We investigate limitations imposed by detector dead-times on the performance of sequential attacks against a differential-phase-shift (DPS) quantum key distribution (QKD) protocol with weak coherent pulses. In particular, we analyze sequential attacks based on unambiguous state discrimination of the signal states emitted by the source and we obtain ultimate upper bounds on the maximal distance achievable by a DPS QKD scheme both in the so-called trusted and untrusted device scenarios, respectively.
The security of a high speed quantum key distribution system with finite detector dead time τ is analyzed. When the transmission rate becomes higher than the maximum count rate of the individual detectors (1/τ), security issues affect the algorithm for sifting bits. Analytical calculations and numerical simulations of the Bennett-Brassard BB84 protocol are performed. We study Rogers et al.'s protocol (introduced in "Detector dead-time effects and paralyzability in high-speed quantum key distribution," New J. Phys. 9 (2007) 319) in the presence of an active eavesdropper Eve who has the power to…
Recent advances in quantum key distribution (QKD) have given rise to systems that operate at transmission periods significantly shorter than the dead times of their component single-photon detectors. As systems continue to increase in transmission rate, security concerns associated with detector dead times can limit the production rate of sifted bits. We present a model of high-speed QKD in this limit that identifies an optimum transmission rate for a system with given link loss and detector response characteristics.
The security of quantum key distribution (QKD) can easily be obscured if the eavesdropper can utilize technical imperfections of the actual implementation. Here we describe and experimentally demonstrate a very simple but highly effective attack which even does not need to intercept the quantum channel at all. Only by exploiting the dead time effect of single photon detectors the eavesdropper is able to gain (asymptotically) full information about the generated keys without being detected by state-of-the-art QKD protocols. In our experiment, the eavesdropper inferred up to 98.8% of the key cor…
In quantum communication systems, the precise estimation of the detector's response to the incoming light is necessary to avoid security breaches. The typical working regime uses a free-running single-photon avalanche diode in combination with attenuated laser pulses at telecom wavelength for encoding information. We demonstrate the validity of an analytical model for this regime which considers the effects of dark counts and dead time on the measured count rate. For the purpose of gaining a better understanding of these effects, the photon detections were separated from the dark counts via a …
Modern single-photon detectors based on avalanche photodiodes offer increasingly higher triggering speeds, thus fostering their use in several fields, prominently in the recent area of Quantum Key Distribution. To reduce the probability of an afterpulse, these detectors are usually equipped with a circuitry that disables the trigger for a certain time after a positive detection event, known as dead time. If the acquisition system connected to the detector is not properly designed, efficiency issues arise when the triggering rate is faster than the inverse of detector's dead-time. Moreover, whe…
Security of Device-independent Quantum Key Distribution under Sequential Attack
S. N. Bose National Centre for Basic Sciences（S.N. 玻色基础科学国家中心）；Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China（电子科技大学前沿与基础科学学院）；Department of Physics and Center for Quantum Frontiers of Research and Technology (QFort), National Cheng Kung University（国立成功大学物理系及量子前沿研究与技术中心(QFort)）；Okinawa Institute of Science and Technology Graduate University（冲绳科学技术大学院大学）；Indian Institute of Technology Indore（印度理工学院印多尔分校）；Department of Physics, Hooghly Mohsin College（胡格利莫辛学院物理系）
The goal of two-party cryptography is to enable two parties, Alice and Bob, to solve common tasks without the need for mutual trust. Examples of such tasks are private access to a database, and secure identification. Quantum communication enables security for all of these problems in the noisy-storage model by sending more signals than the adversary can store in a certain time frame. Here, we initiate the study of device-independent protocols for two-party cryptography in the noisy-storage model. Specifically, we present a relatively easy to implement protocol for a cryptographic building bloc…
We propose a quantum communication protocol that can be used to transmit any quantum state, one party to another via several intermediate nodes, securely on quantum communication network. The scheme makes use of the sequentially chained and approximate version of private quantum channels satisfying certain commutation relation of $n$-qubit Pauli operations. In this paper, we study the sequential structure, security analysis, and efficiency of the quantum sequential transmission (QST) protocol in depth.
We derive a proof of security for the Differential Phase Shift Quantum Key Distribution (DPSQKD) protocol under the assumption that Eve is restricted to individual attacks. The security proof is derived by bounding the average collision probability, which leads directly to a bound on Eve's mutual information on the final key. The security proof applies to realistic sources based on pulsed coherent light. We then compare individual attacks to sequential attacks and show that individual attacks are more powerful.
Quantum secret sharing (QSS) schemes without entanglement have huge advantages in scalability and are easier to realize as they only require sequential communications of a single quantum system. However, these schemes often come with drawbacks such as exact ($n, n$) structure, security flaws and absences of effective cheating detections. To address these problems, we propose a verifiable framework by utilizing entanglement-free states to construct ($t, n$)-QSS schemes. Our work is the heuristic step towards information-theoretical security in entanglement-free QSS, and it sheds light on how to…
We present a simplified framework for proving sequential composability in the quantum setting. In particular, we give a new, simulation-based, definition for security in the bounded-quantum-storage model, and show that this definition allows for sequential composition of protocols. Damgard et al. (FOCS '05, CRYPTO '07) showed how to securely implement bit commitment and oblivious transfer in the bounded-quantum-storage model, where the adversary is only allowed to store a limited number of qubits. However, their security definitions did only apply to the standalone setting, and it was not clea…
An unsymmetrical quantum key distribution scheme is proposed, its security is guaranteed by the correlation of the Greenberger-Horne-Zeilinger triplet state. In the proposed protocol, the distribution of quantum states are unsymmetrical. This unsymmetrical characteristic makes the transmission qubits (except the loss qubits) be useful. Sequentially the proposed protocol has excellent efficiency and security which are very useful in the practical application.
Ultra-high-rate detection of entangled photon pairs
Basic Research Laboratories, NTT, Inc.（NTT公司基础研究实验室）；Advanced ICT Research Institute, National Institute of Information and Communications Technology（信息通信技术研究院高级ICT研究所）
In this paper, we investigate limitations imposed by sequential attacks on the performance of a differential-phase-shift (DPS) quantum key distribution (QKD) protocol with weak coherent pulses. Specifically, we analyze a sequential attack based on optimal unambiguous discrimination of the relative phases between consecutive signal states emitted by the source. We show that this attack can provide tighter upper bounds for the security of a DPS QKD scheme than those derived from sequential attacks where the eavesdropper aims to identify the state of each signal emitted by the source unambiguousl…
In this paper, we discuss the security of the differential-phase-shift quantum key distribution (DPSQKD) protocol by introducing an improved version of the so-called sequential attack, which was originally discussed by Waks et al. Our attack differs from the original form of the sequential attack in that the attacker Eve modulates not only the phases but also the amplitude in the superposition of the single-photon states which she sends to the receiver. Concentrating especially on the "discretized gaussian" intensity modulation, we show that our attack is more effective than the individual att…
We revisit the so-called compressed oracle technique, introduced by Zhandry for analyzing quantum algorithms in the quantum random oracle model (QROM). To start off with, we offer a concise exposition of the technique, which easily extends to the parallel-query QROM, where in each query-round the considered algorithm may make several queries to the QROM in parallel. This variant of the QROM allows for a more fine-grained query-complexity analysis. Our main technical contribution is a framework that simplifies the use of (the parallel-query generalization of) the compressed oracle technique for…
Secret sharing allows a trusted party (the dealer) to distribute a secret to a group of players, who can only access the secret cooperatively. Quantum secret sharing (QSS) protocols could provide unconditional security based on fundamental laws in physics. While the general security proof has been established recently in an entanglement-based QSS protocol, the tolerable channel loss is unfortunately rather small. Here we propose a continuous variable QSS protocol using conventional laser sources and homodyne detectors. In this protocol, a Gaussian-modulated coherent state (GMCS) prepared by on…
A prominent application of quantum cryptography is the distribution of cryptographic keys that are provably secure. Recently, such security proofs were extended by Vazirani and Vidick (Physical Review Letters, 113, 140501, 2014) to the device-independent (DI) scenario, where the users do not need to trust the integrity of the underlying quantum devices. The protocols analyzed by them and by subsequent authors all require a sequential execution of N multiplayer games, where N is the security parameter. In this work, we prove unconditional security of a protocol where all games are executed in p…
In this work, we present a quantum secret sharing scheme based on Bell state entanglement and sequential projection measurements. The protocol verifies the $n$ out of $n$ scheme and supports the aborting of the protocol in case all the parties do not divulge in their valid measurement outcomes. The operator-qubit pair forms an integral part of the scheme determining the classical secret to be shared. The protocol is robust enough to neutralize any eavesdropping on a particular qubit of the dealer. The experimental demonstration of the scheme is done on IBM-QE cloud platform with backends \text…
