Yu Sasaki

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Title: New Impossible Differential Search Tool from Design and Cryptanalysis Aspects

Abstract: This talk introduces a new tool searching for impossible differentials against symmetric-key primitives. Compared to the previous tools, our tool can detect any contradiction between input and output differences, and it can take into account the property inside the S-box when its size is small e.g. 4 bits. In addition, several techniques are proposed to evaluate 8-bit S-box. With this tool, the number of rounds of impossible differentials are improved from the previous best results by 1 round for Midori128 and Lilliput. We manually verify the impossibility of the searched results, which reveals new structural properties of those designs. Our tool can be implemented only by slightly modifying the previous differential search tool using Mixed Integer Linear Programming (MILP).