Web Exploitation 500: Secure Logon

from flask import Flask, render_template, request, url_for, redirect, make_response, flash
import json
from hashlib import md5
from base64 import b64decode
from base64 import b64encode
from Crypto import Random
from Crypto.Cipher import AES

app = Flask(__name__)
app.secret_key = 'seed removed'
flag_value = 'flag removed'

BLOCK_SIZE = 16  # Bytes
pad = lambda s: s + (BLOCK_SIZE - len(s) % BLOCK_SIZE) * \
                chr(BLOCK_SIZE - len(s) % BLOCK_SIZE)
unpad = lambda s: s[:-ord(s[len(s) - 1:])]


@app.route("/")
def main():
    return render_template('index.html')

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.form['user'] == 'admin':
        message = "I'm sorry the admin password is super secure. You're not getting in that way."
        category = 'danger'
        flash(message, category)
        return render_template('index.html')
    resp = make_response(redirect("/flag"))

    cookie = {}
    cookie['password'] = request.form['password']
    cookie['username'] = request.form['user']
    cookie['admin'] = 0
    print(cookie)
    cookie_data = json.dumps(cookie, sort_keys=True)
    encrypted = AESCipher(app.secret_key).encrypt(cookie_data)
    print(encrypted)
    resp.set_cookie('cookie', encrypted)
    return resp

@app.route('/logout')
def logout():
    resp = make_response(redirect("/"))
    resp.set_cookie('cookie', '', expires=0)
    return resp

@app.route('/flag', methods=['GET'])
def flag():
  try:
      encrypted = request.cookies['cookie']
  except KeyError:
      flash("Error: Please log-in again.")
      return redirect(url_for('main'))
  data = AESCipher(app.secret_key).decrypt(encrypted)
  data = json.loads(data)

  try:
     check = data['admin']
  except KeyError:
     check = 0
  if check == 1:
      return render_template('flag.html', value=flag_value)
  flash("Success: You logged in! Not sure you'll be able to see the flag though.", "success")
  return render_template('not-flag.html', cookie=data)

class AESCipher:
    """
    Usage:
        c = AESCipher('password').encrypt('message')
        m = AESCipher('password').decrypt(c)
    Tested under Python 3 and PyCrypto 2.6.1.
    """

    def __init__(self, key):
        self.key = md5(key.encode('utf8')).hexdigest()

    def encrypt(self, raw):
        raw = pad(raw)
        iv = Random.new().read(AES.block_size)
        cipher = AES.new(self.key, AES.MODE_CBC, iv)
        return b64encode(iv + cipher.encrypt(raw))

    def decrypt(self, enc):
        enc = b64decode(enc)
        iv = enc[:16]
        cipher = AES.new(self.key, AES.MODE_CBC, iv)
        return unpad(cipher.decrypt(enc[16:])).decode('utf8')

if __name__ == "__main__":
    app.run()

>>> import base64
>>> hex(ord('0')^ord('1'))
'0x1'
>>> c = '0dAX+nusd7/rVAVbq0ih0tZaLUn3mZYXOfnyMCJdzzJjvu8cPgiP/3C8CKgAOjblGU1Pijpg2qG0hqDcJ3yaZA=='
>>> d = base64.b64decode(c)
>>> d
b'\xd1\xd0\x17\xfa{\xacw\xbf\xebT\x05[\xabH\xa1\xd2\xd6Z-I\xf7\x99\x96\x179\xf9\xf20"]\xcf2c\xbe\xef\x1c>\x08\x8f\xffp\xbc\x08\xa8\x00:6\xe5\x19MO\x8a:`\xda\xa1\xb4\x86\xa0\xdc\'|\x9ad'
>>> hex(d[10])
'\x05'
>>> hex(d[10] ^ 0x01)
'\x04'
>>> new = b'\xd1\xd0\x17\xfa{\xacw\xbf\xebT\x04[\xabH\xa1\xd2\xd6Z-I\xf7\x99\x96\x179\xf9\xf20"]\xcf2c\xbe\xef\x1c>\x08\x8f\xffp\xbc\x08\xa8\x00:6\xe5\x19MO\x8a:`\xda\xa1\xb4\x86\xa0\xdc\'|\x9ad'
>>> base64.b64encode(n)
b'0dAX+nusd7/rVARbq0ih0tZaLUn3mZYXOfnyMCJdzzJjvu8cPgiP/3C8CKgAOjblGU1Pijpg2qG0hqDcJ3yaZA=='