Two attacks against the HBB stream cipher

Abstract

Hiji-Bij-Bij (HBB) is a new stream cipher proposed by Sarkar at Indocrypt'03. In this algorithm, classical LFSRs are replaced by cellular automata (CA). This idea of using CAs in such constructions was initially proposed by Sarkar at Crypto'02, in order to instantiate its new Filter-Combiner model. In this paper, we show two attacks against HBB. First we apply differential cryptanalysis to the self-synchronizing mode. The resulting attack is very efficient since it recovers the secret key by processing a chosen message of length only 2 Kbytes. Then we describe an algebraic attack against the basic mode of HBB. This attack is much faster than exhaustive search for secret keys of length 256 bits. © International Association for Cryptologic Research 2005.