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arXiv:2512.10205

Optical fuse based on the photorefractive effect for defending the light-injection attacks of quantum key distribution

Min Chen, Hong-Yan Song, Jia-Lin Chen, Peng Ye, Guo-Wei Zhang, Fang-Xiang Wang, Li Zhang, Shuang Wang, De-Yong He, Zhen-qiang Yin, Guang-Can Guo, Wei Chen, Zheng-Fu Han

quant-phphysics.opticsSubmitted Dec 11, 2025• Announced Dec 12, 2025• 0 citations
v1 · Dec 11, 2025v2 · Jul 11, 2026
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Abstract

Light-injection attacks pose critical security threats to quantum key distribution (QKD) systems. Conventional defense methods, such as isolators, filters, and optical power monitoring, are confronted with the threats of specific attacks and the limitations in integration. To address this, we propose and experimentally demonstrate an integrated attack sensing and automatic response unit utilizing the photorefractive effect in a thin-film lithium niobate microring resonator. Our unit provides a high rejection ratio against non-resonant injected light. For resonant attacks exceeding tens of microwatts, the unit can autonomously attenuate the transmission of the quantum signal light, leading to a significant suppression of the secret key rate. This work enhances the security of QKD systems against light-injection attacks by providing a highly sensitive, broadband, and on-chip defense mechanism.

Comments
10 pages, 5 figures

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Light-injection attacks pose critical security threats to quantum key distribution (QKD) systems. Conventional defense methods, such as isolators, filters, and optical power monitoring, are confronted with the threats of specific attacks and the limitations in integration. To address this, we propose and experimentally demonstrate an integrated attack sensing and automatic response unit utilizing the photorefractive effect in a thin-film lithium niobate microring resonator. Our unit provides a high rejection ratio against non-resonant injected light. For resonant attacks exceeding tens of microwatts, the unit can autonomously attenuate the transmission of the quantum signal light, leading to a significant suppression of the secret key rate. This work enhances the security of QKD systems against light-injection attacks by providing a highly sensitive, broadband, and on-chip defense mechanism.
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Lithium niobate materials, which have the potential to fabricate lasers, modulation devices, and photodetectors, are widely used in quantum information processing due to their exceptional optical and electro-optical properties. However, the photorefractive effect in lithium niobate materials may cause the quantum device to deviate from its ideal operation model, which is an important assumption for the security of quantum key distribution. Here, we demonstrate the practical security of the continuous-variable quantum key distribution protocol under the photorefractive effect, where the eavesdropper Eve injects a 488 nm visible light into the source-side variable optical attenuator and excites the photorefractive effect phenomenon in a lithium-niobate-based dual-waveguide. In particular, we derive the photorefractive-effect-induced intensity change of a variable optical attenuator and then the corresponding parameter estimation process, showing the effectiveness of this attack for various irradiation powers and waveguide technologies (including proton-exchanged and annealed-proton-exchanged waveguides). To show its effect on practical continuous-variable quantum key distribution systems, we present the composable finite-size security of one-way continuous-variable quantum key distribution and continuous-variable measurement-device-independent quantum key distribution protocols. Numerical results show that this induced-photorefraction attack can break the security even with a low irradiation power, such as 3 [Formula: see text] (or about 0.21 [Formula: see text]). In addition, we find that Eve's optimal attack strategy against continuous-variable measurement-device-independent quantum key distribution is related to the information reconciliation process by comparing three different attack strategies. Finally, we discuss some possible countermeasures to resist induced-photorefraction attacks to enhance the security of the system.
Lithium niobate (LiNbO3, LN) devices play critical roles in quantum information processing. However, for special applications like quantum key distribution (QKD), the characteristics of materials and devices and their impact on practical systems must be intensively inquired. For the first time, we reveal that the photorefractive effect in LN can be utilized as a potential loophole to carry out malicious attacks by the eavesdroppers. We take a commercial LN-based variable optical attenuator as an example to demonstrate the method we named Induced-photorefractive attack (IPA) and propose two techniques to enable controllable attacks. Our results show that eavesdroppers can fulfill an efficient source-side attack by injecting an optimized irradiation beam with only several nanowatts, which is realistic when accessing commercial fiber channels. These measure and techniques can be employed for all individual and on-chip LN devices and initially explored a new security branch for system design and standardization of real-life QKD.
A well-protected and characterized source in a quantum key distribution system is needed for its security.Unfortunately, the source is vulnerable to light-injection attacks, such as Trojan-horse, laser-seeding, and laser-damage attacks, in which an eavesdropper actively injects bright light to hack the source unit.The hacking laser could be a high-power one that can modify properties of components via the laserdamage attack and also further help the Trojan-horse and other light-injection attacks.Here we propose a countermeasure against the light-injection attacks, consisting of an additional sacrificial component placed at the exit of the source.This component should either withstand high-power incoming light while attenuating it to a safe level that cannot modify the rest of the source, or get destroyed into a permanent high-attenuation state that breaks up the line.We demonstrate experimentally that off-the-shelf fiberoptic isolators and circulators have these desired properties, at least under attack by a continuous-wave high-power laser.