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Postselective transformations of quantum states is a broader class of operations than deterministic quantum channels. Here, we describe the possibility of increasing the success probability of postselective operations by using additional information, which has a form of pure quantum states and should not be changed in case of success. We describe the conditions under which assistance becomes useful, and provide application of our method which improves the efficiency of photon number splitting attack for a variant of SARG04 quantum key distribution protocol. In our attack scenario, one extra photon, which is unchanged, plays the role of assistance. [ABSTRACT FROM AUTHOR]

Dynamic quantum secret sharing occupies an important position in quantum cryptography. In this paper, an efficient and secure dynamic quantum direct two-secrets sharing scheme is proposed based on the GHZ state. The proposed scheme is a one-time sharing of a determined classic message and quantum states. For recovering the secret messages, the agents only need to have the ability to perform X-basis measurements on the particles without performing any unitary operation. When dynamically deleting agents, our scheme only requires the other agents to announce some information without transmitting any quantum. Moreover, the analysis shows that our scheme is able to resist dishonest revoked agent attack as well as a range of other common attacks. Compared with the existing dynamic quantum direct secret sharing schemes, the proposed scheme is more efficient and more secure. [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]

In this paper, we propose a novel scheme with a semi-honest third party (TP) to compute the intersection of two parties' sets privately. In our scheme, two groups of particles are firstly prepared by TP and then transmitted circularly among TP and two participants who need the intersection of their private sets. The two participants then perform the unitary operations on their received particles according to an initial encoding rule for their private sets, respectively, to help TP to obtain the result. We analyse the security of our scheme and show that it can resist both outside and inside attacks over ideal and noisy quantum channels. In addition, our scheme is feasible with current quantum technologies as it only requires simple quantum resources and operations. [ABSTRACT FROM AUTHOR]

In many communication scenarios, it is necessary to involve a third party for control and supervision. In the context of controlled bidirectional quantum secure direct communication (CBQSDC) protocols, the transmission of secret messages between two legitimate users is only permitted with the explicit permission of a controller. To address the issue of controlled communication, a CBQSDC protocol (CLYH2015) utilizing Bell states was proposed in the paper (Quant Inf Process 14, 3515–3522, 2015). Bell states have been widely recognized for their significance in the field of quantum secure direct communication. In a subsequent study published in (Quant Inf Process 16, 147, 2017), the research examined whether CLYH2015 protocol strictly requires the initial states to be Bell states. The conclusion drawn from this investigation is that CLYH2015 protocol working properly necessitates the use of Bell states as initial states. To explore alternative possibilities for the initial states in CLYH2015 protocol, a class of CBQSDC protocols employing the generalized Bell states (GBell states), a | 00 ⟩ + b | 11 ⟩ , b ¯ | 00 ⟩ - a ¯ | 11 ⟩ , a | 01 ⟩ + b | 10 ⟩ , and b ¯ | 01 ⟩ - a ¯ | 10 ⟩ , are designed where a and b are complex numbers with | a | = | b | = 1 2 , a ¯ and b ¯ the conjugate complex numbers of a and b, respectively. The class of designed CBQSDC protocols demonstrates several favorable properties, including resistance against information leakage, intercept-and-resend attacks, measure-resend attacks, as well as robustness against collective attacks. In addition, the unconditional security of the class of designed protocols is proved. Finally, to show the advantages of the class of designed protocols, they are compared with some with some previous closely associated protocols. Interestingly, it is worth noting that the Bell states can be considered a special case of the GBell states when both a and b are real numbers. Consequently, CLYH2015 protocol can be regarded as a particular instance of the designed CBQSDC protocols. This insight implies that the initial states in CLYH2015 protocol can be extended to include the GBell states, rather than being limited solely to the Bell states. [ABSTRACT FROM AUTHOR]

The study of classical algorithms is supported by an immense understructure, founded in logic, type, and category theory, that allows an algorithmist to reason about the sequential manipulation of data irrespective of a computation's realizing dynamics. As quantum computing matures, a similar need has developed for an assurance of the correctness of high-level quantum algorithmic reasoning. Parallel to this need, many quantum algorithms have been unified and improved using quantum signal processing (QSP) and quantum singular value transformation (QSVT), which characterize the ability, by alternating circuit ansätze, to transform the singular values of sub-blocks of unitary matrices by polynomial functions. However, while the algebraic manipulation of polynomials is simple (e.g., compositions and products), the QSP/QSVT circuits realizing analogous manipulations of their embedded polynomials are non-obvious. This work constructs and characterizes the runtime and expressivity of QSP/QSVT protocols where circuit manipulation maps naturally to the algebraic manipulation of functional transforms (termed semantic embedding). In this way, QSP/QSVT can be treated and combined modularly, purely in terms of the functional transforms they embed, with key guarantees on the computability and modularity of the realizing circuits. We also identify existing quantum algorithms whose use of semantic embedding is implicit, spanning from distributed search to proofs of soundness in quantum cryptography. The methods used, based in category theory, establish a theory of semantically embeddable quantum algorithms, and provide a new role for QSP/QSVT in reducing sophisticated algorithmic problems to simpler algebraic ones. [ABSTRACT FROM AUTHOR]

Research on quantum computers has advanced significantly in recent years. If humanity ever creates an effective quantum computer, many of the present public key cryptosystems can be compromised. These cryptosystems are currently found in many commercial products. We have devised solutions that seem to protect us from quantum attacks, but they are unsafe and inefficient for use in everyday life. In the paper, hash-based digital signature techniques are analyzed. A Merkle-tree-based digital signature is assessed. Using a Verkle tree and vector commitments, the paper explores novel ideas. The authors of this article present a unique technology for developing a post-quantum digital signature system using state-of-the-art Verkle tree technology. A Verkle tree, vector commitments, and vector commitments based on lattices for post-quantum features are used for this purpose. The concepts of post-quantum signature design utilizing a Verkle tree are also provided in the paper. [ABSTRACT FROM AUTHOR]

This paper presents a new quantum protocol designed to transmit information from one source to many recipients simultaneously. The proposed protocol, which is based on the phenomenon of entanglement, is completely distributed and is provably information-theoretically secure. Numerous existing quantum protocols guarantee secure information communication between two parties but are not amenable to generalization in situations where the source must transmit information to two or more recipients. Hence, they must be executed sequentially two or more times to achieve the desired goal. The main novelty of the new protocol is its extensibility and generality to situations involving one party that must simultaneously communicate different, in general, messages to an arbitrary number of spatially distributed parties. This is achieved in the special way employed to encode the transmitted information in the entangled state of the system, one of the distinguishing features compared with previous protocols. This protocol can prove expedient whenever an information broker, say, Alice, must communicate distinct secret messages to her agents, all in different geographical locations, in one go. Due to its relative complexity compared with similar cryptographic protocols, as it involves communication among n parties and relies on | G H Z n 〉 tuples, we provide an extensive and detailed security analysis so as to prove that it is information-theoretically secure. Finally, in terms of its implementation, the prevalent characteristics of the proposed protocol are its uniformity and simplicity, because it only requires CNOT and Hadamard gates and the local quantum circuits are identical for all information recipients. [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]

The Number Theoretic Transform (NTT) has been widely used to speed up polynomial multiplication in lattice-based post-quantum algorithms. All NTT operands use modular arithmetic, especially modular multiplication, which significantly influences NTT hardware implementation efficiency. Until now, most hardware implementations used Digital Signal Processing (DSP) to multiply two integers and optimally perform modulo computations from the multiplication product. This paper presents a customized Lattice-DSP (L-DSP) for modular multiplication based on the Karatsuba algorithm, Vedic multiplier, and modular reduction methods. The proposed L-DSP performs both integer multiplication and modular reduction simultaneously for lattice-based cryptography. As a result, the speed and area efficiency of the L-DSPs are 283 MHz for 77 SLICEs, 272 MHz for 87 SLICEs, and 256 MHz for 101 SLICEs with the parameters q of 3329, 7681, and 12,289, respectively. In addition, the N − 1 multiplier in the Inverse-NTT (INTT) calculation is also eliminated, reducing the size of the Butterfly Unit (BU) in CRYSTAL-Kyber to about 104 SLICEs, equivalent to a conventional multiplication in the other studies. Based on the proposed DSP, a Point-Wise Matrix Multiplication (PWMM) architecture for CRYSTAL-Kyber is designed on a hardware footprint equivalent to 386 SLICEs. Furthermore, this research is the first DSP designed for lattice-based Post-quantum Cryptography (PQC) modular multiplication. [ABSTRACT FROM AUTHOR]

The secure computation of the graph structure is an important element in the field of secure calculation of graphs, which is important in querying data in graphs, since there are no algorithms for the graph edit distance problem that can resist attacks by malicious adversaries. In this paper, for the problem of secure computation of similarity edit distance of graphs, firstly, the encoding method applicable to the Paillier encryption algorithm is proposed, and the XOR operation scheme is proposed according to the Paillier homomorphic encryption algorithm. Then, the security algorithm under the semi-honest model is designed, which adopts the new encoding method and the XOR operation scheme. Finally, for the malicious behaviors that may be implemented by malicious participants in the semi-honest algorithm, using the hash function, a algorithm for secure computation of graph editing distance under the malicious model is designed, and the security of the algorithm is proved, and the computational complexity and the communication complexity of the algorithm are analyzed, which is more efficient compared with the existing schemes, and has practical value. The algorithm designed in this paper fills the research gap in the existing literature on the problem of graph edit distance and contributes to solving the problem. [ABSTRACT FROM AUTHOR]

Discrete-variable (DV) and continuous-variable (CV) schemes constitute the two major families of quantum key distribution (QKD) protocols. Unfortunately, since the setup elements required by these schemes are quite different, making a fair comparison of their potential performance in particular applications is often troublesome, limiting the experimenters' capability to choose an optimal solution. In this work we perform a general comparison of the major entanglement-based DV and CV QKD protocols in terms of their resistance to the channel noise, with the otherwise perfect setup, showing the definite superiority of the DV family. We analytically derive fundamental bounds on the tolerable channel noise and attenuation for entanglement-based CV QKD protocols. We also investigate the influence of DV QKD setup imperfections on the obtained results in order to determine benchmarks for the parameters of realistic photon sources and detectors, allowing the realistic DV protocols to outperform even the ideal CV QKD analogs. Our results indicate the realistic advantage of DV entanglement-based schemes over their CV counterparts and suggests the practical efforts for maximizing this advantage. [ABSTRACT FROM AUTHOR]

Most prior semi-quantum key distribution (SQKD) protocols are designed in the context of qubits. In this paper, we proposed an SQKD protocol using (d +1) quantum states in two mutually unbiased bases in the context of qudits without invoking the classical party's measurement capability. It not only decreases the quantum states sent by quantum party by half, but also improves the efficiency of key rate than qubits do. To prove the security of present protocol, we first illustrate that the present protocol is completely robust, and then prove its unconditional security from information theoretical perspective by computing its key rate and noise tolerance against cloning-based individual attack. The unconditional security proof demonstrates that the higher dimension of quantum system is, the higher key rate can be obtained and the higher noise tolerance is allowed in depolarization channel. [ABSTRACT FROM AUTHOR]

MQTT, a popular IoT messaging protocol, is frequently associated with numerous vulnerabilities, the majority of which are critical. Many IoT devices that utilize MQTT are susceptible to cyberattacks such as denial-of-service and buffer overflow. In this paper, we unveil a novel Denial of Service (DoS) attack in the MQTT protocol, referred to as Slow Subscribers, which has the potential to cause MQTT brokers to become single points of failure. Unlike existing MQTT DoS attacks, Slow Subscribers can occur on a single compromised node and could potentially disrupt a MQTT broker with minimal subscription permissions. We evaluated the reliability of Mosquitto and NanoMQ, two popular MQTT messaging brokers, to determine the effect of Slow Subscribers. According to the findings of our investigation, NanoMQ outperforms Mosquitto in response to the Slow Subscribers attack at QoS level 0. We also determine that the response to Slow Subscribers at QoS 2 is the worst for both broker implementations. In addition, the results of our experiments indicate that Eclipse Mosquitto achieves a higher rate of reliability than NanoMQ on cloud deployments whereas NanoMQ has proven to be well-suited for edge environments, especially edge IoT devices that require the use of QoS levels 0 and 1. Finally, we propose a Resilient Middleware for Message Queue Telemetry Transport (Remistry) framework that is capable of detecting misconfigurations while providing granular support of resource commitment errors, in particular the out-of-memory (OOM) problems for effectively mitigating the impact of Slow Subscribers attacks on MQTT brokers. [ABSTRACT FROM AUTHOR]

Blockchain technology provides efficient and secure solutions to various online activities by utilizing a wide range of cryptographic tools. In this article, we survey the existing literature on post-quantum secure digital signatures that possess exotic advanced features and that are crucial cryptographic tools used in the blockchain ecosystem for (1) account management, (2) consensus efficiency, (3) empowering scriptless blockchain, and (4) privacy. The exotic signatures that we particularly focus on in this work are the following: multi-/aggregate, threshold, adaptor, blind, and ring signatures. Herein the term "exotic" refers to signatures with properties that are not just beyond the norm for signatures, e.g., unforgeability, but also imbue new forms of functionalities. Our treatment of such exotic signatures includes discussions on existing challenges and future research directions in the post-quantum space. We hope that this article will help to foster further research to make post-quantum cryptography more accessible so that blockchain systems can be made ready in advance of the approaching quantum threats. [ABSTRACT FROM AUTHOR]

Zero-knowledge proof (ZKP) is a fundamental cryptographic primitive that allows a prover to convince a verifier of the validity of a statement without leaking any further information. As an efficient variant of ZKP, noninteractive zero-knowledge proof (NIZKP) adopting the Fiat-Shamir heuristic is essential to a wide spectrum of applications, such as federated learning, blockchain, and social networks. However, the heuristic is typically built upon the random oracle model that makes ideal assumptions about hash functions, which does not hold in reality and thus undermines the security of the protocol. Here, we present a quantum solution to the problem. Instead of resorting to a random oracle model, we implement a quantum randomness service. This service generates random numbers certified by the loophole-free Bell test and delivers them with postquantum cryptography (PQC) authentication. By employing this service, we conceive and implement NIZKP of the three-coloring problem. By bridging together three prominent research themes, quantum nonlocality, PQC, and ZKP, we anticipate this work to inspire more innovative applications that combine quantum information science and the cryptography field. [ABSTRACT FROM AUTHOR]

An original CSIKE post-quantum cryptography algorithm is proposed as a modification of the CSIDH algorithm but with one public key instead of two. The conditions for its implementation on two classes of non-cyclic Edwards curves are substantiated. The properties of quadratic and twisted supersingular Edwards curves that form pairs of quadratic twist of order p + 1 ≡ 0 mod 8 over a prime field Fp are considered. A modification of the CSIDH algorithm and the CSIKE algorithm are presented, which are generated on the isogenies of these curves instead of the traditional arithmetic of curves in the Montgomery form. For isogenies of degrees 3, 5, and 7, the parameters of isogenic chains of non-cyclic supersingular Edwards curves are calculated and tabulated for p = 839. The implementation of the key encapsulation scheme with its encryption by Alice with Bob's public key is considered. A new randomized CSIKE algorithm with random equiprobable selection of the curve from two classes at each step of the isogeny chain is proposed. The probability of a successful side-channel attack in a randomized algorithm is estimated. It is proposed to abandon the calculation of the isogenic function ϕ(R) of a random point R, which significantly speeds up the algorithm. [ABSTRACT FROM AUTHOR]

Most of current public key cryptosystems would be vulnerable to the attacks of the future quantum computers. Post-quantum cryptography offers mathematical methods to secure information and communications against such attacks, and therefore has been receiving a significant amount of attention in recent years. Lattice-based cryptography, built on the mathematical hard problems in (high-dimensional) lattice theory, is a promising post-quantum cryptography family due to its excellent efficiency, moderate size and strong security. This survey aims to give a general overview on lattice-based cryptography. To this end, the authors begin with the introduction of the underlying mathematical lattice problems. Then they introduce the fundamental cryptanalytic algorithms and the design theory of lattice-based cryptography. [ABSTRACT FROM AUTHOR]

Quantum secure direct communication (QSDC) offers a practical way to realize a quantum network which can transmit information securely and reliably. Practical quantum networks are hindered by the unavailability of quantum relays. To overcome this limitation, a proposal has been made to transmit the messages encrypted with classical cryptography, such as post-quantum algorithms, between intermediate nodes of the network, where encrypted messages in quantum states are read out in classical bits, and sent to the next node using QSDC. In this paper, we report a real-time demonstration of a computationally secure relay for a quantum secure direct communication network. We have chosen CRYSTALS-KYBER which has been standardized by the National Institute of Standards and Technology to encrypt the messages for transmission of the QSDC system. The quantum bit error rate of the relay system is typically below the security threshold. Our relay can support a QSDC communication rate of 2.5 kb/s within a 4 ms time delay. The experimental demonstration shows the feasibility of constructing a large-scale quantum network in the near future. [ABSTRACT FROM AUTHOR]

Quantum obfuscation is one of the important primitives in quantum cryptography that can be used to enhance the security of various quantum cryptographic schemes. The research on quantum obfuscation focuses mainly on the obfuscatability of quantum functions. As a primary quantum function, the quantum power function has led to the development of quantum obfuscation because it is applicable to construct new obfuscation applications such as quantum encryption schemes. However, the previous definition of quantum power functions is constrained and cannot be beneficial to the further construction of other quantum functions. Thus, it is essential to extend the definition of the basic quantum power function in a more general manner. In this paper, we provide a formal definition of two quantum power functions called generalized quantum power functions with coefficients, each of which is characterized by a leading coefficient and an exponent that corresponds to either a quantum or classical state, indicating the generality. The first is the quantum power function with a leading coefficient, and the second is the quantum n-th power function, which are both fundamental components of quantum polynomial functions. In addition, obfuscation schemes for the functions are constructed by quantum teleportation and quantum superdense coding, and demonstrations of their obfuscatability are also provided in this paper. This work establishes the fundamental basis for constructing more quantum functions that can be utilized for quantum obfuscation, therefore contributing to the theory of quantum obfuscation. [ABSTRACT FROM AUTHOR]

In the current scenario of information explosion, one of the growing concerns of scientists worldwide is to manage the information storage and transmission by realizing the novel and reliable means of secure communication of data and information. This is essential to avoid any threat of the breaching of secret information on the part of hackers during the communication. In this regard, in contrast to routine classical methods, state-of-the-art robust quantum methods of secure communication such as quantum cryptography and Internet of Things (IoTs) information via quantum coherence medium and quantum networking of IoTs are gaining immense interest. In this context, chiral atomic medium and 2D materials such as graphene have attracted tremendous research interest. This owes to their remarkable linear and nonlinear ultrafast response and tunable structural and optoelectronic properties, which have potential applications in quantum computing, quantum information processing, information storage, and secure communication of IoTs information. In this paper, we explore the potential of Landau-quantized graphene (LQG) for secure communication of IoTs information by investigating quantum coherence-based propagation of light and optical properties of LQG. We report on the tunable optical response of a newly-proposed four-level ladder-type LQG subject to a weak probe field in conjunction with two strong control fields. In particular, employing the density-matrix approach, we report on theoretical analysis of superluminal/subluminal and absorption-free light propagation via quantum coherence in view of tunable electromagnetically induced transparency. Based on the tunable optical response of LQG, we propose a quantum networking model for the secure communication of quantum information via IoTs quantum networking. [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]

Quantum physics has some unique properties, such as quantum entanglement and quantum superposition. Encryption algorithms designed based on quantum physical properties usually have higher security than classical computing. Applying quantum cryptography to data retrieval can realize cloud database encryption of quantum information. We propose a cloud ciphertext retrieval scheme, which combines quantum encryption and quantum search algorithm to ensure the privacy of data while the server completes information retrieval. In this scheme, the data are stored in the form of qubits string and placed in the quantum superposition state. We establish the mapping relationship between classical information and quantum states. Our scheme solves the problem of a large amount of computing and lack of sufficient computing resources at the client, assigns computing tasks to servers with sufficient resources, and ensures the security of information. [ABSTRACT FROM AUTHOR]

Quantum computing research might lead to "quantum leaps," and it could have unanticipated repercussions in the medical field. This technique has the potential to be used in a broad range of contexts, some of which include the development of novel drugs, the individualization of medical treatments, and the speeding of deoxyribonucleic acid sequencing. This work has assembled a list of the numerous methodologies presently employed in quantum medicine and other disciplines pertaining to healthcare. This work has created a list of the most critical concerns that need to be addressed before the broad use of quantum computing can be realized. In addition, this work investigates in detail the ways in which potential future applications of quantum computing might compromise the safety of healthcare delivery systems from the perspective of the medical industry and the patient‐centric healthcare system. The primary objective of this investigation into quantum cryptography is to locate any potential flaws in the cryptographic protocols and strategies that have only very recently been the focus of scrutiny from academic research community members. [ABSTRACT FROM AUTHOR]

As Mobile Communication and Internet Systems (MCIS) have rapidly developed, security issues related to MCIS have become increasingly important. Therefore, the development and research of security technologies for mobile communication and internet systems are actively being conducted. Hash-Based Signature (HBS) uses a hash function to construct a digital signature scheme, where its security is guaranteed by the collision resistance of the hash function used. To provide sufficient security in the post-quantum environment, the length of hash should be satisfied for the security requirement. Modern HBS can be classified into stateful and stateless schemes. Two representative stateful and stateless HBS are eXtended Merkle Signature Scheme(XMSS) and SPHINCS + , respectively. In this paper, we propose two HBS schemes: K-XMSS and K-SPHINCS + , which replace internal hash functions of XMSS and SPHINCS + with Korean cryptography algorithms. K-XMSS is a stateful signature, while K-SPHINCS + is its stateless counterpart. We showcase the reference implementation of K-XMSS and K-SPHINCS + employing Lightweight Secure Hash (LSH) and two hash functions based on block ciphers (i.e., CHAM and LEA) as the internal hash function. In addition, K-XMSS and K-SPHINCS + using Advanced Vector Extensions 2 (AVX2) have been provided, demonstrating that they can be optimized for better performance using advanced implementation techniques than previous approaches. [ABSTRACT FROM AUTHOR]

Quantum secure direct communication is an important branch of quantum cryptography. One of the main requirements of quantum secure direct communication is to ensure that no secret information can be stolen. Recently, a bidirectional quantum secure direct communication protocol [Quantum Information Processing 16, 147 (2017)] was proposed. It was believed that the intercept-and-resend attack and information leakage problem can be avoided via this protocol. However, in this paper, we point out that attackers can obtain useful information about the secret messages by constructing two intercept-and-resend attacks on the above protocol. Attackers can obtain Alice's secret message exclusive OR Bob's secret message by the first attack and both secret messages by the second attack. To resist the two constructed attacks, we design an improved bidirectional quantum secure direct communication protocol. Furthermore, we show that the designed protocol can resist the two constructed attacks and its efficiency has increased. It is interesting that the designed protocol can publish Alice's result states, i.e., Bob's initial states, without affecting its security. The designed protocol can prevent Alice (Bob) from obtaining Bob's (Alice's) secret message before Alice (Bob) sends her (his) secret message. This work can notice researchers to avoid similar security problems in constructing quantum cryptography protocols. [ABSTRACT FROM AUTHOR]

This work researches the implementation of the AES family with Pauli-X gates, CNOT gates and Toffoli gates as the underlying quantum logic gate set. First, the properties of quantum circuits are investigated, as well as the influence of Pauli-X gates, CNOT gates and Toffoli gates on the performance of the circuits constructed with those gates. Based on these properties and the observations on the hardware circuits built by Boyar et al. and Zou et al., it is possible to construct quantum circuits for AES's Substitution-box (S-box) and its inverse (S-box - 1 ) by rearranging the classical implementation to three parts. Since the second part is treated as a 4-bit S-box in this paper and can be dealt with by existing tools, a heuristic is proposed to search optimized quantum circuits for the first and the third parts. In addition, considering the number of parallelly executed S-boxes, the trade-offs between the qubit consumption and T · M values for the round function and key schedule of AES are studied. As a result, quantum circuits of AES-128, AES-192 and AES-256 can be constructed with 269, 333 and 397 qubits, respectively. If more qubits are allowed, quantum circuits that outperform state-of-the-art schemes in the metric of T · M value for the AES family can be reported, and it needs only 474, 538 and 602 qubits for AES-128, AES-192 and AES-256, respectively. [ABSTRACT FROM AUTHOR]

Comprehensive inquisition of wireless communication with flexible quantum electronics and physics can be considered as one of the blooming technology. Quantum Cryptography which extends from combination of quantum electronics and physics is one of the best technology that helps to transfer data securely between various user's, due to its rudimentary concept of Quantum Key Distribution (QKD). There are two major concerns in the communication. The first concern is for the data transmission which is frequently carried out through some entity of the cellular network such as Home subscriber Server (HSS) or Gateway (GW), and Evolved Node B(eNB), which is inadvisable to preserve confidentiality of the message. The second concern is, device-to-device (D2D) communication via prose function which is relatively a threat affected path that can be easily affected by the man in the middle (MitM) attack, message drop attack, replay attack, denial of service (DoS) attack, impersonation attack.. To mitigate these threats, this research work is proposing a Secure Authentication Protocol (SAP). The proposed SAP is categorized into 5 phases namely framework of network, enrolment phase, D2D discovery phase, key production—authentication phase and content conveyance phase. Framework of network phase generates function parameters. Enrolment phase registers all user equipment (UE) for verification and also generate an appropriate user application code for respective UE. In this phase, HSS also manages a database that contains detail about all the enrolled. D2D discovery phase allows the UE to discover the neighbors under that proximity area. During the authentication phase, public as well as private secret keys are generated using Elliptic Curve Cryptography (ECC) and Elliptic Curve Diffie-Hellman (ECDH) algorithm. In addition to that, this phase implements hash based message authentication code (HMAC) to create application associated keys. In the last phase of content conveyance, most important step is to share Shared Secret Key (SSK) as it mainly responsible while decrypting original message. To make this transmission very secure, quantum channel is used. Quantum Cryptography plays a vital role in this phase for providing security to whole transmission process at high level. Now a days, advanced optical technologies are also using quantum cryptography to establish secured communication. The performance of the proposed SAP is evaluated and compared with the existing protocols by using multiple evaluation criteria such as cost of operation, computational overhead, storage overhead and energy consumption. This article also provides insights into various security threats such as MitM, replay attack, DoS attack, impersonation attack, known key attack due to use of ECC and ECDH. Also, SAP provides a strong pillar against eavesdropping attack due to quantum cryptography. Also, Bennett and Gilles Brassard (BB84) protocol linked with quantum electronics and physics, place a significant role for creation of quantum channel over classical channel, which took security of SAP at next level. [ABSTRACT FROM AUTHOR]

In this study, the security implications of utilizing the concept of entanglement in time in the quantum representation of a blockchain data structure are investigated. The analysis reveals that the fundamental idea underlying this representation relies on an uncertain interpretation of experimental results. A different perspective is provided by adopting the Copenhagen interpretation, which explains the observed correlations in the experiment without invoking the concept of entanglement in time. According to this interpretation, the qubits responsible for these correlations are not entangled, posing a challenge to the security foundation of the data structure. The study incorporates theoretical analysis, numerical simulations, and experiments using real quantum hardware. By employing a dedicated circuit for detecting genuine entanglement, the existence of entanglement in the process of generating a quantum blockchain is conclusively excluded. [ABSTRACT FROM AUTHOR]

Privacy comparison is an important research topic in secure multi-party computing, widely used in e-commerce, secret ballots, and other fields. However, the development of quantum computing power poses a growing potential security threat to secure multi-party algorithms based on mathematically tricky problems, and most of the proposed quantum privacy comparison schemes could be more efficient. Therefore, based on the W-state, we offer a more efficient semi-quantum privacy comparison method. The security analysis shows that the scheme can resist third-party, measurement, and entanglement attacks. Compared with the previous work, the scheme significantly improves communication efficiency and has stronger practicability. [ABSTRACT FROM AUTHOR]

Artificial intelligence (AI) is a modern technology that allows plenty of advantages in daily life, such as predicting weather, finding directions, classifying images and videos, even automatically generating code, text, and videos. Other essential technologies such as blockchain and cybersecurity also benefit from AI. As a core component used in blockchain and cybersecurity, cryptography can benefit from AI in order to enhance the confidentiality and integrity of cyberspace. In this paper, we review the algorithms underlying four prominent cryptographic cryptosystems, namely the Advanced Encryption Standard, the Rivest–Shamir–Adleman, Learning with Errors, and the Ascon family of cryptographic algorithms for authenticated encryption. Where possible, we pinpoint areas where AI can be used to help improve their security. [ABSTRACT FROM AUTHOR]

Information security is a fundamental and urgent issue in the digital transformation era. Cryptographic techniques and digital signatures have been applied to protect and authenticate relevant information. However, with the advent of quantum computers and quantum algorithms, classical cryptographic techniques have been in danger of collapsing because quantum computers can solve complex problems in polynomial time. Stemming from that risk, researchers worldwide have stepped up research on post-quantum algorithms to resist attack by quantum computers. In this review paper, we survey studies in recent years on post-quantum cryptography (PQC) and provide statistics on the number and content of publications, including a literature overview, detailed explanations of the most common methods so far, current implementation status, implementation comparisons, and discussion on future work. These studies focused on essential public cryptography techniques and digital signature schemes, and the US National Institute of Standards and Technology (NIST) launched a competition to select the best candidate for the expected standard. Recent studies have practically implemented the public key encryption/key encapsulation mechanism (PKE/KEM) and digital signature schemes on different hardware platforms and applied various optimization measures based on other criteria. Along with the increasing number of scientific publications, the recent trend of PQC research is increasingly evident and is the general trend in the cryptography industry. The movement opens up a promising avenue for researchers in public key cryptography and digital signatures, especially on algorithms selected by NIST. [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]

Public-key cryptography has become a popular way to motivate the teaching of concepts in elementary number theory, abstract algebra, and introduction to proof courses, as well as in cryptography courses. Unfortunately, many experts expect quantum computers to make common forms of public-key cryptography obsolete in the near future. Fortunately, there are several systems being evaluated to replace RSA and the other systems we currently use. While some of the systems are too complicated to be good examples in introductory courses, others are either quite manageable or have simplified versions that are manageable. This article gives a tour of the main types of systems under consideration and the teaching resources available for instructors who want to teach them. [ABSTRACT FROM AUTHOR]

Based on three-particle pure states, a new anonymous semi-quantum privacy comparison is proposed to deal with the threat of quantum computing power faced by users without complete quantum capabilities in the post-quantum era. In this scheme, quantum entanglement and quantum uncertainty principles are used to ensure third party security, measurement attack security and entanglement attack security. Compared with most semi-quantum privacy comparison schemes, it reduces the risk of TP evil and improves communication efficiency. Therefore, the scheme has stronger safety and higher efficiency. [ABSTRACT FROM AUTHOR]

Quantum secret sharing is one of the important techniques in quantum cryptography. In this paper, we propose a novel dynamic hierarchical quantum secret sharing scheme with general access structure. Participants from different levels share the same secret. Firstly, a special hierarchical structure based on the generalized GHZ state is constructed, which expands the application value of the existing hierarchical quantum secret sharing. Secondly, this paper uses the monotone span program (MSP) and the generalized Pauli operator to realize the dynamic property of the scheme, which includes three aspects: The hierarchical access structure is variable; participants can join or leave, and the shared secret can be updated. Moreover, the shares of the participants can be protected so as to reduce communication consumption due to reuse of the shares. Finally, compared with other hierarchical quantum secret sharing schemes, the proposed scheme is not only more flexible but also more secure. [ABSTRACT FROM AUTHOR]

Quantum one-way function provides security for cryptographic protocols in quantum cryptography. Full quantum one-way function is a type of quantum one-way function that maps between quantum states and deals with pure quantum information. It was initially proposed by means of concatenating 'quantum–classical' and 'classical–quantum' quantum one-way functions. The first full quantum one-way function can be applied to quantum authentication, which uses quantum states to authenticate quantum states directly. However, the concatenation format restricts the implementation and cryptographic applications of this function. Considering the advantage of quantum circuit optimization in implementing quantum circuits to physical quantum devices, we propose a dynamic full quantum one-way function based on quantum circuit mapping. Quantum circuit optimization intrinsically generates the remapped quantum circuit which maps between quantum states but does not destroy them. The dynamic process of quantum circuit mapping contributes to the one-wayness of the dynamic full quantum one-way function. The experimental results show that this function is more realizable than the concatenated full quantum one-way function. The dynamic full quantum one-way function can be employed to construct a full quantum trapdoor one-way function which is 'easy to compute and invert' based on a trapdoor. Meanwhile, this new full quantum one-way function is proved to be very useful in quantum cryptography, especially in quantum currency notes. Our work promotes the development from full quantum one-way functions to future quantum cryptographic applications. [ABSTRACT FROM AUTHOR]

Summary: Human‐centered systems play an important role in the modern world, for example, driverless car, autonomous and smart vehicles, drones, and robotics. The internet of things environment demands a faster real‐time response depending on the applications processed in a particular duration. Mobile edge computing (MEC) allows a user to get a real‐time response as compared with cloud computing (CC), although ensuring a number of security attributes in MEC environment remains challenging. In this article, a protocol is designed to achieve mutual authentication, anonymous communication, and security against traceability, as these are very crucial factors to ensure the security of data and user's privacy. Moreover, the proposed scheme ensures mutual authentication between a mobile user and an edge server along with the user's anonymity and untraceability. The proof of security and evaluation of performance of the scheme validates that it ensures security attributes and improves efficiency in terms of communication and computation overheads. [ABSTRACT FROM AUTHOR]

Handover authentication and key agreement protocol is extremely essential to ensure the security of the Internet of Things (IoT), and it enables mobile devices to access roaming services in the trust domain of the foreign agent. The energy and computing capabilities of mobile devices are extremely limited, and the requirements for storage and computing efficiency are higher in IoT. The problem of large integer decomposition and discrete logarithm can be solved in polynomial time on a quantum computer, which makes the massive traditional handover authentication and key agreement protocols based on bilinear pairing and elliptic curve cryptography no longer safe. Due to the participation of the home agent, the traditional handover authentication protocol has a long communication delay and is vulnerable to the session key compromise attacks. Moreover, the session key between the foreign agent and the home agent is randomly specified in advance, and its generation process is not given, which has poor security and is easy to cause the leakage of the session key. Lattice cipher based on NTRU is the lightweight public key primitive that can resist quantum attacks and has a faster calculation speed and smaller key length, which is more suitable for IoT. Therefore, we proposed a secure and lightweight two-party handover authentication protocol based on NTRU for the mobile device without the home agent to prevent these deficiencies. We employ the BAN logic to validate the correctness of the proposed protocol and utilize the random oracle model to evaluate the security of the proposed protocol. In contrast with other current handover authentication protocols, the proposed protocol has greater security, higher efficiency, and lower communication overhead. [ABSTRACT FROM AUTHOR]

As an important practical cryptographic protocol, quantum key distribution (QKD)-based quantum private query (QPQ) has gained widespread attention in the past few decades. However, many of these protocols require classical post-processing, and the number of transmitted qubits is often much larger than the size of the database. Recently, Zhou et al. proposed a QPQ protocol that uses the W state and relies on a third party, which only requires qubits of the same size as the database [37]. Unfortunately, we have discovered a potential attack strategy against this protocol. By using fake entangled photons, a dishonest third party may be able to compromise the privacy of both the database owner and the user. To address this security vulnerability, we propose an improved QPQ protocol. [ABSTRACT FROM AUTHOR]

The rise of modern cryptographic protocols such as Zero-Knowledge proofs and secure Multi-party Computation has led to an increased demand for a new class of symmetric primitives. Unlike traditional platforms such as servers, microcontrollers, and desktop computers, these primitives are designed to be implemented in arithmetical circuits. In terms of security evaluation, arithmetization-oriented primitives are more complex compared to traditional symmetric cryptographic primitives. The arithmetization-oriented permutation Grendel employs the Legendre Symbol to increase the growth of algebraic degrees in its nonlinear layer. To analyze the security of Grendel thoroughly, it is crucial to investigate its resilience against algebraic attacks. This paper presents a preimage attack on the sponge hash function instantiated with the complete rounds of the Grendel permutation, employing algebraic methods. A technique is introduced that enables the elimination of two complete rounds of substitution permutation networks (SPN) in the sponge hash function without significant additional cost. This method can be combined with univariate root-finding techniques and Gröbner basis attacks to break the number of rounds claimed by the designers. By employing this strategy, our attack achieves a gain of two additional rounds compared to the previous state-of-the-art attack. With no compromise to its security margin, this approach deepens our understanding of the design and analysis of such cryptographic primitives. [ABSTRACT FROM AUTHOR]

Guesswork is an information–theoretic quantity which can be seen as an alternate security criterion to entropy. Recent work has established the theoretical framework for guesswork in the presence of quantum side information, which we extend both theoretically and experimentally. We consider guesswork when the side information consists of the BB84 states and their higher-dimensional generalizations. With this side information, we compute the guesswork for two different scenarios for each dimension. We then performed a proof-of-principle experiment using Laguerre–Gauss modes to experimentally compute the guesswork for higher-dimensional generalizations of the BB84 states. We find that our experimental results agree closely with our theoretical predictions. This work shows that guesswork can be a viable security criterion in cryptographic tasks and is experimentally accessible in a number of optical setups. [ABSTRACT FROM AUTHOR]

Quantum teleportation is one of the fundamental primitives of quantum cryptography. In order to achieve a wider range of high-capacity information transfer, we propose a free-space quantum teleportation (QT) protocol with orbital angular momentum (OAM) multiplexed continuous variable (CV) entangled states. The preparation of the entangled states is accomplished by the spontaneous four-wave mixing (SFWM) process occurring in a hot 85 Rb vapor cell, and the mode selection for the Bell-state measurement is achieved by employing the balanced homodyne detection technique. The fidelity of teleporting EPR entangled states carrying different topological charges via a Kolmogorov-type atmospheric turbulence channel is derived, and the superiority of enhancing the system channel capacity via OAM multiplexing is demonstrated. Our work provides a feasible scheme to implement high-capacity quantum communication in atmospheric environments. [ABSTRACT FROM AUTHOR]

Multiparty quantum private comparison (MQPC) protocol enables the comparison of the private information of n parties through the combination of quantum mechanics with classical private comparison. In order to improve efficiency and practicality, this paper proposes an efficient MQPC protocol based on single photons and rotation encryption with the assistance of a semi-honest third party (TP). TP participates in preparing the initial single photon sequence, which is encrypted and sent to the participants one by one. The private inputs of participants are encoded into particular rotation angles that are used to convert the received single photon sequence to an unknown quantum state sequence, which is returned to TP in a closed-loop transfer mode. By implementing rotation encryption and multiplexing of single photons, the qubit efficiency and practicality of the protocol can be significantly improved, without the need for complex quantum technologies, such as entanglement swapping of high-dimensional quantum states, maximal entanglement states with n-particle and entanglement correlation between various particles in a quantum state. Moreover, the proposed protocol is simulated on IBM Quantum Experience to show its feasibility. Security analysis demonstrates that the proposed protocol is resistant to different types of attacks. [ABSTRACT FROM AUTHOR]

Quantum information stored in a qubit is rapidly lost to the environment. The realization of robust qubits is one of the most important challenges in quantum computing. Herein, we propose to embed a logical qubit within the manifold of a qudit as a scheme to preserve quantum information over extended periods of time. Under identical conditions (e.g., decoherence channels), the submanifold of the logical qubit exhibits extended lifetimes compared to a pure two-level system (qubit). The retention of quantum information further improves with separation between the sublevels of the logical qubit. Lifetime enhancement can be understood in terms of entropy production of the encoding and nonencoding subspaces during evolution under a quantum map for a d-level system. The additional pathways for coherent evolution through intermediate sublevels within a d-level manifold provide an information-preserving mechanism: reversible alternative channels to the irreversible loss of information to the environment characteristic of open quantum systems. [ABSTRACT FROM AUTHOR]

In this paper, we prove the unconditional security of a single-state circular mediated semi-quantum key distribution protocol. It starts with a third-party quantum server, TP, sending a string of qubits sequentially through two classical users Alice and Bob, and finally back to TP. We derive an expression for the key rate in the asymptotic scenario. When the communication parties Alice and Bob observe that the error rate is less than a determined threshold, the key rate is always greater than 0, so they can distill a string of secure secret keys. At the end of this paper, we extend this protocol to the multiple users case, where more than two classical users establish a string of security keys. [ABSTRACT FROM AUTHOR]

SHA-2 is a cryptographic hash function used worldwide. The possibility of attacks that exploit quantum computers can no longer be ignored; therefore, it is necessary to verify how the emergence of quantum computers could affect the security of SHA-2. The results of research conducted by my colleague and I indicate--as a world's first--that in a world in which quantum computers are available, the number of breakable steps in a collision attack on SHA-2 will increase. [ABSTRACT FROM AUTHOR]

Proving the non-existence of something is a difficult proposition called "the devil's proof." However, quantum mechanics can be used to prove that private keys used in functional encryption have been deleted (do not exist). It can also be used to prevent duplication of private keys. In this article, the method that my research colleague and I proposed at an international conference held by the International Association for Cryptologic Research in 2022 is overviewed, and the innovations expected when this method is implemented are described. [ABSTRACT FROM AUTHOR]