Uwe Blöcher

Problems with the linear cryptanalysis of DES using more than one active S-box per round

Matsui introduced the concept of linear cryptanalysis. Originally only one active S-box per round was used. Later he and Biham proposed linear cryptanalysis with more than one active S-box per round. They combine equations with the Piling-up Lemma which requires independent random input variables. This requirement is not met for neighbouring S-boxes, because they share input bits. In this paper we study the error resulting from this application of the Piling-up Lemma. We give statistical evidence that the errors are severe. On the other hand we show that the Piling-up Lemma gives the correct probabilities for Matsuis Type II approximation.

Fish: A Fast Software Stream Cipher

This paper describes a fast software stream cipher called Fish based on the shrinking principle applied to the lagged Fibonacci generator (Fish — Fibonacci shrinking). It is designed to make full use of the 32 bit word length of popular processors. On an Intel 486 clocked with 33 MHz a data rate of 15 Mbit/s is achieved with a C implementation.