You've probably heard of public-key cryptography, because it's the basis of HTTPS, the system that puts the padlock in your browser.
The mathematical detail behind public-key crypto is a little abstruse, but you don't need to be a mathematician to understand the principles that make it work.
Here's the story.
Traditional encryption (before 1970, at any rate) relies on the digital equivalent of a padlock. Turn the key clockwise to lock; turn the key anticlockwise to unlock
