MACI

Minimum Anti-Collusion Infrastructure (MACI) is a base layer for bribery-resistant, secure, and private digital voting. Applications like clr.fund build atop MACI to increase privacy and discourage bribery for public goods funding. MACI offers the following guarantees: - Collusion resistance: no-one except a trusted coordinator should be certain of the validity of a vote, reducing the effectiveness of bribery. Receipt-freeness: no-one voter prove (besides to the coordinator) which way they voted. - Privacy: no-one except a trusted coordinator should be able to decrypt a vote. - Uncensorability: no-one — not even the trusted coordinator — should be able to censor a vote. - Unforgeability: only the owner of a user's private key may cast a vote tied to its corresponding public key. - Non-repudiation: no-one may modify or delete a vote after it is cast, although a user may cast another vote to nullify it. - Correct execution: no-one — not even the trusted coordinator — should be able to produce a false tally of votes. Under the hood, MACI uses Ethereum smart contracts and zero-knowledge proofs. It inherits security and uncensorability from the underlying Ethereum blockchain, ensures unforgeability via asymmetric encryption, and achieves collusion resistance, privacy, and correct execution via zk-SNARK proofs. Although MACI can provide collusion resistance only if the coordinator is honest, a dishonest coordinator can neither censor nor tamper with its execution. Note that MACI presumes an identity system where each legitimate member controls a unique Ethereum private key.