Generic cryptanalysis of combined countermeasures with randomized BSD representations

In ICICS'04, Sim et al. proposed an attack against the full version of Ha-Moon's countermeasure which is one of enhanced counter-measures. The analysis technique is based on the fact that the probability for the appearance of an intermediate value is p = 1/2. By our simulations, however, it is proven to be not true. Thus sometimes the output of their attack might be wrong because there exists the case that the probability p is so small that they can make a wrong decision. In this paper we repair the above attack, and then propose a generic analytical technique applicable to all BSD type countermeasures combined with some simple power analysis countermeasures. In order to show that the proposed attack is as practical as the usual differential power analysis (DPA), we estimate the number of samples and computational cost. Furthermore, we enhance the proposed attack in two ways such that it works against right-to-left algorithm in a simpler and more efficient way, and also works against one combined with an extra DPA countermeasure.