Improving Side-Channel Analysis with Optimal Linear Transforms

David Oswald, Chris­tof Paar



Pre-processing techniques are widely used to increase the success rate of side-channel analysis when attacking (protected) implementations of cryptographic algorithms. However, as of today, the according steps are usually chosen heuristically. In this paper, we present an analytical expression for the correlation coefficient after applying a linear transform to the side-channel traces. Doing so, we are able to precisely quantify the influence of a linear filter on the result of a correlation power analysis. On this basis, we demonstrate the use of optimisation algorithms to efficiently and methodically derive “optimal” filter coefficients in the sense that they maximise a given definition for the distinguishability of the correct key candidate. We verify the effectiveness of our methods by analysing both simulated and real-world traces for a hardware implementation of the AES.

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