ValueError: MAC check failed

Question

我正在做一个超级小而简单的程序，它试图更多地了解这个模块，但是发生了一些非常奇怪的事情。

下面的代码returns:

Traceback (most recent call last):
File ".\crypto.py", line 100, in <module> init = Emisor()
File ".\crypto.py", line 15, in __init__ self.encrypt()
File ".\crypto.py", line 71, in encrypt Receptor(cipher_text,tag_mac,self.key)
File ".\crypto.py", line 84, in __init__ self.decrypt(self.cipher_text,self.tag_mac,self.key)
File ".\crypto.py", line 93, in decrypt plain_text = cipher.decrypt_and_verify(cipher_text,tag_mac)
File "C:\Users\EQUIPO\AppData\Local\Programs\Python\Python37-32\lib\site-packages\Crypto\Cipher\_mode_gcm.py", line 569, in decrypt_and_verify self.verify(received_mac_tag)
File "C:\Users\EQUIPO\AppData\Local\Programs\Python\Python37-32\lib\site-packages\Crypto\Cipher\_mode_gcm.py", line 510, in verify raise ValueError("MAC check failed")
ValueError: MAC check failed

我已经阅读了很多 pdf、文档、视频、博客等。但我找不到解决方案。

PDTA：那是 "nonce"，那是 "header" 的，有一个方法叫做 update()，那是我应该放 header 的地方，我对那个和 nonce 有点迷茫。

from Crypto.Cipher import AES
from Crypto.Random import get_random_bytes

class Transmitter():

    def __init__(self):

        self.random_password = None
        self.message_plain = True
        self.key = None

        self.password_option()
        self.text_option()
        self.encrypt()



    def password_option(self):

        while ( self.random_password == None ):

            random = input("\nDo you want to generate a random symmetric key? (y/n)\n\n>>> ").strip().lower()

            if random == "y":
                self.random_password = True
                self.random()

            elif random == "n":
                self.random_password = False
                self.random()

            else:
                pass

    def text_option(self):

        if self.message_plain:

            question = input("\nHow will you enter your message?\n\n[1] file\n\n[2] directly in the program\n\n>>> ").strip()

            if question == "1":
                path = input(r"\nEnter the file path\n\n>>> ").strip()
                name = path.split("\")[-1]
                self.message_plain = open(name,mode = "rb")

            elif question == "2":
                self.message_plain = input("\nEnter your message\n\n>>> ").strip()
                self.message_plain = self.message_plain.encode("utf-8")


    def random(self):

        if self.random_password:
            self.key = get_random_bytes(16)

        else:
            self.key = input("\nEnter your password\n\n>>> ").strip()


    def encrypt(self):

        cipher = AES.new(self.key,AES.MODE_GCM)

        cipher.update(b"header")

        cipher_text,tag_mac = cipher.encrypt_and_digest(self.message_plain)

        Receiver(cipher_text,tag_mac,self.key)



class Receiver():

    def __init__(self,cipher_text,tag_mac,key):

        self.cipher_text = cipher_text
        self.tag_mac = tag_mac
        self.key = key

        self.decrypt(self.cipher_text,self.tag_mac,self.key)

    def decrypt(self,cipher_text,tag_mac,key):

        #try:

        # nonce = aes_cipher.nonce
        cipher = AES.new(key,AES.MODE_GCM)
        cipher.update(b"header")
        plain_text = cipher.decrypt_and_verify(cipher_text,tag_mac)

        #except ValueError:
        #   print("\nAn error has occurred.")

if __name__ == '__main__':

    init = Transmitter()

Answer 1

您忘记转移随机数了。 nonce 可以直接传输，也不需要在 AAD 中，因为 nonce 会自动针对 AEAD 密码（例如 GCM）进行验证。

来自文档：

nonce (bytes) – the value of the fixed nonce. It must be unique for the combination message/key. If not present, the library creates a random nonce (16 bytes long for AES).

所以如果你想使用默认随机生成的16字节1，你需要检索和传输随机数。

但是，由于 GCM 对于 12 字节随机数更安全且性能更高，我宁愿自己生成一个（安全随机）12 字节随机数，并使用/传输它。该库似乎默认使用 16 字节的随机随机数，因为这是 AES 的块大小。这通常是个好主意，但不适用于 GCM。

当然，你不能简单地发送密钥，密钥应该事先建立。

ValueError: MAC check failed

ValueError: MAC check failed

python

encryption

pycrypto