A novel method for reconstructing period with single input in NFSR

Non-Linear Feedback Shift Registers (NFSRs) are a generalization of Liner Feedback Shift Registers (LFSRs). The study of NFSR sequence helps to analyze the cryptographical security of NFSR-based stream cipher. Due to lack of efficient algebraic tools, the period of NFSR still remains an open crucial theoretical problem. In this paper, we view the NFSR as a Boolean network (BN), so that the study about the period of NFSR can be viewed as the study about period of BN. Furthermore, based on the mathematical tool of semi-tensor product (STP), a Boolean network can be mapped into an algebraic form. For these, we put forward a method for reconstructing the period of NFSR with single input. Especially, we propose a procedure to choose the controlled states and steer the controlled states from initial state to desirable one. At last, the general derivation is exemplified by numerical simulations for a kind of NFSR.