Quantum computing is breaking down the barriers of cryptography


Faced with China and the United States, France has some major assets thanks, in particular, to the quality of its public and academic research laboratories.

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It is still early days for the quantum computer. However, cryptography is already sliding into another paradigm by exploiting the properties of quantum physics. The securing of highly critical data that it provides is a national sovereignty issue.

When postulating that the number of transistors on a chip would double every year, cofounder of Intel Gordon Moore predicted that the industry would reach a physical limit around 2020, that of the size of atoms. Quantum physics, which studies atom behaviour, is being called upon to extend “Moore’s law”.

Applied to computing, the quantum physics properties of superposition and entanglement promise unparalleled computing power. In October 2019, Google announced it had achieved “quantum supremacy”. Its processor is said to have performed a complex calculation in two hundred seconds, when a traditional supercomputer would have taken ten thousand years.

Beyond the promises nurtured by the announcement effects of Google, IBM, Microsoft, D-Wave or Honeywell, quantum computing has more concrete applications. In France, the January 2020 report by French member of parliament Paula Fortez entitled “Quantique : Le virage que la France ne ratera pas” (“Quantum: the technology revolution that France will not miss”) opens up another axis for research and development: securing communications by exploiting the quantum properties of photons.

Quantum key distribution, or QKD, makes it possible to produce a random secret key, known only to the sender and the recipient, in order to encrypt and decrypt messages while still relying on a traditional symmetric cryptographic protocol. The European Commission’s OPENQKD project brings together, for this purpose, research centres and telecommunication equipment manufacturers from thirteen countries including, for France: Orange, Thales, the CNRS or the Institut Mines Telecom.

RSA keys soon to be obsolete?

And what if hackers also had access to quantum power? This is the next stage, that of what is known as post-quantum cryptography. It has already been established that once implemented in a quantum computer, Shor’s algorithm would “break” public-key cryptosystems, such as RSA. The latter is commonly used to secure online exchanges, notably for e-commerce.

“Even if this hypothesis only comes into play in twenty years, we must already be thinking about replacement systems”, warns Mathias Van Den Bossche, director of Telecommunication and Navigation Systems R&D, and Quantum Technology Roadmap leader at Thales Alenia Space.


This work concerns the particularly sensitive data of the medical, military and intellectual property areas, and that of critical infrastructures dedicated to power distribution or to air transport.

“Central banks such as the Banque de France or the ECB must also look into the subject, Mathias Van Den Bossche continues. If, in the future, they issue cryptocurrencies or proceed with “tokenisation” of financial securities, they must have absolute trust in the means of protection”.

For these central banks, there are only three time-tested means of security: quantum cryptography, disposable keys, and delivery of keys to several places. However, according to the expert from Thales Alenia Space, bitcoin seems to be condemned in the long run faced with the power of quantum calculation.

The battle for quantum space

The second part of quantum communication deals with a more prospective framework as it is about linking quantum computers or sensors so as to create a super-powerful network, a sort of quantum internet. Bearing in mind that the networking of these quantum computers doesn’t just add their capacities together: it multiplies them.

In order to succeed in this challenge, it will nevertheless be necessary to aim for the sky. This is because, as Mathias Van Den Bossche explains, “photons are absorbed by fibre optics, which means that the signal range is limited to around one hundred kilometres. In free space, we are freed of this constraint. A satellite can direct a laser beam at the Earth and cover thousands of kilometres. The aim will thus be to link large cities using satellite links.”


In this quest for quantum space, China is one step ahead. In January 2020, it announced that it had successfully transmitted secure data via quantum cryptography between a mobile station and a satellite (source Futura Sciences). A world first.

Faced with China and the United States, France has some major assets thanks, in particular, to the quality of its public and academic research laboratories. “At the Institut d’Optique, researcher Philippe Grangier is at the origin of one of the three certifiable quantum cryptography protocols, rejoices Mathias Van Den Bossche. The Inria, for its part, is developing the proofs of security of quantum communication protocols.”

In France, in the coming months, the Forteza report recommendations should lead to a national plan dedicated to quantum development.

Faced with China and the United States, France has some major assets thanks, in particular, to the quality of its public and academic research laboratories.

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