Welcome to MACI
Introduction
Minimal Anti-Collusion Infrastructure (MACI) is an open-source public good that serves as infrastructure for private on-chain voting.
MACI is an Ethereum application that provides privacy and collusion resistance for on-chain voting, both in a quadratic and non-quadratic fashion. A common problem among today’s on-chain voting (or public good funding) processes is how easy it is to bribe voters into voting for a particular option. Since all transactions on the blockchain are public by default, without MACI, voters can easily prove to the briber which option they voted for and therefore receive the bribe rewards.
MACI counters this problem by using encryption and zero-knowledge proofs (zk-SNARKs) to hide how each person voted while still publicly revealing the final result. User’s cannot prove which option they voted for, and therefore bribers cannot reliably trust that a user voted for their preferred option. For example, a voter can tell a briber that they are voting for option A, but in reality they voted for option B. There is no reliable way to prove which option the voter actually voted for, so the briber has less incentive to pay voters to vote their way.
Applications like clr.fund or protocols like Allo build atop MACI to increase user privacy and discourage collusion or bribery for public goods funding.
Features
MACI offers the following guarantees:
| Property | Description |
|---|---|
| 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 can 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, ECDH encryption, 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.
The participants of a MACI voting process are: 1) the voters and 2) a trusted coordinator. The coordinator is in charge of setting up the system, deploying polls, and computing the tally of the votes. Through smart contracts and ZK-proofs, MACI ensures that everything is done in a fair manner. 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.
For information on MACI's latest features, please check out our MACI v2.0.0 release post.
Background
MACI was originally proposed by Vitalik Buterin in this ethresear.ch post and has been maintained and improved since thanks to support from the Ethereum Foundation. For a general overview, the history and the importance of MACI, see Release Announcement: MACI 1.0 by Wei Jie, one of the creators. He also created a helpful overview of MACI video. Kyle Charbonnet wrote a great Technical Introduction to MACI 1.0 that provides a walkthrough on how MACI operates.
Credits
MACI is a public good infrastructure that is supported by the Ethereum Foundation within Privacy & Scaling Explorations (PSE). It's also continuously improved by our open source community! Many people have contributed to MACI, but below are some notable contributors.
MACI v1.0 was originally developed by:
- Barry WhiteHat
- Cory Dickson
- Chih-Cheng Liang
- Han Jian
- Kendrick Tan
- Kirill Goncharov
- Kobi Gurkan
- Koh Wei Jie
- Samuel Gosling
MACI v1.1.1 was primarily developed by:
Currently, MACI (v1.2.0 and beyond) is maintained and continuously improved by a core development team:
Our core team continues to work on improving the protocol and its documentation with help from our open source community.
If you are using one of the previous versions of MACI, see the MACI v0.x documentation.