# Is it possible to use an S-box similar to the one used in DES in AES? How would this work?

I'm reviewing some questions given to me by a professor and am stumped on this one. My initial guess is that yes, this is possible, but I do not know how to explain it, specifically for a function $$\{0,1\}^8\to \{0,1\}^6$$. Any help would be appreciated!

## 1 Answer

DES is a Feistel cipher that doesn't require the $$F$$ function to be reversible, where the S-Boxes are used. DES has a non-reversible $$F$$ function in which the 8 S-boxes $$S:\{0,1\}^6\to \{0,1\}^4$$ is used.

AES is based on Susbstition Permutation Network (SPN) where everything must be reversible. AES is using S-boxes $$S:\{0,1\}^8\to \{0,1\}^8$$. Therefore it is not possible to use the DES Sboxes in the AES.

Besides the functionality, even if we could interchange them, that would require to analyze, too.