Paper 2022/1040

A framework for constructing Single Secret Leader Election from MPC

Abstract

The emergence of distributed digital currencies has raised the need for a reliable consensus mechanism. In proof-of-stake cryptocur- rencies, the participants periodically choose a closed set of validators, who can vote and append transactions to the blockchain. Each valida- tor can become a leader with the probability proportional to its stake. Keeping the leader private yet unique until it publishes a new block can significantly reduce the attack vector of an adversary and improve the throughput of the network. The problem of Single Secret Leader Election (SSLE) was first formally defined by Boneh et al. in 2020. In this work, we propose a novel framework for constructing SSLE proto- cols, which relies on secure multi-party computation (MPC) and satisfies the desired security properties. Our framework does not use any shuffle or sort operations and has a computational cost for N parties as low as O(N) of basic MPC operations per party. We improve the state-of-the- art for SSLE protocols that do not assume a trusted setup. Moreover, our SSLE scheme efficiently handles weighted elections. That is, for a total weight S of N parties, the associated costs are only increased by a factor of logS. When the MPC layer is instantiated with techniques based on Shamir’s secret-sharing, our SSLE has a communication cost of O(N2) which is spread over O(log N) rounds, can tolerate up to t < N/2 of faulty nodes without restarting the protocol, and its security relies on DDH in the random oracle model. When the MPC layer is instantiated with more efficient techniques based on garbled circuits, our SSLE re- quires all parties to participate, up to N − 1 of which can be malicious, and its security is based on the random oracle model.