You can think of modern cryptography as a tower with three essential parts. The first part is the bedrock deep beneath the tower, which is made of hard mathematical problems. The tower itself is the second part—there you can find specific cryptographic protocols that let you send private messages, sign digital documents, cast secret ballots, and more.

In between, securing those day-to-day applications to mathematical bedrock, is a foundation made of building blocks called one-way functions. They’re responsible for the asymmetry inherent in any encryption scheme.