pub fn sbox_spectra(sbox: &[u32], out_bits: usize) -> Option<SboxSpectra>Expand description
The affine-equivalence fingerprint of an S-box: its differential and linear spectra. Two S-boxes that
are affine-equivalent (S′(x) = B·S(A·x⊕a)⊕c for invertible A,B) share both spectra, so a difference
in either certifies inequivalence — the necessary test at the heart of S-box classification. None if
the table length is not a power of two.