diff --git a/ErgometerServer/ClientThread.cs b/ErgometerServer/ClientThread.cs
index f1dbc42..88d79bf 100644
--- a/ErgometerServer/ClientThread.cs
+++ b/ErgometerServer/ClientThread.cs
@@ -55,28 +55,50 @@ namespace ErgometerServer
 
                         break;
                     case NetCommand.CommandType.LOGIN:
-                        if(input.IsDoctor)
+                        if(! server.CheckPassword(input.DisplayName, input.Password))
                         {
-                            server.ChangeClientToDoctor(client, this);
-                            Console.WriteLine("Doctor connected");
-                            running = false;
+                            NetHelper.SendNetCommand(client, new NetCommand(NetCommand.ResponseType.LOGINWRONG, session));
+                            loggedin = false;
                         }
                         else
                         {
-                            name = input.DisplayName;
+                            NetHelper.SendNetCommand(client, new NetCommand(NetCommand.ResponseType.LOGINOK, session));
                             loggedin = true;
-                            Console.WriteLine(name + " (client) connected with password: " + input.Password);
-                            FileHandler.CreateSession(session, name);
+
+                            if (input.IsDoctor)
+                            {
+                                server.ChangeClientToDoctor(client, this);
+                                Console.WriteLine("Doctor connected");
+                                running = false;
+                            }
+                            else
+                            {
+                                name = input.DisplayName;
+                                loggedin = true;
+                                Console.WriteLine(name + " (client) connected with password: " + input.Password);
+                                FileHandler.CreateSession(session, name);
+                            }
                         }
                         break;
                     case NetCommand.CommandType.DATA:
-                        metingen.Add(input.Meting);
-                        server.SendToDoctor(input);
+                        if (loggedin)
+                        {
+                            metingen.Add(input.Meting);
+                            server.SendToDoctor(input);
+                        }
+                        else
+                            NetHelper.SendNetCommand(client, new NetCommand(NetCommand.ResponseType.NOTLOGGEDIN, session));
+
                         break;
                     case NetCommand.CommandType.CHAT:
-                        chat.Add(new ChatMessage(name, input.ChatMessage));
-                        server.SendToDoctor(input);
-                        Console.WriteLine(name + ": " + input.ChatMessage);
+                        if (loggedin)
+                        {
+                            chat.Add(new ChatMessage(name, input.ChatMessage));
+                            server.SendToDoctor(input);
+                            Console.WriteLine(name + ": " + input.ChatMessage);
+                        }
+                        else
+                            NetHelper.SendNetCommand(client, new NetCommand(NetCommand.ResponseType.NOTLOGGEDIN, session));
                         break;
                     case NetCommand.CommandType.LOGOUT:
                         loggedin = false;
diff --git a/ErgometerServer/DoctorThread.cs b/ErgometerServer/DoctorThread.cs
index 21477a2..0ebbea2 100644
--- a/ErgometerServer/DoctorThread.cs
+++ b/ErgometerServer/DoctorThread.cs
@@ -12,33 +12,29 @@ namespace ErgometerServer
         TcpClient client;
         Server server;
 
-        string name;
-
         bool running;
-        bool loggedin;
 
 
         public DoctorThread(TcpClient client, Server server)
         {
             this.client = client;
             this.server = server;
-            this.name = "Unknown";
+
             this.running = false;
-            this.loggedin = false;
         }
 
         public void run()
         {
             running = true;
-            loggedin = true;
-            while (loggedin && running)
+            while (running)
             {
                 NetCommand input = NetHelper.ReadNetCommand(client);
 
                 switch (input.Type)
                 {
                     case NetCommand.CommandType.LOGOUT:
-                        loggedin = false;
+                        running = false;
+                        client.Close();
                         Console.WriteLine("Doctor logged out");
                         break;
                     case NetCommand.CommandType.CHAT:
@@ -49,7 +45,6 @@ namespace ErgometerServer
                         throw new FormatException("Unknown Command");
                 }
             }
-            client.Close();
         }
 
         public void sendToDoctor(NetCommand command)
diff --git a/ErgometerServer/Server.cs b/ErgometerServer/Server.cs
index fabc081..29c675a 100644
--- a/ErgometerServer/Server.cs
+++ b/ErgometerServer/Server.cs
@@ -111,25 +111,39 @@ namespace ErgometerServer
         private void AddUser(string name, string password)
         {
             users.Add(name, password);
+            FileHandler.SaveUsers(users);
         }
 
-        private bool CheckPassword(string name, string password)
+        public bool CheckPassword(string name, string password)
         {
             string pass;
             bool isOk = users.TryGetValue(name, out pass);
+
+            Console.WriteLine($"Checking {name}, {password}: found {isOk} with response {pass}");
+
             if (!isOk) return false;
 
             return pass == password;
         }
 
-        private void ChangePassword(string name, string newpassword)
+        private string GeneratePassword(int len = 8)
         {
+            string pass = "";
 
+            char[] chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".ToCharArray();
+
+            Random rand = new Random();
+
+            for (int i=0; i<=len; i++)
+            {
+                pass += chars[rand.Next(0, chars.Length - 1)];
+            }
+
+            return pass;
         }
 
         private static void OnProcessExit(object sender, EventArgs e)
         {
-            FileHandler.SaveUsers(users);
             Console.WriteLine("Closing server");
         }
     }