International Association
for Cryptologic Research

Let n be a positive integer. An n-stage Galois NFSR has n registers and each register is updated by a feedback function. Then a Galois NFSR is called nonsingular if every register generates (strictly) periodic sequences, i.e., no branch points. In this paper, a generic method for investigating nonsingular Galois NFSRs is provided. Two fundamental concepts that are standard Galois NFSRs and the simplified feedback function of a standard Galois NFSR are proposed. Based on the new concepts, a sufficient condition is given for nonsingular Galois NFSRs. In particular, for the class of Galois NFSRs with linear simplified feedback functions, a necessary and sufficient condition is presented. Hopefully, some new insights are provided on determining nonsingular Galois NFSRs.