Cryptographic key formation in coupled transmit-receiving atmospheric laser systems
Evgenia S. Abramova, E. V. Adamov, V. P. Aksenov, E. A. Bogach, Vadim V. Dudorov, Valeriy V. Kolosov, Mikhail E. Levitsky, Cheslav E. Pogutsa, Ivan I. Pavlov
The security of transmission and retrieval depends on the encryption of information sent over public networks. At present, approaches to data protection based on cryptography methods using one-way mathematical functions are widely used. Symmetric and asymmetric methods of key transmission over open communication channels have been developed. The stability of information protection methods using one-way mathematical functions is based on the algorithmic complexity of their hacking for modern computers. The emergence of quantum computers of sufficient power will radically change the situation. Therefore, at present, the question of developing methods for distributing cryptographic keys based on new principles is acute. Such methods include quantum cryptography and cryptography based on stochastic physical processes. In this work, a brief review of the key generation methods based on the principles of quantum physics is carried out, and then the possibility of using fluctuations of the received radiation power caused by atmospheric turbulence to generate keys is investigated. Numerical and experimental modeling of the process of wave propagation in a system of two coupled transceivers operating in a turbulent medium (atmosphere) has been performed. For this purpose, appropriate algorithms for numerical simulation of the characteristics of optical fields distorted by the atmospheric propagation channel have been developed. An experimental setup has been developed and a model experimental study of the formation of correlated random signals in transmit-receive laser systems has been carried out. The need to use low-frequency filtering of the received signals was found. The efficiency of this filtration has been studied. The results of the work allow us to conclude that the use of atmospheric turbulence as a random signal generator makes it possible to form an almost identical cryptographic key in two communication channels directed towards each other.
The security of transmission and retrieval depends on the encryption of information sent over public networks. At present, approaches to data protection based on cryptography methods using one-way mathematical functions are widely used. Symmetric and asymmetric methods of key transmission over open communication channels have been developed. The stability of information protection methods using one-way mathematical functions is based on the algorithmic complexity of their hacking for modern computers. The emergence of quantum computers of sufficient power will radically change the situation. Therefore, at present, the question of developing methods for distributing cryptographic keys based on new principles is acute. Such methods include quantum cryptography and cryptography based on stochastic physical processes. In this work, a brief review of the key generation methods based on the principles of quantum physics is carried out, and then the possibility of using fluctuations of the received radiation power caused by atmospheric turbulence to generate keys is investigated. Numerical and experimental modeling of the process of wave propagation in a system of two coupled transceivers operating in a turbulent medium (atmosphere) has been performed. For this purpose, appropriate algorithms for numerical simulation of the characteristics of optical fields distorted by the atmospheric propagation channel have been developed. An experimental setup has been developed and a model experimental study of the formation of correlated random signals in transmit-receive laser systems has been carried out. The need to use low-frequency filtering of the received signals was found. The efficiency of this filtration has been studied. The results of the work allow us to conclude that the use of atmospheric turbulence as a random signal generator makes it possible to form an almost identical cryptographic key in two communication channels directed towards each other.
Abstract The potentials for and limitations to the use of intensity fluctuations of laser beams propagating through a turbulent atmosphere for generating random data when keying in confidential optical communication systems are analyzed. The technique is based on the reciprocity theorem for optical fields. Light propagation in a system of two transceivers directed at each other, the signals from which are distorted by an atmospheric channel, is numerically simulated. An experimental setup is created; the generation of random correlated signals in this system is experimentally studied. A need for low-pass filtration of signals received is experimentally ascertained. The efficiency of this filtration is estimated. The dependences of the correlation coefficient on the geometrical parameters of the system and turbulent conditions along the propagation path are derived from the numerical simulation in a wide range of distances, aperture radii, and turbulence strength values. Theoretical results are shown to be in a good agreement with the results of laboratory experiments.
Subject of study. An optical system, composed of transmitting and receiving telescopes, was designed for quantum key distribution, based on the subcarrier wave modulation method, over an atmospheric channel. Aim of study. The aim of the study was to develop an optical system that allowed the use of single-mode fibers as the input and output of the system, ensured the transmission of an ultralow-power optical signal without introducing additional distortion, and implemented a protocol for distributing a quantum key over an atmospheric optical communication channel at a distance of up to 25 m. Method. An experimental setup with an atmospheric quantum communication channel was developed, which showed stable quantum key distribution without interruptions throughout the measurement process. Radiation propagation simulations were also performed to estimate the insertion loss of the optical signal. Main results. Simulations revealed that the optical losses in the quantum key distribution system amounted to approximately 17 dB. The atmospheric communication channel was studied at distances of 5, 10, and 25 m. Considering all optical elements of the system, including the ferrules of the output and input fibers of the quantum key distribution modules, the attenuation of the optical signal was approximately 8, 13, and 18 dB, respectively. Based on the atmospheric optical losses, the quantum key generation rates were of the order of 500, 350, and 190 bits/s with increasing distance and insertion losses. The probability of a quantum error was in the range of 3% to 5%, which was lower than the threshold of 6%, ensuring the legitimacy of the generated key and excluding the possibility of an attack on the communication channel. Practical significance. The compatibility of the developed optical system with single-mode optical fibers allows its integration into the existing infrastructure of data transmission lines without the need for additional optical radiation converters. Owing to the analyzed characteristics of the optical system for distributing a quantum key over an atmospheric communication channel, it can be applied in communication systems based on the Internet of Things, unmanned vehicles, and other moving objects.
The article analyzes the main trends in the field of optimization of information transmission processes using quantum methods. It is shown that numerical modeling of satellite optical communication systems is necessary in order to determine the most effective modes and parameters of communication equipment. This article is devoted to the problem of developing a software package for calculating the characteristics of a communication channel between a ground station and an artificial Earth satellite. A detailed description of the basic functions of the developed software package for calculating the characteristics of an Earth-satellite optical communication channel protected by QKD technology is presented. Based on numerical modeling using the developed software package, a comprehensive study of the influence of atmospheric losses, as well as various parameters of the receiving and transmitting equipment of both the ground station and the satellite, is carried out. In particular, when modeling the efficiency of satellite quantum key distribution and an optical communication channel, atmospheric phenomena such as refraction, absorption, aerosol scattering, as well as the parameters of the QKD equipment were taken into account. Modeling revealed the need to take into account many aspects to achieve maximum efficiency of the QKD in real conditions. It is shown that the developed software for flexible modeling of various scenarios for using atmospheric optical communications opens up new opportunities for research and practical application of quantum technologies in the field of information security, which is important for data protection in the face of growing cybersecurity threats. It is shown that the capabilities of the developed software package can contribute to the creation of standardized approaches to assessing and improving quantum key distribution systems.
Analytical equations for mutual spatial coherence functions of counter-propagating laser beams in integrated transmit/receive optical systems are derived. These equations being fourfold integrals allow estimating the diffraction parameters of transceivers and turbulent propagation conditions, under which a cryptographic key can be generated based on the principle of reciprocity. For particular cases, the degree of coherence of counter-propagating beams and the degree of coherence averaged over the receiver aperture are calculated as functions of generalized parameters describing the turbulence intensity and diffraction at the apertures.
Utilizing reciprocal atmospheric turbulence as a physical entropy source for extracting random secret key is an effective means to achieve physical layer security in wireless channels. To study the impact of turbulence intensity on secret key extraction rate in atmospheric optical channels, this paper conducted a bi-directional synchronous atmospheric channel laser transmission experiment, analyzed the experimental data from three different time periods, and tested the KolmogorovSmirnov (KS) fitting efficiency values for five types of probability distribution normalized received signals. Comparative analysis shows that Johnson SB and Log-Normal distributions have the most ideal fitting effects on data. Based on these distribution parameters, a theoretical model of key capacity was constructed. The Monte Carlo method was used to simulate the secret key extraction rates under different turbulence intensities and different probability distribution models. The analysis results show that under weak turbulence conditions, using Johnson SB distribution yields about 87% higher average maximum secret key extraction rate than using Log-Normal distribution; under medium turbulence conditions, there is no significant difference in secret key extraction rates between the two distribution models. Compared with Log-Normal distribution, Johnson SB distribution is more suitable for secret key extraction under medium to weak turbulence intensities.
This paper presents a comprehensive analysis of the application of quantum key distribution technology in atmospheric optical communication lines to ensure the information security of transmitted information in urban infrastructure conditions and between critical infrastructure industrial facilities. The necessity of applying quantum key distribution technology in atmospheric optical communication channels is substantiated. The results of numerical modeling of quantum key distribution performance indicators confirm the need for their preliminary numerical analysis taking into account regional meteorological statistical data when designing network segments including atmospheric quantum key distribution systems. The developed software package enables optimization of system parameters for specific climatic conditions and channel topology which increases the efficiency of deploying secure networks including atmospheric optical channels for energy, financial and industrial facilities. The developed software package, implementing a physically based methodology for accounting for cumulative losses in such a communication channel, enables a comprehensive assessment of the effectiveness of quantum key distribution taking into account turbulence, absorption, scattering, geometric losses, meteorological conditions and the characteristics of the detection equipment. The practical significance of the complex lies in the ability to optimize system parameters (wavelength, aperture diameter, transmitter power, etc.) for specific climatic conditions and channel topology, which is critical when designing secure networks that include atmospheric optical channels.