A New Variant of Algebraic Attack

Abstract

Algebraic attack is an important attack strategy against symmetric ciphers, particularly stream ciphers. The most vital issue in this attack is to reduce the degree of the algebraic equations as much as possible in order to obtain a lower time complexity. This paper presents one such means of obtaining low degree equations using the decomposition of Boolean functions. This method overcomes the two major drawbacks of fast algebraic attack. We have discussed the general attack strategy using decomposable function. We also demonstrate the decomposition of some Boolean function used in practical stream ciphers. Finally we have given a bound on the degree of a function to be multiplied with a given function so that the product has low degree decomposition. © Springer-Verlag Berlin Heidelberg 2014.