p37.py

from hmac import new as new_hmac
from hashlib import sha256

from main import Solution
from p33 import DiffieHellman
from p36 import Server, start_server

from requests import ConnectionError, post


def p37() -> str:
    server = Server()
    base_url = 'http://0.0.0.0:8080/login'

    N = DiffieHellman.default_p
    I, P = 'foo@bar.com', 'abhorrentaardvark'
    A = 0  # same as N, N^2 etc since they're in the same equivalence class mod N

    print('Sending I and A to server...')
    try:
        args = '?I={}&A={}'.format(I, A)
        response = post(base_url + args)
        response_content = eval(response.content)
    except ConnectionError:
        response_content = server.get_client_ids(I, A)

    salt, B = response_content.get('salt'), response_content.get('B')
    print(f'Server responded with salt = {salt} and B = {str(B)[:20]}...')

    K = sha256(b'0').digest()
    print(f'Client computed K = {K[:20]}...')
    client_hmac = new_hmac(K, salt, sha256).hexdigest()

    print('Sending HMAC to server...')
    try:
        args = '?hmac={}'.format(client_hmac)
        response = post(base_url + args)
    except ConnectionError:
        response = server.check_hmac(client_hmac)

    if response.status_code != 200:
        return 'Server responded with "403 Forbidden"'

    return 'Server responded with "200 OK"'


def main() -> Solution:
    return Solution('37: Break SRP with a zero key', p37)


# BELOW CODE RUNS THE WEBSERVER THAT HANDLES THE POST TO /login
if __name__ == '__main__':
    start_server()