Improving the Resistance of Grain-V1 against Algebraic Attack

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. 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.