The existence conjecture for recursive APN functions

Let nNn\in\mathbb{N} with n2n\geq 2. An APN function Fn ⁣:F2nF2nF_n\colon\mathbb{F}_{2}^n\to\mathbb{F}_{2}^n is recursive if, for each i{2,,n1}i\in\{2,\dots,n-1\}, there exists an APN function Fi ⁣:F2iF2iF_i\colon\mathbb{F}_{2}^i\to\mathbb{F}_{2}^i such that

F2F3Fn1Fn.F_2\prec F_3\prec\dots\prec F_{n-1}\prec F_n.

Recursive APN function conjecture. There exists a recursive APN function in every dimension nNn\in\mathbb{N} with n2n\geq 2.

The conjecture is motivated by examples of quadratic APN functions in dimension 88 containing APN restrictions successively down to dimension 22, together with the authors' construction of many new APN extensions. Its resolution is not given in the source.

Sources & referencesView supporting material

Primary source

Christof Beierle, Gregor Leander and Léo Perrin, “Trims and Extensions of Quadratic APN Functions”, arXiv:2108.13280 (2022).

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