Me and my friend want to sell game server-side software, but we want some sort of control, over use of that software.

For example, we want some sort of serial key system, so only verified/paid systems, can run our software. We are concerned, that software will be exploited/resold/distributed freely and we wont get any income from that.

How should we approach this problem? Is there any ready solutions? How about h-/crackers, is there any medicine against tinkering code and removing/explore/exploit our serial key system? Do we need to encrypt in some sort of way our server side software, so it will be hard to deal with? What about key/license server side solutions?

Not distributing any code, server is compiled C++ executable, running on windows machine.