問題解密文件涉嫌使用.NET中的AES-256 CBC

Question

我正在嘗試解密在Java程序中加密的文件，據稱使用AES-256 CBC和默認IV。

如果我使用通用解密方法（DecryptAesCbc），則只能成功解密第一個塊。

如果我使用Java開發人員建議的解密方法（Decrypt），那么所有文本都會被成功解密+一些附加的字符（可能是填充？）。

1. 如果我理解正確，CBC密碼模式沒有正確使用（ 可視示例 ），因為每個塊都與IV進行異或，而不是使用前一個密文塊？
2. 如果我使用方法Decrypt，從最后一個塊中刪除（和檢測）可能的垃圾字節（垃圾字節值從一個文件更改為另一個文件）的最佳方法是什么？ 我應該嘗試從最后一個塊的末尾刪除任何重復的字節嗎？

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ECB模式下的AES，帶有PKCS7填充 。

如果您使用此配置，它將正確解密並刪除填充：

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

    return algorithm;
}