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Abstract Sometimes it is possible to embed an algebraic trapdoor into a block cipher. Building on previous research, in this paper we investigate an especially dangerous algebraic structure, which is called a hidden sum and which is related to some regular subgroups of the affine group. Mixing group theory arguments and cryptographic tools, we pass from characterizing our hidden sums to designing an efficient algorithm to perform the necessary preprocessing for the exploitation of the trapdoor. [ABSTRACT FROM AUTHOR]

Abstract: S-Boxes are important security components of block ciphers. We provide theoretical results on necessary or sufficient criteria for an (invertible) 4-bit S-Box to be weakly APN. Thanks to a classification of 4-bit invertible S-Boxes achieved independently by De Cannière and Leander–Poschmann, we can strengthen our results with a computer-aided proof. We also propose a class of 4-bit S-Boxes which are very strong from a security point of view. [Copyright &y& Elsevier]