PS\mathcal{P}\mathcal{S} bent functions constructed from finite pre-quasifield spreads

Bent functions are of great importance in both mathematics and information science. The $\mathcal{P}\mathcal{S}$ class of bent functions was introduced by Dillon in 1974, but functions belonging to this class that can be explicitly represented are only the $\mathcal{P}\mathcal{S}_{\text{ap}}$ functions, which were also constructed by Dillon after his introduction of the $\mathcal{P}\mathcal{S}$ class. In this paper, a technique of using finite pre-quasifield spread from finite geometry to construct $\mathcal{P}\mathcal{S}$ bent functions is proposed. The constructed functions are in similar styles with the $\mathcal{P}\mathcal{S}_{\text{ap}}$ functions. To explicitly represent them in bivariate forms, the main task is to compute compositional inverses of certain parametric permutation polynomials over finite fields of characteristic 2. Concentrated on the Dempwolff-M\"uller pre-quasifield, the Knuth pre-semifield and the Kantor pre-semifield, three new subclasses of the $\mathcal{P}\mathcal{S}$ class are obtained. They are the only sub-classes that can be explicitly constructed more than 30 years after the $\mathcal{P}\mathcal{S}_{\text{ap}}$ subclass was introduced.Comment: 14page

On constructing complete permutation polynomials over finite fields of even characteristic

In this paper, a construction of complete permutation polynomials over finite fields of even characteristic proposed by Tu et al. recently is generalized in a recursive manner. Besides, several classes of complete permutation polynomials are derived by computing compositional inverses of known ones.Comment: Stupid mistakes in previous versions are correcte

New constructions of quaternary bent functions

In this paper, a new construction of quaternary bent functions from quaternary quadratic forms over Galois rings of characteristic 4 is proposed. Based on this construction, several new classes of quaternary bent functions are obtained, and as a consequence, several new classes of quadratic binary bent and semi-bent functions in polynomial forms are derived. This work generalizes the recent work of N. Li, X. Tang and T. Helleseth

A general construction of permutation polynomials of the form (x2m+x+δ)i(2m−1)+1+x (x^{2^m}+x+\delta)^{i(2^m-1)+1}+x over \F_{2^{2m}}

Recently, there has been a lot of work on constructions of permutation polynomials of the form $(x^{2^m}+x+\delta)^{s}+x$ over the finite field \F_{2^{2m}}, especially in the case when $s$ is of the form $s=i(2^m-1)+1$ (Niho exponent). In this paper, we further investigate permutation polynomials with this form. Instead of seeking for sporadic constructions of the parameter $i$, we give a general sufficient condition on $i$ such that $(x^{2^m}+x+\delta)^{i(2^m-1)+1}+x$ permutes \F_{2^{2m}}, that is, $(2^k+1)i \equiv 1 ~\textrm{or}~ 2^k~(\textrm{mod}~ 2^m+1)$, where $1 \leq k \leq m-1$ is any integer. This generalizes a recent result obtained by Gupta and Sharma who actually dealt with the case $k=2$. It turns out that most of previous constructions of the parameter $i$ are covered by our result, and it yields many new classes of permutation polynomials as well

Complete permutation polynomials induced from complete permutations of subfields

We propose several techniques to construct complete permutation polynomials of finite fields by virtue of complete permutations of subfields. In some special cases, any complete permutation polynomials over a finite field can be used to construct complete permutations of certain extension fields with these techniques. The results generalize some recent work of several authors

The compositional inverse of a class of bilinear permutation polynomials over finite fields of characteristic 2

A class of bilinear permutation polynomials over a finite field of characteristic 2 was constructed in a recursive manner recently which involved some other constructions as special cases. We determine the compositional inverses of them based on a direct sum decomposition of the finite field. The result generalizes that in [R.S. Coulter, M. Henderson, The compositional inverse of a class of permutation polynomials over a finite field, Bull. Austral. Math. Soc. 65 (2002) 521-526].Comment: 17 page

A remark on algebraic immunity of Boolean functions

In this correspondence, an equivalent definition of algebraic immunity of Boolean functions is posed, which can clear up the confusion caused by the proof of optimal algebraic immunity of the Carlet-Feng function and some other functions constructed by virtue of Carlet and Feng's idea.Comment: 7 page

Linearized polynomials over finite fields revisited

We give new characterizations of the algebra $\mathscr{L}_n(\mathbb{F}_{q^n})$ formed by all linearized polynomials over the finite field $\mathbb{F}_{q^n}$ after briefly surveying some known ones. One isomorphism we construct is between $\mathscr{L}_n(\mathbb{F}_{q^n})$ and the composition algebra $\mathbb{F}_{q^n}^\vee\otimes_{\mathbb{F}_{q}}\mathbb{F}_{q^n}$. The other isomorphism we construct is between $\mathscr{L}_n(\mathbb{F}_{q^n})$ and the so-called Dickson matrix algebra $\mathscr{D}_n(\mathbb{F}_{q^n})$. We also further study the relations between a linearized polynomial and its associated Dickson matrix, generalizing a well-known criterion of Dickson on linearized permutation polynomials. Adjugate polynomial of a linearized polynomial is then introduced, and connections between them are discussed. Both of the new characterizations can bring us more simple approaches to establish a special form of representations of linearized polynomials proposed recently by several authors. Structure of the subalgebra $\mathscr{L}_n(\mathbb{F}_{q^m})$ which are formed by all linearized polynomials over a subfield $\mathbb{F}_{q^m}$ of $\mathbb{F}_{q^n}$ where $m|n$ are also described.Comment: 30 page

More characterizations of generalized bent function in odd characteristic, their dual and the gray image

In this paper, we further investigate properties of generalized bent Boolean functions from $\Z_{p}^n$ to $\Z_{p^k}$, where $p$ is an odd prime and $k$ is a positive integer. For various kinds of representations, sufficient and necessary conditions for bent-ness of such functions are given in terms of their various kinds of component functions. Furthermore, a subclass of gbent functions corresponding to relative difference sets, which we call $\Z_{p^k}$-bent functions, are studied. It turns out that $\Z_{p^k}$-bent functions correspond to a class of vectorial bent functions, and the property of being $\Z_{p^k}$-bent is much stronger then the standard bent-ness. The dual and the generalized Gray image of gbent function are also discussed. In addition, as a further generalization, we also define and give characterizations of gbent functions from $\Z_{p^l}^n$ to $\Z_{p^k}$ for a positive integer $l$ with $l<k$

A new proof to complexity of dual basis of a type I optimal normal basis

The complexity of dual basis of a type I optimal normal basis of $\mathbb{F}_{q^n}$ over $\mathbb{F}_{q}$ was determined to be $3n-3$ or $3n-2$ according as $q$ is even or odd, respectively, by Z.-X. Wan and K. Zhou in 2007. We give a new proof to this result by clearly deriving the dual of a type I optimal normal basis with the aid of a lemma on the dual of a polynomial basis.Comment: 7 page