Construction of Lightweight S-Boxes With Low Boomerang Uniformity
Construction of Lightweight S-Boxes With Low Boomerang Uniformity
Abstract:
The security and area of the substitution boxes (S-boxes) have significant impacts on the security performance and hardware efficiency of lightweight cipher algorithms, respec-tively. However, the current large-sized S-boxes have not yet achieved a good balance in these two aspects. Therefore, a construction method for 6-bit and 8-bit S-boxes that is compatible with security and hardware performance is proposed, focusing on the structure and F-function that affect the security and area of S-boxes. In terms of structures, we theoretically analyse the boomerang uniformity of the three-round Feistel structure and its variants. An unbalanced Feistel structure framework with linear permutation is constructed based on the analysis results. It improves the high boomerang uniformity problem of S-boxes based on Feistel structures. Then, we concentrate on controlling the block length that corresponds to the two branches in the structure and the iteration round numbers to ensure optimal S-box construction. In terms of the F-function, it considers standard cell gates with multiple inputs and the depth of Boolean functions to find the implementation with the smallest area. Compared to existing 6-bit and 8-bit S-boxes, the proposed S-boxes have reduced the area by 65.41% and 67.22%, respec-tively. They achieve lower boomerang uniformity and possess good cryptographic properties. Furthermore, we apply the method to small-sized S-boxes and obtain 4-bit and 5-bit S-boxes that are compatible with encryption characteristics and hardware performance. These S-boxes of different sizes can be adapted to the needs of lightweight cipher algorithms in a variety of application scenarios.
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Construction of Lightweight S-Boxes With Low Boomerang Uniformity
