exploit.py

"""
Just go through game rules and find all counterfeit coins.
"""
from pwn import *
import re


def exploit():
    # connect to server
    con = remote('localhost', 9007)
    # Recieve welcome message of binary file
    con.recv()
    # Count of iterations
    count = 100
    # Main circle
    for i in range(count):
        # Take the number of coins and count of tries
        n, c = re.findall("N=(\d+) C=(\d+)", con.recv().decode('utf-8'))[0]
        binary_search(int(n), int(c), con)
    print(con.recv())
    print(con.recv())


def binary_search(n, c, con):
    # left border
    low = 0
    # right border
    high = n - 1
    while low <= high and c:
        # Find middle of coins
        middle = (low + high) // 2
        # Generate a part to send
        part = ' '.join([str(i) for i in range(low, middle + 1)])
        con.sendline(part)
        response = int(con.recvline()[:-1])
        # Check response
        # if we has a 9 in this range of coins 
        if not response % 10:
            low = middle + 1
        else:
            high = middle - 1
        c -= 1
    # Another useless tries we just send zeros
    while c:
        con.sendline('0')
        con.recvline(1024)
        c -= 1
    # Send correct index of coin with weight 9
    con.sendline(str(low))
    print(con.recv())


if __name__=='__main__':
    exploit()