"""
EXAMPLE: TokyoWesterns 2020 — "mask" (Misc)
https://github.com/p4-team/ctf/tree/master/2020-09-19-tokyowesterns/mask

VULN: each line is `IP/mask`. The HOST bits (IP & ~mask) of the 40 entries
form a base64 string; decode it to get the flag.

Run:
    cd /home/code/ctfkit
    python3 examples/mask/solve.py
Expected flag: TWCTF{Are-you-using-a-mask?}
"""
import ipaddress
from base64 import b64decode

MASKS = """
192.168.55.86/255.255.255.0
192.168.80.198/255.255.255.128
192.168.1.228/255.255.255.128
192.168.90.68/255.255.254.0
192.168.8.214/255.255.255.128
192.168.5.197/255.255.255.128
192.168.71.90/255.255.255.0
192.168.62.55/255.255.255.192
192.168.78.209/255.255.255.128
192.168.76.216/255.255.255.128
192.168.91.202/255.255.255.128
192.168.93.108/255.255.255.0
192.168.74.76/255.255.254.0
192.168.10.88/255.255.254.0
192.168.82.236/255.255.255.128
192.168.13.246/255.255.255.128
192.168.99.228/255.255.255.128
192.168.68.83/255.255.252.0
192.168.23.113/255.255.255.192
192.168.52.113/255.255.255.192
192.168.69.99/255.255.255.0
192.168.19.114/255.255.255.192
192.168.53.236/255.255.255.128
192.168.90.117/255.255.254.0
192.168.35.90/255.255.255.0
192.168.91.121/255.255.255.0
192.168.48.49/255.255.255.192
192.168.27.104/255.255.255.0
192.168.98.204/255.255.255.128
192.168.93.87/255.255.255.0
192.168.44.113/255.255.255.192
192.168.40.104/255.255.248.0
192.168.25.227/255.255.255.128
192.168.57.50/255.255.255.192
192.168.97.115/255.255.255.0
192.168.30.47/255.255.255.192
192.168.10.102/255.255.254.0
192.168.51.209/255.255.255.128
""".strip().split("\n")


def main():
    host_bits = bytearray()
    for line in MASKS:
        ip, mask = line.split("/")
        a = int(ipaddress.IPv4Address(ip))
        m = int(ipaddress.IPv4Address(mask))
        host_bits.append(a & (~m & 0xFFFFFFFF) & 0xFF)
    b64 = bytes(host_bits)
    # base64 length must be a multiple of 4
    b64 += b"=" * (-len(b64) % 4)
    flag = b64decode(b64).decode(errors="replace")
    print("host-bits b64:", b64.decode("latin1"))
    print("FLAG =", flag)
    return flag


if __name__ == "__main__":
    main()