'''
Solution to https://cryptohack.org/courses/symmetric/flipping_cookie/ 
'''

import requests
from datetime import datetime, timedelta

URL = 'https://aes.cryptohack.org/flipping_cookie'

# NOTE: assumes A and B are equal length
def xor_bytes(A: bytes, B: bytes) -> bytes:
    return b''.join([(a ^ b).to_bytes() for (a, b) in zip(A, B)])
def xor_str(A: str, B: str) -> str:
    return ''.join([chr(ord(a) ^ ord(b)) for (a, b) in zip(A, B)])

def gen_expiry() -> str:
    return (datetime.today() + timedelta(days=1)).strftime("%s")

def get_cookie() -> tuple[bytes, bytes]:
    resp = requests.get(f'{URL}/get_cookie/')
    cookie = resp.json()['cookie']
    iv = bytes.fromhex(cookie[:32])
    ciphertext = bytes.fromhex(cookie[32:])
    return iv, ciphertext


def main() -> None:
    # cookie flipping preprocessing step
    admin_len = len('admin=')
    expiry_len = len(';expiry=') + len(gen_expiry())
    admin_mask = '\x00' * admin_len
    expiry_mask = '\x00' * expiry_len
    # we aim to replace "admin=False;" with "admin=True;;"
    # NOTE: double semicolon ("True;;") is intentional
    # NOTE: and the server won't ever realise it happened!
    deletion = admin_mask  + 'False' + expiry_mask
    insertion = admin_mask + 'True;' + expiry_mask
    # determine the value that replaces deletion with insertion
    cookie_flip = xor_str(deletion, insertion)

    # get our new cookie and apply the cookie flip!
    iv, ciphertext = get_cookie()
    flipped_iv = xor_bytes(cookie_flip.encode(), iv)

    print('Flipped Cookie:')
    print('IV:', flipped_iv.hex())
    print('Body:', ciphertext.hex())

    
    
        
    

if __name__ == '__main__':
    main()