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Journal of Experimental and Theoretical Physics Letters

Integration of quantum cryptography into fiber-optic telecommunication systems

S. N. Molotkov

Published Jun 1, 2004• 3 citations
Publisher

Abstract

The prototype of a new quantum cryptosystem is described. Such a cryptosystem is naturally called time-shift quantum cryptography. It realizes all basic quantum-cryptography protocols [BB84, B92, BB84(4+2)] in a common fiber-optic system. This scheme does not involve Mach-Zehnder interferometers, which enables one to naturally realize the multiplex mode of secure key distribution and to naturally integrate this quantum-cryptography scheme into traditional fiber-optic telecommunication systems. The proposed time coding method in quantum cryptography makes it possible to significantly simplify experimental schemes and to exclude the finest fiber-optic part, the interferometer. In essence, the fundamental difference of the time coding method from the phase coding method is that the part using phase relations in superposition between “parts” of a quantum state is eliminated from the phase-coding method, and only the part using the time division principle is retained. The time division principle is common for both methods and is minimally necessary, in contrast to the phasecoding method, which can be excluded altogether. The proposed scheme is briefly compared with the two most developed phase-coding schemes (without self-compensation and with passive self-compensation).

DOI
10.1134/1.1787106

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The prototype of a new quantum cryptosystem is described. Such a cryptosystem is naturally called time-shift quantum cryptography. It realizes all basic quantum-cryptography protocols [BB84, B92, BB84(4+2)] in a common fiber-optic system. This scheme does not involve Mach-Zehnder interferometers, which enables one to naturally realize the multiplex mode of secure key distribution and to naturally integrate this quantum-cryptography scheme into traditional fiber-optic telecommunication systems. The proposed time coding method in quantum cryptography makes it possible to significantly simplify experimental schemes and to exclude the finest fiber-optic part, the interferometer. In essence, the fundamental difference of the time coding method from the phase coding method is that the part using phase relations in superposition between “parts” of a quantum state is eliminated from the phase-coding method, and only the part using the time division principle is retained. The time division principle is common for both methods and is minimally necessary, in contrast to the phasecoding method, which can be excluded altogether. The proposed scheme is briefly compared with the two most developed phase-coding schemes (without self-compensation and with passive self-compensation).
Three fundamentally new experimental prototypes of optical fiber quantum-cryptography schemes are described. They are appreciably simpler than the available prototypes, contain fewer optical fiber components, and do not require adjustment during key generation. These cryptosystems can naturally be called quantum time-shift cryptography. They realize the B92 protocol and use a pair of nonorthogonal single-photon states as information states. One such scheme does not use fiber-optic Mach-Zehnder interferometers and, therefore, provides natural realization of the multiplex secure-key distribution regime.
A new scheme of experimental quantum cryptography on the nonorthogonal states is described. Nonorthogonality is achieved by the time shift of states in different messages. For this scheme to be efficient, it is sufficient to balance the arms of an interferometer at the receiver and transmitter ends to an accuracy of 1–2 cm. This is a fundamental advantage of this scheme over, e.g., the most developed cryptosystem based on phase coding, where the maximum transmission distance has been achieved. In the latter system, the arms of the interferometer need to be balanced with an accuracy of fractions of a micron for a distance of several tens of kilometers.
The main goals of cryptography are the encryption of messages to render them unintelligible to third parties and the authentication of messages to certify that they have not been modified. These goals can be accomplished if the sender ("Alice") and recipient ("Bob") both possess a secret random binary digit (bit) known as "key". It is essential that Alice and Bob acquire the key material with a high level of confidence that any third party ("Eve") does not have even partial information about the random bit sequence. If Alice and Bob communicate solely through classical messages (as opposed to Quantum cryptography), it is impossible for them to generate a certifiably secret key. QKD are the new generation of cryptographic systems which allow two remote parties (Alice and Bob) to generate a secret key with privacy guaranteed by quantum mechanics. They generate a random key securely over an optical fiber connection (also known as Quantum channel). This random key is then used for encryption and decryption of confidential messages, which then can be sent in encrypted form over any non-secure communication channel. In this thesis, we study two fiber-based QKD systems namely "oneway" and "two-way". Both systems have their unique advantage which distinguish them to one another. In one-way, the complexity of the electronic system may reduce. However more attention has to be made on the optical setup due to the requirement of active compensation. In the two-way, the requirement of optical setup may reduce but the attention moves to the electronic system which requires precise and short pulse especially for high speed in Alice system configuration. Our developed prototype is capable to support either one-way and two-way QKD system. We also solved some of the issues from the previous prototype Kumar [2008] which limited the system to be used in high speed. For instance: the synchronization system now uses a single synchronization signal per frame; the frame initialization time delay is reduced to 140ms per frame; pulse shaping distortion due to current consumption. We also introduced the security perspective for B92 protocol with uninformative states. This is done by utilizing the security analysis for BB84 such as entanglement distillation protocol (EDP) [...], smooth Ra'©nyi entropy [...] and composable security [...]. Numerous proposal on smooth Ra'©nyi entropy as general case [...] either for finite security analysis [...] or in asymptotic limit [...] assist us to deduce finite security perspective for B92 with uninformative states. [...] This thesis is organized as follow, initially starts with a general introduction to the cryptography and its relation with quantum cryptography. This is elaborated in Chapter One. In the Second Chapter we will go through the background of quantum mechanics and quantum information and introduce some parameters and theory mostly used in Quantum Key Distribution. These include quantum measurement, state behavior and the security analysis parameters. The second chapter will give the background concepts for the QKD in perspective of quantum information. The Third Chapter will explore more detailed information towards QKD. It starts with the basic architecture algorithm of the quantum cryptography system and details each components of the architecture. Later we focus on the security analysis specifically for the B92 protocol. Finally in the chapter, we will make some finite element analysis for the B92 protocol with uninformative states. In Chapter Four and onwards, we are discussing the experimental implementation and analysis. We begin with the heart of our system which is the field programmable gate array (FPGA) system. We explain the detailed architecture of our FPGA system and how the system works. The module that we develop in our FPGA system in order to work inside the QKD system is also explained in detail. We reserve the modification and advanced work of this system for the future by giving the original codes in the Appendix A. Chapter Five is one of the shortest chapters in this thesis. This chapter explains our electronic development and the opto-electronic device which are used in the QKD system. The main device that we develop for the QKD system is our Mezzanine board for FPGA. This mezzanine board supports some functions that are not available from the FPGA in order to make the system functional. Other developments include opto-electronic board and proportional-integral-derivative (PID) controller with the current driver. Chapter Six is the main experimental part. In this Chapter we start to give the introduction to our optical setup. We detail out our configuration of the setup and finally show our results taken from experimental work. Finally in Chapter Seven we conclude our work and purposed future work which actually need to done for the system.
The problem of unconditional security of quantum cryptography (i.e. the security which is guaranteed by the fundamental laws of nature rather than by technical limitations) is one of the central points in quantum information theory. We propose a relativistic quantum cryptosystem and prove its unconditional security against any eavesdropping attempts. Relativistitic causality arguments allow to demonstrate the security of the system in a simple way. Since the proposed protocol does not empoly collective measurements and quantum codes, the cryptosystem can be experimentally realized with the present state-of-art in fiber optics technologies. The proposed cryptosystem employs only the individual measurements and classical codes and, in addition, the key distribution problem allows to postpone the choice of the state encoding scheme until after the states are already received instead of choosing it before sending the states into the communication channel (i.e. to employ a sort of "antedate" coding).
The exponential growth of global telecommunication networks has heightened the need for robust security frameworks to protect data transmission against evolving cyber threats.Traditional encryption techniques, such as RSA and AES, while effective, are increasingly vulnerable to advances in computational power and the impending threat posed by quantum computing.Quantum cryptography, specifically Quantum Key Distribution (QKD), presents a revolutionary approach to securing telecommunication systems by leveraging the fundamental principles of quantum mechanics.Unlike classical encryption methods, QKD guarantees data security through the use of quantum states that are inherently resistant to interception and eavesdropping due to the no-cloning theorem and Heisenberg's uncertainty principle.From a broader perspective, this paper explores the integration of quantum cryptographic protocols into existing telecommunication infrastructures, emphasizing their potential to safeguard data transmission in fiber-optic and satellite communication networks.It examines the architecture and operational mechanisms of QKD systems, detailing protocols such as BB84 and E91, and evaluates their effectiveness in countering both classical and quantum-enabled cyber-attacks.Additionally, the study delves into the challenges of large-scale deployment, including key distribution range limitations, hardware requirements, and the need for quantum repeaters to support long-distance secure communication.Narrowing the focus, case studies on the implementation of quantum cryptography in 5G networks and global telecommunication hubs are analysed, highlighting their role in enhancing network resilience and ensuring end-to-end encryption.The paper concludes with strategic recommendations for policy development, international standardization, and future research directions to facilitate the widespread adoption of quantum cryptography in the telecommunications sector.