Improved Heuristic guess and determine attack on SNOW 3G stream cipher

Guess and determine (GD) attack is one of the general attacks on stream ciphers. Heuristic guess and determine (HGD) attack is a class of GD attacks designed algorithmically for classes of stream ciphers, holding a certain condition that the variables are of the same size. In this Paper, we introduce an improved version of HGD attack, called IHGD. Using this method, the authors examine the resistant of SNOW 3G, a word oriented stream cipher which is used in the UMTS and LTE confidentiality and integrity algorithms. IHGD attack reduces the complexity and the size of guessed basis from O(2³²⁰) to O(2¹⁶⁰) and 10 to 5, respectively, in comparison with the ad-hoc and heuristic GD attacks.