In encryption schemes, the sender may not generate randomness properly if generating randomness is costly, and the sender is not concerned about the security of a message. The problem was studied by the first author (2016), and was formalized in a game-theoretic framework. In this work, we construct an encryption scheme with an optimal round complexity on the basis of the mechanism of repeated games.

We present a negative result of fuzzy extractors with computational security. Specifically, we show that, under a computational condition, a computational fuzzy extractor implies the existence of an information-theoretic fuzzy extractor with slightly weaker parameters. Our result implies that to circumvent the limitations of information-theoretic fuzzy extractors, we need to employ computational fuzzy extractors that are not invertible by non-lossy functions.