With the huge amounts of data being transmitted and stored online, there is an increasing need to secure that data. Classical cryptographic techniques are no more considered secure since the advent of new mathematical algorithms or powerful computers can easily compromise classical key exchange algorithms. Quantum Mechanics provide us a simple solution to that problem: the Quantum Key Distribution, QKD. Up to now, QKD is considered the only absolute secure way to encrypt and protect data, since security is ensured by the laws of physics.

QKD is the most mature quantum technology, already present in the market. This technology will become essential to secure our communication infrastructures when today’s public key cryptography will be broken. The security of QKD relies upon its physical implementation and all components must be carefully analyzed to prevent security breaches.  INRIM in collaboration with Toshiba Research Europe, in the context of the metrological project EMPIR-MIQC2, published an activity, appeared in the prestigious journal of the Nature group Light: Science & Applications [1], that analyze the most important QKD components, i.e., single photon detectors based on fibre-pigtailed InGaAs SPADs, which can be found in all commercial QKD boxes. The detectors can leak information through ‘backflash’—bursts of light triggered when a photon hits an avalanche photodiode. Alice Meda and her collaborators in INRIM constructed a sensitive new machine detecting backflashes and determined data leakage rates nearing 10%. As well, each photodetector emitted specific signatures that might give attackers another entry point. These results are hugely important to guide the future design of secure QKD systems; for example, narrow-bandwidth filters or special circulators incorporated into the quantum boxes can help secure this breach.

Since this result is important for the practical security of QKD systems, it can be considered as an early uptake. On one side QKD manufacturers should take account of this result in designing their new devices, and on the other side the National Metrological Institutes should develop measurement services necessary for testing the protection strategies implemented. This also fulfills the requirements of the project EMPIR-MIQC2, that aims to accelerate the development and commercial uptake of QKD technologies by developing traceable measurement techniques, apparatus, and protocols that will underpin the characterization and validation of the performance and security of such systems.