Python AES 解密例程（代码帮助）

Question

我根据网上的信息开发了一段代码，用于AES加密和解密。

使用的语言是：Python 2.7.x

完整代码 -

#!/usr/bin/python

import sys, os
import hashlib
import base64
from Crypto.Cipher import AES

## Variables in computation.
IV = u'1234567890123456'
BLOCK_SIZE = 32
INTERRUPT = u'\u0001'
PAD = u'\u0000'
SECRET = os.urandom(32)
filename=sys.argv[1]

def AddPadding(data, interrupt, pad, block_size):
   new_data = ''.join([data, interrupt])
   new_data_len = len(new_data)
   remaining_len = block_size - new_data_len
   to_pad_len = remaining_len % block_size
   pad_string = pad * to_pad_len
   return ''.join([new_data, pad_string])

def StripPadding(data, interrupt, pad):
   return data.rstrip(pad).rstrip(interrupt)

def encAES(cipher_code, file_data):
   data_padded = AddPadding(file_data, INTERRUPT, PAD, BLOCK_SIZE)
   encrypted = cipher_code.encrypt(data_padded)
   return encrypted

def decAES(cipher_code, file_data):
   decrypted  = cipher_code.decrypt(file_data)
   return StripPadding(decrypted, INTERRUPT, PAD)

def FileSave(fwname, fwdata):
   f = open(fwname, 'w')
   f.write(fwdata)
   f.close

def FileRead(frname):
   f = open(frname, 'rb')
   frdata = f.read()
   return frdata

cipher = AES.new(SECRET, AES.MODE_CBC, IV)

## Encryption
data2encrypt = base64.b64encode(FileRead(filename))
encrypted_data = encAES(cipher, data2encrypt)
encrypted_content = base64.b64encode(encrypted_data)

encrypted_filename = "enc_"+filename
FileSave(encrypted_filename, encrypted_content)
print "Encryption complete. File saved as: "+ encrypted_filename

## Decryption
data2decrypt = base64.b64decode(FileRead(encrypted_filename))
decrypted_data = decAES(cipher, data2decrypt)
decrypted_content = base64.b64decode(decrypted_data)

decrypted_filename = "dec_"+filename
FileSave(decrypted_filename, decrypted_content)
print "Decryption complete. File saved as: "+ decrypted_filename

现在，加密的部分运行得很好，但解密的部分出现了错误 -

命令行输入 - python test.py sample.txt

错误信息：

Traceback (most recent call last):
  File "test.py", line 65, in <module>
    decrypted_data = decAES(cipher, data2decrypt)
  File "test.py", line 38, in decAES
    return StripPadding(decrypted, INTERRUPT, PAD)
  File "test.py", line 29, in StripPadding
    return data.rstrip(pad).rstrip(interrupt)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe6 in position 3: ordinal not in range(128)

有什么可能的解决办法吗？

Answer 1

你在把一个字节串和一个Unicode值拼接在一起，这样会自动尝试解码字节串。但这会失败，因为你解密后的文本不能被当作ASCII来解码。

这里不要使用Unicode的INTERRUPT和PAD值；反正你也不是在从文件中读取Unicode数据：

INTERRUPT = '\1'
PAD = '\0'

你需要创建一个新的 AES对象来进行解密；不能重复使用你用来加密的那个对象，因为它的初始化向量（IV）状态已经被加密过程改变了：

decrypt_cipher = AES.new(SECRET, AES.MODE_CBC, IV)
decrypted_data = decAES(decrypt_cipher, data2decrypt)

经过这些修改后，你的代码就能正常工作，可以加密数据然后再解密。