Eavesdropping on quantum cryptography using tailored bright light

Abstract

Cryptography is the art of encoding messages such that they are only readable to the intended parties. Quantum cryptography has been proven completely secure: the best any eavesdropper can do is to try to guess the message being sent. In particular, any attempt to intercept and read the quantum bits (qubits) will fail. The peculiar laws of quantum mechanics postulates that measuring a quantum state will also change the quantum state and that qubits cannot be copied. Therefore, any attempt to measure the qubits will introduce disturbances on the line, and reveal the eavesdropper. In practice, photons (single light particles) are used as qubits, and transmitted over optical fiber.

In my lecture, I will first explain how quantum cryptography works. Then I will explain how we have broken the security of several state-off-the-art commercial quantum cryptography systems through a variety of security loopholes. The eavesdropping techniques includes controlling the single photon detectors using tailored bright illumination.

Biography

Lars Lydersen, Norwegian University of Science and Technology and the University Graduate Center

I live in Hamar, Norway and am a PhD-student at the Quantum Hacking group at the Norwegian University of Science and Technology in Trondheim, Norway and the University Graduate Center of Kjeller, Norway. I received my Master’s degree from the Norwegian University of Science and Technology in 2008, with one semester from TU Delft in 2005. The topic was the security of quantum cryptography with detector efficiency mismatch. Although quantum cryptography offers perfect security in theory, it remains an open question whether quantum cryptography can be implemented securely. The master thesis closed a critical security loophole.

In my PhD-thesis I perused the same question: can quantum cryptography be implemented securely? After a few theoretical publications on security proofs incorporate various imperfections, I moved on to hacking experiments on state-off-the-art commercial quantum cryptography systems, trying to find loopholes in the systems. This led to ground-breaking publications, shocking the research community by showing that the commercial quantum cryptography systems were in fact completely insecure. This is considered a crucial milestone to achieve practical secure quantum cryptography.

On my spare time I like endurance sports like running, cross country skiing and biking as well as wine and food.