xf80) ^ ((x >> 16) & 0xfffffffe) ^ 0xa56
        z = (((x >> 14) ^ (i >> 7)) & 0xfe) ^ (i & 0xff)
        decrypted[x] = unpacked[y] ^ confusion[z]

    print(f'Writing {filename}')
    with open(filename, 'wb') as f:
        f.write(decrypted)

To use it on Windows, make sure Python is installed and available in your PATH. Then download either version of the LZMA SDK from here, extract the files anywhere you like, and copy lzma.exe from the bin folder into the same place as your earthion-unpack.py script (or whatever you might have named it). Finally, place your game.bin file in that directory next to earthion-unpack.py and lzma.exe.

To run it, open a PowerShell window or a command prompt, navigate to the folder where your script is, and type the following:

python earthion-unpack.py

Simply wait for it to finish decompressing and decrypting the games, and take your desired version of the ROM image to your favorite emulator or flash cartridge where you can use it as you normally would.

Seeing as I do not own a flash cartridge, I cannot test on original hardware, but the output runs as expected in Genesis Plus GX, Ares, PicoDrive, and BlastEm.

For convenience's sake, I have attached the script alongside lzma.exe from version 2501 of the SDK to this post. Be sure to install Python if you have not. Python 3.13.6 is the latest stable version available at the time of writing: https://www.python.org/downloads/release/python-3136/

Enjoy your game!

 

[Ikagura Ikagura]

The issue between overprotecting a game or letting it go to the cost of having it pirated easily...