Modified Alternating Step Generators with Non-Linear Scrambler

Abstract

Pseudorandom generators, which produce keystreams for stream ciphers by the exclusiveorsum of outputs of alternately clocked linear feedback shift registers, are vulnerable to cryptanalysis.In order to increase their resistance to attacks, we introduce a non-linear scrambler at the outputof these generators. Non-linear feedback shift register plays the role of the scrambler. In addition,we propose Modified Alternating Step Generator with a non-linear scrambler (MASG1S) built withnon-linear feedback shift register and regularly or irregularly clocked linear feedback shift registerswith non-linear filtering functions.