Cryptanalysis of tree-structured ciphers

Tree structures have been proposed for both the construction of block ciphers by Kam and Davida (1979), and self-synchronous stream ciphers by Kuhn (1988). Attacks on these ciphers have been given by Anderson (1991), and Heys and Tavares (1993). Here the authors demonstrate that a more efficient attack can be conducted when the underlying Boolean functions for the cells are known. It is shown that this attack requires less than one third of the chosen ciphertext of Anderson´s original attack on the Kuhn cipher