challenge11.py

from Cryptodome.Cipher import AES
from Cryptodome.Random import get_random_bytes
from Cryptodome.Random.random import randint
import challenge10
import util

def encryption_oracle(s):
    key = get_random_bytes(16)
    cipher = AES.new(key, AES.MODE_ECB)
    if randint(0, 1) == 0:
        print('Encrypting with ECB')
    else:
        print('Encrypting with CBC')
        IV = get_random_bytes(16)
        cipher = challenge10.CBC(cipher, IV)
    s = get_random_bytes(randint(5, 10)) + s + get_random_bytes(randint(5, 10))
    s = util.padPKCS7(s, 16)
    return cipher.encrypt(s)

def detectMethod(encryption_oracle):
    s = bytes([0] * 47)
    t = encryption_oracle(s)
    if t[16:32] == t[32:48]:
        return 'ECB'
    return 'CBC'

if __name__ == '__main__':
    print(detectMethod(encryption_oracle))