Improvement of the viterbi algorithm applied in the attacks on stream ciphers

This paper improves the conventional Viterbi algorithm so that it can be used for decoding the conventional code with a large constraint length and a very low rate. Through the construction of a Hamming distance table, the novel algorithm greatly improved the performance of the old one. Simulation results indicate that this algorithm could be successfully applied to attack stream cipher, whose LFSR sequence error code rate is 37% and feedback polynomial degree is 60, moreover, the decoding efficiency is about 10 times the conventional one