If DES decryption is the same as encryption done in reverse order, then how can the reversed S-Box convert 4 bits into 6 bits?
I've read about 20 papers about the criteria for choosing best $n$ * $n$ s-boxes. Now, I've got two problems: How to generate (2^24) s-boxes, and how to test them considering the criteria. ...
The Rijndael S-Box design generates a permutation cycle of type $2+27+59+81+87$. What effect would replacing that permutation with a cycle of type $256$ have on the security of AES?
It seems like the S-boxes in DES have essentially random values. How were these chosen?