from Crypto.Cipher import AES
from Crypto.Util.Padding import unpad

# Read Key
with open('key', 'rb') as f:
    aes_key = f.read()

cipher = AES.new(aes_key, AES.MODE_CBC)

# Read message and decrypt

with open('ctext', 'rb') as f:
    ciphertext = f.read()

plaintext = unpad(cipher.decrypt(ciphertext), 16)

print(f'Plaintext: {plaintext}')