Studies on Fault-tolerant Broadcast and Secure Computation

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In this dissertation, we consider the design of broadcast and secure multi-party computation (MPC) protocols in the presence of adversarial faults.

Secure multi-party computation is the most generic problem in fault-tolerant distributed computing. In principle, a multi-party computation protocol can be used to solve any distributed cryptographic problem. Informally, the problem of multi-party computation is the following: suppose we have n parties P_1, P_2, ..., P_n where each party P_i has a private input x_i. Together, the parties want to compute a function of their inputs (y_1,y_2,..., y_n) = f(x_1,x_2,..., x_n). However, some parties can be corrupted and do not execute a prescribed protocol faithfully. Even worse, they may be controlled by an adversary and attack the protocol in a coordinated manner. Despite the presence of such an adversary, a secure MPC protocol should ensure that each (corrupted) party P_i learn only its output y_i but nothing more.

Broadcast in the presence of adversarial faults is one of the simplest special cases of multi-party computation and important component of larger protocols. In short, broadcast allows a party to send the same message to all parties, and all parties to be assured they have received identical messages.

The contribution of this dissertation is twofold. First, we construct broadcast and secure multi-party computation protocols for honest majority in a point-to-point network whose round complexities improve significantly upon prior work. In particular, we give the first expected  constant-round authenticated broadcast protocol for honest majority assuming only public-key infrastructure and signatures. Second, we initiate the study of broadcast in radio networks in the presence of adversarial faults. In radio networks, parties communicate through multicasting messages; a message can only be received by the parties within some radius from the sender. Feasibility and impossibility results are given, and our bounds are tight.