Currently, theoretical and experimental work in the field of quantum cryptography is being carried out in many research centers around the world. Over the past two decades since the start of active research, many quantum cryptographic protocols have been proposed, a significant number of laboratory experiments have been performed on their practical implementation, important work has been done to prove the resistance of the proposed protocols to certain types of attacks, and the first commercial quantum key distribution systems have been developed. However, there are still many tasks and problems in the field of quantum cryptography, the solution of which is of great scientific and technical importance. So, in particular, such a promising direction as quantum protocols for direct secure communication requires further development, allowing, under certain conditions, to transfer secret information without encryption, both between two and between a large number of users. Currently, such protocols have been developed using two-and three-particle entangled states, but there are almost no similar protocols with entangled states of a larger number of qubits that do not require large quantum memory for their implementation and, at the same time, have a large information capacity. Therefore, the development of new quantum direct secure communication protocols with increased information capacity, the analysis of their resistance to attacks, as well as the determination of the best protocols according to the criteria of resistance and information capacity.
Currently, theoretical and experimental work in the field of quantum cryptography is being carried out in many research centers around the world. Over the past two decades since the start of active research, many quantum cryptographic protocols have been proposed, a significant number of laboratory experiments have been performed on their practical implementation, important work has been done to prove the resistance of the proposed protocols to certain types of attacks, and the first commercial quantum key distribution systems have been developed. However, there are still many tasks and problems in the field of quantum cryptography, the solution of which is of great scientific and technical importance. So, in particular, such a promising direction as quantum protocols for direct secure communication requires further development, allowing, under certain conditions, to transfer secret information without encryption, both between two and between a large number of users. Currently, such protocols have been developed using two-and three-particle entangled states, but there are almost no similar protocols with entangled states of a larger number of qubits that do not require large quantum memory for their implementation and, at the same time, have a large information capacity. Therefore, the development of new quantum direct secure communication protocols with increased information capacity, the analysis of their resistance to attacks, as well as the determination of the best protocols according to the criteria of resistance and information capacity.
The development of modern computer technologies endangers the confidentiality of information, which is usually ensured by traditional cryptographic means. This circumstance forces us to look for new methods of protection. In view of modern trends, quantum cryptography methods can become such alternatives, which allow solving a number of important cryptographic problems, for which the impossibility of solving using only classical (that is, non-quantum) communication has been proven. Quantum cryptography is a branch of quantum informatics that studies methods of protecting information by using quantum carriers. The possibility of such protection is ensured by the fundamental laws of quantum mechanics. One of the promising directions of quantum cryptography is Quantum Secure Direct Communication (QSDC) that offers secure communication without any shared key. A characteristic feature of this method is the absence of cryptographic transformations, accordingly, there is no key distribution problem. The purpose of this work is a general overview of quantum cryptography protocols, finding their weak points for further development and improvement, as well as identifying vulnerabilities to different attacks. The article analyzes new methods and protocols, as well as presents their advantages and disadvantages. Based on partial generalizations of theoretical provisions and practical achievements in the field of quantum cryptography, a generalized classification was developed. By comparing various factors of the protocols, and their resistance to certain cyberattacks, we have the opportunity to identify several problems in this field and expand the possibilities for choosing appropriate methods for building modern quantum information protection systems. In accordance with this, conclusions were presented regarding the use of protocols and increasing the level of their effectiveness.
Quantum cryptography promises secure communication protocols that surpass the limitations of classical cryptography. By leveraging the principles of quantum mechanics, particularly the phenomenon of quantum entanglement and the uncertainty principle, quantum cryptography protocols offer provable security guarantees against eavesdropping attacks. In this paper, we provide an overview of quantum cryptography, discussing its theoretical foundations, key protocols such as quantum key distribution (QKD), and experimental implementations. We highlight the advantages of quantum cryptography over classical cryptographic techniques and explore its potential applications in secure communication networks, financial transactions, and data privacy. Furthermore, we discuss ongoing research efforts and challenges in the practical deployment of quantum cryptography systems, including the development of robust quantum hardware and the integration of quantum cryptographic protocols into existing communication infrastructures. Overall, quantum cryptography holds great promise for enabling secure communication channels that are resilient to quantum attacks, paving the way for a new era of ultra-secure information exchange.
Over the last few decades, quantum cryptography has been one of the most important quantum technologies developed. It holds the promise of communicating secure information over untrusted channels. In particular, quantum cryptography is immune to the eventual threats posed by large-scale quantum computers, which is not the case for our current classical cryptography infrastructures. In a world where information, communication and privacy are of paramount importance, the development of secure quantum communication infrastructures becomes imperative. So far, most of the quantum cryptographic systems developed to date are based on two-dimensional encoding schemes, analogous to classical bits, known as qubits. Nevertheless, other than for the polarization of light, photonic degrees of freedom, i.e. position, momentum, time and frequency, naturally occur as high-dimensional quantum systems. Moreover, by considering high-dimensional encoding schemes beyond qubits, advantages in terms of information capacity and noise tolerance are predicted in theory. In this thesis, the basic components of a high-dimensional quantum cryptographic system are investigated. We begin by reviewing important developments in quantum cryptography and high-dimensional quantum information. As a starting point, two different quantum information tasks, i.e. optimal quantum cloning and quantum metrology, are experimentally investigated for high-dimensional quantum systems in order to demonstrate the numerous advantages of performing quantum tasks beyond qubits. The photonic degree of freedom used in these experiments, known as transverse spatial modes, is obtained by combining the position and momentum photonics degrees of freedom. Thus, we develop a novel method to measure high-dimensional quantum states encoded in arbitrary spatial modes. Using a similar characterization technique, several high-dimensional quantum communication channels are characterized to perform high-dimensional quantum cryptography. The tools developed in the laboratory are then brought to realistic conditions in order to test the feasibility of high-dimensional quantum cryptography. Two different types of quantum channels are experimentally investigated, namely an intra-city 300 m long free-space link and a short 3 m outdoor underwater link. Finally, we investigate and compare novel high-dimensional protocols to overcome current limitations.
Quantum entanglement is a fundamental and intriguing phenomenon in quantum mechanics, wherein two or more particles become correlated in such a way that the state of one instantaneously influences the state of the other, regardless of the distance separating them. This research delves into the theoretical foundation of quantum entanglement, exploring its mathematical formulation, key experimental validations, and implications for emerging technologies. A primary focus is placed on its application in secure communication, particularly in Quantum Key Distribution (QKD), where entanglement enables fundamentally secure cryptographic protocols resistant to eavesdropping. We present an in-depth analysis of various QKD protocols, including BB84, E91, and decoy-state methods, assessing their security, efficiency, and practical feasibility. Recent experimental advancements in entanglement-based cryptography are examined, alongside real-world implementations and their technical challenges, such as photon loss, decoherence, and scalability in long-distance quantum communication networks. Additionally, we provide comparative insights into the efficiency of different QKD protocols using a bar chart, while figures and tables illustrate core quantum principles and experimental setups. By addressing both theoretical and practical aspects, this study contributes to a comprehensive understanding of quantum entanglement’s role in secure communication and highlights future directions for overcoming existing technological limitations.
ABSTRACT. The combination of physics, mathematics, and computer science in quantum computing has developed from a visionary idea to one of the most fascinating and promising areas of quantum mechanics in the past two decades. Research in the field of quantum cryptography promises extremely fast, robust, and impenetrable electronic and photonic security; almost unbreakable! Moreover, the long standing eavesdropping problem of the “man in the middle ” attack may finally be solved once and for all. As computing power increases, and as hackers and attackers become more sophisticated, it is feared that sooner or later, traditional cryptography based on mathematically intractable algorithms may be no match for parallelized quantum based processors. For this reason, quantum cryptography, based on the laws of quantum statistical mechanics provides a welcome solution to this fear. This paper explores the basic tenets of quantum cryptography and how the mathematical principles therein apply to the quantum key distribution problem; a central concern in the implementation of quantum cryptography in distributed networks. The quantum key distribution protocol implemented in BB84 protocol is also described and compared to traditional cryptographic systems. A short overview of recent commercial implementations of quantum cryptography is presented with the encountered successes and limitations discussed. This paper explores the development of quantum networks, from the onset of the development of secure communication based on quantum cryptography and concludes with a brief outline of the key challenges facing quantum cryptography implementation in wireless applications and long haul communications.
Quantum cryptography has emerged as a revolutionary technology for ensuring secure communication in the era of quantum computing. While existing research primarily focuses on theoretical frameworks and small-scale experimental setups, significant challenges remain in practical implementation, scalability, and security vulnerabilities. This study aims to bridge the gap between theory and real-world deployment by developing robust quantum cryptographic protocols that address key challenges such as noise management, side-channel attacks, and Trojan horse attacks. Additionally, we propose an optimized quantum key distribution (QKD) mechanism that ensures secure communication over long distances under realistic conditions. Our research integrates post-quantum cryptography with quantum cryptographic techniques to provide a hybrid security model that is resilient against both classical and quantum computing threats. By leveraging commercially available quantum hardware and advanced randomness extraction methods, this study contributes to the development of scalable, secure, and efficient quantum communication networks. The findings of this research will play a crucial role in advancing secure digital communication systems and fortifying data security in the post-quantum era.