Reduced complexity correlation attacks on two clock-controlled generators

In English The Shrinking Generator and the Alternating Step Generator are two of the most well known clock-controlled stream ciphers. We consider correlation attacks on these two generators, based on an identified relation to the decoding problem for the deletion channel and the insertion channel, respectively. Several ways of reducing the decoding complexity are proposed and investigated, resulting in “divide-and-conquer” attacks on the two generators having considerably lower complexity than previously known attacks.