Recently, a source-independent quantum random number generator (SI-QRNG), which can generate secure random numbers with untrusted sources, has been realized. However, the measurement loopholes of the trusted but imperfect devices used in SI-QRNGs have not yet been fully explored. Here, we point out and evaluate the security loopholes of practical imperfect measurement devices in SI-QRNGs. We also provide corresponding countermeasures to prevent these information leakages by recalculating the conditional minimum entropy and adding a monitor. Furthermore, by taking into account the finite-size effect, we show that the influence of the afterpulse can exceed that of the finite-size effect with the large number of sampled rounds. Our protocol is simple and effective, and it promotes the security of SI-QRNG in practice as well as the compatibility with high-speed measurement evices, thus paving the way for constructing ultrafast and security-certified commercial SI-QRNG systems.
Recently, a source-independent quantum random number generator (SI-QRNG), which can generate secure random numbers with untrusted sources, has been realized. However, the measurement loopholes of the trusted but imperfect devices used in SI-QRNGs have not yet been fully explored. Here, we point out and evaluate the security loopholes of practical imperfect measurement devices in SI-QRNGs. We also provide corresponding countermeasures to prevent these information leakages by recalculating the conditional minimum entropy and adding a monitor. Furthermore, by taking into account the finite-size effect, we show that the influence of the afterpulse can exceed that of the finite-size effect with the large number of sampled rounds. Our protocol is simple and effective, and it promotes the security of SI-QRNG in practice as well as the compatibility with high-speed measurement evices, thus paving the way for constructing ultrafast and security-certified commercial SI-QRNG systems.
Abstract A quantum random number generator (QRNG) as a genuine source of randomness is essential in many applications, such as number simulation and cryptography. Recently, a source-independent quantum random number generator (SI-QRNG), which can generate secure random numbers with untrusted sources, has been realized. However, the measurement loopholes of the trusted but imperfect devices used in SI-QRNGs have not yet been fully explored, which will cause security problems, especially in high-speed systems. Here, we point out and evaluate the security loopholes of practical imperfect measurement devices in SI-QRNGs. We also provide corresponding countermeasures to prevent these information leakages by recalculating the conditional minimum entropy and adding a monitor. Furthermore, by taking into account the finite-size effect, we show that the influence of the afterpulse can exceed that of the finite-size effect with the large number of sampled rounds. Our protocol is simple and effective, and it promotes the security of SI-QRNG in practice as well as the compatibility with high-speed measurement devices, thus paving the way for constructing ultrafast and security-certified commercial SI-QRNG systems.
Quantum random number generators (QRNGs) promise secure randomness generation based on the foundational unpredictability of quantum mechanics. However, the unavoidable gaps between theoretical models and practical devices could lead to security invalidation. Recently, a source-independent quantum random number generator (SI-QRNG) has been proposed to solve the issue of uncharacteristic sources. However, in most current analyses of SI-QRNG protocols, the security proofs with imperfect measurements are individual for different factors and very sensitive to small deviations from theoretical models. Here, we establish a unified model for imperfect measurements in the SI-QRNG and provide a tight rate bound based on the uncertainty relation for smooth entropies. Then the performance with large device imperfections is evaluated and the randomness rate in our model can approach a similar order of magnitude of the rate upper bound in common discrete variable QRNGs. In addition, by utilizing the daily illumination and measurement devices with large imperfections, we experimentally demonstrate our scheme at the rate of the order of magnitude of Mbps.
Continuous-variable source-independent quantum random-number generators (CV-SI-QRNGs) generate high-speed secure random numbers without any assumptions about source. Recently, Smith et al. [Phys. Rev. A 99, 062326 (2019)] proposed a CV-SI-QRNG with phase-randomized local oscillator (LO) protocol, which does not require additional active optical components, thus reducing the complexity of the CV-SI-QRNG setup and attracting widespread attention. However, the trusted but imperfect sampling device used in CV-SI-QRNG has not yet been fully investigated, which will lead to performance degradation and security problems. In this work, we investigate the influence of imperfect sampling devices on the CV-SI-QRNG with phase-randomized LO, including the finite-sampling bandwidth, finite-sampling precision, and finite-size effect. Simulation results show that practical imperfections in the sampling device will affect the estimation of lower bound on the conditional min-entropy and reduce the extractable randomness. To improve the performance of CV-SI-QRNG and prevent such information leakages, we also provide some corresponding countermeasures. Our work highlights the influences of imperfect sampling devices on the performance and security of practical CV-SI-QRNG systems, which helps to improve their robustness and practicality.
Abstract Source‐independent quantum random number generators (SI‐QRNGs) can generate secure random numbers with untrusted and uncharacterized sources. Recently, a tomography‐based SI‐QRNG protocol has garnered significant attention for its higher randomness generation rate[Phys. Rev. A 99, 022328 (2019)], achieved through measurements utilizing three mutually unbiased bases. However, imperfect and inadequately characterized measurement devices would impact the security and performance of this protocol. In this work, considering the imperfect basis modulation, afterpulse effect and detection efficiency mismatch, it is demonstrated that the imperfect measurement devices would reduce the extractable randomness and lead to the incorrect estimation of the conditional min‐entropy. Additionally, the influences of the finite‐size effect and the performances of the protocol based on different parameter estimation methods are investigated and compared. To guarantee the security of generated random numbers, accurate conditional min‐entropy estimation methods that are compatible with imperfect factors are also developed. The work emphasizes the significance of considering the imperfections in measurement devices and establishing tighter bounds for parameter estimation, especially in high‐speed systems, thereby enhancing the robustness and performance of the protocol.
The measurement-device-independent quantum random number generator (MDI-QRNG) can resist all security loopholes on measurement devices, and it thus seems very promising in practical implementations. In the MDI-QRNG, sources are often assumed to be perfectly prepared, however, there inevitably exist errors in the quantum state preparation process due to imperfections in realistic equipments and devices. In this paper, we do investigations on the MDI-QRNG with source flaws, showing its performance at different state errors. Besides, we also consider the influence of the finite-size effect, and compare the performance of different sources in MDI-QRNGs. This work provides valuable references for practical implementation of MDI-QRNGs
Quantum random number generators (QRNGs) produce true random numbers based on the inherent randomness of quantum theory, rendering them a foundational segment of quantum cryptography. Distinguished from trusted-device QRNGs whose security depends on characterized devices, semi-device-independent (semi-DI) QRNGs permit partial devices to be defective or even maliciously manipulated, which achieves a good trade-off between generation rate and security. In this paper, we propose a semi-DI QRNG that resists general attacks while accounting for finite-size effects. The protocol requires no rigorous characterization of the source and measurement devices other than limiting the energy of the emitted states, significantly reducing the demands on practical QRNG systems. Leveraging the tight Kato inequality for correlated variables, we show that our protocol generates more randomness than it consumes. Furthermore, we demonstrate the scheme on a continuous-variable system with ternary inputs of states. Heterodyne detection is employed to enable phase compensation through data postprocessing, alleviating the stringent requirement on system stability. The system operates at 100 MHz, achieving a net random number generation rate of 1.165 Mbps at 5.3x10^9 rounds. Our work offers a promising approach to achieve both the robust security and high generation rate with a simple experimental setup.