I had some people asking me as to how one can achieve this so here we go.
This is a simple ClassLoader project is intended inspire some thought as to how one might protect their Spigot plugin using class encryption.
Do note, however, that this kind of protection is atrocious against someone who knows what they are doing. Also, this is the result of a few minutes of playing around and hasn't undergone rigorous testing so don't say you weren't warned.
This software is licensed under the MIT license (not that anyone cares).