Guess and Determine Attack on SOSEMANUK

SOSEMANUK is a new synchronous software-oriented stream cipher with a variable-length key between 128 and 256 bits. In this paper, a guess and determine (GD) attack on the cipher is introduced with a computational complexity of O(2
¹⁹²
), requiring only 7 keystream words. The results show that the cipher does not provide full security when the key of the length more than 192 bits is used.