Patent EA-025791-B1 (EA)
Title: Method for key transmission through a fibre-optic communication line
Inventor: GULAKOV IVAN ROMANOVICH
IPC: H04L9/08
Filed: 2014-10-06
Abstract: The invention is related to means for protection of information transmitted through an optical communication channel, in particular, to methods for transmitting a key for cryptographic protection of information. The invention can be used in fibre-optic communication systems. The objective of the proposed invention is provision of a method for key transmission through a fibre-optic communication line that allows a decrease in a data transmission error connected with depolarization of optical radiation, a simpler procedure for agreement of bases in which symbols are transmitted and received during formation of a key, and, therefore, higher key transmission speed. The method for key transmission through a fibre-optic communication line consists in that a random sequence of binary symbols is formed on the transmitting side; single-photon pulses with a wavelength of λare generated randomly; the symbols are coded by linearly polarized photon states, the polarization angle being selected 0 and 90° for transmission of symbol "0" and symbol "1", respectively; operation of the transmitting and receiving sides is synchronized; single-photon pulses with a wavelength of λare transmitted through a fibre-optic communication line; the optical radiation polarization angle of 0 or 90° is set randomly by an optical radiation polarization analyzer, and single-photon pulses are registered by a photo detector operating in the photon counting mode; additionally, before starting the transmission of a random sequence of binary symbols, dependence of detective quantum efficiency of the photo detector on the optical radiation wavelength is measured, the maximum detective quantum efficiency of the photo detector ηis determined as well as the optical radiation wavelengths λand λto which the value of 0,9ηof detective quantum efficiency of the photo detector is corresponding; the minimum time τrequired for registration of a single-photon pulse is determined; a probability of single-photon pulses registration error Pis set; the number of single-photon pulses contained in a sequence of pulses at an optical wavelength of λand λis calculated by the formula N=-(0,9η)lnP; the time of duration of one symbol transmission is calculated by the formula t=-τ(0,9η)lnP; on the transmitting side, single-photon pulses of wavelength λare generated randomly; optical radiation pulses of λwavelength transmitting the symbols are polarized linearly by photon states with selection of polarization angle of 0 and 90° for transmission of symbol "0" and symbol "1", respectively; on the transmitting side, single-photon pulses with a wavelength of λor with a wavelength λare generated randomly, symbols of the key sequence are generated with random selection of single-photon pulse wavelength λor λfor each symbol; single-photon pulses of λwavelength are transmitted through a fibre-optic communication line; on the receiving side, optical radiation wavelength λor λis established randomly using a monochromator; the numbers of registered symbols constituting the key are transmitted in the reverse direction (from the receiving side to the transmitting one).