New methods suggest usage of evolutionary algorithms in order to introduce non-linearity. Using bruteforce methods, a list of maximum-period n-bit NLFSRs for n ≤ 25 has been made as well as for n=27. It is known how to generate an n-bit NLFSR of maximal length 2 n, generating a De Bruijn sequence, by extending a maximal-length LFSR with n stages but the construction of other large NLFSRs with guaranteed long periods remains an open problem. NLFSRs are known to be more resistant to cryptanalytic attacks than Linear Feedback Shift Registers ( LFSRs). Nonlinear-feedback shift registers are components in modern stream ciphers, especially in RFID and smartcard applications. Where f is the non-linear feedback function. A nonlinear-feedback shift register (NLFSR) is a shift register whose input bit is a non-linear function of its previous state.įor an n-bit shift register r its next state is defined as:
