AES加密Python代码运行报错：TypeError：字符串类型无法传入C代码

问题描述 #

正在学习计算机安全领域的AES加密技术，编写了两段实现AES加解密的代码（encryption.py和decryption.py），运行代码时输入密码"test"触发TypeError，无法正常完成加解密操作。

encryption.py 代码 #

# AES 256 encryption/decryption using pycrypto library
import base64
import hashlib
from Crypto.Cipher import AES
from Crypto import Random

BLOCK_SIZE = 16
pad = lambda s: s + (BLOCK_SIZE - len(s) % BLOCK_SIZE) * chr(BLOCK_SIZE - len(s) % BLOCK_SIZE)
unpad = lambda s: s[:-ord(s[len(s) - 1:])]
 
password = input("Enter encryption password: ")
 

def encrypt(raw, password):
    private_key = hashlib.sha256(password.encode("utf-8")).digest()
    raw = pad(raw)
    iv = Random.new().read(AES.block_size)
    cipher = AES.new(private_key, AES.MODE_CBC, iv)
    return base64.b64encode(iv + cipher.encrypt(raw))
 

def decrypt(enc, password):
    private_key = hashlib.sha256(password.encode("utf-8")).digest()
    enc = base64.b64decode(enc)
    iv = enc[:16]
    cipher = AES.new(private_key, AES.MODE_CBC, iv)
    return unpad(cipher.decrypt(enc[16:]))
 

# First let us encrypt secret message
encrypted = encrypt("This is a secret message", password)
print(encrypted)
 
# Let us decrypt using our original password
decrypted = decrypt(encrypted, password)
print(bytes.decode(decrypted))

decryption.py 代码 #

import base64
from Crypto.Cipher import AES
from Crypto import Random
from Crypto.Protocol.KDF import PBKDF2
 
BLOCK_SIZE = 16
pad = lambda s: s + (BLOCK_SIZE - len(s) % BLOCK_SIZE) * chr(BLOCK_SIZE - len(s) % BLOCK_SIZE)
unpad = lambda s: s[:-ord(s[len(s) - 1:])]
 
password = input("Enter encryption password: ")
 

def get_private_key(password):
    salt = b"this is a salt"
    kdf = PBKDF2(password, salt, 64, 1000)
    key = kdf[:32]
    return key
 

def encrypt(raw, password):
    private_key = get_private_key(password)
    raw = pad(raw)
    iv = Random.new().read(AES.block_size)
    cipher = AES.new(private_key, AES.MODE_CBC, iv)
    return base64.b64encode(iv + cipher.encrypt(raw))
 

def decrypt(enc, password):
    private_key = get_private_key(password)
    enc = base64.b64decode(enc)
    iv = enc[:16]
    cipher = AES.new(private_key, AES.MODE_CBC, iv)
    return unpad(cipher.decrypt(enc[16:]))
 

# First let us encrypt secret message
encrypted = encrypt("This is a secret message", password)
print(encrypted)
 
# Let us decrypt using our original password
decrypted = decrypt(encrypted, password)
print(bytes.decode(decrypted))

报错信息 #

Enter encryption password: test
Traceback (most recent call last):
  File "c:\AES testing\encryptionAES.py", line 31, in <module>
    encrypted = encrypt("This is a secret message", password)
  File "c:\AES testing\encryptionAES.py", line 19, in encrypt
    return base64.b64encode(iv + cipher.encrypt(raw))
  File "C:\Users\xxxx\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0\LocalCache\local-packages\Python310\site-packages\Crypto\Cipher\_mode_cbc.py", line 178, in encrypt
    c_uint8_ptr(plaintext),
  File "C:\Users\xxxx\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0\LocalCache\local-packages\Python310\site-packages\Crypto\Util\_raw_api.py", line 242, in c_uint8_ptr
    raise TypeError("Object type %s cannot be passed to C code" % type(data))
TypeError: Object type <class 'str'> cannot be passed to C code

问题原因 #

报错的核心原因是：PyCryptodome库的AES加密函数cipher.encrypt()要求输入的明文必须是字节串（bytes类型），但代码中传入的是字符串（str类型）。库的底层C实现无法直接处理Python字符串，因此抛出类型错误。

解决方法 #

需要对两个代码文件中的encrypt和decrypt函数做如下修改，确保数据类型匹配：

1. 修改 encryption.py #

• encrypt函数：补位完成后，将字符串编码为字节串再传入加密函数
• decrypt函数：解密得到字节串后，先解码为字符串再执行去补位操作

修改后的代码片段：

def encrypt(raw, password):
    private_key = hashlib.sha256(password.encode("utf-8")).digest()
    raw = pad(raw).encode('utf-8')  # 补位后转字节串
    iv = Random.new().read(AES.block_size)
    cipher = AES.new(private_key, AES.MODE_CBC, iv)
    return base64.b64encode(iv + cipher.encrypt(raw))
 

def decrypt(enc, password):
    private_key = hashlib.sha256(password.encode("utf-8")).digest()
    enc = base64.b64decode(enc)
    iv = enc[:16]
    cipher = AES.new(private_key, AES.MODE_CBC, iv)
    decrypted_bytes = cipher.decrypt(enc[16:])
    return unpad(decrypted_bytes.decode('utf-8'))  # 先转字符串再去补位

2. 修改 decryption.py #

做同样的类型适配修改：

def encrypt(raw, password):
    private_key = get_private_key(password)
    raw = pad(raw).encode('utf-8')  # 补位后转字节串
    iv = Random.new().read(AES.block_size)
    cipher = AES.new(private_key, AES.MODE_CBC, iv)
    return base64.b64encode(iv + cipher.encrypt(raw))
 

def decrypt(enc, password):
    private_key = get_private_key(password)
    enc = base64.b64decode(enc)
    iv = enc[:16]
    cipher = AES.new(private_key, AES.MODE_CBC, iv)
    decrypted_bytes = cipher.decrypt(enc[16:])
    return unpad(decrypted_bytes.decode('utf-8'))  # 先转字符串再去补位

验证修改效果 #

修改后重新运行代码，输入密码"test"，即可正常输出加密后的字节串，以及解密还原后的明文This is a secret message。

内容的提问来源于stack exchange，提问作者Abigiya Terefe