A Fast Correlation Attack on Multiplexer Generators

Abstract The security of multiplexer generators is investigated with respect to a fast correlation attack based on iterative probabilistic decoding. The number of inputs to the multiplexer determines the coefficient of correlation between the keystream sequence and phase-shifts of one of the underlying shift register sequences. This known plaintext attack is successful if the number of low-weight parity-checks used is sufficiently large given the number of inputs, 2 k , to the multiplexer. Successful experimental attacks are conducted for k=2,3 and 4 . For multiplexer generators with large component shift registers, this attack is an improvement on previously described attacks based on similar assumptions.