  Perfect nonlinear functions from a finite group $G$ to another one $H$ are
those functions $f: G \rightarrow H$ 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, $f: G \rightarrow H$ 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.
