我如何修复这个加密程序？

from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend
import os

def encrypt(plaintext, key):
    iv = os.urandom(16)
    cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend())
    encryptor = cipher.encryptor()
    padder = padding.PKCS7(algorithms.AES.block_size).padder()
    padded_data = padder.update(plaintext.encode()) + padder.finalize()
    ciphertext = encryptor.update(padded_data) + encryptor.finalize()
    return iv + ciphertext

def decrypt(ciphertext, key):
    iv = ciphertext[:16]
    actual_ciphertext = ciphertext[16:]
    cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend())
    decryptor = cipher.decryptor()
    padded_data = decryptor.update(actual_ciphertext) + decryptor.finalize()
    unpadder = padding.PKCS7(algorithms.AES.block_size).unpadder()
    plaintext = unpadder.update(padded_data) + unpadder.finalize()
    return plaintext.decode()

# 示例使用
key = os.urandom(32)  # 256位密钥
plaintext = "Hello, World!"
ciphertext = encrypt(plaintext, key)
decrypted_text = decrypt(ciphertext, key)

print("Original:", plaintext)
print("Decrypted:", decrypted_text)