A Correlation attack on the binary sequence generators with time-varying output function

Abstract

A binary sequence generator (BSG) consisting of three regularly clocked linear feedback shift registers combined by a time-varying memoryless function is cryptanalysed. A novel distance measure for the binary sequences comparison relevant for the crypanalysis is proposed, its main characteristics are derived, and the divide and conquer correlation attack based on this distance is presented. It is pointed out that the novel distance based approach to cryptanalysis could be applied for attacking the binary MacLaren-Marsaglia shuffier, for signficant improvement of the correlation attack on the multiplexer BSG, and for attacking a wide class of BSG's in which the output binary sequence is a time-varying function of certain subgenerator output binary sequence.