ACB-Vote: Efficient, Flexible, and Privacy- Preserving Blockchain-Based Score Voting With Anonymously Convertible Ballots.

Blockchain has emerged as a decentralized platform for e-voting. Among various blockchain-based voting systems, score voting provides flexible choices and better reflects public opinions. However, existing blockchain-based score voting systems suffer from heavy range proof overheads, and are much inefficient compared with other blockchain-based voting systems. Besides, voter anonymity in these systems is not rigorously addressed. In this paper, we propose an efficient, flexible and privacy-preserving score voting system, named ACB-Vote, from anonymously convertible ballots. ACB-Vote achieves voting anonymity with BBS+ signature and signature of knowledge. Driven by convertibly linkable signatures (CLS), ACB-Vote allows cast ballots to be converted, where the conversion mechanism prevents anonymous voters from multiple voting. Besides, the proposed system avoids heavy range proofs, enables batch ballot verification and facilitates flexible tallying methods. We formally define a security model for ACB-Vote and provide rigorous security proofs. Experiments show that the efficiency of ACB-Vote is competitive compared with the previous score voting systems and is affordable in blockchain environments.