// (c) 2006 Richard Grimes
// www.grimes.demon.co.uk

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

class Bob
{
   static void Main()
   {
      CspParameters csp = new CspParameters(1, null, "Bob");
      RSACryptoServiceProvider rsaBobPrivKey = new RSACryptoServiceProvider(csp);

      TcpListener listener = new TcpListener(IPAddress.Loopback, 5000);
      listener.Start();
      while (true)
      {
         Console.WriteLine("Waiting for connection...");
         TcpClient client = listener.AcceptTcpClient();
         NetworkStream stm = client.GetStream();
         byte[] buf = new byte[client.ReceiveBufferSize];
         int read = stm.Read(buf, 0, buf.Length);
         string command = Encoding.ASCII.GetString(buf, 0, read);
         if (command.ToLower() != "key")
         {
            client.Close();
            break;
         }
         Console.WriteLine("command: {0}", command);
         byte[] ack = Encoding.ASCII.GetBytes("ACK");
         stm.Write(ack, 0, ack.Length);
         read = stm.Read(buf, 0, buf.Length);

         byte[] key = new byte[read];
         Array.Copy(buf, 0, key, 0, read);

         RSAPKCS1KeyExchangeDeformatter exch = new RSAPKCS1KeyExchangeDeformatter();
         exch.SetKey(rsaBobPrivKey);
         Rijndael session = Rijndael.Create();
         session.Key = exch.DecryptKeyExchange(key);

         stm.Write(ack, 0, ack.Length);
         read = stm.Read(buf, 0, buf.Length);
         byte[] iv = new byte[read];
         Array.Copy(buf, 0, iv, 0, read);
         stm.Write(ack, 0, ack.Length);
         session.IV = iv;

         CryptoStream cryptostm = new CryptoStream(stm, session.CreateDecryptor(), CryptoStreamMode.Read);
         read = cryptostm.Read(buf, 0, buf.Length);
         Console.WriteLine(Encoding.ASCII.GetString(buf, 0, read));
         cryptostm.Clear();
         client.Close();
      }
      Console.WriteLine("Stopping...");
      listener.Stop();
   }
}