python实现CBC模式下的DES加解密代码

下面是Python实现CBC模式下的DES加解密代码：

from Crypto.Cipher import DES
from Crypto.Util.Padding import pad, unpad
from Crypto.Random import get_random_bytes

class CBC_DES:
    def __init__(self, key):
        self.bs = DES.block_size
        self.key = key
    
    def encrypt(self, plain_text, iv):
        cipher_text = b''
        cipher = DES.new(self.key, DES.MODE_CBC, iv)
        padded_plain_text = pad(plain_text, self.bs)
        previous_block = iv
        for i in range(0, len(padded_plain_text), self.bs):
            block = padded_plain_text[i:i+self.bs]
            xored_block = bytes([a ^ b for a, b in zip(block, previous_block)])
            encrypted_block = cipher.encrypt(xored_block)
            cipher_text += encrypted_block
            previous_block = encrypted_block
        return cipher_text
    
    def decrypt(self, cipher_text, iv):
        plain_text = b''
        cipher = DES.new(self.key, DES.MODE_CBC, iv)
        previous_block = iv
        for i in range(0, len(cipher_text), self.bs):
            block = cipher_text[i:i+self.bs]
            decrypted_block = cipher.decrypt(block)
            xored_block = bytes([a ^ b for a, b in zip(decrypted_block, previous_block)])
            plain_text += xored_block
            previous_block = block
        return unpad(plain_text, self.bs)

其中，`key`是DES算法的密钥，`iv`是初始化向量，`plain_text`是要加密的明文，`cipher_text`是要解密的密文。在加密时，先对明文进行填充（使用`pad`函数），然后对每个分组进行加密，加密后的密文与上一个分组的密文进行异或操作，得到本次加密的分组密文，最后将所有分组密文拼接起来得到最终密文。在解密时，先对密文进行分组，对每个分组进行解密，解密后的分组与上一个分组的密文进行异或操作，得到本次解密的分组明文，最后将所有分组明文拼接起来得到最终明文。