在.NET中解密据称使用AES-256 CBC的文件时出现问题

Question

我正在尝试解密一个文件，它是在Java程序加密的，据称使用AES-256 CBC与默认IV。

如果我使用通用解密方法（DecryptAesCbc）,唯一的第一个块被成功解密。

如果我使用来自Java开发人员的建议解密方法（Decrypt）,那么所有文本都被成功解密+末尾的一些附加字符（可能是padding？）。

1. 如果我没有理解错，CBC密码模式没有正确使用（可视示例），因为每个块都与IV异或，而不是与前面的密文块异或？
2. 如果我使用方法decrypt，从最后一个块中删除（和检测）可能的垃圾字节（垃圾字节值在文件之间变化）的最佳方法是什么？我是否应该尝试从最后一个块的末尾删除任何重复的字节？

工作示例：https://dotnetfiddle.net/m1zqbs

using System;
using System.IO;
using System.Net;
using System.Security.Cryptography;
using System.Text;

/* 
Original text:

It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).

Alleged encryption algorithm: AES CBC 256bit key (default IV) - file was encrypted in Java program.
*/

public class Program
{

    //BASE64 encoded cyphertext
    public static string encryptedFileBase64 = "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";
    //BASE64 encoded AES key
    public static string aesKeyBase64 = "lAw0kowr1i//T6Bci78bRX/lIRIwwKeGUz4pHDz0jjo=";

    public static string encryptedFileBase64_2 = "0S0tQ2jupE7bHbVspWCOOSWs/hEm/da+oFSVEU1XkzenZmb+OXWM7+4WUNAUU2hZ4IWJULl34Ha8pIb2btLOuv+KSOmFG5wX+rRMd2y66/HLDcHgOkZUPG3c+MV6261q3U2cFad6kZzRx1td3eXiD2vNljP1VKT1Fcr2c8sVVH2Fo1tQEm21YAjxgvcl3k6r6B0zigL1iAYH5liC65LQLihUyrcPLZ7vy2Wt2tKeFUE/kVXwX9/KHQEsY+j9HCE8zPEGkjieimxY8uaxKvEZBVYZ1EAT92YIpOAaVOX8q61uQOurXqJFJ2COLD3MXH0/Cnp3aSQll/l2LmfiS396JbHw6NYn7GC+2eGiMbXeQs0Wo7b17hkQeSLtsB8U+Wdx";
    public static string aesKeyBase64_2 = "TL9wAPaCWj53zdbAVDdrtpAUtlKxDtySI4QtKQ5KstA=";

    public static void Main()
    {
        byte[] key = Convert.FromBase64String(aesKeyBase64);
        //IV
        byte[] iv = new byte[16] { 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0 };

        Console.WriteLine("------------------First file-----------------\n\n");
        string decrypted = AesUtils.Decrypt(Convert.FromBase64String(encryptedFileBase64), key, iv);
        Console.WriteLine("------------------Proposed decryption process-----------------");
        Console.WriteLine(decrypted);

        Console.WriteLine("\n---------------AES CBC decryption process--------------------");
        string decrypted2 = AesUtils.DecryptAesCbc(Convert.FromBase64String(encryptedFileBase64), key, iv);
        Console.WriteLine(decrypted2);


        Console.WriteLine("\n\n------------------Second file-----------------\n\n");
        key = Convert.FromBase64String(aesKeyBase64_2);

        decrypted = AesUtils.Decrypt(Convert.FromBase64String(encryptedFileBase64_2), key, iv);
        Console.WriteLine("------------------Proposed decryption process-----------------");
        Console.WriteLine(decrypted);

        Console.WriteLine("\n---------------AES CBC decryption process--------------------");
        decrypted2 = AesUtils.DecryptAesCbc(Convert.FromBase64String(encryptedFileBase64_2), key, iv);
        Console.WriteLine(decrypted2);
    }
}


public static class AesUtils
{
    public static string Decrypt(byte[] cipherBytes, byte[] key, byte[] iv)
    {
        using (Aes encryptor = GetCryptoAlgorithm())
        {

            encryptor.Key = key;
            encryptor.IV = iv;

            using (MemoryStream memoryStream = new MemoryStream(cipherBytes.Length))
            {
                string plainText = String.Empty;


                for (int i = 0; i < cipherBytes.Length; i = i + 16)
                {
                    encryptor.IV = iv;
                    ICryptoTransform aesDecryptor = encryptor.CreateDecryptor();
                    CryptoStream cryptoStream = new CryptoStream(memoryStream, aesDecryptor, CryptoStreamMode.Write);
                    cryptoStream.Write(cipherBytes, i, 16);
                    cryptoStream.FlushFinalBlock();
                }
                byte[] plainBytes2 = memoryStream.ToArray();
                plainText = Encoding.UTF8.GetString(plainBytes2, 0, plainBytes2.Length);

                return plainText;
            }
        }
    }

    public static string DecryptAesCbc(byte[] inputArray, byte[] key, byte[] iv)
    {
        using (Aes aes = GetCryptoAlgorithm())
        {
            aes.Key = key;
            aes.IV = iv;

            ICryptoTransform cTransform = aes.CreateDecryptor();
            byte[] resultArray = cTransform.TransformFinalBlock(inputArray, 0, inputArray.Length);
            aes.Clear();

            return Encoding.UTF8.GetString(resultArray);
        }
    }

    private static Aes GetCryptoAlgorithm()
    {
        Aes algorithm = Aes.Create();
        algorithm.Padding = PaddingMode.None;
        algorithm.Mode = CipherMode.CBC;
        algorithm.KeySize = 256;
        algorithm.BlockSize = 128;

        return algorithm;
    }
}

Answer 1

加密是AES在ECB模式下使用PKCS7-padding。

如果使用此配置,它将正确解密并删除填充：

private static Aes GetCryptoAlgorithm()
{
    Aes algorithm = Aes.Create();
    algorithm.Padding = PaddingMode.PKCS7;
    algorithm.Mode = CipherMode.ECB;
    algorithm.KeySize = 256;
    algorithm.BlockSize = 128;

    return algorithm;
}