Quantum hacking on free-space QKD system

Min Soo Lee, Min Ki Woo, Jisung Jung +3 more

We develop a way to hack free-space quantum key distribution (QKD) systems by changing the wavelength of the quantum signal laser using an external laser. Most free-space QKD systems use four distinct lasers for each polarization, thereby making the characteristics of each laser indistinguishable. We also discover a side-channel that can distinguish the lasers by using an external laser. Our hacking scheme identifies the lasers by automatically applying the external laser to each signal laser at different intensities and detecting the wavelength variation according to the amount of incident external laser power. We conduct a proof-of-principle experiment to verify the proposed hacking structure and confirm that the wavelength varies by several gigahertzes to several nanometers, depending on the intensity of the external laser. The risk of hacking is successfully proven through the experimental results. Methods for prevention are also suggested.

Anoop Kumar Pandey

Ming‐Xing Luo

Min Soo Lee, Min Ki Woo, Yong‐Su Kim +3 more

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.

Minchul Kim, Junsang Oh, Byung‐Seok Choi +6 more

We demonstrate the first free-space QKD experiment using an optical phased array chip for compact, fully integrated, and mobile free-space QKD systems. We achieve 1% QBER for a couple of beam steering conditions.

Alberto Carrasco-Casado, Verónica Fernández, Natalia Denisenko