A Faster Shift Register Alternative to Filter Generators

LFSR-based filter generators are used as a basic building block in many stream ciphers. Filter generators are popular because their well-defined mathematical description enables a detailed formal security analysis. In this paper, we show how to modify a filter generator into a nonlinear feedback shift register which is faster, but slightly larger, than the original filter generator. For example, the propagation delay can be reduced 1.54 times at the expense of 1.27% extra area. The presented method might be important for applications which require very high data rates, e.g. 4G mobile communication technology.