Efficient Regression-Based Linear Discriminant Analysis for Side-Channel Security Evaluations: Towards Analytical Attacks against 32-bit Implementations
32-bit software implementations become increasingly popular for embedded security applications. As a result, profiling 32-bit target intermediate values becomes increasingly needed to evaluate their side-channel security. This implies the need of statistical tools that can deal with long traces and large number of classes. While there are good options to solve these issues separately (e.g., linear regression and linear discriminant analysis), the current state of the art lacks efficient tools to solve them jointly. To the best of our knowledge, the best-known option is to fragment the profiling in smaller parts, which is suboptimal from the information theoretic viewpoint. In this paper, we therefore revisit regression-based linear discriminant analysis, which combines linear regression and linear discriminant analysis, and improve its efficiency so that it can be used for profiling long traces corresponding to 32-bit implementations. Besides introducing the optimizations needed for this purpose, we show how to use regression-based linear discriminant analysis in order to obtain efficient bounds for the perceived information, an information theoretic metric characterizing the security of an implementation against profiled attacks. We also combine this tool with optimizations of soft analytical side-channel attack that apply to bitslice implementations. We use these results to attack a 32-bit implementation of SAP instantiated with Ascon’s permutation, and show that breaking the initialization of its re-keying in one trace is feasible for determined adversaries.
Traceable Receipt-Free Encryption
CCA-like game-based security definitions capture confidentiality by asking an adversary to distinguish between honestly computed encryptions of chosen plaintexts. In the context of voting systems, such guarantees have been shown to be sufficient to prove ballot privacy (Asiacrypt'12). In this paper, we observe that they fall short when one seeks to obtain receipt-freeness, that is, when corrupted voters who submit chosen ciphertexts encrypting their vote must be prevented from proving how they voted to a third party. Since no known encryption security notion can lead to a receipt-free ballot submission process, we address this challenge by proposing a novel publicly verifiable encryption primitive coined Traceable Receipt-free Encryption (TREnc) and a new notion of traceable CCA security filling the definitional gap underlined above. We propose two TREnc instances, one generic achieving stronger guarantees for the purpose of relating it to existing building blocks, and a dedicated one based on SXDH. Both support the encryption of group elements in the standard model, while previously proposed encryption schemes aiming at offering receipt-freeness only support a polynomial-size message space, or security in the generic group model. Eventually, we demonstrate how a TREnc can be used to build receipt-free protocols, by following a standard blueprint.