security - What good ways are there to prevent cheating in JavaScript multiplayer games?

Question

Imagine a space shooter with a scrolling level. What methods are there for preventing a malicious player from modifying the game to their benefit? Things he could do that are hard to limit server-side is auto-aiming, peeking outside the visible area, speed hacking and other things.

What ways are there of preventing this? Assume that the server is any language and that the clients are connected via WebSocket.

Always assume that the code is 100% hackable. Think of ways to prevent a client completely rewritten (for the purposes of cheating) from cheating. These can be things such as methods for writing a secure game protocol, server-side detection, etc.

Answer 1

The server is king. Clients are hackable.

What you want to do is two things with your websocket.

Send game actions to the server and receive game state from the server.

You render the game state. and you send input to the server.

• auto aiming - this one is hard to solve. You have to go for realism. If a user hits 10 headshots in 10ms then you kick him. Write a clever cheat detection algorithm.
• peeking outside the visibile area - solved by only sending the visible area to each client
• speeding hacking - solved by handling input correctly. You receive an event that user a moved forward and you control how fast he goes.

You can NOT solve these problems by minifying code. Code on the client is ONLY there to handle input and display output. ALL logic has to be done on the server.

You simply need to write server side validation . The only thing is that a game input is significantly harder to validate then form input due to complexity. It's the exact same thing you would do to make forms secure.

You need to be really careful with your "input is valid" detection though. You do not want to kick/ban highly skilled players from your game. It's very hard to hit the balance of too lax on bot detection and too strict on bot detection. The whole realm of bot detection is very hard overall. For example Quake had an auto aim detection that kicked legitedly skilled players back in the day.

As for stopping a bots from connecting to your websocket directly set up a seperate HTTP or HTTPS verification channel on your multiplayer game for added security. Use multiple Http/https/ws channels to validate a client as being "official", acting as some form of handshake. This will make connecting to the ws directly harder.

Example:

Think of a simple multiplayer game. A 2D room based racing game. Upto n users go on a flat 2D platformer map and race to get from A to B.

Let's say for arguments sake that you have a foolsafe system where there's a complex authetication going over a HTTPS channel so that users can not access your websocket channel directly and are forced to go through the browser. You might have a chrome extension that deals with the authentication and you force users to use that. This reduces the problem domain.

Your server is going to send all the visual data that the client needs to render the screen. You can not obscure this data away. No matter what you try a silled hacker can take your code and slow it down in the debugger editing it as he goes along until all he's left with is a primitive wrapper around your websocket. He let's you run the entire authentication but there is nothing you can do to stop him from stripping out any JavaScript you write from stopping him doing that. All you can achieve with that is limit the amount of hackers skilled enough of accessing your websocket.

So the hacker now has your websocket in a chrome sandbox. He sees the input. Of course your race course is dynamically and uniquely generated. If you had a set amount of them then the hacker could pre engineer the optimum race route. The data you send to visualise this map can be rendered faster then human interaction with your game and the optimum moves to win your racing game can be calculated and send to your server.

If you were to try and ban players who reacted too fast to your map data and call them bots then the hacker adjusts this and adds a delay. If you try and ban players who play too perfectly then the hacker adjusts this and plays less then perfect using random numbers. If you place traps in your map that only algorithmic bots fall into then they can be avoided by learning about them, through trial and error or a machine learning algorithm. There is nothing you can do to be absolutely secure.

You have only ONE option to absolutely avoid hackers. That is to build your own browser which cannot be hacked. Build the security mechanisms into the browser. Do not allow users to edit javascript at runtime in realtime.