Non Abelian Bent Functions

Abstract

Perfect nonlinear functions from a finite group $G$ to another one $H$ are those functions $f:G\to H$ such that for all nonzero $\alpha \in G$, the derivative $d_{\alpha }f:x\mapsto f(\alpha x)f(x{)}^{-1}$ is balanced. In the case where both $G$ and $H$ are Abelian groups, $f:G\to H$ is perfect nonlinear if and only if $f$ is bent i.e for all nonprincipal character $\chi$ of $H$, the (discrete) Fourier transform of $\chi \circ f$ has a constant magnitude equals to $|G|$. In this paper, using the theory of linear representations, we exhibit similar bentness-like characterizations in the cases where $G$ and/or $H$ are (finite) non Abelian groups. Thus we extend the concept of bent functions to the framework of non Abelian groups.

Soumis à la revue "Cryptographie and communications"