Hacking commercial quantum cryptography systems by tailored bright illumination

Understand

The peculiar properties of quantum mechanics allow two remote parties to communicate a private, secret key, which is protected from eavesdropping by the laws of physics.

• So-called quantum key distribution (QKD) implementations always rely on detectors to measure the relevant quantum property of single photons.
• Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumination.
• This makes it possible to tracelessly acquire the full secret key; we propose an eavesdropping apparatus built of off-the-shelf components.