Enhancing Quantum-Safe Cryptography in TLS: The Role of Pre-Shared Keys

Detection-time-bin-shift (DTBS) is a scheme that projects the measurement bases or measured photon values into detection time-bins and then time division multiplexes a single photon detector in a quantum key distribution (QKD) system. This scheme can simplify the structure of a QKD system, reduce its cost and overcome the security problems caused by the dead-time introduced self-correlation and the unbalanced characteristics of detectors. In this paper, we present several DTBS schemes for QKD systems based on attenuated laser pulses and entangled photon sources. We study the security issues of these DTBS schemes, especially the time-bin-shift intercept-resend attack and its countermeasures. A fiber-based DTBS QKD system has been developed and its results are presented in this paper.

We suggest a combined modulation quantum key distribution (QKD) system which encodes each single-photon signal with both phase modulation and polarization modulation. With the aid of dual-velocity protocol of hybrid QKD system, we construct a scheme to realize this combined modulation QKD which generates two-bit key with one signal for increasing the efficiency of QKD. We also develop a combined modulation Michelson QKD system, then solve the stability problem of the combined modulation QKD system in principle.

A Mach–Zehnder modulator (MZM) is necessary for implementing a decoy-state protocol in a practical quantum key distribution (QKD) system. However, an MZM bias control method optimized for QKD systems has been missing to date. In this study, we propose an MZM bias control method using N (≥2) diagnostic pulses. The proposed method can be efficiently applied to a QKD system without any additional hardware such as light sources or detectors. Furthermore, it does not reduce the key rate significantly because it uses time slots allocated to existing decoy pulses. We conducted an experimental demonstration of the proposed method in a field-deployed 1 × 3 QKD network and a laboratory test. It is shown that our method can maintain the MZM extinction ratio stably over 20 dB (bit error rate ≤1%), even in an actual network environment for a significant period. Consequently, we achieved successful QKD performances.

The aim of this chapter is to emphasize the multidisciplinary nature of the research in the field of Quantum Key Distribution Networks (QKDNs). Such networks consist of a number of nodes that can perform security protocols protected by some basic laws of physics. The operation of QKDNs mainly requires the integration of Quantum Key Distribution (QKD) protocols with the already-existing network security infrastructures. The authors report on the current state-of-the-art in the field and give some recommendations for future research. As computer simulation can be very useful in dealing with advanced technology subjects like QKDNs, they outline a simple and efficient modeling and simulation approach for various QKDN configurations. Then, the issue of unconditionally secure authentication of the public channel in QKD is considered. This issue is of crucial importance from both theoretical and practical sides. In this context, the proposed hybrid authentication strategy is reviewed and an authenticated version of the Bennett-Brassard-84 (BB84) QKD protocol based on this strategy is described. Next, a novel extension of the SSL protocol for QKDN settings, which the authors call Quantum SSL (QSSL), is explained. Finally, the chapter is concluded.

Advanced connection and autonomous features are being made possible by the Internet of Vehicles (IoV), which is causing a revolution in transportation. Strong security measures are required, however, because the prevalence of connected devices also increases the likelihood of cyberattacks and data breaches. This study introduces a new method for protecting IoV networks, which combines Blockchain technology with Quantum Key Distribution (QKD), creating a security architecture with two layers. Internet of Vehicles (IoV) technologies enable autonomous driving and real-time data exchange by connecting vehicles to infrastructure and one another. These advancements make things safer and more efficient, but they also put sensitive information at risk of cyberattacks. Modern security measures are essential since traditional encryption methods are becoming more and more insecure. To provide encryption that is theoretically unbreakable, the suggested system uses QKD to create and distribute cryptographic keys based on principles of quantum mechanics. To improve trust and transparency, blockchain technology is used to record these keys and any subsequent transactions in an immutable, distributed ledger. A hybrid architecture, with QKD securing the key exchange and Blockchain ensuring the integrity and authenticity of the communication, is designed as part of the integration process. Improved security and speed have been shown in simulations and prototype implementations of the QKD-Blockchain architecture in IoV networks. By preventing eavesdropping and key interception, the QKD technique kept the communication channel secure. With an average delay of only about 2 milliseconds, QKD performed admirably and was well below the permitted range for real-time vehicular communications. On average, validation durations for transactions were 5 milliseconds, which was a little overhead due to blockchain integration. The system efficiently handled up to 10,000 transactions per second without affecting security or performance, proving that it can serve massive IoV networks, according to scalability testing. Under high-load scenarios, the framework maintained consistent performance and security, proving its robustness in stress tests. Together, QKD and Blockchain provide a scalable and trustworthy option for future vehicular communication networks, and these results show how feasible and robust it is to use them to protect IoV systems. An intriguing approach to the security issues plaguing IoV systems is the integration of QKD with Blockchain technology. An unparalleled level of protection against cyber threats is provided by the dual-layered system, which guarantees strong encryption and data integrity. This fresh method may lead to improved and more trustworthy IoV networks by establishing new benchmarks for secure vehicular communication. In order to optimize the implementation and tackle any new issues that may arise, more research and development should be conducted.

As a practical method, the passive scheme is useful to monitor the photon statistics of an untrusted source in a "Plug & Play" quantum key distribution (QKD) system. In a passive scheme, three kinds of monitor mode can be adopted: average photon number (APN) monitor, photon number analyzer (PNA) and photon number distribution (PND) monitor. In this paper, the security analysis is rigorously given for APN monitor, while for PNA, the analysis including statistical fluctuation and random noise, is addressed with a confidence level. The results show that the PNA can achieve better performance than the APN monitor and can asymptotically approach the theoretical limit of the PND monitor. Also, the passive scheme with the PNA works efficiently when the signal-to-noise ratio ($R^{SN}$) is not too low and so is highly applicable to solve the untrusted source problem in the QKD system.

Usually, a shared reference frame is indispensable for practical quantum key distribution (QKD) systems. As a result, most QKD systems need active alignment of reference frame due to the unknown and slowly variances of reference frame introduced by environment. Quite interestingly, reference-free-independent (RFI) QKD can generate secret-key bits without alignment of reference frame. However, RFI QKD may be still vulnerable to detector side channel attacks. Here, we propose a new RFI QKD protocol, in which all detector side channels are removed. Furthermore, our protocol can still tolerate unknown and slow variance of reference frame without active alignment. And a numerical simulation shows that long security distance is probable in this protocol.

Single-photon detection concept is the most crucial and often difficult factor to determine the performance of quantum key distribution (QKD) systems. One solution to facilitate understanding this concept is to create a virtual environment for modeling, analyzing, and investigating the performance of single photon detectors. In this paper, a simulator for superconducting single photon detectors with time domain visualizer and configurable parameters is presented. The widely used ID281SNSPD in the QKD area was theoretically modeled in terms of pulse analysis, the impact of biasing current and the temperature on the dark counts rate and single photon-detection efficiency and influence of the number of photons per pulse on the single photon-detection efficiency. The simulated results were in good agreement with the theoretical results and the simulator demonstrated its adaptability.

We assess the overall performance of our quantum key distribution (QKD) system implementing the measurement-device-independent (MDI) protocol using components with varying capabilities such as different single-photon detectors and qubit preparation hardware. We experimentally show that superconducting nanowire single-photon detectors allow QKD over a channel featuring 60 dB loss, and QKD with more than 600 bits of secret key per second (not considering finite key effects) over a 16 dB loss channel. This corresponds to 300 and 80 km of standard telecommunication fiber, respectively. We also demonstrate that the integration of our QKD system into FPGA-based hardware (instead of state-of-the-art arbitrary waveform generators) does not impact on its performance. Our investigation allows us to acquire an improved understanding of the trade-offs between complexity, cost and system performance, which is required for future customization of MDI-QKD. Given that our system can be operated outside the laboratory over deployed fiber, we conclude that MDI-QKD is a promising approach to information-theoretic secure key distribution.

One of the most important obstacles for the social deployment of Quantum Key Distribution (QKD) systems is the lack of standards for security certification. Proper selection of application will circumvent other obstacles, such as cost, key generation distance, and rate. Nevertheless, security certification of real systems, or “implementation security certification” is indispensable. Such certification should be clear and tractable for non‐experts and should be performed with standardized characterization methods. Otherwise, the potential users cannot adopt the QKD system with confidence, because the highest level of security is what QKD appeals. This report discusses the process of the implementation security certification and the requirements for device characterization. It also presents several case studies on the requirements and experimental characterization of QKD devices for the security certification.

Quantum key distribution (QKD) ensures information-theoretic security for the distribution of random bits between two remote parties. To extend QKD applications to fiber-to-the-home optical communications, such as gigabit-capable passive optical networks (GPONs), an effective method is the use of wavelength-division multiplexing. However, the Raman scattering noise from intensive classical traffic and the huge loss introduced by the beam splitter in a GPON severely limits the performance of QKD. Here, we demonstrate the integration of QKD and a commercial GPON system with fiber lengths up to 14 km, in which the maximum splitting ratio of the beam splitter reaches 1:64. By placing the QKD transmitter on the optical line terminal side, we reduce the Raman noise collected at the QKD receiver. Using a bypass structure, the loss of the beam splitter is circumvented effectively. Our results pave the way to extending the applications of QKD to last-mile communications.

Security of data transported in telecommunication networks is of primary importance for internet service providers (ISP) as data safety is at the basis of the mutual trust with customers. People were looking for theoretically secure transmission techniques since a long-time to ensure long-term confidentiality of data flows exchanged on these networks. Besides advanced encryption algorithms and the recently proposed post-quantum cryptography (PQC), a physics-based technology using quantum key distribution (QKD) was proposed a long time ago to approach this objective. QKD recently gained a renewed interest with many research programs worldwide supported by public authorities, and some pre-industrial QKD systems delivered to the market. However, some constraints of optical transport networks make sometimes complicated the deployment of such QKD systems in the field, such as the need of a dedicated fiber infrastructure for QKD, or the impossibility for a quantum key to pass through an optical amplifier. In this paper, we report the transmission of a coherent 400-Gbps dual-polarization 16QAM channel that transports QKD-secured 100-GbEthernet data stream with other fifty-four WDM channels at 100-Gbps over 184-km of standard single mode fiber (SSMF) through three QKD links (of 66-km, 50-km and 66-km, respectively) and two trusted nodes. On the two longest sections of the link, the quantum key and WDM signals are propagated on two different fibers, while on the shortest section of 50-km the QKD signal and WDM comb co-propagate on a same fiber. Secret key rates (SKR) and quantum bit error rate (QBER) are measured and reported on each of the three fiber sections. Various analyses are carried out on the co-propagation section of 50-km: the SKR / QBER sensitivity to the optical power of the WDM comb, or to the optical signal-to-noise ratio (OSNR) of the WDM channels co-propagating with the quantum signal is studied. The unique arrangement of the most advanced QKD and WDM technologies reported here constitutes, in our opinion, a world first, and demonstrates that QKD and WDM solutions can coexist in already deployed optical transport networks.

A Single-Photon Avalanche Diode (SPAD) is a specialized optoelectronic device designed for the detection of single photons. It can discern the presence or absence of photons as well as their reception frequency. A significant challenge associated with SPADs is the generation of unintended pulses, which manifest in two primary categories: Dark Count Rate (DCR) and Afterpulse Probability (PAP). Dark counting refers to the occurrence of output pulses in the absence of photon detection, while afterpulse are undesirable outputs resulting from the trapping of carrier’s post-avalanche event within the detector. These trapped carriers are subsequently accelerated by the activation field applied to the detector, causing another avalanche breakdown known as an afterpulse. Both the afterpulse effect and dark counting are considered detrimental phenomena in SPADs, which are commonly utilized in Quantum Key Distribution (QKD) systems. Quantum Key Distribution is a cryptographic method for securely distributing secret keys, leveraging principles of quantum mechanics. Moreover, this method ensures that an eavesdropper cannot intercept or regenerate photon states. In this study, a novel approach is proposed to detect errors induced by these undesirable pulses in a quantum key distribution system. The proposed method, designed to mitigate the effects of unwanted pulses in QKD using the BB84 protocol, employs two quantum channels for photon transmission and a classical channel for coordination between the communicating parties and filtering the secret key (sifting). This method preserves the secure key rate when compared to the traditional BB84 protocol. The reduction of undesirable pulses in the proposed method is contingent upon factors such as the probability of afterpulse occurrence, dark count events, and the efficiency of the single-photon detector, with the reduction being computed in direct proportion to these parameters.

Quantum key distribution (QKD) enables the establishment of shared keys between two distant users, Alice and Bob, based on the fundamental principles of quantum mechanics, and it has proven to possess information-theoretic security. In most of QKD systems, Alice and Bob require a shared reference frame, and real-time calibration of the reference frame increases system costs and reduces its performance. Fortunately, the reference-frame-independent QKD protocol has been proposed, overcoming reference-frame drift issues and receiving widespread attention. However, in practical QKD systems, the non-ideal characteristics of realistic devices introduce certain inconsistency between the theory and the practice. In real-world quantum key distribution systems, device imperfections can lead to security vulnerabilities, thereby reducing system security. For example, imperfections in the encoding apparatus at the source end may result in errors in the quantum states. The inherent defects in the detection part may cause after-pulse effects and dead-time effects, thus reducing the key rate. Therefore, in this work, we propose a practical state-preparation error tolerant reference-frame-independent quantum key distribution protocol by taking imperfections in both the source and the detectors into account. Moreover, a three-intensity decoy-state scheme for modeling analysis and numerical simulations is employed. In this protocol, we reduce the influence of state-preparation errors on the key rate by utilizing virtual state methods to precisely estimate the phase-error rate. Furthermore, by characterizing the effects of after-pulses and dead-time on the key rate, our protocol exhibits higher robustness and can effectively address issues related to detector imperfections. This approach can also be extended to other quantum key distribution protocols with higher security levels, such as measurement-device-independent quantum key distribution protocol and twin-field quantum key distribution, further mitigating the influence of device imperfections on practical implementation of QKD system. Therefore, our present work provide important reference value for putting the quantum key distributions into practical application.

Since the Quantum Key Distribution (QKD)technique makes it possible to construct an absolute secure cryptographic system by combing the One-time pad, QKD has drawn many attention these years. The insufficient implementation speed of the post-processing system of QKD is one of the greatest obstacle to wide application of QKD. The sifting module of QKD post-processing system needs to deal with the heaviest incoming load, it is of crucial importance to study how to design and implement an efficient sifting module to accelerate the QKD post-processing system. In this paper, an efficient FPGA based design scheme of the sifting module is presented. Our scheme can decrease the demands for storage resource and communication traffic obviously.