A Stochastic Model for Differential Side Channel Cryptanalysis

Werner Schindler, Kerstin Lemke-Rust, Chris­tof Paar

Cryptographic Hardware and Embedded Systems - - CHES 2005, 7th International Workshop, Edinburgh, UK. August 29 - September 1, 2005.


Abstract

This contribution presents a new approach to optimize the

eciency of di erential side channel cryptanalysis against block ciphers by advanced stochastic methods. We approximate the real leakage func- tion within a suitable vector subspace. Under appropriate conditions pro ling requires only one test key. For the key extraction we present a `minimum principle' that solely uses deterministic data dependencies and the `maximum likelihood principle' that additionally incorporates the characterization of the noise revealed during pro ling. The theoretical predictions are accompanied and con rmed by experiments. We demon- strate that the adaptation of probability densities is clearly advantageous regarding the correlation method, especially, if multiple leakage signals at di erent times can be jointly evaluated. Though our eciency at key extraction is limited by template attacks pro ling is much more ecient which is highly relevant if the designer of a cryptosystem is bounded by the number of measurements in the pro ling ste

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Tags: DEMA, DPA, Electro- magnetic Analysis, Maximum Likelihood Principle, Mini- mum Principle, power analysis, Stochastic Model, Template Attack