I m new to cryptanalysis and trying to understand differential cryptanalysis. I have read the paper by Howard M. Heys. I understood the concept of differentials but I m not able to understand how to calculate the probability of a differential to occur when we don't know any information regarding the S-boxes.
It is given that, we give 2 inputs with a difference of say, x to an S-box and get outputs of difference y and in this way, we calculate the probabilities of all the differentials possible.
But in general, the details of the S-boxes of a cipher are not disclosed (as far as I know, pls correct me if I m wrong), so how do we calculate these probabilities for each S-box?
Can we somehow use differential cryptanalysis even if we don't know the details of S-boxes used in the cipher?