Ters fonksiyonun CCZ-denkliği üzerine bazı çalışmalar

Most cryptographic systems, like block ciphers, depend heavily on vectorial Boolean functions. A function with good cryptological properties should have low differential uniformity which is invariant under some equivalence classes. The more general one of these is CCZ-equivalence which is introduced by Carlet, Charpin and Zinoviev in 1998. In cryptography, CCZ-equivalence gained an interest since it preserves many significant properties like differential uniformity. Looking for permutations within the CCZ-class of a function for the construction of S-boxes used in block ciphers is also intriguing. In this thesis, we presented a detailed description on the results of Kölsch's paper about nonexistence of permutation polynomials in the form $L_m(x^{-1})+L_{m'}(x)$ over binary finite field. This proves that every permutation CCZ-equivalent to the inverse function is also affine equivalent to it. We also gave a criterian to be a permutation polynomial which is verified by using Kloosterman sums. }