انجمن کامپیوتر ایران

In 2000, Ekdahl and Johansson introduced the stream cipher SNOW, as a proposal for the NESSIE project, but a few Guess and Determine (GD) attacks followed and indicated certain weaknesses in the design. Then a new version of SNOW, called SNOW2.0, was developed as a modified version of SNOW1.0. Yet this stream cipher is also vulnerable against some introduced attacks. This paper gives some criteria of modifying an LFSR-based stream cipher against GD attacks. Next, using one of these criteria, we introduce a modified version of SNOW2.0 with respect to GD attacks. The results of evaluating the modified SNOW2.0 against other general attacks show that the new proposed algorithm is more resistant against other types of general attacks, i.e. TMDTO, distinguishing and algebraic attacks.