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arXiv:1709.10202 · Journal of the Optical Society of America B

Reference pulse attack on continuous variable quantum key distribution with local local oscillator under trusted phase noise

Shengjun Ren, Rupesh Kumar, A. Wonfor, Xinke Tang, Richard V. Penty, Ian H. White

Published Dec 20, 2018• 39 citations
arXivHTMLPDF

Abstract

We show that partially trusting the phase noise associated with estimation uncertainty in a local local oscillator continuous-variable quantum key distribution (LLO-CVQKD) system allows one to exchange higher secure key rates than in the case of untrusted phase noise. However, this opens a security loophole through the manipulation of the reference pulse amplitude. We label this as a “reference pulse attack,” which is applicable to all LLO-CVQKD systems if the phase noise is trusted. We show that, at the optimal reference pulse intensity level, Eve achieves unity attack efficiency at 23.8 km and 32.0 km while using lossless and 0.14 dB/km loss channels, respectively, for her attack. However, to maintain the performance enhancement from partially trusting the phase noise, countermeasures have been proposed. As a result, the LLO-CVQKD system with partially trusted phase noise owns a superior key rate at 20 km by an order 9.5, and an extended transmission distance by 45%, compared to the phase noise untrusted system.

DOI
10.1364/josab.36.0000b7

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We show that partially trusting the phase noise associated with estimation uncertainty in a local local oscillator continuous-variable quantum key distribution (LLO-CVQKD) system allows one to exchange higher secure key rates than in the case of untrusted phase noise. However, this opens a security loophole through the manipulation of the reference pulse amplitude. We label this as a “reference pulse attack,” which is applicable to all LLO-CVQKD systems if the phase noise is trusted. We show that, at the optimal reference pulse intensity level, Eve achieves unity attack efficiency at 23.8 km and 32.0 km while using lossless and 0.14 dB/km loss channels, respectively, for her attack. However, to maintain the performance enhancement from partially trusting the phase noise, countermeasures have been proposed. As a result, the LLO-CVQKD system with partially trusted phase noise owns a superior key rate at 20 km by an order 9.5, and an extended transmission distance by 45%, compared to the phase noise untrusted system.
We study the validity of partially trusting the phase noise associated with estimation uncertainty in a continuous variable quantum key distribution system with a local local oscillator (LLO-CVQKD) and investigate optimal system parameters. We find that the trusted phase noise model enhances the key rate and transmission distance performance but opens a security loophole by manipulating the reference pulse amplitude. Therefore, we propose a “reference pulse attack” on the trusted phase noise LLO-CVQKD system where Eve achieves 100% information hacking without being detected at 23.8km and 32.0km while using lossless and 0.14dB/km loss channels, respectively. Nevertheless, by re-analyzing the attack, countermeasures are also proposed to keep the performance advantages of the trusted phase noise model. As a result, the trusted phase noise LLO-CVQKD can still provide a superior secure key rate (e.g., 9 times higher key rate at 20km) and an increased transmission distance by 45%, compared to that of the untrusted phase noise system.
We reveal a security loophole in the current state-of-art phase reference pulse sharing scheme for Continuous Variable Quantum Key Distribution using a Local Local Oscillator (LLO-CVQKD). The loophole is associated with the amplitude of the phase reference pulses which Eve can manipulate to extract information which cannot be discovered by legitimate users. We call this new attack as the reference pulse attack. We have demonstrated the efficiency of our attack for different LLO-CVQKD transmission distances. Unity attack efficiency can be achieved at a transmission distance greater than 21.2 km in the case of a zero loss channel. The distance extends to 24.3 km where hollow-core fibre channels are used. We also propose possible countermeasures.
In practical continuous-variable quantum key distribution system using local local oscillator (LLO CV-QKD), the phase noise related to coherent detection and phase-reference pulse intensity can be locally calibrated at the receiver side. Therefore, it can be regarded as trusted noise in order to obtain a higher secret key rate and transmission distance. However, security loopholes will be opened for the eavesdropper to launch attacks without appropriate countermeasures. To this end, we propose two practical phase-reference pulse intensity attack strategies, where Eve can reduce the trusted phase noise by manipulating the intensity of the phase-reference pulse, thereby hiding her attack on the signal pulse. The performance of the LLO CV-QKD system under these attacks has been analyzed. We show that precisely monitoring the intensity of the phase-reference pulse in real time is an essential countermeasure to prevent the proposed attacks. Moreover, an intensity-monitoring scheme for the phase-reference pulse is proposed to strengthen the security of the practical LLO CV-QKD system and make the trusted phase noise model more robust.
The trusted phase noise model for continuous-variable quantum key distribution protocol with a real local oscillator (LLO CVQKD) has been established recently, which can lead to a better quantum key distribution (QKD) performance by moving part of the phase noise from the untrusted channel-added noise to the trusted detector-added noise. However, the calibration of the trusted phase noise is related to the intensity of the phase-reference pulse, which can be used by the eavesdropper to hack the QKD system. Here, we present a polarization attack scheme against the phase-reference pulse. In practical LLO CVQKD systems, only a part of the phase-reference pulses are used to measure and compensate for the polarization drift of the signal pulses due to the limitation of polarization measurement. We show that Eve can manipulate the polarization of the unmeasured part of the phase-reference pulses to control the trusted phase noise. Simulations show that improving the polarization measurement ratio to 100% or monitoring the phase-reference pulse intensity in real time is necessary to guarantee the security of the practical LLO CVQKD system.
In practical continuous-variable quantum key distribution system using local local oscillator (LLO CV-QKD), the phase noise related to coherent detection and phase-reference pulse intensity that can be locally calibrated at the receiver side is considered to be trusted noise to improve the performance. However, if the intensity of the phase-reference pulse is not monitored precisely in real-time, a security loophole will be opened for the eavesdropper to launch attacks. To this end, we propose two practical phase-reference pulse intensity attack strategies, where Eve can reduce the trusted phase noise by manipulating the intensity of the phase-reference pulse, thereby hiding her attack on the signal pulse if the total excess noise remains unchanged. The performance of the LLO CV-QKD system under these attacks has been analyzed. We show that precisely monitoring the intensity of the phase-reference pulse in real-time is an essential countermeasure to prevent the proposed attacks. Moreover, an intensity-monitoring scheme for the phase-reference pulse is proposed to strengthen the security of the practical LLO CV-QKD system and make the trusted phase noise model more robust.
The estimation of phase noise of continuous-variable quantum key distribution protocol with a local local oscillator (LLO CVQKD), as a major process in quantifying the secret key rate, is closely relevant to the intensity of the phase reference. However, the transmission of the phase reference through the insecure quantum channel is prone to be exploited by the eavesdropper (Eve) to mount attacks. Here, we introduce a polarization attack scheme against the phase reference. Presently, in a practical LLO CVQKD system, only part of the phase reference pulses are measured to compensate for the polarization drift of the quantum signal pulses in a compensation cycle due to the limited polarization measurement rate, while the other part of the phase reference pulses are not measured. We show that Eve can control the phase noise by manipulating the polarization direction of the unmeasured phase reference to hide her attack on the quantum signal. Simulations show that Eve can obtain partial or total key rates information shared between Alice and Bob as the transmission distance increases. Improving the polarization measurement rate to 100% or monitoring the phase reference intensity in real-time is of great importance to protect the LLO CVQKD from polarization attack.