I was thinking about using real encrypted messeages, but more encrypted on harder levels, and with more hints on starter ones.
Actual coding will require extra work, because the game needs to know what each part of the puzzle does. It's like making a game engine, just simpler. If it's your first game idea, and first game prototype, I would suggest starting with a simple game of pac man or something similar.
Making sure you can move a player, have key input controls and things like that is essential to programming. One of my first learning projects was pac man, and it improved my programming skills by a lot, and all the mechanics that I used then, I use all the time now.