Francesco Mazzoncini

We present complementary theoretical and experimental contributions bridging quantum cryptography and communication complexity. In our theory paper, we introduce a hybrid key distribution protocol achieving everlasting security while transmitting multiple photons per channel use, potentially surpassing fundamental QKD rate limits. The security proof for this protocol is based on a reduction that leverages the quantum advantage in communication cost between classical and quantum one-way communication complexity problems. Building on this theoretical foundation, our experimental work investigates the feasibility of demonstrating such quantum advantages in communication complexity using a reconfigurable and scalable optical platform based on wavefront shaping techniques.

We have shown how to conduct QKD vulnerability assessment in practice, based on a sound methodology inherited from Common Criteria. Taking a running CV-QKD system as a reference platform, we have experimentally tested and rated two different attack paths exploiting a common threat: detector saturation. Our results illustrate the importance of rating attacks in order to prioritize the implementation of countermeasures and to steer the design and engineering of practical QKD systems towards the highest possible security standards, paving the way to their security certification.

We introduce an explicit construction for a key distribution protocol in the Quantum Computational Timelock (QCT) security model, where one assumes that computationally secure encryption may only be broken after a time much longer than the coherence time of available quantum memories. Taking advantage of the QCT assumptions, we build a key distribution protocol called HM-QCT from the Hidden Matching problem for which there exists an exponential gap in one-way communication complexity between classical and quantum strategies.