Higher Key Rate Research Articles

Composable security for continuous variable quantum key distribution: Trust levels and practical key rates in wired and wireless networks

Continuous variable (CV) quantum key distribution (QKD) provides a powerful setting for secure quantum communications, thanks to the use of room-temperature off-the-shelf optical devices and the potential to reach much higher rates than the standard discrete-variable counterpart. In this work, we provide a general framework for studying the composable finite-size security of CV-QKD with Gaussian-modulated coherent-state protocols under various levels of trust for the loss and noise experienced by the parties. Our study considers both wired (i.e., fiber-based) and wireless (i.e., free-space) quantum communications. In the latter case, we show that high key rates are achievable for short-range optical wireless (LiFi) in secure quantum networks with both fixed and mobile devices. Finally, we extend our investigation to microwave wireless (WiFi) discussing security and feasibility of CV-QKD for very short-range applications.

Model for optimizing quantum key distribution with continuous-wave pumped entangled-photon sources

Quantum key distribution (QKD) allows unconditionally secure communication based on the laws of quantum mechanics rather than assumptions about computational hardness. Optimizing the operation parameters of a given QKD implementation is indispensable in order to achieve high secure key rates. So far, there exists no model that accurately describes entanglement-based QKD with continuous-wave pump lasers. We analyze the underlying mechanisms for QKD with temporally uniform pair-creation probabilities and develop a simple but accurate model to calculate optimal tradeoffs for maximal secure key rates. In particular, we find an optimization strategy of the source brightness for given losses and detection-time resolution. All experimental parameters utilized by the model can be inferred directly in standard QKD implementations, and no additional assessment of device performance is required. Comparison with experimental data shows the validity of our model. Our results yield a tool to determine optimal operation parameters for already existing QKD systems, to plan a full QKD implementation from scratch, and to determine fundamental key rate and distance limits of given connections.

Differential Phase Shift Quantum Secret Sharing Using a Twin Field with Asymmetric Source Intensities

As an essential application of quantum mechanics in classical cryptography, quantum secret sharing has become an indispensable component of quantum internet. Recently, a differential phase shift quantum secret sharing protocol using a twin field has been proposed to break the linear rate-distance boundary. However, this original protocol has a poor performance over channels with asymmetric transmittances. To make it more practical, we present a differential phase shift quantum secret sharing protocol with asymmetric source intensities and give the security proof of our protocol against individual attacks. Taking finite-key effects into account, our asymmetric protocol can theoretically obtain the key rate two orders of magnitude higher than that of the original protocol when the difference in length between Alice’s channel and Bob’s is fixed at 14 km. Moreover, our protocol can provide a high key rate even when the difference is quite large and has great robustness against finite-key effects. Therefore, our work is meaningful for the real-life applications of quantum secret sharing.

Secure and Usable Handshake Based Pairing for Wrist-Worn Smart Devices on Different Users

Wrist-worn smart devices are being used to share various sensitive personal information in various fields such as social, medical treatment, sports, etc. Secure pairing establishing a trusted channel between involved devices is a prerequisite to ensure data transmission security. Handshake has been employed to realize secure pairing between devices worn by different users without pre-shared knowledge, the participation of third parties or complicated user interactions. However, existing schemes cannot meet the practical requirement in terms of time delay and security. In this paper, we present a secure and usable pairing scheme utilizing the handshake acceleration data. Specifically, we propose an optimal feature selection algorithm based on Euclidean distance sorting which improves the success rate and security of the system. In addition, we use Pearson correlation coefficient based feature sequence similarity measurement approach to enhance the accuracy of pairing scheme. Theoretical and experimental security analysis indicates that our solution can resist active and passive attacks. What’s more, the experimental results demonstrate that the proposed solution has a high key generation rate of 87 bits per second, and completes security pairing in less than 4 s.

Device-independent quantum key distribution from generalized CHSH inequalities

Device-independent quantum key distribution aims at providing security guarantees even when using largely uncharacterised devices. In the simplest scenario, these guarantees are derived from the CHSH score, which is a simple linear combination of four correlation functions. We here derive a security proof from a generalisation of the CHSH score, which effectively takes into account the individual values of two correlation functions. We show that this additional information, which is anyway available in practice, allows one to get higher key rates than with the CHSH score. We discuss the potential advantage of this technique for realistic photonic implementations of device-independent quantum key distribution.

Rate compatible reconciliation for continuous-variable quantum key distribution using Raptor-like LDPC codes

In the practical continuous-variable quantum key distribution (CV-QKD) system, the postprocessing process, particularly the error correction part, significantly impacts the system performance. Multi-edge type low-density parity-check (MET-LDPC) codes are suitable for CV-QKD systems because of their Shannon-limit-approaching performance at a low signal-to-noise ratio (SNR). However, the process of designing a low-rate MET-LDPC code with good performance is extremely complicated. Thus, we introduce Raptor-like LDPC (RL-LDPC) codes into the CV-QKD system, exhibiting both the rate compatible property of the Raptor code and capacity-approaching performance of MET-LDPC codes. Moreover, this technique can significantly reduce the cost of constructing a new matrix. We design the RL-LDPC matrix with a code rate of 0.02 and easily and effectively adjust this rate from 0.016 to 0.034. Simulation results show that we can achieve more than 98% reconciliation efficiency in a range of code rate variation using only one RL-LDPC code that can support high-speed decoding with an SNR less than -16.45 dB. This code allows the system to maintain a high key extraction rate under various SNRs, paving the way for practical applications of CV-QKD systems with different transmission distances.

Conceptual provisions of management percentage risk in international practice

In the face of the COVID-19 pandemic world banking system is being severely tested. The last time such shocks occurred during the global fi nancial crisis of 2008–2009. However, the crisis of the global banking system in 2020 caused by the COVID-19 pandemic is very diff erent from the global fi nancial crisis of 2008–2009. During the previous global fi nancial crisis, central banks around the world were able to cut key rates to stimulate the aff ected economy, while the current crisis is taking place in conditions of extremely low and even negative key rates. Consequently, the central banks of the economically developed countries of the world lack one of the most eff ective tools to stimulate the economy in the face of a global crisis. Since the maximum income of commercial banks is generated by the operation of high key rates, the downward trend in recent years is a serious risk to the business of commercial banks. The article analyses the dynamics of key rates in the economically developed countries of the world in comparison with China and the Russian Federation, based on the results of this document, the main trends and patterns were identified, the most dangerous risks for commercial banks are shown. Besides the article discusses the modern conceptual provisions of interest rate risk management in commercial banks of the Russian Federation. They form the basis for the development of constructive methods for assessing commercial risk and the formation of managerial decisions that ensure its prevention or reduction of negative consequences in the event of the implementation of risk events that determine it.

Strategies for achieving high key rates in satellite-based QKD

Quantum key distribution (QKD) is a pioneering quantum technology on the brink of widespread deployment. Nevertheless, the distribution of secret keys beyond a few 100 km at practical rates remains a major challenge. One approach to circumvent lossy terrestrial transmission of entangled photon pairs is the deployment of optical satellite links. Optimizing these non-static quantum links to yield the highest possible key rate is essential for their successful operation. We therefore developed a high-brightness polarization-entangled photon pair source and a receiver module with a fast steering mirror capable of satellite tracking. We employed this state-of-the-art hardware to distribute photons over a terrestrial free-space link with a distance of 143 km, and extracted secure key rates up to 300 bits per second. Contrary to fiber-based links, the channel loss in satellite downlinks is time-varying and the link time is limited to a few minutes. We therefore propose a model-based optimization of link parameters based on current channel and receiver conditions. This model and our field test will prove helpful in the design and operation of future satellite missions and advance the distribution of secret keys at high rates on a global scale.

A Lightweight Key Generation Scheme for Secure Device‐to‐Device (D2D) Communication

Key agreement is one the most essential steps when applying cryptographic techniques to secure device‐to‐device (D2D) communications. Recently, several PHY‐based solutions have been proposed by leveraging the channel gains as a common randomness source for key extraction in wireless networks. However, these schemes usually suffer a low rate of key generation and low entropy of generated key and rely on the mobility of devices. In this paper, a novel secret key extraction protocol is proposed by using interference in wireless D2D fading channel. It establishes symmetrical keys for two wireless devices by measuring channel gains and utilizing artificial jamming sent by the third party to change the measured value of channel gains. We give a theoretically reachable key rate of the proposed scheme from the viewpoint of the information theory. It shows that the proposed scheme can make hundred times performance gain than the existing approaches theoretically. Experimental results also demonstrate that the proposed scheme can achieve a secure key distribution with a higher key rate and key entropy compared with the existing schemes.

High Key Rate Quantum Conference Key Agreement With Unconditional Security

Quantum cryptography is a major ingredient of the future quantum internet that promises various secure communication tasks. Quantum conference key agreement (CKA) is an important cryptographic primitive of quantum cryptography, which provides the conference key among multiple users simultaneously. However, quantum CKA is currently far from practical application due to the low conference key rate. Here, we propose a quantum CKA protocol of three users with information-theoretic security. Our protocol only requires phase-randomized weak coherent sources and threshold single-photon detectors, and is anticipated to be experimentally demonstrated over 600 km under current technology. Our scheme can be widely implemented in the approaching large-scale quantum network.

Long-Distance Free-Space Measurement-Device-Independent Quantum Key Distribution.

Measurement-device-independent quantum key distribution (MDI-QKD), based on two-photon interference, is immune to all attacks against the detection system and allows a QKD network with untrusted relays. Since the MDI-QKD protocol was proposed, fiber-based implementations aimed at longer distance, higher key rates, and network verification have been rapidly developed. However, owing to the effect of atmospheric turbulence, MDI-QKD over a free-space channel remains experimentally challenging. Herein, by developing a robust adaptive optics system, high-precision time synchronization and frequency locking between independent photon sources located far apart, we realized the first free-space MDI-QKD over a 19.2-km urban atmospheric channel, which well exceeds the effective atmospheric thickness. Our experiment takes the first step toward satellite-based MDI-QKD. Moreover, the technology developed herein opens the way to quantum experiments in free space involving long-distance interference of independent single photons.

AnchorHash: A Scalable Consistent Hash

Consistent hashing is a central building block in many networking applications, such as maintaining connection affinity of TCP flows. However, current consistent hashing solutions do not ensure full consistency under arbitrary changes or scale poorly in terms of memory footprint, update time and key lookup complexity. We present AnchorHash, a scalable and fully-consistent hashing algorithm. AnchorHash achieves high key lookup rate, low memory footprint and low update time. We formally establish its strong theoretical guarantees, and present an advanced implementation with a memory footprint of only a few bytes per resource. Moreover, evaluations indicate that AnchorHash scales on a single core to 100 million resources while still achieving a key lookup rate of more than 15 million keys per second.

Recent Advances on Quantum Key Distribution Overcoming the Linear Secret Key Capacity Bound

AbstractA crucial goal for quantum key distribution (QKD) is to transmit unconditionally secure keys over long distances. Previous studies show that the key rate of point‐to‐point QKD is limited by a secret key rate capacity bound, and higher key rates would require quantum repeaters. In 2018, the seminal twin‐field (TF) QKD protocol is proposed to provide a remarkable solution to overcoming the linear secret key capacity bound. This article presents an up‐to‐date survey on recent developments in this area, including the security proofs of phase‐matching QKD and other TF‐QKD type protocols, the theoretical examinations of these protocols under realistic conditions, and the recent experimental demonstrations.

Measurement-device-independent quantum key distribution of multiple degrees of freedom of a single photon

Measurement-device-independent quantum key distribution (MDI-QKD) provides us a powerful approach to resist all attacks at detection side. Besides the unconditional security, people also seek for high key generation rate, but MDI-QKD has relatively low key generation rate. In this paper, we provide an efficient approach to increase the key generation rate of MDI-QKD by adopting multiple degrees of freedom (DOFs) of single photons to generate keys. Compared with other high-dimension MDI-QKD protocols encoding in one DOF, our protocol is more flexible, for our protocol generating keys in independent subsystems and the detection failure or error in a DOF not affecting the information encoding in other DOFs. Based on above features, our MDI-QKD protocol may have potential application in future quantum communication field.

Twin-field quantum key distribution with passive-decoy state

Twin-Field quantum key distribution (TF-QKD) and its variants, e.g. phase-maching QKD, sending-or-not-sending QKD, and no phase post-selection TFQKD promise high key rates at long distance to beat the rate distance limit without a repeater. The security proof of these protocols are based on decoy-state method, which is usually performed by actively modulating a variable optical attenuator together with a random number generator in practical experiments, however, active-decoy schemes like this may lead to side channel and could open a security loophole. To enhance the source security of TF-QKD, in this paper, we propose passive-decoy based TF-QKD, in which we combine TF-QKD with the passive-decoy method. And we present a simulation comparing the key generation rate with that in active-decoy, the result shows our scheme performs as good as active decoy TF-QKD, and our scheme could reach satisfactory secret key rates with just a few photon detectors. This shows our work is meaningful in practice.

Continuous-variable source-device-independent quantum key distribution against general attacks

The continuous-variable quantum key distribution with entanglement in the middle, a semi-device-independent protocol, places the source at the untrusted third party between Alice and Bob, and thus has the advantage of high levels of security with the purpose of eliminating the assumptions about the source device. However, previous works considered the collective-attack analysis, which inevitably assumes that the states of the source has an identical and independently distributed (i.i.d) structure, and limits the application of the protocol. To solve this problem, we modify the original protocol by exploiting an energy test to monitor the potential high energy attacks an adversary may use. Our analysis removes the assumptions of the light source and the modified protocol can therefore be called source-device-independent protocol. Moreover, we analyze the security of the continuous-variable source-device-independent quantum key distribution protocol with a homodyne-homodyne structure against general coherent attacks by adapting a state-independent entropic uncertainty relation. The simulation results indicate that, in the universal composable security framework, the protocol can still achieve high key rates against coherent attacks under the condition of achievable block lengths.

Sending-or-Not-Sending with Independent Lasers: Secure Twin-Field Quantum Key Distribution over 509 km

Twin-field (TF) quantum key distribution (QKD) promises high key rates over long distances to beat the rate-distance limit. Here, applying the sending-or-not-sending TF QKD protocol, we experimentally demonstrate a secure key distribution that breaks the absolute key-rate limit of repeaterless QKD over a 509-km-long ultralow loss optical fiber. Two independent lasers are used as sources with remote-frequency-locking technique over the 500-km fiber distance. Practical optical fibers are used as the optical path with appropriate noise filtering; and finite-key effects are considered in the key-rate analysis. The secure key rate obtained at 509km is more than seven times higher than the relative bound of repeaterless QKD for the same detection loss. The achieved secure key rate is also higher than that of a traditional QKD protocol running with a perfect repeaterless QKD device, even for an infinite number of sent pulses. Our result shows that the protocol and technologies applied in this experiment enable TF QKD to achieve a high secure key rate over a long distribution distance, and is therefore practically useful for field implementation of intercity QKD.

The Decoy-State Measurement-Device-Independent Quantum Key Distribution with Heralded Single-Photon Source

Based on heralded single-photon source (HSPS), a decoy-state measurement-device-independent quantum key distribution (MDI-QKD) protocol is proposed in this paper. The MDI-QKD protocol mainly uses orbital angular momentum (OAM) states and pulse position modulation (PPM) technology to realize the coding of the signal states in heralded single-photon source. The three-intensity decoy states are used to avoid the attacks against the light source. Moreover, the formula of key generation rate is given by computing the lower bound of the yield of single-photon pairs and the upper bound of the error rate of single-photon pairs. Numerical simulation shows that the new MDI-QKD protocol has high key generation rate and low error rate. Moreover, the secure communication distance can be up to 450 km.

Asymptotic Security Analysis of Discrete-Modulated Continuous-Variable Quantum Key Distribution

Continuous-variable quantum key distribution (CV QKD) protocols with discrete modulation are interesting due to their experimental simplicity and their great potential for massive deployment in the quantum-secured networks, but their security analysis is less advanced than that of Gaussian modulation schemes. In this work, we apply a numerical method to analyze the security of discrete-modulation protocols against collective attacks in the asymptotic limit, paving the way for a full security proof with finite-size effects. While our method is general for discrete-modulation schemes, we focus on two variants of the CV QKD protocol with quaternary modulation. Interestingly, thanks to the tightness of our proof method, we show that this protocol is capable of achieving much higher key rates over significantly longer distances with experimentally feasible parameters compared with previous security proofs of binary and ternary modulation schemes and also yielding key rates comparable to Gaussian modulation schemes. Furthermore, as our security analysis method is versatile, it allows us to evaluate variations of the discrete-modulated protocols, including direct and reverse reconciliation, and postselection strategies. In particular, we demonstrate that postselection of data in combination with reverse reconciliation can improve the key rates.

The enhanced measurement-device-independent quantum key distribution with heralded pair coherent state

With heralded pair coherent states (HPCS), orbital angular momentum (OAM) states and pulse position modulation (PPM) technology, a decoy-state measurement-device-independent quantum key distribution (MDI-QKD) protocol is proposed. OAM states and PPM technology are used to realize the coding of the signal states in the HPCS light source. The use of HPCS light source, OAM coding and PPM coding cannot only reduce the error rate but also improve the key generation rate and communication distance. The new MDI-QKD protocol also employs three-intensity decoy states to avoid the attacks against the light source. By calculating the error rate and key generation rate, the performance of the MDI-QKD protocol is analyzed. Numerical simulation shows that the protocol has very low error rate and very high key generation rate. Moreover, the maximum communication distance can reach 455 km.