-1
$\begingroup$

I am new to cryptography. I am looking to understand how to answer this question from my class:

Find below the S-box of AES. Given the input 01010011 in binary, calculate the output.

enter image description here

$\endgroup$
  • $\begingroup$ be aware that is not the AES s-box, but rather the inverse s-box $\endgroup$ – Richie Frame Feb 27 '18 at 4:26
2
$\begingroup$

An AES S-box is nothing else than a permutation. You give it a input, and it give you the corresponding output.

Here the S-box is represented by a 2D array. If your input is $01010011$, you have to get it's hexadecimal representation : $0x53$ (because an hexadecimal is represented by four bits, $0101 = 5$ and $0011 = 3$).

Now you only have to get the corresponding output of the Sbox ($5$ is the left nibble, en $3$ the right nibble).

$\endgroup$
1
$\begingroup$

Since $0011$ is your right nibble and $0101$ is your left nibble, row 5 and column 3 give the output of 50 (hex) or $01010000$ in binary.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.