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URSI General Assembly and Scientific Symposium

Source monitor in quantum key distribution

Xiang Peng, Hong Mei Guo

Published Aug 1, 2011• 0 citations
Publisher

Abstract

The core value of a quantum-key-distribution (QKD) system is the unconditional security. In the standard security analysis, the characteristics of QKD source are assumed to be known and fixed. In a real QKD experiment, this assumption may be deviated. Especially, in commercial Plug&Play QKD system, the source is untrusted. Source monitor can close this security loophole. This paper analyzes passive source-monitor scheme, and shows that this scheme can be well implemented in practice.

DOI
10.1109/ursigass.2011.6050668

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The core value of a quantum-key-distribution (QKD) system is the unconditional security. In the standard security analysis, the characteristics of QKD source are assumed to be known and fixed. In a real QKD experiment, this assumption may be deviated. Especially, in commercial Plug&Play QKD system, the source is untrusted. Source monitor can close this security loophole. This paper analyzes passive source-monitor scheme, and shows that this scheme can be well implemented in practice.
Quantum key distribution (QKD) has been proven to be unconditionally secure in theory. The light source of QKD is assumed to be trusted in the standard security analysis. However, this assumption may be deviated in a real system, which will cause `untrusted source' problem. To solve the problem, several source monitoring schemes have been proposed, in which passive schemes are more practical than active schemes. In this paper, we first review of these passive schemes, and then propose a new demonstration of the passive scheme with two-threshold detection using a low-pass filter, which can be well implemented in practical.
We present a passive approach to the security analysis of quantum key distribution (QKD) with an untrusted source. A complete proof of its unconditional security is also presented. This scheme has significant advantages in real-life implementations as it does not require fast optical switching or a quantum random number generator. The essential idea is to use a beam splitter to split each input pulse. We show that we can characterize the source using a cross-estimate technique without active routing of each pulse. We have derived analytical expressions for the passive estimation scheme. Moreover, using simulations, we have considered four real-life imperfections: Additional loss introduced by the "plug & play" structure, inefficiency of the intensity monitor, noise of the intensity monitor, and statistical fluctuation introduced by finite data size. Our simulation results show that the passive estimate of an untrusted source remains useful in practice, despite these four imperfections. Also, we have performed preliminary experiments, confirming the utility of our proposal in real-life applications. Our proposal makes it possible to implement the "plug & play" QKD with the security guaranteed, while keeping the implementation practical.
We present a passive approach to the security analysis of quantum key distribution (QKD) with an untrusted source. A complete proof of its unconditional security is also presented. This scheme has significant advantages in real-life implementations as it does not require fast optical switching or a quantum random number generator. The essential idea is to use a beam splitter to split each input pulse. We show that we can characterize the source using a cross-estimate technique without active routing of each pulse. We have derived analytical expressions for the passive estimation scheme. Moreover, using simulations, we have considered four real-life imperfections: additional loss introduced by the 'plug&play' structure, inefficiency of the intensity monitor noise of the intensity monitor, and statistical fluctuation introduced by finite data size. Our simulation results show that the passive estimate of an untrusted source remains useful in practice, despite these four imperfections. Also, we have performed preliminary experiments, confirming the utility of our proposal in real-life applications. Our proposal makes it possible to implement the 'plug&play' QKD with the security guaranteed, while keeping the implementation practical.
The SARG04 protocol is one of the most frequently used protocol in commercial plug-and-play quantum key distribution (QKD) system, where an eavesdropper can completely control or change the photon number statistics of the QKD source. To ensure the security of SARG04 protocol in plug-and-play QKD system with an unknown and untrusted source, the bounds of a few statistical parameters of the source need to be monitored. An active or a passive source monitor schemes are proposed to verify these parameters. Furthermore, the practical issues due to statistical fluctuation and detection noise in the source monitoring process are quantitatively analyzed. Our simulation results show that the passive scheme can be efficiently applied to plug-and-play system with SARG04 protocol.
The SARG04 protocol is one of the most frequently used protocol in commercial plug-and-play quantum key distribution (QKD) system, where an eavesdropper can completely control or change the photon number statistics of the QKD source. To ensure the security of SARG04 protocol in plug-and-play QKD system with an unknown and untrusted source, the bounds of a few statistical parameters of the source need to be monitored. An active or a passive source monitor schemes are proposed to verify these parameters. Furthermore, the practical issues due to statistical fluctuation and detection noise in the source monitoring process are quantitatively analyzed. Our simulation results show that the passive scheme can be efficiently applied to plug-and-play system with SARG04 protocol.
As a practical method, the passive scheme is useful to monitor the photon statistics of an untrusted source in a ``Plug Play'' quantum key distribution (QKD) system. In a passive scheme, three kinds of monitor mode can be adopted: average photon number (APN) monitor, photon number analyzer (PNA), and photon number distribution (PND) monitor. In this paper, the security analysis is rigorously given for the APN monitor, while for the PNA, the analysis, including statistical fluctuation and random noise, is addressed with a confidence level. The results show that the PNA can achieve better performance than the APN monitor and can asymptotically approach the theoretical limit of the PND monitor. Also, the passive scheme with the PNA works efficiently when the signal-to-noise ratio (RSN{\mathrm{R}}^{\mathrm{SN}}RSN) is not too low and so is highly applicable to solve the untrusted source problem in the QKD system.