In effect "traffic analysis" applied at the bus level.
This may be either quite easy or quite difficult to counter.
Basically you need to keep a constant(ish) power level in the system. If that's possible then it will be more difficult to pick the signal out of the noise. Keep the data paths filled with dummy data so there are no (or quite shallow) spikes in the noise.
It's intriguing that they were able to chop the search space into byte size segments and thereby exclude a lot of it.
Clever but depressing, give AES256 seemed pretty strong.
Biting the hand that feeds IT
