I have worked all summer with ChipWhisperer, and I am now going to head on to my greatest challenge so far; attack an FPGA-board(CW305) with AES-256. I am able to recover the key with AES-128 utilizing your course “PA_HW_CW305_1-Attacking_AES_on_an_FPGA”.
However, I do not know how to approach the attack with AES-256. To do the AES-128, one attacks the last round. This also work for AES-256, but now this is just half of what one need to recover the master key. And one can not repeat this for round 13, since round 1-13 are done in one clock-cycle. Locating and extracting the round-key for round 13 therefore is impossible this way( I think ).
How would you do this sort of attack?