Improving Keystream Generation for Sosemanuk Stream Cipher Using Twofish Block Cipher

Abstract

This paper will introduce two proposal algorithms (Snowfish 1) and the (Snowfish 2) to improve the Sosemanuk stream cipher algorithm by benefiting from the efficient properties of the Twofish block cipher and also use its key schedule, keydependent Sbox to increase the security, randomness and try to avoid the guess and determine attack of Sosemanuk. These two proposals use Twofish algorithm rather than Serpent algorithm which was used in the Sosemanuk and also they use keydependent Sbox rather than static Sbox. They are similar in the same key length (128 to 256 bit), IV length (128 bit), LFSR length, FSM functions and output transformation. In this paper will make a comparison between Snowfish 1, Snowfish 2 and Sosemanuk algorithms by using the tests of randomness, the structural tests and the complexity of the algorithm. These tests give results that show the two proposed algorithms have good results in increasing the security and randomness compared with Sosemanuk algorithm.