Finite-key analysis for measurement-device-independent quantum key distribution

Security in quantum cryptography [1, 2] is continuously challenged by inventive attacks [3][4][5][6][7] targeting the real components of a cryptographic setup, and duly restored by new countermeasures [8][9][10] to foil them. Due to their high sensitivity and complex design, detectors are the most frequently attacked components. Recently it was shown that two-photon interference [11] from independent light sources can be exploited to avoid the use of detectors at the two ends of the communication channel [12,13]. This new form of detection-safe quantum cryptography, called Measurement-Device-Independent Quantum Key Distribution (MDI-QKD), has been experimentally demonstrated [13][14][15][16][17][18], but with modest delivered key rates.Here we introduce a novel pulsed laser seeding technique to obtain high-visibility interference from gain-switched lasers and thereby perform quantum cryptography without detector vulnerabilities with unprecedented bit rates, in excess of 1 Mb/s. This represents a 2 to 6 orders of magnitude improvement over existing implementations and for the first time promotes the new scheme as a practical resource for quantum secure communications. * marco.lucamarini@crl.toshiba.co.uk arXiv:1509.08137v2 [quant-ph] In Quantum Cryptography, a sender Alice transmits encoded quantum signals to a receiver Bob, who measures them and distils a secret string of bits with the sender via public discussion [1].Ideally, the use of quantum signals guarantees the information-theoretical security of the communication [2]. In practice, however, Quantum Cryptography is implemented with real components, which can deviate from the ideal description. This can be exploited to circumvent the quantum protection if the users are unaware of the problem [19].Usually the most complex components are also the most vulnerable. Therefore the vast majority of the attacks performed so far have targeted Bob's single photon detectors [3][4][5][6][7]. 13] is a recent form of Quantum Cryptography conceived to remove the problem of detector vulnerability. As depicted in Fig. 1(a), two light pulses are independently encoded and sent by Alice and Bob to a central node, Charlie. This is similar to a quantum access network configuration [20], but in MDI-QKD the central node does not need to be trusted and could even attempt to steal information from Alice and Bob. To follow the MDI-QKD protocol, Charlie must let the two light pulses interfere at the beam splitter inside his station and then measure them. The result can disclose the correlation between the bits encoded by the users, but not their actual values, which therefore remain secret. If Charlie violates the protocol and measures the pulses separately, he can learn the absolute values of the bits, but not their correlation. Therefore he cannot announce the correct correlation to the users, who will then unveil his attempt through public discussion.Irrespective of Charlie's choice, the users' apparatuses no longer need a detector and the detection vulnerability of Quantum Cryp...

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“…[8] (see also [9] for a detailed analysis of this subject). We assume that the statistical fluctuations obey a Gaussian distribution [10].…”

Section: Finite Size Key Ratementioning

confidence: 99%

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mentioning

confidence: 99%

Quantum key distribution without detector vulnerabilities using optically seeded lasers

Comandar¹,

Lucamarini²,

Fröhlich³

et al. 2016

Nature Photon

249

193

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“…Such an assumption is not necessarily justified when one considers a rigorous security proof. Recently, this Gaussian assumption was removed from the security proof by applying the Chernoff bound and the Hoeffding inequality [24,25]. We refer to this latter technique as the Chernoff-Hoeffding method.…”

Section: Introductionmentioning

confidence: 99%

Improved key-rate bounds for practical decoy-state quantum-key-distribution systems

et al. 2017

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The decoy-state scheme is the most widely implemented quantum-key-distribution protocol in practice. In order to account for the finite-size key effects on the achievable secret key generation rate, a rigorous statistical fluctuation analysis is required. Originally, a heuristic Gaussian-approximation technique was used for this purpose, which, despite its analytical convenience, was not sufficiently rigorous. The fluctuation analysis has recently been made rigorous by using the Chernoff bound. There is a considerable gap, however, between the key-rate bounds obtained from these techniques and that obtained from the Gaussian assumption. Here we develop a tighter bound for the decoy-state method, which yields a smaller failure probability. This improvement results in a higher key rate and increases the maximum distance over which secure key exchange is possible. By optimizing the system parameters, our simulation results show that our method almost closes the gap between the two previously proposed techniques and achieves a performance similar to that of conventional Gaussian approximations.

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“…Considering the statistical fluctuation, there exists a gap between e e b and e t p . Random sampling method provides a upper bound for this gap with a fixed failure probability ǫ [29,30], in our security analysis, ǫ = 10 −10 . Here, the Serfling inequality [31] is applied to estimate this gap.…”

Section: Appendix A: Phase Error Rate Estimationmentioning

confidence: 97%

Entanglement swapping with independent sources over an optical-fiber network

et al. 2017

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Teleportation of an entangled state, known as entanglement swapping, plays an essential role in quantum communication and network. Here we report a field-test entanglement swapping experiment with two independent telecommunication band entangled photon-pair sources over the optical fibre network of Hefei city. The two sources are located at two nodes 12 km apart and the Bell-state measurement is performed in a third location which is connected to the two source nodes with 14.7 km and 10.6 km optical fibres. An average visibility of 79.9 ± 4.8% is observed in our experiment, which is high enough to infer a violation of Bell inequality. With the entanglement swapping setup, we demonstrate a source independent quantum key distribution, which is also immune to any attack against detection in the measurement site.With the help of quantum entanglement and Bell state measurement (BSM), entanglement swapping [1, 2] can entangle two remote particles sharing no common history without interacting them. Therefore, except for its interest in the fundamental study of quantum information science, entanglement swapping also constitutes a core part for quantum repeater [3,4] in long distance quantum communication [5] and quantum internet [6] for distributed quantum computation [7].For all these quantum communication applications, photons are the most suitable carriers due to its flying nature and robustness against environmental decoherence. In the past two decades, various photonic entanglement swapping experiments have been implemented [8][9][10][11][12]. Recently, a field test of entanglement swapping was demonstrated through free space link [13]. However, in most of the previous demonstrations of entanglement swapping, the same femtosecond laser was used in producing two entangled photon-pair sources [8,9], making them impractical to be implemented in quantum network where the sources should be placed in distant nodes. Pioneering works have been done to synchronize two sources which are pumped independently in laboratory [10][11][12]14]. Owing to the difficulties in guaranteeing the indistinguishability of photons after they are transmitted through the realistic channel, a field test of entanglement swapping with independent entangled photon-pair sources remains an experimental challenge.Besides its applications in quantum repeater, the nonlocal correlation created by entanglement swapping can also be employed in quantum cryptography. Although quantum key distribution (QKD) can in principle provide information-theoretical security based on quantum mechanics, practical QKD systems are suffering from side-channel attacks that explore the device flaws in real-life implementation. Recently, the detector side-channel attacks have been removed by employing measurement-deviceindependent (MDI) QKD protocol [15]. However, potential loopholes still exist on the source side. When the photon source is not well prepared according to the security proof model, attacks would be possible [16].When entanglement swapping is used for QKD, each ...

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Finite-key analysis for measurement-device-independent quantum key distribution

Cited by 393 publications

References 53 publications

Quantum key distribution without detector vulnerabilities using optically seeded lasers

Quantum key distribution without detector vulnerabilities using optically seeded lasers

Improved key-rate bounds for practical decoy-state quantum-key-distribution systems

Entanglement swapping with independent sources over an optical-fiber network

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