Statistical fluctuation analysis for measurement-device-independent quantum key distribution

Abstract

Measurement-device-independent quantum key distribution with a finite number of decoy states is analyzed under finite-data-size assumption. By accounting for statistical fluctuations in parameter estimation, we investigate vacuum+weak-and vacuum+two-weak-decoy-state protocols. In each case, we find proper operation regimes, where the performance of our system is comparable to the asymptotic case for which the key size and the number of decoy states approach infinity.Our results show that practical implementations of this scheme can be both secure and efficient. * xma@tsinghua.edu.cnQuantum key distribution (QKD) [1,2] is one of the most successful applications of quantum information processing, which allows two distant parties, Alice and Bob, to grow secret keys with information-theoretic security [3][4][5][6][7][8]. Conventional security proofs of QKD assume certain physical models for the employed devices -source and detection units. Forinstance, the squashing model is widely assumed for the measurement [9-11] in a standard security analysis [12]. Practical implementations, however, could fall short of meeting all requirements set by the models, hence security could be compromised in reality. In fact, side channels have been identified and exploited to break QKD security. These side-channel attacks include the fake-state attack [13,14], the time-shift attack [15,16], the phaseremapping attack [17,18], and the detector-blinding attack [19,20].Several approaches have been proposed to counter the side-channel attacks. One way is to sufficiently characterize the behavior of the devices and analyze the security by taking into account all device parameters [21][22][23]. This, however, can be difficult to implement in practice. A second approach that can defeat all side-channel attacks is device-independent QKD [24][25][26], in which the security can be proven without knowing the specifications of the devices used. Security, in this case, is derived from nonlocal correlations by violating Bell's inequality [27,28]. In order to avoid the detection efficiency loophole [29], however, a large fraction of the transmitted signals must be detected by the receiver, resulting in impractical requirements for the transmission efficiency (e.g., 82.8% [30] for the Clauser-Horne-Shimony-Holt (CHSH) inequality [28]).Instead of full device independence, a detection-device independent QKD scheme is proposed [31,32], in which the detection system is assumed to be untrusted. Since most of practical hacking strategies focus on the detection site, and the source site is relatively simple for characterization, such a scheme can close most loopholes in a QKD system. Unfortunately, these schemes still need stringent requirements on the transmission efficiency of more than 50% [31]. Recently, Lo, Curty, and Qi [33] proposed efficient schemes that are measurement-device independent (MDI). Alice and Bob send some signals to a willing participant who can even be an eavesdropper, Eve. Eve performs a Bell-state measurement (BSM) and announces the...

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

“…Nevertheless, so far the security of mdiQKD has only been proven in the asymptotic regime 23 , which assumes that Alice and Bob have access to an unlimited amount of resources, or in the finite regime but only against particular types of attacks 30,31 . In summary, until now, a rigorous security proof of mdiQKD that takes full account of the finite size effects [32][33][34] has appeared to be missing and, for this reason, the feasibility of long-distance implementations of mdiQKD within a reasonable time frame of signal transmission has remained undemonstrated.…”

Quantum key distribution without detector vulnerabilities using optically seeded lasers

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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.

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Memory-assisted quantum key distribution resilient against multiple-excitation effects

“…In principle, they can use the decoy-state version of BB84, but, for the sake of our comparison, it would be sufficient to assume that both memory-assisted and memory-less systems use single photons to encode their bits. The multi-photon terms in a decoy-state protocol can be characterized by statistical analysis and they will not impose a change in the rate scaling [16]. The pulse duration is denoted by t p , and it is assumed to be equal to T in our numerical analysis.…”

“…We use phase encoding in the dual rail setup, or, equivalently, and if allowed by the quantum memory setups, time-bin encoding in a single-rail setup, in bases Z and X [16]. We assume that efficient QKD protocols are in use [53], where basis Z is chosen most often.…”

“…Here, in each round, one entangles quantum memories A 1 and A 2 , and, similarly, B 1 and B 2 , with two optical modes in the vacuum or single-photon state. At the transmitters, users encode their bits using phase encoded BB84 as explained in [16]. The BSM is performed using two singlephoton detectors and a 50:50 beam splitter on each rail; see the BSM box for memory A 1 .…”