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The title basically says it. We have a 16 by 16 s-box, $256$ entries total. And the first value is the multiplicative inverse of $257$, so

$1 \times k \bmod 257, \space k = 1$.

$2 \times k \bmod 257, \space k = 129$.

$3 \times k \bmod 257, \space k = 86$

$\ldots$

Would this be secure? and if the value is higher then $255$, then we choose the lowest unused number.

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  • $\begingroup$ what about the entry of zero ? is it equal to zero? $\endgroup$ – hardyrama Apr 24 '20 at 10:09
  • $\begingroup$ @hardyrama yes, would that be a problem? $\endgroup$ – Ömer Enes Özmen Apr 24 '20 at 11:02
  • $\begingroup$ Fixed point . it will be good to calculate the DDT , LAT , BCT and compare it to AES sbox $\endgroup$ – hardyrama Apr 24 '20 at 11:55
  • $\begingroup$ Okay, But is just the sbox I described above good? $\endgroup$ – Ömer Enes Özmen Apr 24 '20 at 12:03
  • $\begingroup$ I personally see the question "is this a good sbox" to be similar to the question "is a hammer a good tool" - it rather depends on what you intend to use it for. A hammer is good if you have a nail; it is less good if you're trying to paint a wall (a paintbrush works rather better in that case) $\endgroup$ – poncho Apr 24 '20 at 15:29

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