Quantum hacking on a free-space quantum key distribution system without measuring quantum signals

We hack a practical free-space quantum key distribution (QKD) system using active wavelength control attacks without measuring quantum signals. This method is a hacking method that uses a wavelength change according to Alice’s laser diodes’ internal temperature change caused by Eve’s external laser source, unlike the existing hack, which simply analyzes the initial characteristic difference between transmitter signal laser diodes. In this paper, beyond a feasibility test, the proposed QKD hacking method is verified with the complete QKD system. Furthermore, we also suggest a new quantum hacking scheme in which the quantum signal does not need to be measured during the hacking process. Hence, Eve does not require complex hardware such as single-photon detectors and sources. Using the proposed quantum hacking method, we confirm that Eve can acquire not only a complete quantum key but also basis information without revealing her presence.