That's not the point. The point is it's extremely difficult (pretty much impossible) to go backwards once you perform a hash function. Yes you can do the reverse but it might take you 2 million years...
Extremely difficult
only for you. The enemy developed the cipher they know better. You are applying the wrong algorithm.
You think that after SHA 256 being public for how long that not a single person on the planet has been able to figure out some secret cipher? That's VERY unlikely... It's ok to wear a tin foil hat buddy, but you're really pushing it on this one..