Asymmetric Encryption Conceptually
There are some special functions that, though what they do is simple enough, and how they do what they do is utterly transparent, figuring out how to undo what they do is a diabolical task. Such a creature is a trapdoor function. Anyone can fall through a trapdoor, but only those who know where the hidden lever is can climb back out again.
(terminology may be unreliable, transcription may be unreliable, but ideas seem clear otherwise)