WTCTF2017, BabyDLP

babydlp.py

#!/usr/bin/env python2

import os

import pwn

from Crypto.Util.number import long_to_bytes

p = 160634950613302858781995506902938412625377360249559915379491492274326359260806831823821711441204122060415286351711411013883400510041411782176467940678464161205204391247137689678794367049197824119717278923753940984084059450704378828123780678883777306239500480793044460796256306557893061457956479624163771194201
g = 2

if __name__ == '__main__':
    if 'REMOTE' in os.environ:
        r = pwn.remote('ppc2.chal.ctf.westerns.tokyo', 28459)
    else:
        r = pwn.process('./server.py')

    flag = 0

    r.sendline(hex(0))
    ini = int(r.readline().strip(), 16)
    for n in range(p.bit_length()):
        r.sendline(hex(1 << n))
        c = int(r.readline().strip(), 16)
        if ini == (c * pow(g, 1 << n, p)) % p:
            flag += (1 << n)
        prev = c
        print(n)

    print(flag)
    print(long_to_bytes(flag))