INVESTIGATIONS OF SHIFT REGISTERS WITH NONLINEAR FEEDBACKS AS COMBINING AND FILTERING FUNCTIONS

The cryptographic resistance of a stream cipher is determined, among other things, by the ability of a generated pseudo-random sequence to resist analytic attacks. The combining and filtering Boolean functions are the main components of the generation algorithm of a pseudo- random sequence of a stream cipher. The possibility of using shift registers with nonlinear feedbacks of the second order is considered and a sequence of the maximum period as combining or filtering functions is formed. The main indicators of a cryptographic stability of such functions are investigated, namely: balance, presence of inhibitions, correlation immunity and nonlinearity. Experimental indications of the correlation immunity and nonlinearity for all M-PSH33-shift registers with nonlinear second-order feedbacks with a dimension of up to 9 cells inclusive are investigated and represented.