BB84 Protocol

What

BB84, named after Charles Bennett and Gilles Brassard who invented it in 1984, is how quantum key distribution actually works. Alice wants to send Bob a secret key. She takes single photons and encodes each bit by choosing randomly between two measurement bases - think of it like choosing whether to wear polarized sunglasses horizontally or diagonally. Bob also chooses randomly how to measure each photon. After transmission, they publicly announce which bases they used (but not the actual bits). They keep the bits where they happened to use the same basis and throw away the rest. Here's the quantum magic: if Eve tries to eavesdrop, she has to measure the photons without knowing which basis Alice used. Her measurements disturb the quantum states, creating errors Alice and Bob can detect. If errors exceed 11%, they abort because someone's listening.

Why

BB84 has been tested in real networks for over 20 years. Banks in Tokyo, government agencies in Europe, and defense networks in the U.S. use it daily. It's the only key distribution method with security guaranteed by physics rather than computational assumptions.

Impact

BB84 makes quantum key distribution practical. QNu Labs' Armos uses an enhanced version with "decoy states" that fixes practical issues with real-world photon sources. This means you can deploy quantum-safe key distribution today on existing fiber networks.

Use Cases

Securing key distribution for government classified networks, protecting financial institution communications, enabling secure telecom infrastructure, military command and control systems, metropolitan quantum networks

Links

https://www.qnulabs.com/quantum-key-distribution | https://www.youtube.com/c/QNuLabs

Tags

BB84 protocol, quantum key distribution protocol, QKD, Bennett-Brassard, quantum cryptography, single-photon encoding, eavesdropping detection, prepare-and-measure QKD, quantum security, photon polarization