On the Maximum Nonlinearity of De Bruijn Sequence Feedback Function
The nonlinearity of Boolean function is an important cryptographic criteria in the Best Affine Attack approach. In this paper, based on the definition of nonlinearity, we propose a new design index of nonlinear feedback shift registers. Using the index and the correlative necessary conditions of de Bruijn sequence feedback function, we prove that when n ≥ 9, the maximum nonlinearity Nl(f)max of arbitrary n−order de Bruijn sequence feedback function f satisfies 3 · 2n−3 − (Zn + 1) < Nl(f)max ≤ 2n−1 − 2 n−1 2 and the nonlinearity of de Bruijn sequence feedback function, based on the spanning tree of adjacency graph of affine shift registers, has a fixed value. At the same time, this paper gives the correlation analysis and practical application of the index.