Nicolas Sangouard: “The quantum computer does not exist yet, but it already poses a threat” | engineering techniques

The arrival of the quantum computer poses a real threat to certain cryptographic protocols based on supposedly difficult mathematical problems. In a matter of hours, a quantum computer could crack RSA and Diffie-Hellman-like cryptographic protocols in common use today. The confidentiality of health data or sensitive business information stored on servers or in the cloud would no longer be guaranteed. Researchers from the CEA, the Universities of Geneva, Oxford and the Swiss Federal Institutes of Technology in Lausanne and Zurich have laid the foundations for cryptographic keys that are particularly resistant to quantum attacks. A world first. Explanations with Nicolas Sangouard, researcher at CEA-IphT (Institute for Theoretical Physics).

Nicolas Sangouard is a CEA physicist and researcher working at the Institute of Theoretical Physics. He is a specialist in optics and quantum information and is particularly involved in the development of quantum communication and quantum computing.

Engineering Techniques: Even if the quantum computer is not yet a reality, do companies and states have to reckon with these threats now?

Nicholas Sanguard: If we refer to the technology developed by Google or IBM, it would take a quantum computer with millions of qubits to decode these logs. By the end of this year, however, IBM plans to launch a quantum machine with just over 1,000 qubits. So it will be a few more years before the quantum computer can take on such a task. But physicists and engineers are actively working on this scaling problem.

In particular, we have already shown that with a quantum memory (used in particular for quantum communication) we could break the RSA system with a quantum processor that would only have 10,000 qubits left. Going from 1,000 to 10,000 qubits significantly reduces the time scale compared to scaling to millions of qubits.

In addition, there is data, especially health data, that we want to keep for a very long time. Currently we cannot guarantee the security of this data from quantum attacks when it is transmitted between my GP and a hospital for example. I don’t know how long it will take to develop a large quantum computer. But given the advances we’ve seen over the past few years, I imagine that in 5 or 10 years we’ll be able to have such a machine capable of maintaining the security of the protocols currently in use to break. That means if my health data is kept encrypted until a quantum computer is available, it can be publicly disclosed in 5 or 10 years. This is a technology that does not yet exist, but which already poses a threat today.

That’s why 5 years ago the implementation of a new concept of quantum key distribution started?

The actual idea of ​​using quantum technology for secure communication dates back to the 1980s and in 1991 the idea appeared in a formulation very close to the experiment we conducted. To understand the idea underlying quantum cryptography, we must rely on the notion of entanglement. When two particles are entangled, a quantum principle states that when we measure one particle, we get a random result. When measuring the second particle, a result is obtained that is also locally random, but correlates perfectly with the result of the first measurement. This principle makes it possible to obtain a key; If we repeat this measurement, we get two strings of perfectly correlated, unpredictable results. This quantum key can then be used to encrypt and decrypt messages.

What are the advantages of this key distribution?

First, the security of encrypting and decrypting data with this key is not based on the difficulty of solving mathematical problems, as in the case of RSA or Diffie-Hellmanle. Security is based on a quantum principle: that of measuring entangled states. Secondly, security is guaranteed even if the origin and functionality of the devices used to obtain the keys are not known. In fact, security relies on the ability to demonstrate that individuals seeking a key are in an entangled state. And with a test called Bell, we can confirm that a state is entangled without knowing how the devices used to generate that key work. It is the whole innovative aspect of our research that brings double security. Not only can we have a very secure cryptographic protocol, also against quantum attacks, but we can also have security even if the devices used by a banker, for example, are not well characterized and whose trust level n is not specified. If the devices aren’t working properly, our protocol won’t work and tells users not to use them.

The next step will be to propose a marketable system, in particular by increasing the distance between the two devices with photonic systems?

The experiment we set up is very complicated. It is a prototype that can be realized in a very small number of laboratories around the world. For commercialization, we need to achieve this cryptography with simpler elements. Hence the idea of ​​using commercial photonic devices that have been around for decades and are capable of generating and measuring this entanglement. The goal is twofold: to have access to systems that are much easier to integrate into communication networks, but also allow access to higher key rates and longer distances. This will require years of development. National and European quantum plans are helping us to achieve this ambitious goal.

The announcement of the CEA comes at a time when NIST has unveiled the solutions it has adopted to resisting quantum. Is your solution complementary?

Europeans are at the forefront of research in this area, be it post-quantum cryptography (selected by the American agency NIST) or so-called quantum cryptography, as we are discussing in this interview. These two ways complement each other because the post-quantum is based on mathematical problems like RSA and Diffie-Helmann. Our solution offers more security and is particularly suitable for securing very sensitive data over very long periods of time. But it’s harder to implement.

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