poc.cs

// client 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Collections;
using System.Text;
using System.Threading.Tasks;
using System.Net.Sockets;
using System.Net;
using System.Runtime.InteropServices;

namespace poc_client
{
    class Client
    {
        [DllImport("kernel32", CharSet = CharSet.Ansi, ExactSpelling = true, SetLastError = true)]
        static extern IntPtr GetProcAddress(IntPtr hModule, string procName);

        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
        public static extern IntPtr GetModuleHandle(string lpModuleName);

        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        private delegate bool IsDbg();

        static void Main(string[] args)
        {
            Connect2Server("127.0.0.1", "Send Me APIs");
        }

        public static List<string> StringToList(string data)
        {
            var list = new List<string>();
            foreach (var str in data.Split())
                list.Add(str);
            return list;
        }

        static void Connect2Server(String server, String message)
        {
            try
            {
                Int32 port = 30333;
                TcpClient client = new TcpClient(server, port);
                Byte[] data = System.Text.Encoding.ASCII.GetBytes(message);
                NetworkStream stream = client.GetStream();
                data = new Byte[256];
                String apis = String.Empty;
                Int32 bytes = stream.Read(data, 0, data.Length);
                apis = System.Text.Encoding.ASCII.GetString(data, 0, bytes);
                List<string> APIs = StringToList(apis);
                IntPtr ModHandle = GetModuleHandle("kernel32.dll");
                IntPtr Proc = GetProcAddress(ModHandle, APIs[0]);
                IsDbg Isdbg = (IsDbg)Marshal.GetDelegateForFunctionPointer(Proc, typeof(IsDbg));
                if (Isdbg())
                    Console.WriteLine("Under A Debugger Ouch");
                stream.Close();
                client.Close();
            }
            catch (ArgumentNullException e)
            {
                Console.WriteLine("ArgumentNullException: {0}", e);
            }
            catch (SocketException e)
            {
                Console.WriteLine("SocketException: {0}", e);
            }

            Console.WriteLine("\n Press Enter to continue...");
            Console.Read();
        }
    }
}

// Server

using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;

class Server
{
    public static void Main()
    {
        server();
    }

    public static void server()
    {
        TcpListener server = null;
        string[] apis = new string[]
        {
            "IsDebuggerPresent",
            "WriteProcessMemory",
            "ReadProcessMemory",
            "LoadLibraryA"
        };

        try
        {
            Int32 port = 30333;
            IPAddress ip = IPAddress.Parse("127.0.0.1");
            server = new TcpListener(ip, port);
            server.Start();

            Byte[] bytes = new Byte[256];

            while (true)
            {
                Console.Write("Waiting for a connection... ");
                TcpClient client = server.AcceptTcpClient();
                Console.WriteLine("Connected!");
                NetworkStream stream = client.GetStream();
                using (StreamWriter writer = new StreamWriter(stream))
                {
                    foreach (var api in apis)
                        writer.WriteLine(api);
                }
                client.Close();
            }
        }
        catch (SocketException e)
        {
            Console.WriteLine("SocketException: {0}", e);
        }
        finally
        {
            server.Stop();
        }

        Console.WriteLine("\nHit enter to continue...");
        Console.Read();
    }
}