Abstract
Establishing the CCZ-equivalence of a pair of APN functions is generally quite difficult. In some cases, when seeking to show that a putative new infinite family of APN functions is CCZ inequivalent to an already known family, we rely on computer calculation for small values of n. In this paper we present a method to prove the inequivalence of quadratic APN functions with the Gold functions. Our main result is that a quadratic function is CCZ-equivalent to the APN Gold function \({x^{2^r+1}}\) if and only if it is EA-equivalent to that Gold function. As an application of this result, we prove that a trinomial family of APN functions that exist on finite fields of order 2n where n ≡ 2 mod 4 are CCZ inequivalent to the Gold functions. The proof relies on some knowledge of the automorphism group of a code associated with such a function.
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Communicated by J. Bierbrauer.
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Bracken, C., Byrne, E., McGuire, G. et al. On the equivalence of quadratic APN functions. Des. Codes Cryptogr. 61, 261–272 (2011). https://doi.org/10.1007/s10623-010-9475-8
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DOI: https://doi.org/10.1007/s10623-010-9475-8