Revisiting Higher-Order DPA Attacks:

Abstract

Security devices are vulnerable to side-channel attacks that perform statistical analysis on data leaked from cryptographic computations. Higher-order (HO) attacks are a powerful approach to break protected implementations. They inherently demand multivariate statistics because multiple aspects of signals have to be analyzed jointly. However, most works on HO attacks follow the approach to first apply a pre-processing function to map the multivariate problem to a univariate problem and then to apply established 1^st order techniques. We propose a novel and different approach to HO attacks, Multivariate Mutual Information Analysis (MMIA), that allows to directly evaluate joint statistics without pre-processing. While this approach can benefit from a good power model, it also works without an assumption. We present the first experimental results for 2^nd and 3^rd order MMIA as well as state-of-the-art HO attacks based on real measurements. A thorough empirical evaluation confirms the advantage of the new approach: 3^rd order MMIA attacks require about 800 measurements to achieve 100% success while state-of-the-art HODPA requires 1000 measurements to achieve about 40% success. As a consequence, the security provided by the masking countermeasure needs to be reconsidered as 3^rd and possibly higher order attacks become more practical.