ON THE EFFICIENCY OF THE PROBABILISTIC NEUTRAL BITS METHOD IN STATISTICAL CRYPTANALYSIS OF SYNCHRONOUS STREAM CIPHERS

摘要

Achievable upper bounds are obtained for the relative distance between a Boolean function f and a function nearest to it and independent of variables with numbers from a given set and also between the function f and its subfunction obtained by fixing the mentioned variables to zeros. The expressions for the obtained bounds depend on metric characteristics of derivatives of the function f, which makes it possible to apply these bounds to the estimation and substantiation of the efficiency of the probabilistic neutral bits method.