Extractors for sumset sources

Abstract

We propose a new model of weak random sources which we call sumset sources. A sumset source X is the sum of C independent sources, with each source on n bits source having min-entropy k. We show that extractors for this class of sources can be used to give extractors for most classes of weak sources that have been studied previously, including independent sources, affine sources (which generalizes oblivious bit-fixing sources), small space sources, total entropy independent sources, and interleaved sources. This provides a unified approach for randomness extraction. A known extractor for this class of sources, prior to our work, is the Paley graph function introduced by Chor and Goldreich, which works for the sum of 2 independent sources, where one has min-entropy at least 0.51n and the other has logarithmic min-entropy. To the best of our knowledge, the only other known construction is from the work of Kamp, Rao, Vadhan and Zuckerman, which can extract from the sum of exponentially many independent sources. Our main result is an explicit extractor for the sum of C independent sources for some large enough constant C, where each source has polylogarithmic min-entropy. We then use this extractor to obtain improved extractors for other well studied classes of sources including small-space sources, affine sources and interleaved sources.