Algebraic description and simultaneous linear approximations of addition in snow 2.0.

Abstract

In this paper we analyse the algebraic properties over the field GF(2) of the addition modulo 2 n . We look at implicit quadratic equations describing this operation, and at probabilistic conditional linear equations. We show that the addition modulo 2 n can be partly or totally linearized when the output is fixed, and this for a large family of outputs. We apply these results to analyse the resistance of the stream cipher Snow 2.0 against algebraic attacks. © 2008 Springer Berlin Heidelberg.