In this work, we employ the concept of
composite representation
of Boolean functions, which represents an arbitrary Boolean function as a composition of one Boolean function and one vectorial ...function, for the purpose of specifying new secondary constructions of bent/plateaued functions. This representation gives a better understanding of the existing secondary constructions and it also allows us to provide a general construction framework of these objects. This framework essentially gives rise to an
infinite number
of possibilities to specify such secondary construction methods (with some induced sufficient conditions imposed on initial functions) and in particular we solve several open problems in this context. We provide several explicit methods for specifying new classes of bent/plateaued functions and demonstrate through examples that the imposed initial conditions can be easily satisfied. Our approach is especially efficient when defining new bent/plateaued functions on larger variable spaces than initial functions. For instance, it is shown that the indirect sum methods and Rothaus’ construction are just special cases of this general framework and some explicit extensions of these methods are given. In particular, similarly to the basic indirect sum method of Carlet, we show that it is possible to derive (many) secondary constructions of bent functions without any additional condition on initial functions apart from the requirement that these are bent functions. In another direction, a few construction methods that generalize the secondary constructions which do not extend the variable space of the employed initial functions are also proposed.
In the mid 1960s, Rothaus proposed the so-called "most general form" of constructing new bent functions by using three (initial) bent functions whose sum is again bent. In this paper, we utilize a ...special case of Rothaus construction when two of these three bent functions differ by a suitably chosen characteristic function of an n/2-dimensional subspace. This simplification allows us to treat the induced bent conditions more easily, also implying the possibility to specify the initial functions in the partial spread class and most notably to identify several instances of the so-called non-normal bent functions. Affine inequivalent bent functions within this class are then identified using a suitable selection of initial bent functions within the partial spread class (stemming from the complete Desarguesian spread). It is also shown that when the initial bent functions belong to the class D, then, under certain conditions, the constructed functions provably do not belong to the completed Maiorana-McFarland class. We conjecture that our method potentially generates an infinite class of non-normal bent functions (all tested ten-variable functions are non-normal but unfortunately they are weakly normal) though there are no efficient computational tools for confirming this.
In the mid-sixties, Rothaus introduced the notion of bent function and later presented a secondary construction of bent functions (building new bent functions from already defined ones), called ...Rothaus’ construction. In Zhang et al. 2017 (‘Constructing bent functions outside the Maiorana–Mcfarland class using a general form of Rothaus,’ IEEE Transactions on Information Theory, 2017, vol. 63, no. 8, pp. 5336–5349.’) provided two constructions of bent functions using a general form of Rothaus and showed that the obtained classes lie outside the completed Maiorana–McFarland (${\rm {\cal M}{\cal M}}$MM) class. In this study, the authors propose two similar methods for constructing bent functions outside the completed ${\rm {\cal M}{\cal M}}$MM class but with significantly simplified sufficient conditions compared to those in Zhang et al. 2017. These simplified conditions do not induce any serious restrictions on the choice of permutations used in the construction apart from a simple requirement on their algebraic degree and the request that the component functions of one permutation do not admit linear structures. This enables us to generate a huge class of bent functions lying outside the completed ${\rm {\cal M}{\cal M}}$MM class. Even more importantly, they prove that the new classes of bent functions are affine inequivalent to the bent functions in Zhang et al. 2017.
In this article a construction of bent functions from an n-dimensional vector space Vn over Fp to Fp is presented for arbitrary primes p and dimensions n≥5. The construction can be seen as ...generalization of the Rothaus construction for Boolean bent functions. Since vectorial bent functions are used, we recall some classes of vectorial bent functions and employ them to obtain both, weakly regular and non-weakly regular bent functions. The suggested construction provides the second known procedure to design non-weakly regular bent functions.
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