BB84 — Quantum Key Distribution

The CrypTool project now provides a comprehensive interactive simulation of the quantum key distribution scheme BB84. BB84 was originally proposed by Charles Bennett and Gilles Brassard in 1984 and uses quantum mechanics to allow the secure establishment of a shared key between two parties.

In this app, the user plays a game based on a simulation of BB84 where they attempt to break the security of the scheme by eavesdropping. Taking the role of Eve, the user intercepts photons transmitted between Alice and Bob in an attempt to figure out the secret key being established. However, the scheme has multiple ways of detecting interception. Because measuring a photon disturbs its state, Eve inevitably leaves traces that Alice and Bob can spot. Only by being lucky can Eve intercept the key and remain undetected.

This app is a good starting point for learning some basic principles of photons (choosing and revealing bases, polarization, no-cloning theorem, transmitter, receiver, splitter, exact analysis of the eavesdropper probability for a successful attack), and how they can be applied to cryptography — no physics lab required. A dynamic setup graph provides an overview of the situation.

Development of this app was sponsored by the MuQuaNet project.