Bent Functions and (Partial-)spreads

Given a bent function $$f(\varvec{x})$$ of n variables, its max-weight and min-weight functions are introduced as the Boolean functions $${f}^{+}(\varvec{x})$$ and $${f}^{-}(\varvec{x})$$ whose supports are the sets $$\{\varvec{a} \in {\mathbb {F}}_{2}^{n} | w(f \oplus l_{\varvec{a}}) = 2^{n-1}+2^{\frac{n}{2}-1}\}$$ and $$\{\varvec{a} \in {\mathbb {F}}_{2}^{n} | w(f \oplus l_{\varvec{a}}) = 2^{n-1}-2^{\frac{n}{2}-1}\}$$ respectively, where $$w(f \oplus l_{\varvec{a}})$$ denotes the Hamming weight of the Boolean function $$f(\varvec{x}) \oplus l_{\varvec{a}}(\varvec{x})$$ and $$l_{\varvec{a}}(\varvec{x})$$ is the linear function defined by $$\varvec{a} \in {\mathbb {F}}_{2}^{n}$$ . $${f}^{+}(\varvec{x})$$ and $${f}^{-}(\varvec{x})$$ are proved to be bent functions. Furthermore, combining the 4 minterms of 2 variables with the max-weight or min-weight functions of a 4-tuple $$(f_{0}(\varvec{x}), f_{1}(\varvec{x}), f_{2}(\varvec{x}), f_{3}(\varvec{x}))$$ of bent functions of n variables such that $$f_{0}(\varvec{x}) \oplus f_{1}(\varvec{x}) \oplus f_{2}(\varvec{x}) \oplus f_{3}(\varvec{x}) = 1$$ , a bent function of $$n+2$$ variables is obtained. A family of 4-tuples of bent functions satisfying the above condition is introduced, and finally, the number of bent functions we can construct using the method introduced in this paper are obtained. Also, our construction is compared with other constructions of bent functions.

Bent functions are maximally nonlinear Boolean functions. They are important functions introduced by Rothaus and studied firstly by Dillon and next by many researchers for four decades. Since the complete classification of bent functions seems elusive, many researchers turn to design constructions of bent functions. In this paper, we show that linear involutions (which are an important class of permutations) over finite fields give rise to bent functions in bivariate representations. In particular, we exhibit new constructions of bent functions involving binomial linear involutions whose dual functions are directly obtained without computation. The existence of bent functions from involutions heavily relies on solving systems of equations over finite fields.

Let G be a finite nonabelian group. Bent functions on G are defined by the Fourier transforms at irreducible representations of G. We introduce a dual basis $${\widehat{G}}$$ , consisting of functions on G determined by its unitary irreducible representations, that will play a role similar to the dual group of a finite abelian group. Then we define the Fourier transforms as functions on $${\widehat{G}}$$ , and obtain characterizations of a bent function by its Fourier transforms (as functions on $${\widehat{G}}$$ ). For a function f from G to another finite group, we define a dual function $${\widetilde{f}}$$ on $${\widehat{G}}$$ , and characterize the nonlinearity of f by its dual function $${\widetilde{f}}$$ . Some known results are direct consequences. Constructions of bent functions and perfect nonlinear functions are also presented.

Generalized bent functions and their properties

In this article we study two party Communication Complexity of Boolean bent functions from Maiorana–McFarland class. In particular, we describe connections between Maiorana–McFarland construction of bent functions and operations on matrix form of Boolean functions and show that bent functions of 2n variables from Maiorana–McFarland class have deterministic communication complexity equal n + 1. Finally, we show that not all bent functions have high communication complexity lower bound by giving the example of such function.

In this paper we report the following computational results on partial spread functions in eight variables: (i) the numbers of equivalence classes of partial spread functions (in eight variables) of all possible orders; (ii) the total number of partial spread bent functions in eight variables; (iii) the distribution of the cardinalities of stabilizers (in GL(8, F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )) of partial spread bent functions in eight variables. The computational method is also described.