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Acta Sinica Quantum Optica

Security Research of Practical QKD System Based on Weak Coherent Light

Ding Liang-En

Published Jan 1, 2006• 0 citations
OpenAlex

Abstract

The single-photon sources used in most of the practical QKD systems are obtained through attenuating the weak laser pulse.It is not a perfect single-photon source,but is a quasisingle-photon source which follows the Poissonian distribution.The probability of every nonempty light pulse containing multiphoton is nonzero,the powerful eavesdropper(Eve) can take advantage of this to obtain some information about the final key.So it is necessary to study the security of the practical QKD system.Supposing,Eve launches photon-number-splitting(PNS) attack on multiphoton signals,and optimal attack(OA) on single-photon signals,adopting Shannon′s information theory to analyze the security of the practical QKD system based on weak coherent light.The result shows that the practical QKD system is secure against the attacks of PNS and OA,and the upper bound of the error rate that the legitimate users(Alice and Bob) can tolerate is also derived from are study.

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Physical Review A•Apr 21, 2011•22 citations
The single-photon sources used in most of the practical QKD systems are obtained through attenuating the weak laser pulse.It is not a perfect single-photon source,but is a quasisingle-photon source which follows the Poissonian distribution.The probability of every nonempty light pulse containing multiphoton is nonzero,the powerful eavesdropper(Eve) can take advantage of this to obtain some information about the final key.So it is necessary to study the security of the practical QKD system.Supposing,Eve launches photon-number-splitting(PNS) attack on multiphoton signals,and optimal attack(OA) on single-photon signals,adopting Shannon′s information theory to analyze the security of the practical QKD system based on weak coherent light.The result shows that the practical QKD system is secure against the attacks of PNS and OA,and the upper bound of the error rate that the legitimate users(Alice and Bob) can tolerate is also derived from are study.
For a start, Quantum Key Distribution offers security not depending on any fundamental assumption. However, actual realizations choose to use weak coherent pulses as photon sources, rather than the ideal single-photon state, which bears security weaknesses due to the emission of sporadic multi-photon states. These states can be used in Photon-Number Splitting (PNS) attacks, where the attacker intercepts and buffers photons of multi-photon pulses and forwards the rest, enabling partial recovery of the key without inducing detectable perturbations. This article presents a simulation-based approach to analyze PNS attacks with realistic channel conditions like losses, detector imperfections, and finite key lengths. The research also examines the performance of decoy-state countermeasures, that use variable-intensity pulses to statistically reveal eavesdropping and Simulation results confirm the dominant character of PNS on raw key rates for the no-countermeasure scenario and ensure optimal decoy-state schemes restore security by cutting single-photon contributions. Results establish that although WCP QKD is vulnerable to PNS attacks in theory, strict adoption of decoy-state protocols aided with monitoring and finite-key analysis can provide immunity against an adversary. The paper emphasizes the need for simulation-based, implementation-dependent security analysis in direction towards well-designed practical quantum cryptographic systems. [1] [2] [3] [4] [10] [8]
For a start, Quantum Key Distribution offers security not depending on any fundamental assumption. However, actual realizations choose to use weak coherent pulses as photon sources, rather than the ideal single-photon state, which bears security weaknesses due to the emission of sporadic multi-photon states. These states can be used in Photon-Number Splitting (PNS) attacks, where the attacker intercepts and buffers photons of multi-photon pulses and forwards the rest, enabling partial recovery of the key without inducing detectable perturbations. This article presents a simulation-based approach to analyze PNS attacks with realistic channel conditions like losses, detector imperfections, and finite key lengths. The research also examines the performance of decoy-state countermeasures, that use variable-intensity pulses to statistically reveal eavesdropping and Simulation results confirm the dominant character of PNS on raw key rates for the no-countermeasure scenario and ensure optimal decoy-state schemes restore security by cutting single-photon contributions. Results establish that although WCP QKD is vulnerable to PNS attacks in theory, strict adoption of decoy-state protocols aided with monitoring and finite-key analysis can provide immunity against an adversary. The paper emphasizes the need for simulation-based, implementation-dependent security analysis in direction towards well-designed practical quantum cryptographic systems. [1] [2] [3] [4] [10] [8]
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.
Quantum Key Distribution (QKD) provides Alice and Bob with a secure key to prevent third-party eavesdropping. Due to the lack of an ideal single-photon source, weak coherent light sources are widely used. The decoy state method can make up for the security loophole brought by weak coherent light sources - photon number splitting attack (PNS). The specific method of decoy state quantum key distribution is to send light pulses of different intensity levels. Taking the three-intensity decoy state method as an example, one is a signal state with an average photon number of u; one is a decoy state with an average photon number of d; and one is a vacuum state with an average photon number of v. Even if the eavesdropper is more powerful, he cannot distinguish which state the pulse comes from. Therefore, the accuracy of the light pulse intensity is crucial to the security of decoy state quantum key distribution [1] .
We propose a class of quantum cryptography protocols that are robust against photon-number-splitting attacks (PNS) in a weak coherent-pulse implementation. We give a quite exhaustive analysis of several eavesdropping attacks on these schemes. The honest parties (Alice and Bob) use present-day technology, in particular an attenuated laser as an approximation of a single-photon source. The idea of the protocols is to exploit the nonorthogonality of quantum states to decrease the information accessible to Eve due to the multiphoton pulses produced by the imperfect source. The distance at which the key distribution becomes insecure due to the PNS attack is significantly increased compared to the existing schemes. We also show that strong-pulse implementations, where a strong pulse is included as a reference, allow for key distribution robust against photon-number-splitting attacks.
Any imperfections in a practical quantum key distribution (QKD) system may be exploited by an eavesdropper to collect information about the key without being discovered. We propose a modified photon-number-splitting attack scheme against QKD systems based on weak laser pulses taking advantage of possible multiphoton pulses. Proof-of-principle experiments are demonstrated. The results show that the eavesdropper can get information about the key generated between the legitimate parties without being detected. Since the equivalent attenuation introduced by the eavesdropper for pulses of different average photon numbers are different, the decoy-state method is effective in fighting against this kind of attack. This has also been proven in our experiments.