Quantum Key Distribution (QKD).

A method that uses quantum-mechanical properties of photons to let two parties share a secret key while detecting any eavesdropper on the channel. It belongs to the Cryptography category of cybersecurity.

A method that uses quantum-mechanical properties of photons to let two parties share a secret key while detecting any eavesdropper on the channel.

Quantum Key Distribution (QKD) lets two parties, classically called Alice and Bob, derive a shared symmetric key whose secrecy is guaranteed by quantum physics rather than computational hardness. Single photons or entangled pairs are sent over fiber or free space, and any measurement by an eavesdropper disturbs the quantum state, introducing detectable errors. The most cited protocol is BB84 (Bennett and Brassard, 1984); newer variants include E91, B92, and measurement-device-independent (MDI) QKD. QKD complements but does not replace classical cryptography: it requires authenticated classical channels, dedicated hardware, and is currently distance-limited, so it is mainly deployed for high-value links between data centers, financial centers, or government sites.

Defences for Quantum Key Distribution (QKD) typically combine technical controls and operational practices, as detailed in the full definition above.

Common alternative names include: QKD, Quantum cryptography (key exchange).