BreizhCTF 2019 - Hallowed be thy name

exploit.py

import base64

from pwn import *

context.log_level = 'info'

PROMPT = '>>> '

def get_con():
    p = remote('ctf.bzh', 11000)
    return p

def xor(a, b):
    cipher = ''
    for i in range(len(a)):
        cipher += chr(ord(a[i]) ^ ord(b[i]))
    return cipher

p = get_con()
p.recvuntil(PROMPT)
p.sendline('1')
p.recvuntil('Enter plain : ')
p.sendline('\x00'*64)
mask = base64.b64decode(p.recvline().split(': ')[1])

p = get_con()
p.recvuntil(PROMPT)
p.sendline('2')
flag = p.recvline()
flag = base64.b64decode(flag.split('Your secret : ', 1)[1])
flag = xor(flag, mask)

print('Flag: %s' % flag)