<![CDATA[Substitution boxes are essential nonlinear modules that are popular in block cipher algorithms. They also play a significant role in the security area because of their robustness to different linear cryptanalysis. Each element of the state in a S-box is nonlinearly replaced using a lookup table. This research presents the S-box, one of the fundamental parts of the advanced encryption standard (AES) algorithm. The S-box represents the confusion part in the AES. However, when information is shared between different devices in an authorized manner, the algorithm should be able to combine a sufficient number of confusion layers to guarantee the avalanche effect (AE). Subsequently, this research selects the best S-box by comparing different sizes (4×4, 8×8, and 16×16) and measuring them on the basis of the million-bit encryption. The AE is the main criterion used in choosing the best S-box. A robust and strong cryptography algorithm should be able to confirm the AEs. Results indicate that the 16×16 S-box with a 52% AE ratio is the superior S-box]]>
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