There are infinitely many bent functions for which the dual is not bent

TL;DR

This paper introduces the first known infinite class of non-weakly regular bent functions whose duals are not bent, expanding the understanding of bent function duality and providing new constructions.

Contribution

It presents the first construction of non-weakly regular bent functions with non-bent duals and shows how to generate infinitely many such functions from a single example.

Findings

First construction of non-weakly regular bent functions with non-bent duals.

Infinite families of non-dual-bent functions can be generated.

Existing sporadic examples can be extended to infinite classes.

Abstract

Bent functions can be classified into regular bent functions, weakly regular but not regular bent functions, and non-weakly regular bent functions. Regular and weakly regular bent functions always appear in pairs since their duals are also bent functions. In general this does not apply to non-weaky regular bent functions. However, the first known construction of non-weakly regular bent functions by Ce\c{s}melio\u{g}lu et {\it al.}, 2012, yields bent functions for which the dual is also bent. In this paper the first construction of non-weakly regular bent functions for which the dual is not bent is presented. We call such functions non-dual-bent functions. Until now, only sporadic examples found via computer search were known. We then show that with the direct sum of bent functions and with the construction by Ce\c{s}melio\u{g}lu et {\it al.} one can obtain infinitely many non-dual-bent functions once one example of a non-dual-bent function is known.