Analyzing and Optimizing the Dummy Rounds Scheme

Abstract

The dummy rounds protection scheme, intended to offer resistance against Side Channel Attacks to Feistel and SP ciphers, has been introduced in earlier work. Its experimental evaluation revealed weaknesses, most notably in the first and last round. In this contribution, we show that the situation can be greatly improved by controlling the transition probabilities in the state space of the algorithm. We derived necessary and sufficient conditions for the round execution probabilities to be uniform and hence the minimum possible. The optimum trajectories over the state space are regular and easy to implement.