Design Criteria
The Rijndael S-Box was specifically designed to be resistant to linear and differential cryptanalysis. This was done by minimizing the correlation between linear transformations of input/output bits, and at the same time minimizing the difference propagation probability.
In addition, to strengthen the S-Box against algebraic attacks, the affine transformation was added. In the case of suspicion of a backdoor being built into the cipher, the current S-box might be replaced by another one. The authors claim that the Rijndael cipher structure should provide enough resistance against differential and linear cryptanalysis, even if an S-Box with "average" correlation / difference propagation properties is used.
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