The F1 classification conjecture for Niho type locally-APN power functions

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Let n=2mn=2m. For integers r<mr<m with gcd⁡(r,m)=1\gcd(r,m)=1, define ss by

s={2r(2r−1)−1,if gcd⁡(2r−1,2m+1)=1,2r(2r+1)−1,if gcd⁡(2r+1,2m+1)=1.s=\begin{cases}2^r(2^r-1)^{-1},&\text{if }\gcd(2^r-1,2^m+1)=1,\\[4pt]2^r(2^r+1)^{-1},&\text{if }\gcd(2^r+1,2^m+1)=1.\end{cases}

Set F1(x)=xs(2m−1)+1F_1(x)=x^{s(2^m-1)+1} over F22m\mathbb{F}_{2^{2m}}. A power function is Niho type locally-APN if it is both of Niho type and locally-APN. F1 classification conjecture. The function F1(x)=xs(2m−1)+1F_1(x)=x^{s(2^m-1)+1} covers all Niho type locally-APN power functions over F22m\mathbb{F}_{2^{2m}}. The conjecture is presented as equivalent to a classification of all Niho type locally-APN power functions and remains unresolved in the supplied text.

References

Primary source

Yuehui Cui, Jinquan Luo and Can Xiang, “Walsh Spectrum and Boomerang Properties of Locally-APN Niho Functions”, arXiv:2605.01786 (2026).

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