关于python3 aes_cbc_128加密的一些问题

[Lllzhu]

class AESCipher:

def __init__(self, key):
self.key = key[0:16] #只截取16位
self.iv = "YFGIVPARAMETERAA"

def __pad(self, text):
text_length = len(text)
amount_to_pad = AES.block_size - (text_length % AES.block_size)
if amount_to_pad == 0:
amount_to_pad = AES.block_size
pad = chr(amount_to_pad)
return text + pad * amount_to_pad

def __unpad(self, text):
pad = ord(text[-1])
return text[:-pad]

def encrypt(self, raw):
"""加密"""
raw = self.__pad(raw)
cipher = AES.new(self.key, AES.MODE_CBC, self.iv)
return base64.b64encode(cipher.encrypt(raw))

def decrypt(self, enc):
"""解密"""
enc = base64.b64decode(enc)
cipher = AES.new(self.key, AES.MODE_CBC, self.iv )
return self.__unpad(cipher.decrypt(enc).decode("utf-8"))


if __name__ == '__main__':
e = AESCipher('YFGPASSWORDAAAAA')
secret_data = "123456"
enc_str = e.encrypt(secret_data)
print('enc_str: ' + enc_str.decode())
dec_str = e.decrypt(enc_str)
print('dec str: ' + dec_str)

代码如上，运行之后报错
TypeError: Object type <class 'str'> cannot be passed to C code
这个偏移量需要怎么填写的？