Practical Large-Scale Distributed Key Generation

Generating a distributed key, where a constant fraction of the players can reconstruct the key, is an essential component of many large-scale distributed computing tasks such as fully peer-to-peer computation and voting schemes. Previous solutions relied on a dedicated broadcast channel and had at least quadratic cost per player to handle a constant fraction of adversaries, which is not practical for extremely large sets of participants. We present a new distributed key generation algorithm, sparse matrix DKG, for discrete-log based cryptosystems that requires only polylogarithmic communication and computation per player and no global broadcast. This algorithm has nearly the same optimal threshold as previous ones, allowing up to a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\frac{1}{2}-\epsilon$\end{document} fraction of adversaries, but is probabilistic and has an arbitrarily small failure probability. In addition, this algorithm admits a rigorous proof of security. We also introduce the notion of matrix evaluated DKG, which encompasses both the new sparse matrix algorithm and the familiar polynomial based ones.