A weakness of the linear part of stream cipher MUGI

Abstract

The linearly updated component of the stream cipher MUGI, called the buffer, is analyzed theoretically by using the generating function method. In particular, it is proven that the intrinsic response of the buffer, without the feedback from the nonlinearly updated component, consists of binary linear recurring sequences with small linear complexity 32 and with extremely small period 48. It is then shown how this weakness can in principle be used to facilitate the linear cryptanalysis of MUGI with two main objectives: to reconstruct the secret key and to find linear statistical distinguishers. © International Association for Cryptologic Research 2004.