Today’s side channel attack targets are often complex devices in which instructions are processed in parallel and work on 32-bit data words. Consequently, the state that is involved in producing leakage in these modern devices is large, and basing evaluations (i.e. worst case attacks), simulators, and assumptions for (masking) countermeasures on a potentially incomplete state can lead to drastically wrong conclusions.

We put forward a novel notion for the “completeness” of an assumed state, together with an efficient statistical test that is based on “collapsed models”. Our novel test can be used to recover a state that contains multiple 32-bit variables in a grey box setting. We illustrate how our novel test can help to guide side channel attacks and we reveal new attack vectors for existing implementations. We also show how the application of our statistical test shows where even the most recent leakage simulators do not capture all available leakage of their respective target devices.

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