Blockchain-based e-voting system with verifiability and voter privacy

Abstract

This dissertation presents the design, implementation and evaluation of a blockchain-based e-voting prototype which supports ballot confidentiality, verifiability and auditability by combining homomorphic encryption, zero-knowledge proofs and Merkle inclusion proofs. The key innovation of this work lies in a unified on-chain protocol that cryptographically binds each ballot's Poseidon commitment to its ElGamal ciphertext through a shared binding hash, enabling Groth16-verified tallying and anonymous receipt-based audit without any trusted middleware. In the voting phase, the voter encrypts a one-hot ballot, computes a commitment and a ciphertext-binding hash, and submits them together with a zero-knowledge proof that the ballot is well formed without revealing the selected candidate. During the tallying stage, all encrypted ballots are off-chain aggregated, the final results are accompanied by a proof of correct decryption. Voters can confirm their ballots are included by using locally stored receipts and an audit bundle provided by the administrator. The prototype is implemented with Solidity for the smart contracts, Circom and snarkjs for zero-knowledge circuits, JavaScript for frontend interaction and Python for local serving and cryptographic validation. It was tested locally with Hardhat and then deployed to the Sepolia testnet for more realistic on-chain execution and gas measurement. The results show that the system functions as a research prototype, although further hardening is still needed before any production use.