A simple algorithm for fast correlation attacks on stream ciphers

A new simple algorithm for fast correlation attacks on stream ciphers is presented. The advantages of the new approach are at least two. Firstly, the new algorithm significantly reduces the memory requirements compared with some recent proposals [2],[3]. This allows more powerful attacks than previously. Secondly, the simplicity of the algorithm allows us to derive theoretical results. We determine the relation between the number of observed symbols, the correlation probability, and the allowed computational complexity, required for a successful attack. Hence, we can get theoretical estimates on the required computational complexity in cases when simulation is not possible