Inlook-1-signature-flaw.py

#!/usr/bin/env python3

import sys
import string
import random
import json
from client import Client
from math import gcd
from Crypto.Util.number import *
from cipher import *
from gmpy2 import iroot


PORT = 1337
alphabet = string.ascii_letters + string.digits


def get_random_str(len):
    return ''.join(random.choice(alphabet) for i in range(len))

def exploit(ip, flag_id):
    client = Client(ip, PORT)
    client.connect()
    client.register(get_random_str(20), get_random_str(20), get_random_str(20), get_random_str(20))
    my_p, my_q = client.sk
    target_result = client.get_encrypted_email(flag_id["address"], flag_id["email_id"])
    target_n, target_g, _ = target_result["pk_sig"]
    enc_flag = bytes.fromhex(target_result["content"])

    target_q = gcd(target_g-1, target_n)

    assert target_q != 1 and target_q != target_n and target_n%target_q == 0
    target_p = iroot(target_n//target_q, 2)
    assert target_p[1]
    target_p = int(target_p[0])
    return decrypt(enc_flag, (target_p, target_q))

if __name__ == "__main__":
    ip = sys.argv[1]
    flag_id = json.loads(sys.argv[2])
    print(exploit(ip, flag_id))