Tornado Vote: Anonymous Blockchain-Based Voting

Decentralized apps (DApps) often hold significant cryptocurrency assets. In order to manage these assets and coordinate joint investments, shareholders leverage the underlying smart contract functionality to realize a transparent, verifiable, and secure decision-making process. That is, DApps implement proposal-based voting. Permissionless blockchains, however, lead to a conflict between transparency and anonymity; potentially preventing free decision-making if individual votes and intermediate results become public. In this paper, we therefore present Tornado Vote, a voting DApp for anonymous, fair, and practical voting on the Ethereum blockchain. We propose to use a cryptocurrency mixer such as Tornado Cash to reconcile transparency and anonymity. To this end, we adapt Tornado Cash and develop a voting protocol that implements a fair voting process. While Tornado Vote can technically process 10 k votes on Ethereum in approximately two hours, this is not feasible under realistic conditions: Third-party transactions on the Ethereum Mainnet reduce the possible throughput, and transaction fees make it infeasible to use all available block capacities. We therefore present various Gas cost models that yield lower bounds and economic estimations with respect to the required number of blocks and voting costs to assess and adjust Tornado Vote's feasibility trade-off.