WhiteHat 2017 - Secure Token

server.py

import socket
import time
import threading
import SocketServer
import random
import hashlib
from Crypto.Cipher import AES
from Crypto.Util.number import *
from secret import key, seed
host, port = '0.0.0.0', 3333

iv = hashlib.md5(seed).digest()
key = hashlib.md5(key).hexdigest()

# def block(s):
# 	return [s[x:x+AES.block_size] for x in range(0, len(s), AES.block_size)]
query = '{{\"a\": \"{}\", \"flag\": \"{}\"}}'

def create_query(s):
	return query.format(s,key)

def pad(s):
	pad_len = 16 - len(s)%AES.block_size
	return s+chr(pad_len)*pad_len

def encrypt(msg):
	# print msg
	aes = AES.new(key, AES.MODE_CBC, iv)
	return aes.encrypt(pad(msg))

class ThreadedTCPServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer):
	allow_reuse_address = True

class ThreadedTCPRequestHandler(SocketServer.BaseRequestHandler):
	def handle(self):
		while True:
			self.request.sendall("Give me a string and i'll search it for you:\n")
			self.request.sendall("Hex string:\n")
			msg = self.request.recv(1024).strip()
			msg = msg.decode('hex')
			msg = create_query(msg)
			print msg
			cipher = encrypt(msg).encode('hex')
			print cipher
			self.request.sendall("Your query: "+ cipher+ '\n')
			self.request.sendall("Continue? \n")
			con = self.request.recv(1024)
			if con.strip().lower() != "y":
				self.request.sendall("Bye+\n")
				self.request.close()
				break
			# pass
		
while True:
	server = ThreadedTCPServer((host, port), ThreadedTCPRequestHandler)
	# Start a thread with the server -- that thread will then start one
	# more thread for each request
	server_thread = threading.Thread(target=server.serve_forever)
	# Exit the server thread when the main thread terminates
	server_thread.daemon = True
	server_thread.start()
	print "Server loop running in thread:", server_thread.name
	server_thread.join()

solve.py

import socket
host = 'secure-token.grandprix.whitehatvn.com'
port = 3333

# {"a": "aaaaaaaaa|aaaaaaaaaaaaaaaa|aaaaaaaaaaaaaaaa|aaa", "flag": "c|73664568e17cd0e3|d5b084da07c3f5f"|}
# {"a": "aaaaaaaaa|aaaaaaaaaaaaaaaa|aaaaaaaaaaaaaaaa|aaa", "flag": "k|aaaaaaaaaaaaaaaa|aaaaaaaaaaaaaaa"|flag": "|c73664568e17cd0e3d5b084da07c3f5f"}
# *******--------------------------------------------- controlled ------------------------------------*********************************************

def get_payload(payload):
	soc = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
	soc.connect((host,port))
	rep = soc.recv(1024)
	rep = soc.recv(1024)
	# print rep
	soc.send(payload.encode('hex')+'\n')
	rep = soc.recv(1024)
	# print rep
	res = rep.split()[-1]
	soc.close()
	return res

flag_length = 32
big_a = 12+32
flag = ''

query = '{{\"a\": \"{}\", \"flag\": \"{}\"}}'
key = 'c73664568e17cd0e3d5b084da07c3f5f'

def create_query(s):
	return query.format(s,key)

for index in range(33):
	if len(flag) == 32:
		break
	payload_0 = '0'*(big_a-index)
	print create_query(payload_0)
	c0 = get_payload(payload_0).decode('hex')
	for k in '0123456789abcdef':
		payload_1 = '0'*(big_a-index) + '", "flag": "' + flag + k
		print create_query(payload_1)
		c1 = get_payload(payload_1).decode('hex')
		if c0[:64] == c1[:64]:
			# print c0
			# print c1
			# print
			flag += k
			break
	print flag

# c73664568e17cd0e3d5b084da07c3f5f