Unbreakable Keys from Random Noise

Virtually all presently used cryptosystems can theoretically be broken by an exhaustive key-search, and they might even be broken in practice due to novel algorithms or progress in computer engineering. In contrast, by exploiting the fact that certain communication channels are inherently noisy, one can achieve encryption provably secure against adversaries with unbounded computing power, in arguably practical settings. This chapter discusses secret key-agreement by public discussion from correlated information in a new definitional framework for information-theoretic reductions.