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On the conjecture on APN functions and absolute irreducibility of polynomials

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Abstract

An almost perfect nonlinear (APN) function (necessarily a polynomial function) on a finite field \(\mathbb {F}\) is called exceptional APN, if it is also APN on infinitely many extensions of \(\mathbb {F}\). In this article we consider the most studied case of \(\mathbb {F}=\mathbb {F}_{2^n}\). A conjecture of Janwa–Wilson and McGuire–Janwa–Wilson (1993/1996), settled in 2011, was that the only monomial exceptional APN functions are the monomials \(x^n\), where \(n=2^k+1\) or \(n={2^{2k}-2^k+1} \) (the Gold or the Kasami exponents, respectively). A subsequent conjecture states that any exceptional APN function is one of the monomials just described. One of our results is that all functions of the form \(f(x)=x^{2^k+1}+h(x)\) (for any odd degree h(x), with a mild condition in few cases), are not exceptional APN, extending substantially several recent results towards the resolution of the stated conjecture. We also show absolute irreducibility of a class of multivariate polynomials over finite fields (by repeated hyperplane sections, linear transformations, and reductions) and discuss their applications.

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Acknowledgments

The authors are thankful to R.M. Wilson, B. Mishra, H.F. Mattson, Jr., F. Castro, F. Piñero for helpful discussions, and the referees for helpful suggestions.

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Correspondence to Heeralal Janwa.

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Communicated by A. Pott.

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Delgado, M., Janwa, H. On the conjecture on APN functions and absolute irreducibility of polynomials. Des. Codes Cryptogr. 82, 617–627 (2017). https://doi.org/10.1007/s10623-015-0168-1

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