UQ-Vote: Consensus-Authorized Threshold Decryption for End-to-End Verifiable Elections

Abstract

End-to-end verifiable electronic voting requires more than encrypted ballots and a published tally. Auditors also need a consistent election transcript, and trustees need a clear rule for deciding when decryption is allowed. Existing systems often combine threshold tallying with a bulletin board. However, the condition for releasing decryption shares is usually left to trustee-side procedures. UQ-Vote instead adopts a unified-quorum architecture for consensus-authorized threshold decryption: the same authority committee maintains a PBFT-backed bulletin board and holds shares of a threshold ElGamal key. With <inline-formula> <tex-math notation="LaTeX">$n\ge 3f+1$ </tex-math></inline-formula> authorities and threshold <inline-formula> <tex-math notation="LaTeX">$t=2f+1$ </tex-math></inline-formula>, transcript finality and decryption authorization are linked. After closing, honest replicas derive the same finalized ballot set, compute the same aggregate ciphertexts, commit a locked target set, and release shares only for consensus-authorized targets. We specify the workflow, state its security claims, and evaluate a Go prototype in both single-host and multi-machine settings. In the single-host evaluation, throughput decreases from 97.0 to 67.2 ballots/s and mean ballot commit latency rises from 2732.6 to 4640.8 ms as the committee grows from <inline-formula> <tex-math notation="LaTeX">$n=4$ </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$n=13$ </tex-math></inline-formula>. In the multi-machine evaluation, the protocol preserves correctness under view change, withheld-share, and invalid-share scenarios.