Can anyone explain what a branch number is and how to calculate it? I have checked several books on matrices but it seems uncommon. In particular, the matrix:
02030101
These entries are hexadecimals (or bytes), e.g. in bits 02 is 00000010, and comes from the Mix column layer in the AES cipher (just in case that makes a difference).
I have read this matrix has the maximum branch number of n+1=5, but I do not understand where this came from or what it means.
I also read this is an MDS matrix and I think branch numbers and MDS matrices are linked somehow but, again, I don't know how. I have looked for video tutorials on MDS matrices and branch numbers but there is nothing for beginners.
A couple of simple examples for branch numbers and/or MDS matrices would be really helpful.