New quantum encryption method could lead to truly secure communication

27 Jul 2022

The experiment involved two single ions (one for the sender and one for the receiver) confined in separate traps that were connected with an optical-fibre link. This is one of the ion traps used in the experiment. Image: David Nadlinger/University of Oxford

By tapping into quantum entanglement, researchers said they could develop secure communications that are ‘fundamentally beyond’ an adversary’s control.

An international team of researchers has tested a new form of quantum cryptography that could lead to the ultimate standard in secure communications with real-world devices.

It is based on quantum key distribution (QKD), which is a method of sharing encryption keys between two parties that can be used to encrypt and decrypt messages. This promises communication security unattainable in conventional cryptography.

Encryption involves complex maths problems that modern computers cannot solve to keep data secure. But as technology advances, quantum computers will likely be able to solve these problems and bypass current cryptographic protocols.

The researchers said existing forms of QKD rely on communication between two ‘trusted’ quantum devices. This requires detailed knowledge of the devices, which can open up the potential for quantum hacking.

However, their new approach allows for secure communication between devices without needing to know much about them, paving the way for secure cryptography for real-world devices.

Two boxes with keys and blue orbs in them, connected by wires that lead to a third box. Used to represent a form of quantum cryptography.

A representation of device-​independent quantum key distribution. Image: Scixel/Enrique Sahagú

“The real breakthrough here is that we were not just able to show that our quantum network had theoretically good enough performance to do this new kind of QKD, but that we were actually able to do it in practice and get all the way to distributing a shared secret key,” said Prof David Lucas of the University of Oxford.

Device independence

The research was a collaborative effort between the University of Oxford, the French Alternative Energies and Atomic Energy Commission, and Swiss universities ETH Zurich, EPFL and the University of Geneva.

In their study, published in Nature, the researchers said they successfully demonstrated an approach to QKD between two devices based on high-quality quantum entanglement. This is the relationship between two particles that can span vast distance, but still be connected and operate in tandem.

The experiment involved two single ions (one for the sender and one for the receiver) confined in separate traps that were connected with an optical-fibre link. While these devices were in the same room, the researchers said there is a “clear route” to extend the distance to kilometres and beyond.

The sender and receiver can produce shared outcomes through the entangled quantum system, without a third party being able to interfere.

The researchers said this method could lead to forms of communication between two parties that are “fundamentally beyond” any adversary’s control, and that an equivalent security guarantee is impossible with classic cryptography methods.

The team also said this method can guarantee communication privacy with only a few general assumptions about the physical devices used. This helps lay the foundation for “device-independent QKD”.

ETH Zurich’s Prof Renato Renner said the history of cryptography has been a competition between cryptographers and the cryptoanalysts who attack new encryption methods.

“But device-independent quantum cryptography may finally bring this competition to an end – there simply is hardly any room left for an attack,” Renner said.

Earlier this month, the US National Institute of Standards and Technology selected four encryption algorithms that it believes can withstand the assault of a quantum computer, which will become part of a new quantum-resistant cryptographic standard.

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Leigh Mc Gowran is a journalist with Silicon Republic