Fu, Shihui, Xiutao Feng, and Baofeng Wu. 2017. “Differentially 4-Uniform Permutations With the Best Known Nonlinearity from Butterflies”. IACR Transactions on Symmetric Cryptology 2017 (2): 228-49. https://doi.org/10.13154/tosc.v2017.i2.228-249.