#!/bin/env python3
from sys import argv

def info(msg):
    print(f"[+] {msg}")

def success(msg):
    print(f"[*] {msg}")

def KSA(key):
    S = list(range(256))
    j = 0
    for i in range(256):
        j = (j + S[i] + key[i % len(key)]) % 256
        S[i], S[j] = S[j], S[i]
    return S

def PRGA(sbox):
    i, j = 0, 0
    while True:
        i = (i+1) % 256
        j = (j + sbox[i]) % 256
        sbox[i], sbox[j] = sbox[j], sbox[i]
        K = sbox[(sbox[i] + sbox[j]) % 256]
        yield K

def rc4(data, key):
    S = KSA(key)
    gen = PRGA(S)
    result = "".join(chr(c ^ n) for c, n in zip(data, gen))
    return str(result)

def main():
    CIPHER_FILE = argv[1]
    KEY_FILE = argv[2]

    # load cipher
    cipher = b''
    with open(CIPHER_FILE, 'rb') as f:
        cipher = f.read()

    # load key
    key = b''
    with open(KEY_FILE, 'rb') as f:
        key = f.read()

    # execute RC4
    sbox = KSA(key)

    # output result
    result = rc4(cipher, key)
    success(result)


if __name__ == "__main__":
    main()