Black-Box Constructions of Bounded-Concurrent Secure Computation.

We construct a general purpose secure multiparty computation protocol which remains secure under (a-priori) bounded-concurrent composition and makes only black-box use of cryptographic primitives. Prior to our work, constructions of such protocols required non-black-box usage of cryptographic primitives; alternatively, black-box constructions could only be achieved for super-polynomial simulation based notions of security which offer incomparable security guarantees. Our protocol has a constant number of rounds and relies on standard polynomial-hardness assumptions, namely, the existence of semi-honest oblivious transfers and collision-resistant hash functions. Previously, such protocols were not known even under sub-exponential assumptions.