Improving the Resistance of Grain-V1 against Algebraic Attack

Abstract

Grain-v1 is an 80-bit hardware oriented stream ciphers that has been selected for the final portfolio of eSTREAM project. It has been proved experimentally that an algebraic attack can be devised against Grain-v1 which can recover almost half of its 160 internal state bits within limited resources [1]. This attack is possible because of the algebraic structure of the equations relating the internal state and output bits of the cipher. In this article a small modification in the Grain-v1 is proposed which can resist the recovery of internal state bits due to solving algebraic equations. Grain-128 a revised version of Grain-v1 has already been proposed but focus of this article is to give a modification of Grain-v1 without increasing its internal sate bits. The proposed modification does not make any change in the basic design philosophy of Grain-v1 nor does it add in the complexity of enciphering. An analysis of the proposed design and its comparison with the original version is also presented.