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In this paper, we provide a simple approach for determining the rate of secure key production when single-photon and two-photon pulses are used to generate the secure key. For both BB84 and SARG04, we offer estimation and optimization of decoy-state parameters for a single decoy state protocol and two decoy state protocols. This method can be used to determine the lower bound on the fraction of single-photon counts (y1), the fraction of two-photon counts (y2), the upper bound on the QBER of single-photon pulses (e1), the upper bound on the QBER of two-photon pulses (e2), and the lower bound on the key generation rate for both BB84 and SARG04. Due to the limited data size in real-world experiments, we estimate the statistical fluctuations of several parameters, including the gain and QBER of the signal state, as well as the gain and QBER of the decoy state, which are used to estimate the lower bound of key generation rate. We propose formulae that specify the optimal decoy and signal state percentages and intensities. Then we can determine the maximum and optimal key generation rate. For both SARG04 and BB84, we simulated a free space-based QKD system using our decoy state strategy. The simulation results show that free space-based QKD systems that use the suggested approach for BB84 can achieve a higher secret key rate and a greater safe distance than SARG04-based systems. [ABSTRACT FROM AUTHOR]

An effective post-processing algorithm is essential for achieving high rates of secret key generation in quantum key distribution. This work introduces an approach to quantum key distribution post-processing by integrating the three main steps into a unified procedure: syndrome-based error estimation, rate-adaptive reconciliation, and subblock confirmation. The proposed scheme employs low-density parity-check codes to estimate the quantum bit error rate using the syndrome information, and to optimize the channel coding rates based on the Slepian–Wolf coding scheme for the rate-adaptive method. Additionally, this scheme incorporates polynomial-based hash verification in the subblock confirmation process. The numerical results show that the syndrome-based estimation significantly enhances the accuracy and consistency of the estimated quantum bit error rate, enabling effective code rate optimization for rate-adaptive reconciliation. The unified approach, which integrates rate-adaptive reconciliation with syndrome-based estimation and subblock confirmation, exhibits superior efficiency, minimizes practical information leakage, reduces communication rounds, and guarantees convergence to the identical key. Furthermore, the simulations indicate that the secret key throughput of this approach achieves the theoretical limit in the context of a BB84 quantum key distribution system. [ABSTRACT FROM AUTHOR]

Time synchronization is one of the most crucial issues that must be addressed in developing quantum key distribution (QKD) systems. It not only lets the transmitter and the receiver to assign a sequence number to each event and then do correct basis reconciliation, but also allows to increase signal-to-noise ratio. Time synchronization in satellite communications is especially complicated due to such factors as high loss, signal fading, and Doppler effect. In this work, a simple, efficient, and robust algorithm for time synchronization is proposed. It was tested during experiments on QKD between Micius, the world's first quantum communications satellite, and an optical ground station located in Russia. The obtained synchronization precision lies in the range from 467 to 497 ps. The authors compare their algorithm for time synchronization with the previously used methods. The proposed approach can also be applied to terrestrial QKD systems. [ABSTRACT FROM AUTHOR]

The main purpose of a quantum key distribution network is to provide secret keys to any users or applications requiring a high level of security, ideally such as to offer the best protection against any computational attack, even of a quantum nature. The keys shared through a point-to-point link between a source and a detector using a quantum key distribution protocol can be proven information-theoretically secure based on the quantum information theory. However, evaluating the security of a quantum key distribution network, especially if it is based on relay nodes, goes far beyond the quantum security of its single quantum links, involving aspects of conventional security for devices and their communication channels. In this contribution, we perform a rigorous threat analysis based on the most recent recommendations and practical network deployment security issues. We show that, at least in the current state of our understanding of quantum cryptography, quantum key distribution networks can only offer computational security and that their security in practical implementations in the shorter term requires resorting to post-quantum cryptography. [ABSTRACT FROM AUTHOR]

Cryptography is processing for securing communication between two people. The opponent wants to know the message that is encrypted using a secret key. Although the opponent can eavesdrop the message sent between the sender and the receiver, the opponent is unable to decrypt to read the message. Therefore, the secret key is very important. The sender and the receiver agree with the secret key in an insecure channel by using key distribution protocol such as the Diffie–Hellman protocol. Since quantum computer is coming soon, Diffie–Hellman protocol is not secure. We will develop a quantum key distribution protocol. The benefit of the quantum system is the quantum state that cannot copy by no‐cloning theorem. Thus, the opponent does not copy and keeps the message that is quantum. In this paper, a novel quantum key distribution protocol between two people (Alice and Bob) based on quantum operators is developed. The opponent (Eve) wants to know the secret key. Although Eve knows this quantum key distribution protocol, Eve does not behave similarly to Alice and Bob. For example, Eve eavesdrops Alice's quantum state that was sent to Bob, and Eve sends another quantum state. Therefore, we cannot control Eve's behavior. So we give the upper bound of mutual information between the user and opponent by using Holevo's bound. We verify the usual security definition for quantum key distribution that is equality‐and‐uniformity and privacy in the mutual information sense. [ABSTRACT FROM AUTHOR]

With the rise of quantum technologies, data security increasingly relies on quantum cryptography and its most notable application, quantum key distribution (QKD). Yet, current technological limitations, in particular, the unavailability of quantum repeaters, cause relatively low key distribution rates in practical QKD implementations. Here, we demonstrate a remarkable improvement in the QKD performance using end-to-end line tomography for the wide class of relevant protocols. Our approach is based on the real-time detection of interventions in the transmission channel, enabling an adaptive response that modifies the QKD setup and post-processing parameters, leading, thereby, to a substantial increase in the key distribution rates. Our findings provide everlastingly secure efficient quantum cryptography deployment potentially overcoming the repeaterless rate-distance limit. [ABSTRACT FROM AUTHOR]

Security of quantum key distribution (QKD) protocols rely solely on quantum physics laws, namely, on the impossibility to distinguish between non-orthogonal quantum states with absolute certainty. Due to this, a potential eavesdropper cannot extract full information from the states stored in their quantum memory after an attack despite knowing all the information disclosed during classical post-processing stages of QKD. Here, we introduce the idea of encrypting classical communication related to error-correction in order to decrease the amount of information available to the eavesdropper and hence improve the performance of quantum key distribution protocols. We analyze the applicability of the method in the context of additional assumptions concerning the eavesdropper's quantum memory coherence time and discuss the similarity of our proposition and the quantum data locking (QDL) technique. [ABSTRACT FROM AUTHOR]

Data security and secure communication is one of the most important issues of today. In this study, a quantum-based method for secure communication is proposed. In the proposed method, the necessary secret key in communication is generated locally by each participant through quantum gates. The quantum gates are taught by using quantum reinforcement learning (QRL). The proposed study is simulated using the Qiskit library for Python. The proposed study performs the learning action with an accuracy of 87.95% for 195 gates, 85.47% for 128 gates, 83.59% for 64 gates, 76.25% for 32 gates. As the key size increases, the performance of the method increases. The participants do not share the secret key in the presented method. Thus, the communication becomes more secure. In the study, the method is also examined in terms of security. Security analysis shows that the proposed method provides secure communication. [ABSTRACT FROM AUTHOR]

We Haar uniformly generate random states of various ranks and study their performance in an entanglement-based quantum key distribution (QKD) task. In particular, we analyze the efficacy of random two-qubit states in realizing device-independent (DI) QKD. We first find the normalized distribution of entanglement and Bell-nonlocality which are the key resource for DI-QKD for random states ranging from rank-1 to rank-4. The number of entangled as well as Bell-nonlocal states decreases as rank increases. We observe that the decrease in the secure key rate is more pronounced in comparison with that of the quantum resource with the increase in rank. We find that the pure state and Werner state provide the upper and lower bound, respectively, on the minimum secure key rate of all mixed two-qubit states possessing the same magnitude of entanglement under general as well as optimal collective attack strategies. [ABSTRACT FROM AUTHOR]

The finite sampling bandwidth of an analog-to-digital converter has a negative effect on the continuous-variable quantum key distribution (CVQKD), which leaves a potential loophole for an eavesdropper and weakens the practical security of the system. To compensate for the loss in free space, we deploy an adaptive optics (AO) unit in the detector of the CVQKD system with discrete modulations. Since the closed-loop control bandwidth of the embedded AO unit can be optimized with the sampling frequency, the practical security of the system can be enhanced in terms of the secret key rate. The security analysis is demonstrated on the basis of the derived secret key rate with numerical simulations, providing a feasible implementation of CVQKD in realistic free-space environments. [ABSTRACT FROM AUTHOR]

Quantum Key Distribution is a secure method that implements cryptographic protocols. The applications of quantum key distribution technology have an important role: to enhance the security in communication systems. It is originally inspired by the physical concepts associated with quantum mechanics. It aims to enable a secure exchange of cryptographic keys between two parties through an unsecured quantum communication channel. This work proposes a secure half-duplex bidirectional quantum key distribution protocol. The security of the proposed protocol is proved against collective attacks by estimating the interception of any eavesdropper with high probability in both directions under the control of the two parties. A two-qubit state encodes two pieces of information; the first qubit represents the transmitted bit and the second qubit represents the basis used for measurement. The partial diffusion operator is used to encrypt the transmitted qubit state as an extra layer of security. The predefined symmetry transformations induced by unitary in conjunction with the asymmetrical two-qubit teleportation scheme retain the protocol's secrecy. Compared to the previous protocols, the proposed protocol has better performance on qubit efficiency. [ABSTRACT FROM AUTHOR]

The current theoretical analysis model for high-dimensional quantum key distribution (QKD) was developed without carefully considering the dead time and after-pulse of the single-photon detectors. Here, we propose a new model that accounts for these two effects. With this model, we analyze the effects of various properties of the single-photon detector on the performance of the high-dimensional quantum key distribution and show numerically that the high-dimensional quantum key distribution can be achieved up to 180 km with InGaAs/InP-type single-photon detectors. This work can improve our understanding of the factors that determine the performance of high-dimensional quantum key distribution and will help to promote the application of single-photon detectors based on avalanche photodiodes in high-dimensional quantum key distribution. [ABSTRACT FROM AUTHOR]

Recently, Cui et al. [Sci. China Phys. 62, 110311 (2019)] proposed a measurement-device-independent quantum key distribution (MDI-QKD) scheme based on high-dimensional encoding to increase the channel capacity of each individual photon. A secret key is shared among two legitimate parties via the help of a dishonest third-party (TP). They claimed that the proposed protocol can improve the drawback of the low-key generation rate that existed in the past MDI-QKD schemes. However, this study pointed out a loophole during the security check of TP. That is, the two legitimate participants merely use the corresponding qubit pairs that are both generated in the diagonal basis for the discussion, which leads to a potential attack that not only allows TP to avoid the security check but also creates partial inconsistency of key bits for both communicating sides. Fortunately, this problem can be fixed by a minor correction of the protocol. [ABSTRACT FROM AUTHOR]

Semi-quantum key distribution (SQKD) protocols attempt to establish a shared secret key between users, secure against computationally unbounded adversaries. Unlike standard quantum key distribution protocols, SQKD protocols contain at least one user who is limited in their quantum abilities and is almost "classical" in nature. In this paper, we revisit a mediated semi-quantum key distribution protocol, introduced by Massa et al. (Experimental quantum cryptography with classical users, 2019. arXiv preprint arXiv:1908.01780), where users need only the ability to detect a qubit, or reflect a qubit; they do not need to perform any other basis measurement; nor do they need to prepare quantum signals. Users require the services of a quantum server which may be controlled by the adversary. In this paper, we show how this protocol may be extended to improve its efficiency and also its noise tolerance. We discuss an extension which allows more communication rounds to be directly usable; we analyze the key-rate of this extension in the asymptotic scenario for a particular class of attacks and compare with prior work. Finally, we evaluate the protocol's performance in a variety of lossy and noisy channels. [ABSTRACT FROM AUTHOR]

Autonomous "Things" is becoming the future trend as the role, and responsibility of IoT keep diversifying. Its applicability and deployment need to re-stand technological advancement. The versatile security interaction between IoTs in human-to-machine and machine-to-machine must also endure mathematical and computational cryptographic attack intricacies. Quantum cryptography uses the laws of quantum mechanics to generate a secure key by manipulating light properties for secure end-to-end communication. We present a proof-of-principle via a communication architecture model and implementation to simulate these laws of nature. The model relies on the BB84 quantum key distribution (QKD) protocol with two scenarios, without and with the presence of an eavesdropper via the interception-resend attack model from a theoretical, methodological, and practical perspective. The proposed simulation initiates communication over a quantum channel for polarized photon transmission after a pre-agreed configuration over a Classic Channel with parameters. Simulation implementation results confirm that the presence of an eavesdropper is detectable during key generation due to Heisenberg's uncertainty and no-cloning principles. An eavesdropper has a 0.5 probability of guessing transmission qubit and 0.25 for the polarization state. During simulation re-iterations, a base-mismatch process discarded about 50 percent of the total initial key bits with an Error threshold of 0.11 percent. [ABSTRACT FROM AUTHOR]

This paper presents a communication algorithm in which a grayscale image, shared between two parties, can be used to transmit a secret message, by applying the idea introduced in the B92 quantum protocol. The least significant qubits of the pixels' representation in certain regions of the image are used. With the help of a server, the algorithm generates a random message, which can further act as a secret key for cryptographic algorithms in order to secure the data that two parties might want to exchange later on. The chosen representation of the image is NEQR (novel enhanced quantum representation) and the platform used for testing the described idea is IBM Quantum Experience, along with the open-source Python framework called Qiskit. This solution allows users to design, implement quantum circuits (containing various quantum gates), and simulate them using real devices and local simulators. An implementation using this platform for a sample image and the corresponding results are also presented in this paper. [ABSTRACT FROM AUTHOR]

In this study, we analyse the efficiency of a protocol with discrete modulation of continuous variable non-Gaussian states, that is, the coherent states having the addition of one photon followed by the subtraction of one photon (PASCS). We calculate lower bounds of the asymptotic key rates against Gaussian collective attacks based on the fact that for sufficiently small modulation variances we remain close to the protocol with Gaussian modulation. We compare the results of a four-state protocol (quadrature phase-shift-keying) using PASCS with the ones using coherent states, and show that under the same environmental conditions, the former always outperforms the latter, allowing to increase the maximum possible distance for secret key generation. Interestingly, we find that for the protocol using discrete-modulated PASCS, the noisier the line, the better will be its performance compared to the protocol using coherent states, showing that continuous variable non-Gaussian states can be considerably more advantageous for performing quantum key distribution in non-ideal situations. [ABSTRACT FROM AUTHOR]

The wireless body area network (WBAN) has emerged as a promising networking paradigm thanks to embedded systems, integrated circuit technologies, and wireless communications advancements. WBAN has the ability to send real-time biomedical data to remote medical personnel for clinical diagnostics through intelligent medical sensors in or around the patient’s body. Moreover, WBANs have played an increasingly important role in modern medical systems over the past decade as part of the Internet of Things (IoT). In addition to their conveniences, WBANs present us with the data confidentiality challenge and protecting patient’s privacy. The system requires a robust security mechanism to protect against threats because of the massive production of delay-sensitive data. This article presents a quantum key distribution (QKD) protocol-based authentication scheme for secure communication within WBAN infrastructure to prevent attacks and provide services free of security risks. To the best of our knowledge, we proposed a privacy preserving quantum authentication scheme for secure data sharing in WBANs to enhance security by encrypting medical data and safeguarding patients identities. Simulations conducted using Mathematica evaluate the proposed quantum authentication protocol both theoretically and practically, showing strong encryption performance against recent schemes. Results include computational cost of 6.832 ms, communication costs of 588 bits, and energy consumption of 432.98 μJ\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\mu J$$\end{document} indicating the proposed quantum authentication protocol model exhibits superior reliability, feasibility, and efficiency in safeguarding WBAN data during transmission and storage. [ABSTRACT FROM AUTHOR]

Ji et al. [Mod. Phys. Lett. A 34, 1950229 (2019)] and Fan et al. [Mod. Phys. Lett. A 37, 2250026 (2022)] proposed two-party quantum private comparison (QPC) protocols based on 7-qubit and 8-qubit states, respectively. However, these two QPC protocols did not consider third-party (TP) attacks. Therefore, this study focuses on TP attacks and demonstrates that the property of a 7-qubit or 8-qubit entanglement state is useless in this attack situation; that is, the participant wastes resources to maintain the qubits. For the same assumption environment proposed by Ji et al. and Fan et al., this study proposes an improvement and simplification protocol that allows participants to reach the goal of private comparison by using only classical computation and the classical communication channel without any entanglement state. [ABSTRACT FROM AUTHOR]

The paper describes a quantum technique for relativistic high-dimensional key distribution without public announcement of bases, also known as quantum key expansion, which securely transfers 2 bits per setup usage given that a pre-shared bit is at disposal to the parties. This becomes possible by utilizing both phase and polarization encodings. The work presents both single-photon and weak-coherent-state interferometric setups for the purpose of the proposed scheme. The proposed key distribution is characterized with higher rate than any existing protocols of such type. Also, the proposed scheme has the highest efficiency of the existing quantum key expansion protocols. It should be noted that the highest efficiency is obtained only for the case of single-photon regime of the scheme; the weak-coherent-pulse regime manifests lower efficiency. Moreover, compared to other relativistic quantum key distribution schemes, the proposed one shows better rate and efficiency (weak-coherent-pulse regime is considered). The improvement comes at no security cost. However, at the cost of improving efficiency and rate, the practicality of the scheme reduces. [ABSTRACT FROM AUTHOR]

In this paper, a passive decoy state phase matching quantum key distribution scheme is proposed based on the heralded pair coherent state light source to make the protocol more practical and safe. Without changing the intensity of the light source, we can derive four different data sets by dividing the raw key data into four groups according to the combined results of detectors in source end. The scheme can make use of the different data sets to estimate the parameters and extract the secret key. The key generation rate formula is derived after the parameter estimation. The performance of the proposed scheme is analyzed with and without taking statistical fluctuation into consideration. The simulation results show that compared with the existing active decoy-state method, the proposed passive method has slightly lower key rate when the transmission distance is short, and has obviously higher key rate when the transmission distance exceeds 406 km. The maximum safety transmission distance of the proposed scheme is 452 km which is relatively further. According to the influence of statistical fluctuation, the performance of the proposed scheme declines as the length of the data falls. Even though the data size is 1 0 1 1 , the max safety transmission distance is also more than 400 km. [ABSTRACT FROM AUTHOR]

The Quantum Key Distribution (QKD) is a well-researched secure communication method for exchanging cryptographic keys only known by the shared participants. The vulnerable problem of a secret key distribution is the negotiation and the transfer over an insecure or untrusted channel. Novel further developments of the QKD communication method are part of in-field technologies and applications in communication devices, such as satellites. However, expensive physical test setups are necessary to improve new application possibilities of cryptographic protocol involving components of quantum mechanics and quantum laws of physics. Therefore, optical simulation software can play a part in essential QKD simulating and further developing quantum-based cryptosystems. In the paper, the authors consider a feasible QKD setup based on the BB84 protocol to create a symmetric key material based on achieving a linear key rate via optical simulation software. The paper still provides two experimental architecture designs to use the QKD for a cryptosystem. [ABSTRACT FROM AUTHOR]

The first quantum computers are becoming a reality, and scientists working in various areas look forward to taking advantage of their enormous computational potential. At the same time, the high performance of quantum computers imposes serious risks for cybersecurity. We can expect an arms race between rival parties: a defensive side trying to ensure the privacy and dependability of stored and transmitted information and their adversaries. With this article, the authors aim to provide an overview of the status of quantum computer development, project the next steps, and investigate the impact future quantum systems may have on cybersecurity and military operations. We first discuss the basic aspects that differentiate quantum computing from classical computing and find that analogies between both domains are quite limited. The world of quantum computers is remarkably diverse already, and we elaborate that quantum simulators and universal quantum computers have "qubits" in common but still work in fundamentally different ways. Since security experts focus on upcoming trends in quantum computing, we take a look at the latest technologies and at the race for first reaching "quantum supremacy." Finally, we provide a detailed analysis of the specific risks future quantum computers represent for established cryptosystems and conclude that asymmetric algorithms like the RSA protocol are particularly vulnerable. The dangers of quantum computing for cryptography are obvious, as is the high relevance of the safety of stored and transmitted data to the defense sector. However, we examine the capability spectrum of quantum technologies and discover that breaking asymmetric encryption algorithms is just one facet, and other features like Grover's quantum algorithm may revolutionize the logistics of the armed forces. Satellite Quantum Key Distribution is another promising concept that may change the communication between military units. To NATO, quantum computing is a doubleedged sword: the alliance needs to use the developments to benefit from the potential and be ready to counter the cyber threats. We derive ideas of what NATO should do in order to prepare for the quantum era. [ABSTRACT FROM AUTHOR]

Quantum cryptography is a well-stated field within quantum applications where quantum information is used to set secure communications, authentication, and secret keys. Now used in quantum devices with those purposes, particularly Quantum Key Distribution (QKD), which proposes a secret key between two parties free of effective eavesdropping, at least at a higher level than classical cryptography. The best-known quantum protocol to securely share a secret key is the BB84 one. Other protocols have been proposed as adaptations of it. Most of them are based on the quantum indeterminacy for non-orthogonal quantum states. Their security is commonly based on the large length of the key. In the current work, a BB84-like procedure for QKD based on double quantum teleportation allows the sharing of the key statement using several parties. Thus, the quantum bits of information are assembled among three parties via entanglement, instead of travelling through a unique quantum channel as in the traditional protocol. Asymmetry in the double teleportation plus post-measurement retains the secrecy in the process. Despite requiring more complex control and resources, the procedure dramatically reduces the probability of success for an eavesdropper under individual attacks, because of the ignorance of the processing times in the procedure. Quantum Bit Error Rate remains in the acceptable threshold and it becomes configurable. The article depicts the double quantum teleportation procedure, the associated control to introduce the QKD scheme, the analysis of individual attacks performed by an eavesdropper, and a brief comparison with other protocols. [ABSTRACT FROM AUTHOR]

In order to prevent the collusion between an auctioneer and the bidders, a novel quantum sealed-bid auction protocol with the help of a trusted third-party center is proposed, which adopts quantum authentication and quantum public key with single particles. In this protocol, the honest and trusted third-party center first issues a pseudonym for each bidder, further generates the public and private keys for the auctioneer, and finally verifies the legitimacy of the winning bid announced by auctioneer. This protocol only needs single particles and a limited number of entangled Bell states, which can effectively reduce quantum resources. Compared with the previous proposed protocols, our proposed protocol has higher security properties and better feasibility. [ABSTRACT FROM AUTHOR]

Measurement-device-independent quantum key distribution (MDI-QKD) provides a method for secret communication whose security does not rely on trusted measurement devices. In all existing MDI-QKD protocols, the participant Charlie has to perform Bell state measurement or other joint measurements. Here, we propose an MDI-QKD protocol which requires individual measurements only. Meanwhile, all operations of the receiver Bob are classical, without the need for preparing and measuring quantum systems. Thus, the implementation of the protocol has a lower technical requirement on Bob and Charlie. [ABSTRACT FROM AUTHOR]

What is the minimum number of guesses needed on average to guess a realization of a random variable correctly? The answer to this question led to the introduction of a quantity called guesswork by Massey in 1994, which can be viewed as an alternate security criterion to entropy. In this paper, we consider the guesswork in the presence of quantum side information, and show that a general sequential guessing strategy is equivalent to performing a single quantum measurement and choosing a guessing strategy based on the outcome. We use this result to deduce entropic one-shot and asymptotic bounds on the guesswork in the presence of quantum side information, and to formulate a semi-definite program (SDP) to calculate the quantity. We evaluate the guesswork for a simple example involving the BB84 states, both numerically and analytically, and we prove a continuity result that certifies the security of slightly imperfect key states when the guesswork is used as the security criterion. [ABSTRACT FROM AUTHOR]

A modified thermal states quantum cryptography is proposed by adding the noise at Bob's side and the impact of finite‐size effects focused on by performing the channel estimation. An optimal noise which can maximize the key rate is demonstrated to exist and, by using numeric simulations, is shown to vary with the transmission distance. Adding the optimal noise can enhance the effectiveness of the thermal states quantum cryptography protocol under noisy and lossy channel in terms of secret key rate, the maximum transmission distance and the tolerable channel noise. Although finite‐size effects deteriorate the performance of thermal quantum cryptography, this approach can compensate the impact of this degradation, and even make the performance of the modified protocol in the finite‐size regime better than that of the original protocol in the ideal asymptotic regime. [ABSTRACT FROM AUTHOR]

We present a three-party reference frame independent quantum key distribution protocol which can be implemented without any alignment of reference frames between the sender and the receiver. The protocol exploits entangled states to establish a secret key among three communicating parties. We derive the asymptotic key rate for the proposed protocol against collective attacks and perform a finite-size key security analysis against general attacks in the presence of statistical fluctuations. We investigate the impact of reference frame misalignment on the stability of our protocol, and we obtain a transmission distance of 180 km, 200 km, and 230 km for rotation of reference frames β = π /6, β = π /8 and β = 0, respectively. Remarkably, our results demonstrate that our proposed protocol is not heavily affected by an increase in misalignment of reference frames as the achievable transmission distances are still comparable to the case where there is no misalignment in reference frames (when β = 0). We also simulate the performance of our protocol for a fixed number of signals. Our results demonstrate that the protocol can achieve an effective key generation rate over a transmission distance of about 120 km with realistic 107 finite data signals and approximately achieve 195 km with 109 signals. Moreover, our proposed protocol is robust against noise in the quantum channel and achieves a threshold error rate of 22.7%. [ABSTRACT FROM AUTHOR]

This work proposes an encoding–decoding procedure, which is characterized with higher efficiency, i.e., it increases the size of the sifted key. The contribution comes from using a novel way of decoding the data carried by the quantum systems. The proposed approach is analyzed in terms of efficiency, security, randomness, error rate, and capability of high dimensionality. It is shown that the newly proposed technique demonstrates higher efficiency, slightly better security, similar randomness, compatibility with high dimensionality, but less error robustness than the standard encoding–decoding scheme. [ABSTRACT FROM AUTHOR]

A common problem of a discrete-variable quantum key distribution (QKD) protocol is that related to its key rate. This work proposes a solution to this problem: the procedure key expanding. The key expanding not only increases the key size (respectively, key rate) of the final secret key, but also increases the efficiency of a QKD scheme. The contribution comes from using a part of the classical data exchanged in the QKD. This process can be implemented along with privacy amplification, thus not requiring any additional time resource. Also, it can be used in combination with the other solution to the mentioned problem, namely high-dimensionality. The combination allows key rates that have not been obtainable so far. The key expanding is verified to be a secure procedure—it does not leak information about the final key to an eavesdropper. Moreover, the paper presents the key expanding in the case of the well-known measurement-device-independent QKD protocol. [ABSTRACT FROM AUTHOR]

In this work, a one‐sided measurement‐device‐independent quantum key distribution protocol that uses Bell and Greenberger–Horne–Zeilinger (GHZ) states is proposed. The protocol considers three parties: Alice and Bob, who will share the key at the end of the protocol; and Charlie, who plays the role of facilitating the key distribution without having access to the key itself. Alice and Charlie are trusted users, while Bob is uncharacterized. The protocol is asymmetrical, meaning that Alice sends one qubit while Bob sends two; this allows Bob to identify himself via a previously assigned ID; if this authentication fails, the key distribution also will. [ABSTRACT FROM AUTHOR]

In order to eliminate the influence of the channel noise, two new measurement-device-independent quantum key distribution (MDI-QKD) protocols are proposed with logical quantum states. They can resist collective-dephasing noise and collective-rotation noise, respectively. This paper produces logical quantum states by adding the auxiliary light sources, the CNOT operations and the Hadamard transforms in the system model. The main light sources and auxiliary light sources are flexible and easily implemented, since they can be weak coherent state (WCS) sources, heralded single-photon sources (HSPSs) or heralded pair coherent state (HPCS) sources. To generate one key bit, the new MDI-QKD protocols only need one logical qubit with two particles so that they have high qubit efficiency. Moreover, the new protocols also use partial Bell-state measurement (BSM) which is very easily implemented with existing technologies. [ABSTRACT FROM AUTHOR]

We investigate the security against the intercept/resend and translucent attacks on the quantum key distribution protocol based on the pre- and post-selection effect. In 2001, Bub proposed the quantum cryptography scheme, which was an application of the so-called mean king's problem. We evaluate a probability that legitimate users cannot detect eavesdropper's malicious acts for Bub's protocol. We also estimate a probability that the eavesdropper guesses right at the random secret key one of the legitimate users tries to share with the other one. From rigorous mathematical and numerical analyses, we conclude that Bub's protocol is weaker than the Bennett–Brassard protocol of 1984 (BB84) against both the intercept/resend and translucent attacks. Because Bub's protocol uses a two-way quantum channel, the analyses of its security are tough to accomplish. We refer to their technical points accurately in the current paper. For example, we impose some constraints upon the eavesdropper's strategies in order to let their degrees of freedom be small. [ABSTRACT FROM AUTHOR]

The main challenge in the current era is how to secure the communication networks on which the information is transmitted from source to destination. Different techniques and algorithms are used for securing the communication system and providing a more secure system that ensures confidentiality and the integrity of data. The secret in this system includes the shared key algorithm and the public key. By using the Quantum Cryptography technique, a more secure communication network is achieved. This technique of Quantum Cryptography is based on the following two elements, photon polarization and the principle of uncertainty. Photon polarization ensures that an eavesdropper cannot copy or even try to read the information which is being transmitted by using photons. The principle of uncertainty states that it is impossible to measure or observe the state of photons without disturbing their actual state. The main focus of this paper is on photon Cryptography and how this can be used to make the network more secured. Finally, we discuss the future of Quantum Cryptography. [ABSTRACT FROM AUTHOR]

Quantum networks open the way to an unprecedented level of communication security. However, due to physical limitations on the distances of quantum links, current implementations of quantum networks are unavoidably equipped with trusted nodes. Consequently, the quantum key distribution can be performed only on the links. Due to this, some new authentication and key exchange schemes must be considered to fully benefit from the unconditional security of the links. One such approach uses Multiple Non-Overlapping Paths (MNOPs) for key exchange to mitigate the risk of an attack on a trusted node. The scope of the article is to perform a security analysis of this scheme for the case of both uncorrelated attacks and correlated attacks with finite resources. Furthermore, our analysis is extended to the case of Multiple Overlapping Paths (MOPs). We prove that introducing overlapping paths allows one to increase the security of the protocol, compared to the non-overlapping case with the same number of additional links added. This result may find application in optimising architectures of large-scale (hybrid) quantum networks. [ABSTRACT FROM AUTHOR]

In this paper, we analyze quantum key distribution (QKD) protocols through a game-theoretic framework. In particular, we assume parties and adversaries are “rational.” Unlike other game theoretic models, we show how important key-rate and noise tolerance computations may be performed through our system allowing for interesting comparisons to the “standard adversarial model” of QKD. We show that, depending on the relative cost of operating devices, increased noise tolerance and improved secure communication rates are possible if one assumes adversaries are rational as opposed to being malicious. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) enables unconditionally secure communication between distinct parties using a quantum channel and an authentic public channel. Reducing the portion of quantum-generated secret keys, that is consumed during the authentication procedure, is of significant importance for improving the performance of QKD systems. In the present work, we develop a lightweight authentication protocol for QKD based on a ‘ping-pong’ scheme of authenticity check for QKD. An important feature of this scheme is that the only one authentication tag is generated and transmitted during each of the QKD post-processing rounds. For the tag generation purpose, we design an unconditionally secure procedure based on the concept of key recycling. The procedure is based on the combination of almost universal2 polynomial hashing, XOR universal2 Toeplitz hashing, and one-time pad (OTP) encryption. We demonstrate how to minimize both the length of the recycled key and the size of the authentication key, that is required for OTP encryption. As a result, in real case scenarios, the portion of quantum-generated secret keys that is consumed for the authentication purposes is below 1%. Finally, we provide a security analysis of the full quantum key growing process in the framework of universally composable security. [ABSTRACT FROM AUTHOR]

A quantum key distribution protocol with single-particle and Bell state is proposed, in which one player Alice sends the states from some special single-particles and Bell states, the other player Bob measures these states in the single-particle basis or Bell basis, and then establish their secret key. Through combining the single-particle and Bell state novelly, the error rate of eavesdropping in our protocol can be increased up to 3 8 . Compared to BB84, our protocol can get higher secure key rate in practice. [ABSTRACT FROM AUTHOR]

High-dimensional quantum key distribution (HD-QKD) can higher the secret-key capacity and tolerate more errors. Several HD-QKD experiments have been demonstrated over deployed fibers to show promising future toward high-dimensional quantum communication networks. However, the practical security of HD-QKD systems should be widely considered before large-scale application of HD-QKD systems. In this paper, we focus on the HD-QKD based on the dispersive optics (DO-QKD) with both statistical and intensity fluctuations. For the condition only with statistical fluctuations, we present the parameter estimation based on an improved Chernoff bound. When considering the condition with both statistical and intensity fluctuations, we present the parameter estimation based on Azuma's inequality. By numerical simulations, we find that the parameter estimation for DO-QKD based on the improved Chernoff bound is tighter than the previous work in terms of the secret-key capacity and the maximum transmission distance. Moreover, we find that intensity fluctuations affect the performance of DO-QKD greatly and the effect on smaller data size is more obvious. [ABSTRACT FROM AUTHOR]

This work illustrates a possible application of quantum game theory to the area of quantum information, in particular to quantum cryptography. The study proposed two quantum key‐distribution (QKD) protocols based on the quantum version of the Monty Hall game devised by Flitney and Abbott. Unlike most QKD protocols, in which the bits from which the key is going to be extracted are encoded in a basis choice (as in BB84), these are encoded in an operation choice. The first proposed protocol uses qutrits to describe the state of the system and the same game operators proposed by Flitney and Abbott. The motivation behind the second proposal is to simplify a possible physical implementation by adapting the formalism of the qutrit protocol to use qubits and simple logical quantum gates. In both protocols, the security relies on the violation of a Bell‐type inequality, for two qutrits and for six qubits in each case. Results show a higher ratio of violation than the E91 protocol. [ABSTRACT FROM AUTHOR]

The security of previously proposed Quantum Sealed-bid Auction (QSA) protocols is analyzed. It is shown that there may be a malicious bidder to disrupt the auction that he sends a true bid to auctioneer and commits a fake bid to other bidders. Consequently, these honest bidders may mistakenly think the auctioneer is dishonest. To avoid this security flaw, we propose an improved protocol which can more perfectly meet the security of QSA. [ABSTRACT FROM AUTHOR]

Summary: In a multicarrier continuous‐variable quantum key distribution (CVQKD) protocol, the information is granulated into Gaussian subcarrier CVs and the physical Gaussian link is divided into Gaussian sub‐channels. Here, we propose a combined mathematical framework of order statistics and random matrix theory for multicarrier continuous‐variable quantum key distribution. The analysis covers the study of the distribution of the sub‐channel transmittance coefficients in the presence of a Gaussian noise and the utilization of the moment generation function (MGF) in the error analysis. We reveal the mathematical formalism of sub‐channel selection and formulation of the transmittance coefficients and show a reduced complexity progressive sub‐channel scanning method. We define a framework to evaluate the statistical properties of the information flowing processes in multicarrier CVQKD protocols. Using random matrix theory, we express the achievable secret key rates and study the efficiency of the adaptive multicarrier quadrature division‐multiuser quadrature allocation (AMQD‐MQA) multiple‐access multicarrier CVQKD. The proposed combined framework is particularly convenient for the characterization of the physical processes of experimental multicarrier CVQKD. [ABSTRACT FROM AUTHOR]

The multicarrier continuous-variable quantum key distribution (CVQKD) protocol is defined. In a CVQKD protocol, the information is conveyed by coherent quantum states. The quantum continuous variables are sent through a noisy quantum channel. For a quantum channel with additive-multiplicative noise both additive and multiplicative disturbances are present in the transmission. The multiplicative disturbance is an inherent attribute of diverse physical environments. Physical links with additive and multiplicative disturbances can represent a more general approach than purely additive noise links in several practical scenarios. In a standard CVQKD setting, the noise is modeled as an additive white Gaussian noise caused by an eavesdropper (Gaussian quantum link). As a corollary, standard CVQKD protocols are not optimal for arbitrary Gaussian quantum channels if multiplicative disturbances are also present in the physical link. Here, we define the adaptive multicarrier quadrature division (AMQD) modulation technique for CVQKD. The AMQD method is optimal for arbitrary Gaussian quantum channels with arbitrary multiplicative disturbances. The protocol granulates the Gaussian random input into Gaussian subcarrier continuous variables in the encoding phase, which are then decoded by a continuous unitary transformation. The subcarrier coherent variables formulate sub-channels from the physical link which leads to improved transmission efficiency, higher tolerable loss, and excess noise in comparison to standard CVQKD protocols. We also derive the security proof of multicarrier CVQKD at optimal Gaussian attacks in the finite-size and asymptotic regimes. [ABSTRACT FROM AUTHOR]

Moving at the speed of light, the photon is the ideal physical support to transmit information. Polarization of a photon is the predominant quantum property used to encode information, but other encoding domains, such as the spatial-mode degree of freedom, have been considered. In this paper, we put forward the entanglement degree of freedom of a photon as an exploitable resource for encoding information in quantum cryptographic protocols. We show how classical information can be extracted from the quantum state of a photon by distinguishing between a singular, independent state and an entangled state through interferometry. We also give a direct application of our technique to quantum key distribution as a proof of concept for future quantum protocols that may use coding in the entanglement domain in combination with other degrees of freedom that are currently exploited for cryptographic purposes. [ABSTRACT FROM AUTHOR]

We improve the thermal states quantum cryptography by inserting the linear optics cloning machine (LOCM) into Bob's side. This approach can enhance the effectiveness of the practical quantum cryptography under noisy resources and channel in terms of secret key rate and transmission distance. We show that the security of the thermal states protocol with LOCM has advantages over that of the original protocol at various wavelengths. [ABSTRACT FROM AUTHOR]

We define the singular value decomposition (SVD) assisted multicarrier continuous-variable quantum key distribution (CVQKD) protocol. The proposed protocol uses the singular value decomposition of the Gaussian quantum channel, which yields an additional degree of freedom for the phase space transmission. This additional degree of freedom can further be exploited in a multiple-access scenario. The SVD-assistance defines the eigenchannels of the Gaussian physical link, which can be used for the simultaneous reliable transmission of multiple user data streams. Our transmission model also includes the singular interference avoider (SIA) precoding scheme. The proposed SIA precoding scheme prevents the eigenchannel interference to reach an optimal transmission over a Gaussian link. We demonstrate the results through the adaptive multicarrier quadrature division–multiuser quadrature allocation (AMQD-MQA) CVQKD multiple-access scheme. The singular value assisted transmission provides improved simultaneous transmission rates for the users, particularly in crucial low signal-to-noise ratio regimes. [ABSTRACT FROM AUTHOR]

Quantum Cryptography uses the counter-intuitive properties of Quantum Mechanics for performing cryptographic tasks in a secure and reliable way. The Quantum Key Distribution (QKD) protocol BB84 has been proven secure against several important types of attacks: collective attacks and joint attacks. Here we analyze the security of a modified BB84 protocol, for which information is sent only in the z basis while testing is done in both the z and the x bases, against collective attacks. The proof follows the framework of a previous paper [1] , but it avoids a classical information-theoretical analysis and proves a fully composable security. We show that this modified BB84 protocol is as secure against collective attacks as the original BB84 protocol, and that it requires more bits for testing. [ABSTRACT FROM AUTHOR]

The subcarrier domain of multicarrier continuous-variable quantum key distribution (CVQKD) is defined. In a multicarrier CVQKD scheme, the information is granulated into Gaussian subcarrier CVs and the physical Gaussian link is divided into Gaussian sub-channels. The subcarrier domain injects physical attributes to the description of the subcarrier transmission. We prove that the subcarrier domain is a natural representation of the subcarrier-level transmission in a multicarrier CVQKD scheme. We also extend the subcarrier domain to a multiple-access multicarrier CVQKD setting. We demonstrate the results through the adaptive multicarrier quadrature-division (AMQD) CVQKD scheme and the AMQD-MQA (multiuser quadrature allocation) multiple-access multicarrier scheme. The subcarrier domain representation provides a general apparatus that can be utilized for an arbitrary multicarrier CVQKD scenario. [ABSTRACT FROM AUTHOR]

With rapid development of quantum computing technology in recent years, the cryptanalytic algorithms based on quantum characteristics can be realized in the near future. Therefore, the security of the traditional symmetric or asymmetric cryptography may not be guaranteed as in the past, especially the key-distribution protocols and cryptosystems which are either based on the hard problems of calculating discrete logarithm or factoring. The purpose of this article is to explain how the Grover and Shor algorithms threat the security of the modern cryptography. Meanwhile, the strategy to enhance the security of the symmetric cryptography under the threat of Grover algorithm is also provided. Moreover, the development of the quantum key distribution (QKD) and the post-quantum cryptography (PQC), which will be used to replace the traditional key distribution techniques in the future, is also described. Related suggestions to deal with the threats of the quantum computing are also provided in this article for the references of the network security-related departments to establish the corresponding strategies. [ABSTRACT FROM AUTHOR]