quantum key distribution

While the physics of QKD are theoretically unbreakable because observing a quantum state alters it, the physical hardware used to build these systems can be hacked. Hackers can exploit vulnerabilities in the photon detectors or the random number generators used in commercial QKD devices. This is known as a side-channel attack and requires rigorous hardware auditing to prevent.

BB84 is the first and most famous quantum cryptography protocol, developed by Charles Bennett and Gilles Brassard in 1984. It uses the polarization states of individual photons to transmit a cryptographic key between two parties. If an eavesdropper intercepts the photons, their measurement collapses the quantum state, introducing errors that the legitimate parties can detect.

Currently, QKD is limited by the distance light can travel through fiber optic cables without losing photons, typically capping at a few hundred kilometers. Beyond this distance, repeaters are needed, but standard repeaters destroy the quantum state, requiring complex 'quantum repeaters' that are still in development. Researchers have successfully tested satellite-based QKD to bypass these terrestrial limits.

No, QKD does not require a full quantum computer for the sender or receiver to generate and exchange keys. It relies on relatively simple quantum mechanics, utilizing single-photon emitters and standard fiber-optic networks. However, it is highly relevant to quantum computing because it provides a method to secure communications against future quantum computer attacks.