From Existing Quantum Key Distribution Systems Towards Future Quantum Networks

With the current development of quantum computing, some existing cryptographic protocols may be broken in the future, such as RSA with Shor's algorithm.To secure the future secret communications, but also the current ones from retrospective decryption, Pre-Shared Keys (PSK) can be used today, and two types of complementary solutions are currently being studied: Post Quantum Cryptography (PQC) and Quantum Key Distribution (QKD).The objective of this paper is to describe the latest, which relies on the laws of quantum physics to secure the sharing of secret keys.Among the current QKD systems, some are already commercially available.Their distance range is limited, generally around 100 km.To overcome this distance limitation, a first solution is currently being deployed in field trials using trusted nodes, forming the so-called Quantum Communication Infrastructure (QCI).The drawback is that users must trust QCI nodes, in which quantum communication are stopped, going back to classical data processing that can be eavesdropped.To overcome this problem, researchers are investigating solutions to build future quantum networks and Quantum Internet (QI), in which the processing in the networks remains quantum, using quantum buffers and entanglement swapping in quantum repeaters to increase the distance range of QKD.We briefly discuss the advantages and disadvantages of QKD versus PQC, with the two actually being complementary.