Communication For Omniscience by a Neutral Observer and Information-Theoretic Key Agreement of Multiple Terminals

We derive a new upper bound on the secrecy capacity in the source model with eavesdropper which strictly improves the currently best upper bound, i.e. the double intrinsic information bound of Renner and Wolf. Furthermore, unlike that bound, which is defined only in the case of two terminals, the new upper bound is not specific to the two terminals case. We define a problem of communication for omniscience by a neutral observer and establish the equivalence between this new problem and the problem of secret key agreement.