Network traffic encryption

I have a proxy program which resend network traffic. It listens specific port, and addresses server with another port. It works, but I need to add some encryption between 2 instances of my proxy. When encryption is not enabled two sequential proxy work good, but with encryption don't work. Here is code:

public class CommunicationContext
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   /// <summary>Define buffer max size. Influence on memory usage.</summary>
   public const int MaxBuffer = 16 * 1024;

   /// <summary>Unique counter...</summary>
   private static int _uniqueCounter = 0;

   public readonly Socket SocketIn;
   public readonly Socket SocketOut;
   public readonly PortMapping Mapping;
   public byte[] BufferIn;
   public byte[] BufferOut;
   public bool IsShutdown;
   public readonly object SyncObject = new object();
   public readonly int UniqueId;

   public CommunicationContext(Socket socketIn, Socket socketOut, PortMapping map){
       SocketIn = socketIn;
       SocketOut = socketOut;
       Mapping = map;

       UniqueId = Interlocked.Increment( ref _uniqueCounter );
   }

   public void InitializeBuffers(){
       this.BufferIn = new byte[MaxBuffer];
       this.BufferOut = new byte[MaxBuffer];
   }
}

private static void ReadInputSocket( IAsyncResult ar ){
  CommunicationContext context = (CommunicationContext)ar.AsyncState;

  try{
    int length = context.SocketIn.EndReceive( ar );

    if( length <= 0 )
      throw new NoDataSocketException();

    lock( context.SyncObject ){
        Switches.GeneralLog.Verbose( "==> Client data size: " + length );
        SocketFlags flags = ( context.SocketIn.Available == 0 ) ? SocketFlags.None : SocketFlags.Partial;

        if(!CryptoTools.CryptEnabled){
            //without encrypion works fine
        }
        else if(CryptoTools.CryptInner){
            context.BufferIn = CryptoTools.Crypt(context.BufferIn);
        }else{
            context.BufferIn = CryptoTools.Decrypt(context.BufferIn);
        }

        context.SocketOut.Send(context.BufferIn, 0, length, flags);  
    }

    Thread.Sleep( 0 );

    context.SocketIn.BeginReceive(context.BufferIn, 0, MaxBuffer, SocketFlags.None, ReadInputSocket, context);
  }
  catch( Exception ex ){
    Switches.GeneralLog.Verbose( ex );
    Switches.GeneralLog.Info( ex.Message );
    ShutdownCommunication( context );
  }
}

private static void ReadOutputSocket(IAsyncResult ar ){
  CommunicationContext context = (CommunicationContext)ar.AsyncState;

  try{
    int length = context.SocketOut.EndReceive( ar);

    if( length <= 0 )
      throw new NoDataSocketException();

    lock( context.SyncObject )
    {
      Switches.GeneralLog.Verbose( "<== Server data size: " + length );
      SocketFlags flags = ( context.SocketOut.Available == 0 ) ? SocketFlags.None : SocketFlags.Partial;


      if (!CryptoTools.CryptEnabled){
          //without encrypion works fine
      }
      else if (CryptoTools.CryptInner){
          context.BufferOut = CryptoTools.Decrypt(context.BufferOut);
      }
      else{
          context.BufferOut = CryptoTools.Crypt(context.BufferOut);
      }

      context.SocketIn.Send(context.BufferOut, 0, length, flags);
    }

    context.SocketOut.BeginReceive(context.BufferOut, 0, MaxBuffer, SocketFlags.None, ReadOutputSocket, context);
  }
  catch( Exception ex )
  {
    Switches.GeneralLog.Verbose( ex );
    Switches.GeneralLog.Info( ex.Message );

    ShutdownCommunication( context );
  }
}

Edit from comments:

What not works: Data keep getting corrupted.

I get no exceptions. Just malformed data. I used different methods for Crypt/Decrypt. I made them even both equal - simple XOR. Encryption algorithm has not significance, for example, XOR was used.

My configuration is like this Client <--> Proxy1 <--enc--> Proxy2 <---> Server. Between two proxies must be the encrypted stream.