Decrypt ca.bin, config.bin, stunnel.conf.bin, stunnel.pem.bin for YAS-109

yamaha_rc4_decrypt.py

import os.path
import sys

from Crypto.Cipher import ARC4

INDICES = [3, 1, 10, 7, 5, 1]

ROWS = [
    [0xA3, 0x42, 0xB4, 0x9D, 0xAC, 0x60, 0xF4, 0x57, 0xAB, 0xE4, 0x12, 0x93, 0x82, 0x9F, 0x23, 0x10],
    [0xEB, 0x39, 0x84, 0x89, 0x6D, 0xD7, 0x0B, 0xA3, 0x78, 0x76, 0x83, 0x93, 0x01, 0x01, 0x82, 0x73],
    [0x4D, 0x01, 0x72, 0xF4, 0xD3, 0xF5, 0xA0, 0x1E, 0x68, 0x0E, 0xBA, 0x8A, 0x20, 0x10, 0x12, 0x32],
    [0xF1, 0x30, 0x45, 0x95, 0x32, 0xA8, 0xF2, 0x87, 0x70, 0xC3, 0xDF, 0x9E, 0xAA, 0x11, 0x10, 0xA1],
    [0xD1, 0x1C, 0x52, 0xA3, 0x31, 0xBD, 0x6C, 0x73, 0x81, 0xB6, 0xDF, 0xAD, 0x55, 0x55, 0xFF, 0xEE],
    [0xB2, 0x40, 0x41, 0xDB, 0x02, 0x98, 0x92, 0x9C, 0x4B, 0x01, 0xFF, 0xFE, 0xA5, 0xA5, 0x3D, 0xF2]
]


def decrypt(key, buf):
    rc4 = ARC4.new(key)
    return rc4.decrypt(buf)


def prep_key():
    data_idx = 0
    edata = bytearray()

    for i in range(len(INDICES)):
        edata.extend(ROWS[i][data_idx:data_idx+i+1])
        data_idx = INDICES[len(INDICES) - i - 1]

    return bytes(edata)[:16]


def main(path):
    key = prep_key()

    with open(path, 'rb') as f:
        fn, _ = os.path.splitext(path)

        dec = decrypt(key, f.read())

        with open(fn, 'wb') as w:
            w.write(dec)


if __name__ == '__main__':
    main(sys.argv[1])