The most suitable algorithm for encryption in the hydroacoustic communication channel is the RC4 cipher. It allows to encrypt and decrypt information quickly and use keys with variable length. But even this algorithm needs to be improved. The main problem is the generation of efficient keys. They are usually formed by pseudo-random sequence generators (PRS) and it is important that these generators generate “pure” random sequences for the highest cipher strength. In addition, it should be noted that it may be necessary to change the size of the keys from 5 to 64 bytes, in depend of the distance between objects and the speed of their movement, and that will make it possibleto choose a key of either greater or lesser length. The second problem is the need for synchronization of sending and receiving messages, so a strict synchronization system is needed. The purpose of this work is consideration of possible ways to solve the first problem (creation of the necessary set of effective encryption keys). In order to obtain the best encryption that provides the highest level of protection for the transmitted information, a comparative analysis of the schemes of construction of PRS generators.was carried out. The analysis leads to the conclusionthat it is recommended to use the Fibonacci scheme to increase the strength of speech encryption algorithms. In addition, an assessment of the degree of influence on the characteristics of the PRS generators of the number of generating polynomials was made for the Fibonacci scheme. The analysis of residual intelligibility showed that not a single word can be parsed in the encrypted file, therefore residual intelligibility is zero, which confirms the effectiveness of the proposed method of information security.

1 Filippov B.I., Chernetskii G.A. Analiz statisticheskikh kharakteristik signalov i pomekh v gidroakusticheskikh kanalakh svyazi [Analysis of statistical characteristics of signals and noises in hydroacoustic communication channels]. Vestnik Astrakhanskogo gosudarstvennogo tekhnicheskogo universiteta. Seriya: Upravlenie, vychislitel'naya tekhnika i informatika – Vestnik of Astrakhan State Technical University. Series: Management, Computer Science and Informatics, 2015, no. 3, pp. 78–84.

2. Kekal K.G., Kebkal V.K., Kebkal A.G., Petroccia R. Experimental estimation of delivery success of navigation data packages transmitted via digital hydroacoustic communication channel. Gyroscopy and Navigation, 2016, vol. 7, no. 4, pp. 343–352.

3. Filippov B.I., Malahova E.A. Printsipy postroeniya sistem gidroakustiches-koi svyazi [Principles of hydroacoustic communication systems creation]. Vestnik Ryazanskogo gosudarstvennogo radiotekhnicheskogo universiteta – Vestnik of Ryazan State Radio Engineering University, 2017, no. 4 (62), pp. 36–43.

4. Filippov B.I. Energeticheskii raschet gidroakusticheskikh linii svyazi [Energy calculation of hydroacousticcommunication lines]. Vestnik Astrakhanskogo gosudarstvennogo tekhnicheskogo universiteta. Seriya: Upravlenie, vychislitel'naya tekhnika i informatika – Vestnik of Astrakhan State Technical University. Series: Management, Computer Science and Informatics, 2016, no. 3, pp. 81–91.

5. Basalova G.V. Osnovy kriptografii [Basics of cryptography]. 2^nd ed. Moscow, Intuit Publ., 2016. 283 p.

6. Filippov B.I., Chernetsky G.A. Vybor ansamblya signalov dlya peredachi komand upravleniya v gidroakusticheskikh kanalakh svyazi [Choice of ensemble of signals for transfer of teams management in the hydroacoustic communication channels]. Izvestiya Volgogradskogo gosudarstvennogo tekhnicheskogo universite-ta – Izvestia of Volgograd State Technical University, , no. 3 (161), pp. 69–72.

7. Filippov B.I. Vybor metoda razdeleniya signalov v gidroakusticheskom kanale upravleniya [The choice of signal separation method in hydroacoustic control channel]. Vestnik Ryazanskogo gosudarstvennogo radiotekhnicheskogo universiteta – Vestnik of Ryazan State Radio Engineering University, no. 4 (66), pt. 1, pp. 29–34.

8. Filippov B.I., Malahova E.A. Raschet nadezhnosti donnoi chasti apparatury gidroakusticheskogo kanala svyazi [Calculation of reliability of ground part of the equipment hydroacoustic communication channel]. Sbornik nauchnykh trudov Novosibirskogo gosudarstvennogo tekhnicheskogo universiteta – Transaction of scientific papers of the Novosibirsk state technical university, 2015, no. 3 (81),

pp. 79–97.

9. Filippov B.I., Malahova E.A. Raschet nadezhnosti apparatury gidroakusticheskogo kanala svyazi [Calculation of reliability of the equipment hydroacoustic communication channel]. Sbornik nauchnykh trudov Novosibirskogo gosudarstvennogo tekhnicheskogo universiteta – Transaction of scientific papers of the Novosibirsk state technical university, 2015, no. 4 (82), pp. 67–91.

10. Filippov B.I., Chernetsky G.A. Povyshenie dostovernosti peredachi blokov tsifrovoi informatsii po gidroakusticheskomu kanalu svyazi [Increase of reliability of transfer of blocks the digital information on the hydroacoustic communication channel]. Zhurnal Sibirskogo federal'nogo universiteta. Tekhnika i tekhnologii – Journal of Siberian Federal University. Engineering & Technologies, 2016, no. 9, pp. 490–498.

11. Filippov B.I. Issledovanie i razrabotka ustroistva zashchity ot oshibok dlya sistemy peredachi izobrazhenii po gidroakusticheskomu kanalu svyazi [Research and development of the device of protection against mistakes for system of transfer of images on the hydroacoustic communication channel]. Informatsionnye techno-logii – Information Technologies, vol. 23, no. 12, pp. 897–904.

12. Zhdanov O.N. Metodika vybora klyuchevoi informatsii dlya algoritma blochnogo shifrovaniya [The of of key information for a algorithm]. Moscow, Infra-M Publ., 2018. 89 p.

13. Kovtun V.Yu. Generatory sluchainykh i psevdosluchainykh posledova-tel'nostei. Statisticheskie testy. Kriptograficheski bezopasnye generatory psevdosluchainykh posledovatel'nostei [Random and pseudorandom sequence generators. Statistical test. Cryptographically secure pseudorandom sequence generators]. NRJETIX Ltd., 2000–2008. 16 p. Available at: www.nrjetix.com/fileadmin/doc/

publications/Lectures_security/Lecture2.pdf (accessed 18.03.2019).

14. Babenko L.K., Ishchukova E.A. Kriptograficheskaya zashchita informatsii: simmetrichnoe shifrovanie [Cryptographic protection of information: symmetric encryption]. Moscow, Yurait Publ., 2018. 220 p. ISBN 978-5-9916-9244-1.

15. Potochnye shifry: rezul'taty zarubezhnoi otkrytoi kriptologii [Stream cipher. The results of the open foreign cryptology]. Moscow, 1997, pp. 32–33.

16. Schneier B. Applied cryptography: protocols, algorithms and source code in C]. 2nd ed. New York, Wiley, 1996 (Russ. ed.: Shnaier B. Prikladnaya kriptografiya: protokoly, algoritmy i iskhodnye teksty na yazyke Si. 2^nd ed. Moscow, Dialektika Publ., 2003. 610 p. ISBN 5-89392-055-4).