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

Maintaining a decentralized system requires a collective governance mechanism that allows participants to agree on changes to the system. In particular, the governance mechanism should offer a voting functionality for casting, collecting, and tallying 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 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, our approach to scalability realizes the protocol in a layer-2 fashion: 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 F_L2Gov. Our definition offers high levels of confidentiality and verifiability. Moreover, in the case of misbehavior, it allows faults to be attributed so that appropriate action (such as the slashing of on-chain funds) can be taken. Second, we demonstrate that our protocol UC-realizes the F_L2Gov functionality based on a blockchain, an off-chain bulletin board, a distributed homomorphic encryption functionality (F_DHE), and 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.