PoC decrypter for Yohane the Parhelion - NUMAZU in the MIRAGE - Demo

yohanuma_decrypt.py

import Crypto.Cipher.AES
import Crypto.Hash.SHA1

import sys
import pathlib

filepath = pathlib.Path(sys.argv[1])
decoded_path = 'decrypted_' + filepath.name

enc_file = open(filepath, 'rb')
dec_file = open(decoded_path, 'wb')

password = 'Yohane the Parhelion - NUMAZU in the MIRAGE - Demo'
salt = filepath.stem.encode()

# Cryptodome's PBKDF1 does not support more then 8 bytes of salt.

hash_ = Crypto.Hash.SHA1.new(password.encode() + salt)
for _ in range(99):
    hash_ = Crypto.Hash.SHA1.new(hash_.digest())
aes_key = hash_.digest()[:16]

aes = Crypto.Cipher.AES.new(aes_key, Crypto.Cipher.AES.MODE_ECB)

cnt = 1
keystream = bytearray()
while True:
    data = enc_file.read(0x4000)
    if not data:
        break
    if len(data) > len(keystream):
        ks = bytearray()
        for i in range((len(data) // 16) + 1):
            ks += cnt.to_bytes(16, 'little')
            cnt += 1
        keystream += aes.encrypt(ks)
    dec_file.write(bytes(map(lambda x: x[0] ^ x[1], zip(data, keystream))))
    del keystream[:len(data)]