Attacking Stream Ciphers Using Genetic Algorithm

The proposed system considers a new approach to cryptanalysis based on the application of a directed random search algorithm called genetic algorithm (GA). It uses GA to attack stream ciphers knowing part of plaintext, i.e., known-plaintext attack. GA attacks a stream cipher system by determining the equivalent Linear Feedback Shift Register of minimum length that generates the known keystream. Thus, in this work, we attempt to find the linear equivalence of a given keystream.The proposed algorithm provides the attacker with the following information: the initial state of the Linear Feedback Shift Register (LFSR), the characteristic polynomial defined as a feedback function of the LFSRandthe length of the register, i.e., the number of its stages. The aim of this work is to study the applicability of GA in finding the linear equivalence.