Probabilistic algebraic attack on plantlet lightweight stream cipher

Abstract

Plantlet is a new variant of Sprout lightweight stream cipher. It uses 61 bit LFSR and 40 bit NFSR. This paper presents a study of Plantlet stream cipher with probability based approach for making algebraic attack on Plantlet. In this paper, we have used low degree multiple of Boolean function to apply algebraic attack. The low degree multiple of Boolean function is multiplied to output keystream function in order to get output equation such that it consists of only LFSR state variables. These equations are further solved to find secret key and internal states. In this manner, the complexity of solving equations is reduced. In this paper, it takes 260:99 Plantlet encryptions to solve system of equations. Commonly, standard algebraic attack and fast algebraic attack have been applied on various stream ciphers. However, the probabilistic algebraic attack has been implemented on Grain family of stream ciphers but not on Plantlet. The probabilistic algebraic attack can be applied on other stream ciphers.