Building on known definitions, we present a unified general framework for defining and analyzing security of cryptographic protocols. The framework allows specifying the security requirements of a large number of cryptographic tasks, such as signature, encryption, authentication, key exchange, commitment, oblivious transfer, zero-knowledge, secret sharing, general function evaluation, and more. ... more >>>

We show that any concurrent zero-knowledge protocol for a non-trivial language (i.e., for a language outside $\BPP$), whose security is proven via black-box simulation, must use at least $\tilde\Omega(\log n)$ rounds of interaction. This result achieves a substantial improvement over previous lower bounds, and is the first bound to rule ... more >>>

Following Dwork, Naor, and Sahai (30th STOC, 1998), we consider concurrent execution of protocols in a semi-synchronized network. Specifically, we assume that each party holds a local clock such that a constant bound on the relative rates of these clocks is a-priori known, and consider protocols that employ time-driven operations ... more >>>

We construct a secure protocol for any multi-party functionality that remains secure (under a relaxed definition of security) when executed concurrently with multiple copies of itself and other protocols. We stress that we do *not* use any assumptions on existence of trusted parties, common reference string, honest majority or synchronicity ... more >>>

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 >>>