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International Conference Laser Optics (ICLO)

Laser-pumping attack on QKD sources

Михаил Арсеньевич Фадеев, Anastasiya Ponosova, Roman Shakhovoy, Vadim Makarov

Published Jul 1, 2024• 0 citations
Publisher

Abstract

For the first time, we demonstrate a new type of attack on QKD systems based on laser pumping of a photon source. It includes injection of cw laser emission into a source at a wavelength that shorter than the system operating one. Particularly, we show that laser emission at 1310 nm induces increase in photon number at 1550 nm, changes in pulse shape and width. The QKD risk evaluation due to laser-pumping attack is presented.

DOI
10.1109/iclo59702.2024.10624559

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For the first time, we demonstrate a new type of attack on QKD systems based on laser pumping of a photon source. It includes injection of cw laser emission into a source at a wavelength that shorter than the system operating one. Particularly, we show that laser emission at 1310 nm induces increase in photon number at 1550 nm, changes in pulse shape and width. The QKD risk evaluation due to laser-pumping attack is presented.
We report a new type of vulnerability based on a physical principle that has not been previously exploited in quantum hacking—optical pumping of a laser in practical implementations of quantum key distribution (QKD) systems. We show that it is possible to increase the pulse energy of a source laser diode not only by injection-locking it with external light near its emission wavelength of 1550 nm, but also by optically pumping it at a much shorter wavelength. We experimentally demonstrate a 10% increase in pulse energy when exposing the laser diode to continuous-wave (cw) laser light at 1310 nm with a power of 1.6 mW via its fiber pigtail. This effect may allow an eavesdropper to steal the secret key. A possible countermeasure is to install broadband optical filters and isolators at the source output and to characterize them during security certification.
Advanced laser modulation techniques have enabled the development of versatile and efficient light sources for quantum communications [1]. In fact, semiconductor lasers are normally used as single-photon sources in most commercial and research quantum key distribution (QKD) systems [2]. In particular, modulated single-mode semiconductor lasers, utilizing gain-switching, optical injection locking and direct phase modulations have been used to implement a great variety of QKD protocols [1]. In recently introduced protocols, like the measurement-device-independent one (MDI) based on the interference of pulses generated by two remote semiconductor laser sources, timing-jitter in gain-switched lasers affects the temporal overlap of the pulses producing a dramatic reduction in the interference visibility [1]. Very recently MDI-QKD systems using optical injection from a semiconductor laser into a gain-switched semiconductor laser have been demonstrated [1]. A reduction of timing-jitter induced by optical injection is then desirable to improve the interference visibility in this type of MDI-QKD systems.
A standard laser produces a coherent state of light with a Poissonian photon number distribution. Generation of single photons on demand is a key requirement for quantum key distribution and quantum information processing systems based on photonic qubits. One of the generation schemes for single photons is to use a single semiconductor quantum dot embedded in a monolithic microcavity. An optical pump pulse or electrical pump pulse generates more than one electron–hole pairs in a quantum dot. Those electron–hole pairs recombine to generate photons one by one via spontaneous emission. The last photon emitted from a quantum dot has a unique wavelength, differing from the other photons, because the multiparticle interaction inside a quantum dot modulates an emission wavelength. One can selectively extract this last photon by a narrow band optical filter, so that single photons are extracted from the system no matter how many electron–hole pairs are injected into the quantum dot initially.
Quantum key distribution introduces a new way of key exchange through a public quantum channel between two communicating nodes. However, the first introduced BB84 protocol was theoretically verifying security based on single photon sources. At this time, it was hard to achieve such device. Therefore, it was a challenging aspect to prove the security of QKD system using coherent light sources or “multi emitting photon source”, which introduces Photon number splitting attacks. We are interested to simulate and investigate the QKD system using coherent laser sources and study the PNS attack. The idea involves that; Eve can crash a beam of light, absorbing some photons using QND measurement and transmit the others. Such attack can make Eve dominant to the situation and gain much information of the key without the fear of getting exposed to the communicating parties. Herein, this paper discusses some useful solution to detect such attack and proves the security of QKD even with weak laser sources.
In this paper, we investigate spectral vulnerabilities in quantum key distribution systems arising from the use of shorter-wavelength radiation in the 400–800 nm range, with particular focus on the induced photorefraction attack (IPA). Crucial elements influenced by the IPA include various types of both phase and intensity modulators, and we consider different scenarios and their implications. Through combined theoretical and experimental analysis, we demonstrate that optical components commonly used as countermeasures in the telecom band (1000–2100 nm) exhibit significantly reduced effectiveness at shorter wavelengths. The efficiency of IPA is shown to increase as the wavelength decreases, posing a substantial threat to phase-modulation-based QKD protocols. We analyze the impact of IPA across different QKD architectures and assess the feasibility of potential countermeasures under realistic implementation scenarios. Our results highlight the necessity of broadband security evaluations and wavelength-aware component design in future QKD systems.
Quantum key distribution (QKD) systems provide quantum-safe key exchange. Therefore, complete security analysis of implementations of QKD protocols is in the focus of interest of a worldwide information-security community. For today, a number of QKD loopholes are closed by countermeasures, which are also considered in emerging QKD security evaluation and certification [1]–[3]. However, new threats to practical QKD implementations are still found, such as the laser-damage attack, which is a powerful hacking strategy. In investigations, CW laser radiation is most often used, but in contrast to it, the interaction of pulsed laser radiation with optical materials may lead to a wide range of effects, like nonlinear effects, dielectric breakdown, etc.