Secret communication using sources and channels

Alice wants to send Bob a secret message in the presence of an eavesdropper Eve. Alice has two resources available: a noisy broadcast channel and source observations correlated with observations at Bob and Eve. We consider two cases, the first in which the source observations and channel are independent and the second in which they can depend on each other. For the independent case, we consider a strategy that exploits the sources and channels separately and show this separation strategy is optimal for a class of sources and channels that includes a Gaussian example. For the case in which the sources and channels depend on each other, this separation strategy does not work, and an optimal strategy has yet to be established. For this setting, we improve on the best known upper bound to the secret message capacity.