C# RFC2898DeriveBytes 正在工作，但 Python PBKDF2 生成的密钥和 IV 不适用于 Python AES 解密

Question

我在解密符合规范的 AES 加密密文时遇到了问题密文包括： · 256 字节的 RFC2898 派生盐，后跟使用密码 'password' 和派生 IV 进行 AES 加密的消息。示例消息为 "This is my secret string, lorem ipsum"，密码为 "password"，使用 C# 代码加密使用以下 c# 代码可以很好地解密此消息

private static readonly int SALT_SIZE = 256;
public static void Decrytor(){
// Encrypted Message
           var cipherText = "i+EKwmlAF0VYh4GwDd+bGf3+yreYsPJW2Oq/w9FXjsp7RI3VqRiqtnqiAD4n6U0JJSTe2ct4B7lgrG+dHxeGcXYEYIERXvU0xnUdH+z3mRwmgYOqCU9HRUKy/z3GKISTm8qH030KTYm3YMBjnKpU8gaRcoDPP/nCiB3o5fPdyspgJgT/qt5BuvwYq7n0qg6ez/Wi4447gq/qHwG3wuuYLSBUCfmIkgGaO1KXqv3SsR8EAhrmMBmPDJfjc3sydNqs5B8J9/JvZFEZULTb8rLQZKQvgHhH9/53Bzs3zmoq0RFbgSueUbyeWb9rLAzYieTz8Yj0srG4GtwPrTPoItc6/hvx5stZ6pX8tgyk9Y3baT0JFMtGgxve7yduy8idTCQdAwRc5NOo4+CBk7P/sIw6+Q==";
            var key = "password";
            // Extract the salt from our cipherText
            var allTheBytes = Convert.FromBase64String(cipherText);
            var saltBytes = allTheBytes.Take(SALT_SIZE).ToArray();
            var cipherTextBytes = allTheBytes.Skip(SALT_SIZE).Take(allTheBytes.Length - SALT_SIZE).ToArray();

            var keyDerivationFunction = new Rfc2898DeriveBytes(key, saltBytes);
            // Derive the previous IV from the Key and Salt
            var keyBytes = keyDerivationFunction.GetBytes(32);
            var ivBytes = keyDerivationFunction.GetBytes(16);

            // Create a decrytor to perform the stream transform.
            // Create the streams used for decryption.
            // The default Cipher Mode is CBC and the Padding is PKCS7 which are both good
            var aesManaged = new AesManaged();
            var decryptor = aesManaged.CreateDecryptor(keyBytes, ivBytes);
            var memoryStream = new MemoryStream(cipherTextBytes);
            var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);
            var streamReader = new StreamReader(cryptoStream);

            // Return the decrypted bytes from the decrypting stream.
            Console.WriteLine("\n{0}\n", streamReader.ReadToEnd());
        }

输出为："This is my secret string, lorem ipsum"

但是当我尝试按照 Python2.7 等效实现来解密消息时，它没有正确解密前几个字符

import base64
from Crypto.Cipher import AES
from Crypto.Protocol import KDF

def p_decrypt( self, text ):
    text_dec = base64.b64decode(text)
    salt = text_dec[:256]
    enc_txt = text_dec[256:]
    key_bytes = KDF.PBKDF2(self.key, salt, dkLen=32)
    iv = KDF.PBKDF2(self.key, salt)
    cipher = AES.new(key_bytes, AES.MODE_CBC, iv)
    return cipher.decrypt(enc_txt)

输出为：“��增��"j��"t string, lorem ipsum”

预期输出："This is my secret string, lorem ipsum"

当我使用 C# RFC2898DeriveBytes 方法生成的 keyBytes 和 IV 时，我试图找出问题所在，该方法也可以正常工作 python 代码，但 python 代码无法正确解密整个消息PBKDF2 生成的 keyBytes 和 IV.

C# RFC2898DeriveBytes 和 python PBKDF2 都使用 HMACSHA1 哈希算法生成 keyBytes 但 C# RFC2898DeriveBytes 方法生成不同的 keyBytes 和 IV 而 Python PBKDF2 返回前 16 个字节为 IV 调用生成的 keyBytes.

请给我一些有用的指南。

谢谢， M 乌默

Answer 1

Rfc2898DeriveBytes 是一个流响应对象，因此连接两个连续的调用与将两个长度加在一起进行一个调用是一样的。

var pbkdf2WithTwoCalls = new Rfc2898DeriveBytes(...)
var pbkdf2WithOneCall = new Rfc2898DeriveBytes(sameParametersAsAbove);

byte[] twoCallA = pbkdf2WithTwoCalls.GetBytes(32);
byte[] twoCallB = pbkdf2WithTwoCalls.GetBytes(16);

byte[] oneCall = pbkdf2WithOneCall.GetBytes(32 + 16);

if (!oneCall.SequenceEquals(twoCallA.Concat(twoCallB))
    throw new TheUniverseMakesNoSenseException();

因此您在 Python 中的解决方案是对 PBKDF2 进行一次 48 字节调用，然后将其拆分为 32 字节 AES 密钥和 16 字节 IV。

您的解密响应表明密钥正确，但 IV 不正确。

Answer 2

# coding:utf8
# python3
# pip3 install pycryptodome

import base64
from Crypto.Cipher import AES
from Crypto.Protocol import KDF
from Crypto.Util.Padding import unpad

cipherText = 'i+EKwmlAF0VYh4GwDd+bGf3+yreYsPJW2Oq/w9FXjsp7RI3VqRiqtnqiAD4n6U0JJSTe2ct4B7lgrG+dHxeGcXYEYIERXvU0xnUdH+z3mRwmgYOqCU9HRUKy/z3GKISTm8qH030KTYm3YMBjnKpU8gaRcoDPP/nCiB3o5fPdyspgJgT/qt5BuvwYq7n0qg6ez/Wi4447gq/qHwG3wuuYLSBUCfmIkgGaO1KXqv3SsR8EAhrmMBmPDJfjc3sydNqs5B8J9/JvZFEZULTb8rLQZKQvgHhH9/53Bzs3zmoq0RFbgSueUbyeWb9rLAzYieTz8Yj0srG4GtwPrTPoItc6/hvx5stZ6pX8tgyk9Y3baT0JFMtGgxve7yduy8idTCQdAwRc5NOo4+CBk7P/sIw6+Q=='
the_pass = 'password'

text_dec = base64.b64decode(cipherText)
salt = text_dec[:256]
enc_txt = text_dec[256:]
key_iv_bytes = KDF.PBKDF2(the_pass, salt, dkLen=48)

key = key_iv_bytes[:32]
iv = key_iv_bytes[32:]
cipher = AES.new(key, AES.MODE_CBC, iv)
plaintext = cipher.decrypt(enc_txt)
plaintext = unpad(plaintext, 16)

print(plaintext)
# b'This is my secret string, lorem ipsum'

C# RFC2898DeriveBytes 正在工作，但 Python PBKDF2 生成的密钥和 IV 不适用于 Python AES 解密

C# RFC2898DeriveBytes is working but Python PBKDF2 generated key and IV are not working with Python AES Decryption

c#

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pbkdf2

pycrypto

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