This is an old Win32 crackme, but still, has quite a lot of things that we can learn from it. I have solved it on IDA. You can download the target and the commented IDA database of this project. I will try to explain what you need to focus on if you are solving it without totally spoiling it for the people that, like me, are starting into the world of reverse engineering. After the explanation, I will link to the source code of the keygen, which is on Github.