Smart Card Research and Advanced Applications by Sonia Belaïd & Tim Güneysu

Author:Sonia Belaïd & Tim Güneysu
Language: eng
Format: epub
ISBN: 9783030420680
Publisher: Springer International Publishing

4.1 Random Space Exploration

The random space exploration algorithm is described in Algorithm 1.4

The algorithm returns a key candidate that maximizes the sum of scalar products over the small set of key candidates we explore. Hence, the algorithm tries to find the maximizing key of the distinguisher. We note that the term in step 14: results in matching the leakage of S-box with a kind of template given by the sum of the leakages of the S-boxes to . If the guess for the keys to is correct, that template converges for larger values of s to the true leakage function value and the chance to recover the correct key increases with greater s. Actually this observation could already have been the starting point for designing the algorithm. Another design idea was based on the observation, that when having a set of different pairs of S-boxes there is a good chance to have one pair for which the correct key can be found. This pair then results in a better template for matching the leakage of the third S-box, and so on.

The cost of the proposed algorithm is modest in terms of memory, we just need to store the maximum key. In terms of time, the algorithm is also efficient and it has a running time .

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