Hub investigators have published a new research paper exploring the implementation of quantum secured encryption through (almost) classical devices. 

Sending private messages across long distances is possible using pairs of shared, secret keys, which hide data from everyone except the intended recipient. Secret key distribution is therefore essential for modern day society, where we depended on privacy more than ever. But, how can we ensure a given key distribution procedure is secure, especially given the advent of quantum computing, which leaves our most commonly used algorithms vulnerable to attack?

One way is to use quantum resources, such as entanglement, which ensures the resulting keys are fundamentally unguessable according to the laws of physics. To avoid modelling the physical process enabling security, which is time consuming and prone to errors, the “device-independent” approach aims to generate privacy with as few assumptions as possible, making it the pinnacle of security guarantees.

Fundamentally, how “quantum” does the physics need to be to enable key distribution? We show that even a tiny amount of nonlocality, the resource required for device-independence, can be used for perfect key distribution. This runs counter to the intuition that the strongest form of security would require highly “quantum” resources. That this is not the case furthers our understanding of the fundamental limitations on cryptography imposed by the laws of physics, and the findings can be used to improve protocols in practice.

The research findings have been published at Physical Review Letters.

Wooltorton L, Brown P, and Colbeck R. “Device-Independent Quantum Key Distribution with Arbitrarily Small Nonlocality”. Phys. Rev. Lett. 132, 210802. DOI: 10.1103/PhysRevLett.132.210802