One of the central questions in Cryptography today is proving security of the protocols ``on the Internet'', i.e., in a concurrent setting where there are multiple interactions between players, and where the adversary can play so called ``man-in-the-middle'' attacks, forwarding and modifying messages between two or more unsuspecting players. Indeed, ... more >>>

We develop new tools to study the relative complexities of secure
multi-party computation tasks (functionalities) in the Universal
Composition framework. When one task can be securely realized using
another task as a black-box, we interpret this as a
qualitative, complexity-theoretic reduction between the two tasks.
Virtually all previous characterizations of ... more >>>

In his seminal work, Cleve [STOC 1986] has proved that any r-round coin-flipping protocol can be efficiently biassed by ?(1/r). The above lower bound was met for the two-party case by Moran, Naor, and Segev [Journal of Cryptology '16], and the three-party case (up to a polylog factor) by Haitner ... more >>>