Beyond Blockchain Ballots: UC-Secure Layer-2 Voting and Governance

Abstract

Maintaining a decentralized system requires a collective governance mechanism that allows participants to agree on possible changes to the system. In particular, the governance mechanism should offer a voting functionality that allows for the casting, collection, and tallying of votes in a confidential yet verifiable manner. Scaling this functionality for millions of participants in a cost-effective manner is a critical requirement for permissionless blockchains that currently remains unmet. We put forward a “layer-2” approach to meet this requirement in a setting where a permissionless blockchain acts as the fallback “layer-1” mechanism. Specifically, the key to our approach to scalability is that the protocol is realized in a layer-2 fashion-i.e., the bulk of the protocol is executed off-chain, but secured on the blockchain with a minimal footprint. We prove our protocol secure in the Universal Composability (UC) framework. First, we formalize a governance ideal functionality ${\mathcal{F}}_{\text {L2Gov }}$. Our definition offers high levels of confidentiality and verifiability. Moreover, in the case of misbehavior, it is designed to allow for the attribution of faults so that appropriate action (such as the slashing of on-chain funds) can be taken. Second, we demonstrate that our protocol UC-realizes the ${\mathcal{F}}_{\text {L2Gov }}$ functionality based on a blockchain, an off-chain bulletin board, a distributed homomorphic encryption functionality $\left({\mathcal{F}}_{\text {DHE }}\right)$, and a number of other standard hybrids. To the best of our knowledge, this work presents the first layer-2 blockchain voting protocol with a rigorous security analysis. We also point out some challenges that arise when applying the UC framework to layer-2 protocols.