Local Correlation Breakers and Applications to Three-Source Extractors and Mergers

We introduce and construct a pseudorandom object which we call a local correlation breaker (LCB). Informally speaking, an LCB is a function that gets as input a sequence of r (arbitrarily correlated) random variables and an independent weak-source. The output of the LCB is a sequence of r random variables with the following property. If the i´th input random variable is uniform then the i´th output variable is uniform even given a bounded number of any other output variables. That is, an LCB uses the weak-source to break local correlations between random variables. Our construction of LCBs has applications to three-source extractors, mergers with weak-seeds, and a variant of non-malleable extractors, that we introduce.