Understanding Quantum Cryptography

This post is a brief primer on quantum cryptography and quantum cryptanalysis. It aims to be an accessible read.

We begin by defining Claude Shannon’s elementary unit of classical information: the bit. We then define Benjamin Schumacher’s elementary unit of quantum information: the qubit. We use photons as a way to illustrate both.

We use this understanding of quantum information to describe quantum computers. We introduce the concepts of superposition and entanglement. We show how powerful quantum computers are relative to classical computers. We briefly discuss Shor’s algorithm and Grover’s algorithm.

We end with a description of quantum key generation and distribution (QKD). We show that QKD provides a method for parties to have full certainty as to whether a key was intercepted by an eavesdropper because all eavesdropping measurements perturb the quantum information.