[Resource Topic] 2015/591: How much randomness can be extracted from memoryless Shannon entropy sources?

Welcome to the resource topic for 2015/591

Title:
How much randomness can be extracted from memoryless Shannon entropy sources?

Authors: Maciej Skorski

Abstract:

We revisit the classical problem: given a memoryless source having a certain amount of Shannon Entropy, how many random bits can be extracted? This question appears in works studying random number generators built from physical entropy sources. Some authors use a heuristic estimate obtained from the Asymptotic Equipartition Property, which yields roughly n extractable bits, where n is the total Shannon entropy amount. However the best known precise form gives only n-O(\sqrt{\log(1/\epsilon) n}), where \epsilon is the distance of the extracted bits from uniform. In this paper we show a matching n-\Omega(\sqrt{\log(1/\epsilon) n}) upper bound. Therefore, the loss of \Theta(\sqrt{\log(1/\epsilon) n}) bits is necessary. As we show, this theoretical bound is of practical relevance. Namely, applying the imprecise AEP heuristic to a mobile phone accelerometer one might overestimate extractable entropy even by 100\%, no matter what the extractor is. Thus, the ``AEP extracting heuristic’’ should not be used without taking the precise error into account.

ePrint: https://eprint.iacr.org/2015/591

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