MMO Client-Server Spoofing Vulnerabilities

Question

Ive created a working authoritative client-server system using LiteNetLib for my game however im wondering if packet sniffing+modification is a real worry i should be developing for.

I read some information that other Client sniffing the packets of another client is pretty much impossible since the packets are routed through their ISP. Therefore: should i only worry about the client causing problems for the server, instead of also worrying about clients causing problems for other clients?

Currently im encrypting every packet sent by the client including movement commands such as 'move left'. My idea is that this will make packet-sniffing fail, packet-modification fail, and packet-spoofing fail.

If i remove my encryption doesn't that mean someone can spoof a packet by changing the packet source in the header? (thus sending game commands for another client - moving another player!). Usually when its encrypted i know that only the client with the secret key could have sent it, thus validating the packet source.

I see everyone saying that people shouldn't encrypt general traffic like this, but whats the truth here! Whats the best way?

Answer 1

IP spoofing on the public Internet has become difficult because most ISPs take countermeasures to prevent it.

There isn't much one can do to screw with people's games, unless they control a router between the victim and the server. This in practice means the attacker would need to be (or have the powers to compel) an internet service provider or be on the same network as the victim and control their home router.

Unless your game is very, very competitive, most people won't bother with the logistics which are required to do MITM attacks or packet spoofing just to cheat. But there are a couple scenarios which might be worth protecting:

• Password authentication. If you send unencrypted passwords over the Internet, they might get eavesdropped. Not only could that lead to people getting their accounts on your game stolen, they could also lose accounts on other services, because there are still people who reuse passwords (even if they really should not).
• Real money trading. Does your game allow players to trade? Trade items which are so rare that people might pay real-world money for them? Then you need to secure those transactions, or people will try to perform MITM attacks to steal items from players.

For those reasons, adding encryption to your network protocol certainly doesn't hurt. Howerver, remember the golden rule of cryptography: Never invent your own crypto! Use tried and true algorithms and protocols, invented and implemented by people who know what they are doing. One out-of-the-box solution for this very scenario is TLS. One nice thing about TLS is that it starts every connection by exchanging an unique cryptographic key for that session. And that exchange happens in a very clever way so it can not be intercepted. That means one client doesn't have the knowledge to eavesdrop or impersonate other clients.