墨者学院-逆向分析实训-dll(第1题)

1.下载文件，解压得到ClassLibrary1.dll

2.利用dnSpy对ClassLibrary1.dll做逆向分析。

3.在vs 2010 中创建新项目dll，语言选择C#,代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;

namespace dll1
{
    class Program
    {
        private static string GetAesKey(int index)
        {
            string result;
            if (index >= 0 && index < 10)
            {
                string[] array = new string[]
          {
           "VZ6MvKGnCvDSjqDK8v2XUeKaVtqhdpxv",
           "qz1y3YtZ4NrzKgmxdhADn4pgp4VGfyBT",
           "BmfnYp8l8fvnTa93fByUkq7pPDQu9KsS",
           "ZlVjJThM6z8qc3nSWqcm22vqbycFFy4S",
           "yZJfLzMJEx7ykmBmEPkbXBEb5lUnmaHW",
           "6DQqrGzSft8PVpJP826F6kL9zD2SQgZu",
           "NYmEN7fUdQ6azhXtaN87mFauhl2fjBfj",
           "zl6Ccl6brngPDCy4waMlxE8AH9VFFj1Q",
           "UzM5er77PnedGxtCFDS3Pp2nk5SGL2Em",
           "RfCFclQgXBydflxZ3njg4akzySDZC2Cb"
          };
                result = array[index];
            }
            else
            {
                result = "";
            }
            return result;
        }

        static void Main(string[] args)
        {
            string result;
            string toDecrypt = "K0sUkIPChQ1825EQmCO8i_NiDA6atB94/Nc1NF96s2M1IT9w6nS8teUneBJbNIcya";
            try
            {
                int index = Convert.ToInt32(toDecrypt.Substring(19, 1));
                string text = toDecrypt.Substring(0, 19) + toDecrypt.Substring(20);
                byte[] bytes = Encoding.UTF8.GetBytes(GetAesKey(index));
                byte[] array = Convert.FromBase64String(text.Replace("_", "+"));
                byte[] bytes2 = new RijndaelManaged
                {
                    Key = bytes,
                    Mode = CipherMode.ECB,
                    Padding = PaddingMode.PKCS7
                }.CreateDecryptor().TransformFinalBlock(array, 0, array.Length);
                result = Encoding.UTF8.GetString(bytes2);
            }
            catch
            {
                result = "";
            }

            Console.WriteLine(result);
            Console.ReadKey();
        }
    }
}

4.得到结果：