Anastasiya Ponosova

Our study shows that the rate of random number generation by QRNG based on interference of laser pulses is significantly more limited than expected. An increase in generation speed requires shortening the duration of laser pulses. However, the interference of short laser pulses from a single laser diode is problematic due to jitter and phase modulation (chirp). The optically injection-locked configuration proposed by L. C. Comandar for MDI QKD does not have the above disadvantages and therefore enables the design of QRNG with a high speed of random number generation.

In this work, we demonstrate a new kind of attack on laser sources in quantum key distribution systems - the optical-pumping attack. We investigated its influence on a single distributed feedback laser diode and an optically injection-locked source configuration. The spectral dependency of this attack was also examined. We managed to increase the energy of emitted pulses using attackers light at several wavelengths. The developed optical-pumping attack should be considered as a possible threat to the security of QKD systems because the increase of pulse energy leads to overestimation of secret key rate between Alice and Bob, giving more information about secret key to Eve.

We report recent advances in the development of certification for quantum key distribution (QKD) systems. We give an example of a commercial QKD system that we have analysed for possible loopholes, improved to close the vulnerabilities identified, and designed a set of tests for that can be used by a certification lab [arXiv:2310.20107]. We explain some of the testbenches in this lab, such as an ultrawide spectral characterisation testbench, automated detector testing, and laser damage testbench that verifies the quality of a power limiter. This work is in line with the requirements of the ISO standard for QKD and paves the way for the creation of certification services.

Quantum key distribution (QKD) technology allows sharing secret keys between two parties over an insecure channel. But there are vulnerabilities in the technical implementation of systems. Laser seeding attack is one of the examples of imperfections in QKD systems. Recent works have demonstrated that Eve can manipulate output power of Alice's laser. This leads to an increase of the average photon number, emitted by Alice. But this attack can be prevented by using passive fiber-optic elements such as isolators or DWDM-filters. In this work, we demonstrate a new kind of attack namely, the optical pumping attack. This attack utilises imperfections in passive optic elements that are used in QKD systems to prevent other types of attack. Eve can use source at different wavelength to seed Alice laser, 1064 nm for example. This radiation would be absorbed by crystal within laser and create additional population inversion to inversion created by bias current, that drives Alice laser. This pumping would change average photon number at the output of Alice, leading to wrong estimation of lower bound on the secret key rate. This creates a side-channel for Eve for obtaining key information. In this work we performed this kind of attack for several wavelengths: 1064 nm, 1310 nm, 1480 nm and 2000 nm, measured changing of pulse energy, average output power and pulse shape under attacks at different wavelengths. Finally, we provide theoretical estimation of required isolation at the tested wavelengths to protect the source against the optical-pumping attack.

We propose an original device that can protect quantum key distribution (QKD) systems from the effects of intense laser radiation. Carbon nanomaterials dispersed in a polymer can be used as a fuse that interrupts key distribution when Eve tries to hack the system by high-power laser emission. Moreover, it saves system components from laser damage.

In the age of measurement-device-independent quantum key distribution (MDI QKD) and twin- field QKD (TF QKD), the source units of these QKD schemes may become a new ``Achilles' heel" of the whole system. An adversary, Eve, can conduct various attacks on the sources by injecting lasers, whose power is limited by the laser-induced damage threshold of the quantum channel. Such an amount of power may modify the characteristics of components in a source. In this work, we study possible components to protect the source from the light-injected attacks, i.e., Trojan-horse attack, the laser-seeding attack, and the laser-damage attack. Experimental testing shows that fiber-optics isolators and circulators are good passive countermeasures because they sacrifice themselves' isolation under a high-power laser to protect other components behind them. Moreover, we find that illuminated by the high-power laser, integrated photonics QKD chips only lose the transmission of the coupler before any other change happens for the other components in the chips.