Atmospheric and Oceanic Optics

The Analysis of Intensity Correlation in Laser Transceiving Systems for Formation of a Cryptographic Key

V. P. Aksenov, Vadim V. Dudorov, В. В. Колосов, Ch. E. Pogutsa, Mikhail E. Levitsky

Published Nov 1, 2020• 1 citation

Abstract

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.

DOI: 10.1134/s1024856020060032

Related papers

Cryptographic key formation in coupled transmit-receiving atmospheric laser systems

Evgenia S. Abramova, E. V. Adamov, V. P. Aksenov +6 more

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.

T-Comm - Телекоммуникации и ТранспортJan 1, 20230 citations

Coherence of counter-propagating beams in a confidential communication system based on generation of cryptographic keys at the expense of atmospheric turbulence

V. P. Aksenov, Vadim V. Dudorov, В. В. Колосов +1 more

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.

XXVIII Международный симпозиум «Оптика атмосферы и океана. Физика атмосферы»Dec 16, 20210 citations

Experimental Study of Random Secret Key Extraction From Atmospheric Optical Channels

Shengya Zhao, Zixin Dou, Chunyi Chen +3 more

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.

IEEE photonics journalApr 21, 20251 citation

Optical key distribution system using atmospheric turbulence as the randomness generating function: classical optical protocol for information assurance

Marvin D. Drake, Christophe F. Bas, David R. Gervais +6 more

We describe an experimental laboratory system that generates and distributes random binary sequence bit streams between two optical terminals (labeled Alice and Bob). The random binary sequence is generated through probing the optical channel of a turbulent atmosphere between the two terminals with coincident laser beams. The two laser beams experience differential phase delays while propagating through the atmospheric optical channel. The differential phase delays are detected and sampled at each terminal to yield raw random bit streams. The random bit streams are processed to remove bit errors and, through privacy amplification, to yield a bit stream known only to Alice and Bob. The same chaotic physical mechanism that provides randomness also provides confidentiality. The laboratory system yielded secret key bit rates of a few bits/second . For external optical channels over longer channel lengths with atmospheric turbulence levels, secret bit rates of 10 s of bits/second are predicted.

Optical EngineeringMay 29, 201315 citations

Quantum optics in the turbulent atmosphere: fundamental issues and applications

Andrii Semenov, M. Klen, I. Pechonkin

Quantum light propagation through turbulent atmosphere has become a subject of intensive research, spanning both theoretical and experimental studies. This interest is driven by its important applications in free-space quantum communication, remote quantum sensing, and environmental monitoring. At the same time, this phenomenon itself poses an intriguing fundamental problem. A consistent theoretical description typically makes explicit assumptions about the measurement scheme at the receiver station and/or the method of quantum-information encoding. A common and straightforward approach encodes the information in quantum states of a quasi-monochromatic mode, representing a pulsed Gaussian beam. Atmospheric turbulence induces random distortions of the pulse shape and, consequently, random fluctuations of the transmittance through the receiver aperture. These fluctuations, characterized by the probability distribution of transmittance (PDT), directly affect the quantum state of the received light. In this paper we examine various analytical models of the PDT, validate them through numerical simulations, and assess their range of applicability. Furthermore, we extend the analysis beyond the standard ensemble-averaging approach, recognizing that realistic experiments typically involve time averaging. This requires a detailed examination of the underlying random process, including the study of temporal correlations and their impact on nonclassical properties of electromagnetic radiation.

arXiv:2509.06022SPIE Quantum Technologies for Defence and SecurityOct 29, 20251 citation

Shared secret key generation from signal fading in a turbulent optical wireless channel using common-transverse-spatial-mode coupling

Chunyi Chen, Huamin Yang

Common randomness arising from turbulence-induced signal fading in reciprocal optical wireless channels is a beneficial resource that can be used to generate secret keys shared by two legitimate parties. The concept of optical wireless channels using common-transverse-spatial-mode coupling (CTSMC) that can maintain perfect fading reciprocity in atmospheric turbulence is first developed in a general manner. Subsequently, by performing Monte Carlo simulations, the Johnson SB probability distribution is demonstrated to be appropriate for statistical description of turbulence-induced signal fading in an optical wireless channel constructed by use of two identical CTSMC transceivers, and the nature of correlation between signal fadings detected by two contiguous reception spatial modes is further quantitatively characterized, revealing that rapid spatial decorrelation between signal fadings observed by a legitimate party and an eavesdropper holds for scenarios of practical interest. Finally, the information theoretic capacity for generating secret keys from CTSMC-based optical wireless channels is theoretically formulated and quantitatively examined under different conditions, manifesting that the turbulence strength and average electrical signal-to-noise ratio have a noticeable combined impact on the secret key capacity, especially in the far-field case.

Optics ExpressJun 13, 201824 citations