On vectorial functions with maximal number of bent components

We study vectorial functions with maximal number of bent components in this paper. We first study the Walsh transform and nonlinearity of $F(x)=x^{{2e}h(\Tr_{2{2m}/2m}(x))$,} where $e\geq0$ and $h(x)$ is a permutation over $\F{2^m}$. If $h(x)$ is monomial, the nonlinearity of $F(x)$ is shown to be at most $ 2^{{2m-1}-2{\lfloor\frac{3m}{2}\rfloor}$} and some non-plateaued and plateaued functions attaining the upper bound are found. This gives a partial answer to the open problems proposed by Pott et al. and Anbar et al. If $h(x)$ is linear, the exact nonlinearity of $F(x)$ is determined. Secondly, we give a construction of vectorial functions with maximal number of bent components from known ones, thus obtain two new classes from the Niho class and the Maiorana-McFarland class. Our construction gives a partial answer to an open problem proposed by Pott et al., and also contains vectorial functions outside the complete Maiorana-McFarland class. Finally, we show that the vectorial function $F: \F{2^{{2m}}\rightarrow} \F_{2^{2m}}$, $x\mapsto x^{{2m+1}+x{2i+1}$} has maximal number of bent components if and only if $i=0$.