Edit distance correlation attack on the alternating step generator

Abstract

A novel edit distance between two binary input strings and one binary output string of appropriate lengths which incorporates the stop/go clocking in the alternating step generator is introduced. An efficient recursive algorithm for the edit distance computation is derived. The corresponding correlation attack on the two stop/go clocked shift registers is then proposed. By systematic computer simulations, it is shown that the minimum output segment length required for a successful attack is linear in the total length of the two stop/go clocked shift registers. This is verified by experimental attacks on relatively short shift registers.