If you shift the alphabet code by 26, each letter is replaced by itself. This is easy to decipher. If you do not know the code, you cannot decipher it. The able debate. Modular arithmetic is our friend.
Modular math is useful, like the clock turning around on the wall.
I'm having one of those days. Today I have encoded your entire lecture. Literally they work. If it wasn't impossible it ought to be. If you are here, you are right.