Security of data transmitted via telephone, fibre optics and microwaves

Jane Harrad

Marcin Kowalski, M. Życzkowski

Abstract We propose and study a new technique for securing fibre data communication. The paper presents a method for optical encryption of information transmitted with a traditional fibre link. The encryption method uses a spatial light modulator which converts light pulses representing original data into pseudo-random patterns. A linear combination of light pulses with pseudo-random patterns provides a required encryption performance. The main element of the encryptor is the spatial light modulator which comprises a matrix of cells selectively transmitting or blocking the light beam depending on the pseudo-random configuration of cells. The encrypted information is transmitted through the optical fibre. The decryption process relies on a computational solving of linear program or greedy pursuit. We present a brief description of the method, theoretical analysis and results of numerical simulation. A physical model concept of the method is also presented.

Marco Baldi, Stefano Tomasin

Andy Schreier, Obada Alia, Rui Wang +7 more

In this article a fibre free-space fibre link that allows a quantum key distribution (QKD) signal and high-speed data to be transmitted in a single optical beam is presented. This setup has the potential to provide ultra-high data rate secure wireless connectivity within indoor spaces. Both quantum and classical channels were transmitted using wavelengths in the C band, over a range of 2.5 m in free space and in the presence of a 200 lx background illumination. Raman noise caused by the light propagating in the optical fibres which provide connections to the free-space segment, together with geometric loss of the free-space link are the major impairments. Results yield secret key rates of 2.343 kbit/s when the QKD signal is sent without high-speed data (and associated Raman noise), and rates of 1.305–1.996 kbit/s when high-speed data is also transmitted (depending on spectral separation of QKD and classical information). Further, it is shown that the secret key rate can be optimised by increasing loss to attenuate the Raman noise by misalignment of the link. Improvement of the secret key rate from 1.305 kbit/s to 1.887 kbit/s was shown using this method.

Mateusz Karol, M. Życzkowski, M. Szustakowski

Current solutions used for protection of information transmitted in fibre optic networks are based on direct detection of fibre optic cable eavesdropping and encryption of transmitted information. Protection of fibre optic cables from physical intrusion in to the transmission channel is realized on dark optical fibres, not used in the transmission of information. Security of encrypted information is based on the assumption of limited computing power used for cryptanalysis, what with the introduction of operating quantum computers will cease to apply. So ideal solution for information protection is physical it coding that makes eavesdropping near to impossible, in the same time allows of constant monitoring of fibre physical integrity. The article describes the construction and principle of operation used in fibre optic pulse interferometer, that allows to detect mechanical disorders of fibre optic transmission line with simultaneous transmission of information. Operation of the system relies on encoding information in phase of optical radiation pulses and for monitoring the status of the transmission line by analysis polarization of radiation in interferometer. System configuration provides stabilized work of pulse interferometer over several kilometres, under varying environmental conditions. Unique capabilities of detection system enable the use of two independent criteria for alarm signal excitation. The aim of the study was to determine the security degree provided by system to protection of transmitted information in proposed arrangement.

Alan Friedberg, Robert W. Harper