How to protect your program from copying?

Question

Copy protection

A game was ordered in the work, the game was written in Unity, the game is simple, for schools. The game is only in one exe file.
Conditions.
One game = one computer, not tied to a computer.
Offline mode.
Previously used StarForce services with disks. But problems constantly arose, the installer did not start with the drive emulator. And I would like to know the ways of protection. It can be simple ... I would be very grateful for your advice.

Answer 1

License key, with online verification (activation). The program, if possible, sends a Request to the manufacturer's website through a proxy or directly. Launches and launch sources (computer/user names) are fixed. Periodic offline activation is also possible. If you detect a license violation, you block the key.

Answer 2

Electronic key

An electronic key (also a hardware key, sometimes a dongle from the English dongle) is a hardware tool designed to protect software (software) and data from copying, illegal use and unauthorized distribution.

Article : how to turn a USB flash drive into a "key" of copy protection.