from base64 import *
import requests

def payload(b64string):
      r = requests.post('http://chall04-crypto02.wargame.whitehat.vn/',data = {"crypto":b64string})
      return r.text.split('<p>')[1].split('</p>')[0].split('\n')[0].split(' ')[1]
#AES_ECB
#s = "something!" + "a"*21 + flag
#s = "something!aaaaaa" + a*15 + flag
#-> can brute 1 characters of flag
flag = ''
for i in range(0,16):
    n = 21 - i
    encoded = b64decode(payload(b64encode(n*'a')))[16:32]
    for c in range(32,127):
        brute = n*'a' + flag + chr(c)
        if b64decode(payload(b64encode(brute)))[16:32] == encoded:
            flag+= chr(c)
	    break

print flag
#Easy_point_c13