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Securing practical quantum cryptosystems with optical power limiters

Gong Zhang, Ignatius William Primaatmaja, Jing Yan Haw, Xiao Gong, Chao Wang, Charles Ci Wen Lim

Published Dec 16, 2020• 0 citations
OpenAlex

Abstract

Controlling the energy of unauthorized light signals in a quantum cryptosystem is an essential task for implementation security. Here, we propose a passive optical power limiter device based on thermo-optical defocusing effects, which provides a reliable power limiting threshold that can be readily adjusted to suit various quantum applications. In addition, the device is robust against a wide variety of signal variations (e.g. wavelength, pulse width), which is important for implementation security. To show its practical utility for quantum cryptography, we demonstrate and discuss three potential applications: (1) measurement-device-independent quantum key distribution with enhanced security against a general class of Trojan-horse attacks, (2) using the power limiter as a countermeasure against bright illumination attacks, and (3) the application of power limiters to potentially enhance the implementation security of plug-and-play quantum key distribution.

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Physical Review A•Nov 27, 2023•17 citations
Controlling the energy of unauthorized light signals in a quantum cryptosystem is an essential task for implementation security. Here, we propose a passive optical power limiter device based on thermo-optical defocusing effects, which provides a reliable power limiting threshold that can be readily adjusted to suit various quantum applications. In addition, the device is robust against a wide variety of signal variations (e.g. wavelength, pulse width), which is important for implementation security. To show its practical utility for quantum cryptography, we demonstrate and discuss three potential applications: (1) measurement-device-independent quantum key distribution with enhanced security against a general class of Trojan-horse attacks, (2) using the power limiter as a countermeasure against bright illumination attacks, and (3) the application of power limiters to potentially enhance the implementation security of plug-and-play quantum key distribution.
Controlling the energy of unauthorized light signals in a quantum cryptosystem is an essential criterion for implementation security.Here, we propose a passive optical power limiter device based on thermooptical defocusing effects, providing a reliable power limiting threshold that can be readily adjusted to suit various quantum applications.In addition, the device is robust against a wide variety of signal variations (e.g., wavelength, pulse width), which is important for implementation security.We experimentally show that the proposed device does not compromise quantum communication signals.It only has a minimal impact (if not, negligible impact) on the intensity, phase, or polarization degrees of freedom of the photons, thus making it suitable for general communication purposes.To show its practical utility for quantum cryptography, we demonstrate and discuss three potential applications: (1) measurement-device-independent quantum key distribution with enhanced security against a general class of Trojan-horse attacks, (2) using the power limiter as a countermeasure against bright illumination attacks, and (3) the application of power limiters to potentially enhance the implementation security of plug-and-play quantum key distribution.
Unauthorized light injection has always been a vital threat to the practical security of a quantum-key-distribution (QKD) system. An optical-power limiter (OPL) based on the thermo-optical defocusing effect has been proposed and implemented, limiting the injected hacking light. As a hardware countermeasure, the performance of the OPL under various light-injection attacks will be tested to clarify the security boundary before it is widely deployed. To investigate the security boundary of the OPL in quantum cryptography, we comprehensively test and analyze the behavior of the OPL under continuous-wave (cw) light-injection attacks and pulse-illumination attacks with pulse repetition rates of 0.50.50.5 Hz, 404040 MHz, and 111 GHz. The test results illuminate the security boundary of the OPL, which allows one to properly employ the OPL in use cases. The methodology of testing and analysis proposed here is applicable to other power-limitation components in a QKD system.
In the quantum version of a Trojan-horse attack, photons are injected into the optical modules of a quantum key distribution system in an attempt to read information direct from the encoding devices.To stop the Trojan photons, the use of passive optical components has been suggested.However, to date, there is no quantitative bound that specifies such components in relation to the security of the system.Here, we turn the Trojan-horse attack into an information leakage problem.This allows us to quantify the system security and relate it to the specification of the optical elements.The analysis is supported by the experimental characterization, within the operation regime, of reflectivity and transmission of the optical components most relevant to security.
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.
Light-injection attacks pose critical security threats to quantum key distribution (QKD) systems. Conventional countermeasures, such as isolators, filters, and optical power monitoring, suffer from limited on-chip compatibility and inherent security vulnerabilities. To overcome these limitations, 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. The unit provides a rejection ratio exceeding 25 dB against non-resonant injected light. Under resonant attacks with power levels above tens of microwatts, the unit autonomously attenuates the signal transmission, with 14 dB attenuation measured at the maximum tested attack power of 10 dBm, leading to a significant suppression of the secure key rate. We further verify its response to pulsed light injection and incorporate possible residual leakage associated with finite response time into the key-rate analysis. This work provides a highly sensitive, broadband, and fully on-chip defense mechanism that significantly enhances the physical-layer security of QKD systems against light-injection attacks.
Laser-seeding attack enables an attacker to control the source output and eavesdrops on the key information, compromising the security of the continuous-variable (CV) quantum key distribution (QKD) system. In this paper, we suggest an improved optical power limiter (OPL) to defend against a laser-seeding attack on CV QKD systems. The proposed OPL utilizes a temperature monitor to detect Eve's attacks through temperature changes, providing an effective optical component for improving the security and reliability of the CV QKD system in practical environments, which is called an OPL-T scheme. In particular, we consider the security threats of a laser-seeding attack on two common CV QKD systems and prove their theoretical security degradation. Experiments are conducted to verify the effective OPL-T, and the results show that this defense scheme has an advantage in resisting the laser-seeding attack. Numerical simulations demonstrate the security analysis on CV QKD equipped with an OPL-T, which further confirms the effectiveness of our scheme. This work provides a practical solution for the security enhancements of continuous-variable quantum communication in practical applications.