We are pleased to announce the release of MACI v2.0.0!

This is our second big release of the year, after the MACI v1.2 release in February of this year. MACI v2.0 brings a more secure and efficient protocol, with improved developer experience, and clearer documentation for users looking to learn about and use MACI.

Background​

MACI - Minimal Anti-Collusion Infrastructure - is an application that provides privacy and collusion resistance for on-chain voting. If you're new to MACI, we first recommend reading our documentation for background information and technical details.

New Features and improvements​

More compact codebase​

We have removed some features that were never used in production, namely Topup and Subsidy. This allowed us to reduce the codebase size, making it cheaper to deploy, as well as reducing the complexity of the zk-SNARK circuits.

We highly thank Chao for his work on these two features over the past years, and look forward to integrating similar features in the future as we come up with new use cases and performance improvements.

On top of that, the merkle tree-like structure holding the signups has been swapped out for a more efficient incremental merkle tree (LazyIMT). This offers some savings for users signing up, as well as simplifies the steps required to finalise a poll, by merging all leaves together and removing the need to compute the subroots and root of the tree.

Improved contract tasks​

It is now possible to deploy contracts and finalise polls using the contracts tasks only. This makes the protocol much easier to use, as there is no need to use the maci-cli anymore, which often came with a large number of flags and options. You will just need to fill a json file with the correct parameters and run few simple commands.

Concurrent Polls​

It is now finally possible to run multiple polls concurrently from a single MACI instance. Users will no longer need to signup again to vote on proposals published by a single organiser. One thing to note is that each poll will have the same amount of voting power, and new users will need to pass the same gating process as existing users.

We believe this feature will work best when used for coordinating several polls for the participants of a single event where signup is gated by the conference ticket and there are multiple voting rounds, like at Devcon or Devconnect.

New Gatekeepers​

Custom Gatekeepers are a great way to guard MACI against Sybil attacks, and with this release we have integrated a number of new protocols, together with the help of our community:

• Hats Protocol
• Gitcoin Passport
• Zupass
• Semaphore

For instance, with Gitcoin Passport as the gatekeeper, the MACI round organiser can set a threshold score and only allow new users with a passport score greater or equal to that threshold. Additionally, with Zupass, we can now gate access to holders of specific event tickets.

We expect to continue to expand our gatekeeper capabilities and welcome the community to come up with new and innovative ways to grant access to MACI's rounds, helping make MACI more customizable and sybil-resilient.

Documentation​

You gave us the feedback that the MACI documentation was way too tough to digest, and we heard you! To make it easier to understand, we have grouped documentation entries under a more logical structure, with different sections for different audiences and objectives.

We continue to use our docs website as the definitive resource for all information related to MACI, including blog releases, documentation updates, and roadmap progress. As always, we welcome suggestions on how to make it better and encourage you to report any inconsistencies you may find.

Security Audit​

As usual before a major release, the protocol has been thoroughly audited by PSE's internal Audit team, and this time no significant issues were found. However, thanks to the auditors' hard work, we have been able to further optimise the protocol and clean up our technical documentation.

For more details on this recent audit, please refer to our audit docs or view the full report.

With more and more eyes on the protocol, we feel more and more confident about MACI's security posture.

Trusted Setup Ceremony​

We are preparing for a new ceremony to cover the changes in our v2.0.0 circuits. To accomplish this, we'll leverage the tooling of p0tion, which helps to streamline and automate Groth16 phase2 ceremonies.

We'll update this page after the ceremony completes to include the production-ready zkey artifacts. In the meantime, the artifacts for v.1.2 can be found on our website, and the artifacts can still be used in production for releases 1.2.0 up to 1.2.5.

Get Involved​

MACI is deeply committed to our community, through our open initiatives like public roadmaps, transparent repository management, and a public Discord channel for interaction with our team.

With every issue, PR, feature and roadmap iteration, we welcome feedback to ensure that the continued development of MACI reflects your and the community's needs. Keep an eye on our documentation, GitHub discussions and our official Twitter/X account for updates.

For those looking to contribute directly, report bugs, or offer feedback, our GitHub repository is open for issues and discussions. We're eager to assist with your projects or contributions.

For practical implementation insights, review our docs as well as the clr.fund, Allo Stack with MACI, and maci-platform repositories as reference implementations. The first two integrations are quadratic funding implementations, a mechanism which otherwise is highly susceptible to collusion and bribery.

For any other questions or feedback, please reach out to us via PSE's Discord, in our #🗳️-maci channel. We're excited to connect and collaborate with you!

References​

• MACI GitHub repository
• MACI documentation
• A technical introduction to MACI 1.0 - Kyle Charbonnet
• Minimal anti-collusion infrastructure - Vitalik
• PSE Discord server
• Allo Stack with MACI
• maci-platform
• clr.fund

Release​

Here's the link to the new release code in GitHub: v2.0.0 Release.

Greetings anon,

We’re excited to share with you what we're building over the next few months. You'll see some of the same themes as our Q2 roadmap as we strive to make MACI and MACI-RPGF more user-friendly and accessible.

If you haven’t read the Q2 in review yet to learn what we’ve been up to the last three months you can check that out here.

MACI Platform​

The team is doubling down efforts to build a comprehensive voting platform with MACI powering it all. Initially called maci-rpgf, the project is soon turning into an all-in-one solution for hosting voting, quadratic funding, and rpgf rounds. We plan to work on improving the product with the following high-level initiatives:

• Complete the integration of the PSE's design team’s new design
• Bootstrap an e2e testing framework to ensure the code is more robust and reliable
• Support quadratic voting
• Support the use of different signup mechanisms
• Move application's data storage from Vercel to IPFS
• Support contributing/voting to multiple rounds on the same deployment

Our efforts will include supporting community organisers who want to fork and operate MACI Platform rounds in production. If you're interested in running a round for your community, please get in touch!

Coordinator Service​

After successfully implementing a proof generation service as part of our effort of reducing the burden on round organisers, we have plans to continue automating all MACI related operations. This includes contract deployment, proof generation and submission, contract details storage, automatic upload of final tally results to IPFS and more.

We see the “Coordinator Service” as the ultimate automation of MACI’s main pain-points, and look forward to building a secure and efficient service that will abstract away all the operational burdens of using MACI. For more information on the full feature list that this service will include, please refer to this GitHub issue.

Explore Account Abstraction​

It is clear that mass adoption of blockchain applications will be difficult if users, especially first time users, must pay to interact with dapps. Furthermore, having a crypto wallet installed and configured to work on a specific chain might also not be straightforward for an average user.

To support this thesis, the MACI team will start a collaboration with other PSE teams involved in researching and implementing account abstraction (AA) solutions. We look forward to bringing some proof of concepts (PoC) for MACI Paymasters and more, which will help remove friction when it comes to web3 UX.

MACI Protocol Improvements​

As always, we plan to improve the MACI protocol both in terms of making it cheaper and easier to use, as well as making it more secure.

As part of this effort, we are currently working with the 3327 team to integrate their Anonymous Poll Joining grant work into a new MACI version. The effort can be tracked in this public GitHub board. This work enables unconditional voter privacy, further strengthening user privacy in the protocol. For more details, please refer to this blog post.

On top of this, the team will begin the ground work to implement Vitalik’s latest MACI proposal Mostly Offchain Happy Path - in a nutshell, the proposal seeks to completely remove transaction costs for users by moving certain operations offchain. For maximum privacy and trustlessness, voters will still be able to go directly on-chain and submit their own signup/vote actions.

How does that sound?​

Questions? Concerns? Ideas? We’d love to hear from you!

If there is a feature you think we should work on, or an initiative you'd like to collaborate with us on, please let us know! We welcome input from anyone in the community. The best ways to get in touch are to hop in our Discord (#🗳️-maci channel), tag us on X, or create an issue on GitHub.

Onward and upward 🚀

Greetings anon,

Glad to have you here! It's that time of the year where we have a few MACI roadmap updates to share. We’re going to take a moment to look at what we accomplished in Q2, as the most active project in the entire PSE GitHub org.

Before we start, we would like to express our gratitude to all our collaborators and contributors to the MACI protocol.

Q2 in review​

In our q2 roadmap, we aimed at a few major Q2 goals that all tied together:

✅ MACI-RPGF​

A lot has happened with MACI-RPGF this last quarter. Much time has been spent improving the product in order to provide a more functional and stable product with a better overall user experience.

PSE's design team came up with a beautiful design that will soon be merged into the stable version of the code. We are looking forward to implementing this major update and are excited for you to try it!

On the outreach and support side, we also engaged with several communities to run a round using MACI-RPGF. There are three rounds ongoing with EthMexico, ETH Tegucigalpa and Cryptoversidad. Our developers have been working closely with their development teams to deploy and run MACI-RPGF. We look forward to supporting them throughout their rounds and helping facilitate the distribution of funds directly into community members building amazing things in the Ethereum ecosystem.

✅ MACI Coordinator Service​

The use of a Coordinator Service would greatly simplify the operation requirements when running MACI. To better support communities running MACI polls, whether as a QF round or a simple voting application, the team has prioritised the development of a Coordinator Service that can be used by any Round Operator.

In the last three months we successfully completed the first iteration of a proof generation service, which can be used to more easily finalise MACI polls. Additionally, work on a frontend dashboard has started. This dashboard can be used to more easily deploy contracts in a customisable way via an intuitive user interface.

✅ MACI Core Protocol Improvements​

To achieve our Q2 goal of “Unconditional Privacy" we worked with the 3327 team (responsible for the ElGamal on MACI implementation) to come up with an effective solution and a better user experience that we could have hoped for. More on this can be found in our blog, but we have now started this grant work and are looking forward to seeing this in action in the coming months.

We have also been busy working on some new features and improvements to the codebase. It is now easier than ever to deploy MACI instances, as well as re-use certain smart contracts that have already been deployed and will not need changing.

Furthermore, we have managed to slightly reduce the costs for users by removing unused features, as well as using different and more optimised data structures. This brought several improvements, such as allowing for concurrent polls to be run from one MACI instance (finally!).

Finally, we worked with the community to integrate a number of different gatekeepers:

• Semaphore
• Gitcoin Passport
• Zupass - thanks gasperpre for the implementation

You can now use these (plus more) to gatekeep signups to MACI and shoot down those sybil attacks!!.

Stay tuned for an upcoming MACI release where all these efforts can be seen in action.

✅ Support Gitcoin Allo protocol integration​

Throughout May and June, Gitcoin and Nick Lionis in particular worked hard to integrate MACI in the Allo Stack. You can find the code on their GitHub. The stack will soon be used in production by Gitcoin to support running grant rounds privately.

We are excited to see rounds being run with this integration, and look forward to continue to collaborate with the Allo team to improve MACI and integrate new versions into their stack.

✅ Support ETHDam hackathon QV round​

In April, we successfully supported the ETHDam team to run a private quadratic voting (QV) round for the ETHDam hackathon, powered by MACI. Conference attendees used clr.fund to vote on their favourite hackathon projects in order to allocate $10,000 to projects building novel privacy and security solutions in the ecosystem.

✅ MACI starter kit​

We've teamed up with Buidl Guild and the Scaffold-ETH team to build a MACI starter kit: a web app that integrates MACI in order to run polls. Thanks to Yash's efforts we now have a ready-to-use MACI starter kit. This has already been used in two hackathons (as an example here's an Eth Berlin project) to quickly prototype projects using MACI. We thank Yash for all his effort with this and are looking forward to see what the community will build with it.

That was a lot, and there’s more to come! Be sure to keep an eye out here for our next post where we look forward to what is coming for MACI in Q3, 2024.

What are Public Goods?​

Public goods are services or products that are available for everyone to consume, regardless of whether they contribute to their creation. Examples include clean air, public parks, and open-source software. These goods are essential for community welfare but often face funding challenges due to their non-excludable and non-rivalrous nature. This is where blockchain technology steps in, offering a decentralised approach to funding these vital initiatives. Through blockchain, transparency and community participation in funding decisions are greatly enhanced.

What is MACI and how does it help fund Public Goods?​

At its core, MACI is a tool that ensures privacy and prevents collusion in voting and decision-making processes. This function is crucial in public goods funding scenarios, as it ensures that the allocation of funds is fair and uninfluenced by external factors.

Current state​

MACI can be used in different forms of decision making and voting.

Quadratic funding is one of the ways in which we could utilise MACI for public goods funding. Quadratic funding is a democratic mechanism for crowdfunding that seeks to promote equitable, inclusive funding for public goods such as open-source software, scientific research, and public art initiatives. By incorporating MACI, these platforms guarantee that votes on how funds are distributed are not swayed by bribery or external pressures. This approach ensures a democratic and equitable distribution of funds, leading to more effective and genuinely representative support for public goods.

Another way in which MACI is utilised is for communities to be able to vote in Retroactive Public Goods Funding (RetroPGF) rounds. For example, Optimism runs RetroPGF rounds which involve allocating funds to projects based on past contributions to the ecosystem, incentivising and rewarding valuable contributions retrospectively. We’ve incorporated MACI to the RPGF stack and thus communities would be able to independently run future rounds in a private and secure manner using maci-rpgf!

The Future looks bright​

As we look to the future, the potential of MACI in reshaping public goods funding is significant. MACI could be used for larger and more diverse funding initiatives, expanding its impact, potentially influencing even governmental approaches to public goods funding. The role of MACI in fostering a transparent, fair, and democratic process for funding public goods is set to be a game-changer. Learn more about MACI by reading through our documentation. Join us in our mission, connect with our team on Discord today!

Welcome to the intriguing world of blockchain! This guide delves into Minimal Anti-Collusion Infrastructure (MACI), essential for those exploring secure, private voting on the blockchain.

Understanding MACI’s Strengths​

MACI stands as a lighthouse of private, secure voting in blockchain voting. Key features include:

• Collusion Resistance: MACI combats collusion, a significant issue in blockchain voting, by making it impossible for voters to verify their choices to others.
• Privacy: A cornerstone of MACI, ensuring vote secrecy.
• Receipt-Freeness: Ensuring voters can’t prove beyond any reasonable doubt their vote to others.
• Hinders bribery: As anyone looking to bribe voters can’t confirm how voters placed their votes, this potentially discourages bribery.

These strengths make MACI vital in enhancing trustworthiness, especially for newcomers.

Use Cases for MACI​

Some potential use cases for MACI are as follows

• DAO Voting: For Decentralized Autonomous Organizations (DAOs), MACI secures votes for crucial decisions, maintaining democracy in these organizations.
• Public Goods Funding: On platforms like clr.fund , MACI ensures fair funding decisions, free from external influences via Quadratic Funding.
• Elections: MACI could also be used in governmental elections for people to cast secure votes for the leaders of their state!

These use cases demonstrate MACI's transformative role in making voting more accessible and trustworthy.

Where MACI May Not Be Ideal​

MACI's powerful features may not suit every scenario. For example:

• Transparent Governance: Where individual vote transparency is key, MACI’s privacy might not be the best option
• Simple Polling: In basic, non-sensitive blockchain polling, MACI's complexity might not be needed.

Recognising the context of the situation helps in choosing the right tool for blockchain voting needs.

Conclusion​

MACI is a significant advancement for secure, private voting. Understanding its strengths and appropriate applications is key to leveraging this technology. As the blockchain landscape evolves, tools like MACI will play an increasingly vital role. Dive deeper into MACI and its application via our documentation and by joining our team’s discussion via our Discord channel!

Hey Anon!

In this blog post, we’ll give a high-level, beginner friendly introduction of what Minimal Anti-Collusion Infrastructure (MACI) is, and how it could be used in a real-world context. We’ll take you through the essentials of MACI, making complex concepts accessible regardless of your background in the blockchain space.

What is MACI?​

MACI is a cutting-edge solution that ensures private, reliable voting on the blockchain.

Blockchain Voting Challenges for Beginners​

On-chain voting is a method of casting votes directly on the blockchain, leveraging its decentralized and transparent nature. While this provides us with censorship resistance and guarantees correct execution, the transparency of blockchains can be a double-edged sword. Given all transaction data is public by default, it means everyone can see how anyone voted. This ensures all votes are correctly counted but the visibility could lead to undue influence on voters' decisions, and potentially opens doors for unethical practices like voter bribery. The challenge, therefore, lies in preserving the privacy of each vote while maintaining the core principles of blockchain: transparency, process integrity, and security.

How MACI Offers a Solution​

Minimal Anti-Collusion Infrastructure, or MACI, steps in as an elegant solution to these challenges. Despite operating on-chain, it protects the privacy of voters and votes, thereby significantly reducing the chances of vote manipulation through bribery. How does it achieve this? By employing advanced cryptographic techniques like zero-knowledge proofs (zk-SNARKs), MACI ensures that while the outcome of the vote is public and transparent, individual voting choices remain private. For instance, let's say you vote in an election using MACI, you could claim to everyone that you voted for a particular candidate, but in reality, you might have voted for someone else. There's no way for anyone to verify your claim, making bribery less appealing.

Key Features of MACI​

MACI isn't just a tool; it's a fortress safeguarding the integrity of on-chain voting. Let's break down its key features:

• Collusion Resistance: MACI makes it virtually impossible for voters to be swayed by bribes, as they can't prove how they voted.
• Privacy: Your vote is your secret. Only you know where your support lies, thanks to the encryption technology MACI employs.
• Uncensorability: Every vote counts and cannot be blocked, edited or removed, ensuring a fair voting process.
• Unforgeability: Your vote is tied to your unique digital identity, preventing anyone else from casting a vote in your place.
• Non-repudiation: Once cast, your vote is set in stone. You can change your mind and vote again, but you can't erase your previous vote.
• Correct Execution: The final tally is accurate and tamper-proof, ensuring that the true voice of the voting population is heard.

These features come together to create a voting environment where your voice is heard, loud and clear, without fear of external influence or manipulation.

Technical Overview Simplified​

At its heart, MACI is built on Ethereum, a blockchain platform. This foundation provides a high level of security and trust. The real magic, however, lies in something called zk-SNARKs. Think of zk-SNARKs as a cloak of invisibility for your vote; they hide your voting choices while still guaranteeing the overall vote count to be tallied accurately. This blend of Ethereum's robust framework and the innovative use of zk-SNARKs makes MACI a reliable and secure choice for on-chain voting, ensuring that your vote is both private and counted.

If you’re interested in more of the technical details, check out the MACI documentation.

Real-World Applications and Limitations​

Imagine a world where funding for public goods, like community projects or open-source software, is decided through fair and transparent voting. This is where MACI shows its true potential. Quadratic funding is already harnessing MACI's capabilities to enhance user privacy and discourage any form of collusion in funding decisions.

However, like any system, MACI isn't perfect. Its effectiveness hinges on the honesty of the coordinator – the entity or person overseeing the voting process and tallying the results. A dishonest coordinator could pose risks, but thankfully, MACI is designed to minimise even this possibility, maintaining a high level of integrity in the voting process.

Conclusion​

As we've explored, Minimal Anti-Collusion Infrastructure (MACI) stands as a testament to the innovative solutions being developed in the blockchain space, especially for those new to this technology. It addresses the critical need for privacy and fairness in on-chain voting, ensuring that your vote remains your own, free from external pressures and manipulation.

Blockchain technology is continually evolving, and with tools like MACI, it's becoming more accessible and trustworthy. Whether you're a blockchain enthusiast, a developer, or someone just starting to explore this exciting field, MACI represents a significant step forward in creating a more democratic and transparent digital world.

We encourage you to delve deeper into MACI and the broader world of blockchain by reading through our documentation and installing MACI. Join us too on our Discord to report any bugs or to chat with our team. Your involvement can help shape a future where digital voting is not just secure, but also truly representative of the people's voice.

Together, let's embrace these advancements and contribute to a fairer, more transparent digital voting landscape.

Minimal Anti Collusion Infrastructure (MACI) is a public good that allows one to run secure, private, on-chain voting polls.

Given MACI's open source nature, it's common for our core team to develop new features or to fix issues based on community feedback. However, it's been less common for external contributors to make significant changes to the core protocol.

Well, this soon will be a reality thanks to a MACI improvement proposal sent by the 3327 team. 3327 is collective of 10+ people working on improving blockchain technologies, with a focus on research and engineering. Their engineering team previously worked on implementing the ElGamal flow into MACI (here's a nice presentation on it from Marija Mikić at EthCC [6]). The work described in this post aims to be its direct replacement due to its simplified nature and several additional benefits.

This proposal can be divided into two parts:

1. bring unconditional privacy to MACI's voters
2. optimise inefficient merkle tree structure holding messages, by replacing it with a hash chain

1) Enable unconditional voter privacy​

Currently with MACI, if a voter performs a key change, the voter's new key would not be anonymous to the coordinator. The coordinator could collude with a bad actor to inform the latter of the key change, as the coordinator would have access to all decrypted messages.

The key focus of this improvement is to enable users to be completely anonymous by removing the link between the original signup key and the key used for voting. How would this work? Well, users sign up to vote via the MACI contract, and depending on the gatekeeper in use, they'd have to prove that they've passed the entry condition. Now, given knowledge of this key, they can signup with a new key to polls deployed by this same MACI contract.

Thus, voters can prove anonymously that they know the preimage of a StateLeaf, by passing this information to a zk-SNARK circuit, and validating this proof within the poll contract when joining with the new key. You might be thinking that everyone knows the preimage of a state leaf, as it's public information that can be taken from the contracts' logs. However, the circuit will not accept the public key directly but would instead take the private key and use it to generate the public key. This way, only users with knowledge of a specific private key can generate a valid inclusion proof.

Now after signing up to the Poll with this new key, there will not be any link to the original key, and users will effectively be anonymous. Of course users should ensure that they are using different wallets where possible.

Finally, with the use of a nullifier, it will not be possible for the same original key to be used to signup more than once for each new poll.

Are there any drawbacks? Well, yes. There will be an extra step for users to register to individual Polls. We aim to offset this cost and additional step soon either with gasless transactions or by moving some logic off-chain.

2) Message structure optimisation​

On top of the improvements to anonymity, the 3327 team aims to also replace the Merkle tree used for storing messages with a hash chain. Some of the benefits of this approach are:

• unlimited number of messages
• removal of expensive merge operations from the coordinator
• cheaper to send messages as only one hash is required to update the hash chain
• less constraints on the circuits due to simplified logic

Unlimited messages

Merkle trees are usually bound by a depth property. Together with the number of leaves per node, we can calculate the max capacity of a tree. For instance, for a binary tree with a depth of 10, we can host up to 2^10 (1024) leaves. On the other hand, hash chains do not have a limit, unless if we wanted to set one, so we technically can support an unlimited number of messages.

Cheaper operations

Hashing the previous hash chain with the message is cheaper than inserting into a Merkle tree. Additionally, removing the need for the coordinator to perform merge operations on the accumulator queues that were used on chain will greatly reduce costs and processing time.

Smaller circuits

As cited in their proposal, processing message inclusion proofs for k messages in a tree with height h requires k * h hashing operations within the circuit with 2 * k * h signal values for inclusion proofs. Processing messages with chain hashes removes the unnecessary inclusion proofs and requires only k hashes to be computed for k messages without any extra signals, as the requirement is to prove that the order and inclusion of all messages are correct.

A call for MACI grant proposals​

So what does this mean for you, Anon?

As an open-source project of PSE with support from the Ethereum Foundation, MACI is fortunate to have the resources to invest in the maintenance and improvement of the protocol. This means we're able to fund full-time developers as well as allocate grants for various research and development initiatives.

We encourage all community members to contribute to the improvement and ongoing development of MACI! After all, our goal is to build the most secure e-voting system, and this cannot be accomplished without all of your support.

As a team, we are incredibly excited about this proposal and will continue to work hard to help the 3327 team get this upgrade production-ready over the next 3 months.

To contribute to MACI, submit issues, or learn more about it, you can reach out to us either via Discord or GitHub issues.

If you have an ambitious idea you'd like to work on, reach out to us and we could create a proposal to build together! If you don't yet have a specific idea but are still keen to work on MACI, we have some research ideas which might inspire you and we could collaborate on a grant together. Feel free to explore these ideas below and get in touch:

• MACI coordinator in a TEE
• Group wise matching
• Folding schemes for MACI's circuits

References​

• 3327 team
• 3327 ElGamal flow
• 3327 ElGamal API
• Marija Mikić - Anonymity in MACI - EthCC [6]
• MACI Original idea
• MACI Anonymization

Minimal Anti-Collusion Infrastructure (MACI), is making waves in the world of private, digital voting. But where did this technology originate? Vitalik Buterin is the mind that thought of MACI. In this post, we’ll dive into his vision for a more secure and private digital voting system.

Who is Vitalik Buterin?​

For those unfamiliar with the name, Vitalik Buterin is a Russian-Canadian programmer who co-founded Ethereum. Ethereum is a blockchain platform that has been a game-changer in the world of cryptocurrency and beyond. Vitalik’s passion for blockchain technology led him to explore various applications, including digital voting, which eventually culminated in the proposal of MACI.

What Inspired MACI?​

Vitalik was deeply concerned with the issues plaguing traditional and digital voting systems, such as fraud, lack of privacy, and potential manipulation. He imagined a system that could handle digital voting with utmost integrity, transparency, and security, ensuring that people’s votes would genuinely make a difference. This led to the birth of Minimum Anti-Collusion Infrastructure or MACI.

Breaking Down MACI​

MACI is a system designed for digital voting that protects against collusion and bribery, while ensuring privacy, authenticity, and that no vote can be censored. How? Through cleverly employing smart contracts on the Ethereum blockchain and something called Zero-Knowledge Proofs (ZKPs). This combination makes sure that no one, aside from a trusted coordinator who helps tally results, can view the votes. However, absolutely no one, not even the coordinator, can tamper with the results.

The Importance of Privacy​

One of Vitalik’s major concerns was the privacy of voters. In a world where data is often exposed or misused, the anonymity of a voter is of utmost importance in maintaining the integrity of the voting process. MACI ensures that votes remain a secret, and that only a trusted coordinator has the ability to decrypt them.

A Democratic Revolution​

Through MACI, Vitalik sought to revolutionise the democratic process. Imagine a world where communities could make decisions without fear of interference or manipulation. Where funds could be raised and allocated for public goods and services in a fair and transparent way. That’s what MACI is all about.

Final Thoughts​

Vitalik’s vision for MACI was not just a technological advancement, but a stride towards a more just and democratic society. Through blockchain technology, he has shown how innovation can be harnessed for the greater good, by protecting the sanctity of each vote. MACI is a testament to how technology can be a powerful tool in upholding democratic values and ensuring that every voice is heard. If you’re keen on learning more, dig in to our documentation here. Also, join us in building our future, connect with our team on Discord!

During ETHDam's Quadratic Funding round, run on clr.fund, we discovered a critical bug in MACI. The issue stemmed from the lack of validation on MACI public keys within the Poll contract. A user (spoiler alert, it was a self-inflicted denial of service (DoS)) was able to submit a MACI public key which was not a point of the Baby JubJub elliptic curve, and it broke everything.

So... what happened, really?​

Well, during the ETHDam round, there was an issue with the subgraph that caused the frontend web app to incorrectly display that the voting period had ended, which prevented users from voting.

A quick way for us to identify the issue was to directly call the Poll's smart contract to submit an invalid vote. If the contract accepted votes, that meant that it was not a MACI issue. Given the contract accepted votes, it immediately helped us confirm that the bug was a frontend issue. What we didn't know at the time was that this vote, as well as its associated key, would cause a denial of service.

The message in question can be seen on Gnosis Chain's block explorer. Below is proof that the wallet which submitted the invalid key is from one of our teammates (just in case you thought we'd want to censor it :P).

{
  "address": "0xc59975735ed4774b3Ee8479D0b5A26388B929a34",
  "msg": "This is proof that I control this wallet and dossed MACI by mistake while doing an invalid vote",
  "sig": "0x8962b66462630f12476d7bdb348f08af574ba40dd32c6f149ea26717830f13f50f4e95574e8fc909dd3dd1e20bcd85ae2c3caaf41bed6b123973353635483b7f1b",
  "version": "2"
}

One can verify the message using etherscan, paste the address, message and signature. Don't take our word for it, verify!

The message was sent alongside an invalid MACI public key. As a result, due to how MACI messages are processed, the zk-SNARK circuit failed to generate a proof, which prevented the QF round from finalizing.

A MACI public key is (supposedly, at least) a point on the Baby JubJub elliptic curve. The mistake that MACI's code made was to not validate at the smart contract level that the keys accepted as arguments were actually valid points on the curve. At the time the bug was triggered, the two coordinates of the point (x and y) were only checked to be less or equal to the curve prime order.

The MACI key in question looked like the below object:

{
  "x": 1,
  "y": 1
}

In MACI, messages are (well, should be) encrypted using a shared key generated using a random keypair and the coordinator's public key. This allows for the coordinator to reverse the process - as long as they have the random public key - and decrypt the message using the same shared key. This is achieved using Elliptic-curve Diffie–Hellman (ECDH).

Shared key generation from the user's side:

ECDH(randomKeyPair.privateKey, coordinatorPublicKey)

Shared key generation from the coordinator's side:

ECDH(coordinatorPrivateKey, randomKeyPair.publicKey)

The randomKeyPair.publicKey that was sent as {x: 1, y: 1} was eventually passed by the coordinator to a zk-SNARK circuit to try and decrypt the corresponding message and perform further processing.

When passed to the circuit, the code would perform the ECDH operation by performing a scalar multiplication between the public and the coordinator private key. This happens inside the MessageToCommand template, which calls the ECDH template. Here, there is a call to escalarMulAny which in turns calls SegmentMulAny, where we encounter the final call to Edwards2Montgomery where the error pops up.

Looking inside the Edwards2Montgomery template, we can see the operation that is performed on the public key. In short, the point is converted from the Twisted Edwards form to Montgomery form, as it allows for cheaper operations inside the circuit (whereas outside it is represented in its original Twisted Edward form).

The equation to convert between the two forms is presented below:

                1 + y       1 + y
    [u, v] = [ -------  , ---------- ]
                1 - y      (1 - y)x

We can see how passing a y of 1, the equation would result in a division by zero. Below you can see the full stack trace of the error:

Error in template Edwards2Montgomery_349 line: 38
Error in template SegmentMulAny_362 line: 81
Error in template EscalarMulAny_364 line: 163
Error in template Ecdh_365 line: 23

Please note that passing x as 0 would also trigger this error, though within the EscalarMulAny template, this case is handled and the G8 point is passed instead, preventing an error while generating the proof.

Given this issue, we weren't able to complete the proof generation for message processing. It is somewhat good news, as once a message is posted to MACI's smart contracts, it's not possible to censor it even if these messages trigger bugs.

How was the round saved?​

After understanding the bug, the team came up with a solution that would both allow EthDAM to pay out projects with cryptographic guarantee of the results, as well as provide a solution that is fully transparent and verifiable. After all, MACI is all about verifiability.

Given that the clr.fund round was run using a token with no monetary value (EthDAMToken), instead of spinning up a new round and asking users to re-submit their votes, we opted for an automated solution which would scrap all signups and contribution of this token, as well as all messages, and to re-submit them to the new clr.fund round contracts.

This way, voters can validate that all signups and votes were included, and by not submitting this invalid message, being able to generate zk-SNARK proofs and validate publicly the final tally result.

The script in question can be found in a gist. In a nutshell, the script pulled all signups from the original round fundingRound contract, and submitted them on the new contract, after having approved the new contract to spend all EthDAMToken tokens. Then, it pulls the messages, aside from the invalid one, and posts them to the new Poll contract.

After this, the EthDAM team was able to complete the tally alongside ZK proofs to be submitted on chain.

How did we fix MACI?​

To fix the bug, we added code to validate that a given point is on the curve. The Solidity library, found within the original Baby JubJub paper, was originally developed by yondonfu and for sake of simplicity, it was copied over to the MACI's repo. The code needed just a couple of small upgrades to work with more recent Solidity versions (0.8.20).

/**
 * @dev Check if a given point is on the curve
 * (168700x^2 + y^2) - (1 + 168696x^2y^2) == 0
 */
function isOnCurve(uint256 _x, uint256 _y) internal pure returns (bool) {
  uint256 xSq = mulmod(_x, _x, Q);
  uint256 ySq = mulmod(_y, _y, Q);
  uint256 lhs = addmod(mulmod(A, xSq, Q), ySq, Q);
  uint256 rhs = addmod(1, mulmod(mulmod(D, xSq, Q), ySq, Q), Q);
  return submod(lhs, rhs, Q) == 0;
}

As seen in the code above, the function will evaluate the Baby JubJub equation using the input public key x and y values. Any value that is not on the curve, will be rejected, as shown below:

// check if the public key is on the curve
if (!CurveBabyJubJub.isOnCurve(_encPubKey.x, _encPubKey.y)) {
  revert InvalidPubKey();
}

The bug was fixed with this PR. On top of preventing such invalid values from being accepted by the contract, we also added more validation across the TypeScript libraries to make it harder for users to make such mistakes.

Footnote​

The MACI team would like to first of all thank EthDAM's team for their patience while we navigated through this issue, and trusting us with coming up with a transparent solution for the round.

Furthermore, we thank mikerah from HashCloak for helping to review the fix, and their expertise in handling security incidents like this. Together with them, we looked at other repositories using similar code, looking for the same mistake, though we did not find similar protocols where an invalid key would cause a denial of service. If you are a ZK developer reading this, we hope this was a lesson that would help remind us all to always validate user input for future scenarios.

Finally, a big thank you to Raphael for explaining the math behind the issue, and suggesting that full point validation would end up being a much better solution than just not accepting y = 1.

Contract addresses​

Below is a list of the contract addresses for this EthDAM round. All code is verified on Gnosis's block explorer and can be reviewed.

RoundToken

• EthDAMToken

clr.fund Instance

• clr.fund

Original round

• FundingRound
• MACI
• Poll

New Round

• Funding Round
• MACI
• Poll
• Tally
• MessageProcessor

MACI New Version​

We decided to publish a new version of MACI with the fix (and other changes made since the 1.2 release). The new version is 1.2.1.

Please do not use the 1.2 version of the contracts for any new deployments, as it contains the bug described in this post. All other packages are safe, though 1.2.1 is the recommended version to use.

Greetings anon,

Glad to have you here! We have a few MACI roadmap updates to share.

Before we hop into our Q2 plans, let's take a look at what we did in Q1:

Q1 in review​

In our kickoff of 2024, we aimed at a few major Q1 goals that all tied together:

✅ Release MACI v1.2​

We completed a significant refactor to simplify the codebase and improve developer experience. After an internal audit and revamped documentation, we released a new MACI version - see our MACI v1.2 release post to read up on the details of that upgrade.

✅ Support clr.fund upgrade​

clr.fund, a quadratic funding (QF) project which has distributed millions of dollars to Ethereum public goods, is the longest-running production application built on MACI (since 2020!). Thanks primarily to the hard work of their core dev yuetloo, clr.fund successfully upgraded from MACI 0.x to our fresh v1.2 release. Nicely done!

✅ Support ETH Latam QF round​

We teamed up with ETH Latam to help them run a QF round using the clr.fund stack (running on MACI v1.2). Over 60 conference attendees participated (using Zupass tickets as the gatekeeper to the faucet and round) to distribute over 30,000 DAI to public good projects across Central America and the Caribbean - view the round results and learn more in ETH Kipu's ETH Latam recap post!

✅ Support ETH Colombia QF round​

The ETH Colombia team ran a QF round for their community - view the round results here.

✅ Community engagement via events​

We participated in our first hackathons (ETHGlobal Circuit Breaker, ETHGlobal London, ETH Latam, ETHTaipei and ETHDam) and distributed over $10,000 in bounties. We had a blast engaging with hackers from around the world, receiving feedback, and seeing innovative project ideas on MACI come to life. Thank you to all those who participated!

Q2 Roadmap​

Now let's look at what we're excited to build over the next few months:

🎯 MACI-RPGF​

Retroactive Public Goods Funding (RPGF) has been building momentum over the past few years and really took the crypto space by storm after Optimism's recent round of 30 million OP.

In February we proposed MACI as a solution for Optimism's RPGF tech stack, thanks to MACI's strong guarantees of correct execution, censorship resistance, privacy, and collusion resistance. Since releasing a demo of our full-stack MACI-RPGF implementation in March, we've received positive feedback and interest from various communities in running RPGF rounds on MACI.

This quarter we're excited to keep building out MACI-RPGF with additional functionality and improved UX. Our efforts will include supporting community organizers who want to fork and operate MACI-RPGF rounds in production. If you're interested in running a round for your community, please get in touch!

🎯 MACI Coordinator Service​

From years of supporting QF rounds on MACI we've learned a lot about the pain-points of community organizers. The blunt truth is that many technical barriers still exist - in order to operate a MACI poll (whether in a QF round or a simple voting application), you essentially must be a developer to deploy the smart contracts, execute on-chain transactions, and run tooling to generate zero-knowledge proofs to guarantee the integrity of a MACI poll. This is no trivial feat, and as a result, MACI is simply not a viable option for many communities to use today.

We're aiming to change this by building a "Coordinator Service" to simplify the role of the coordinator, automate tasks, and remove technical barriers to running MACI-RPGF (and all MACI) rounds. This will include a web interface to deploy and operate MACI instances as well as a server to generate proofs and submit them on-chain. We're confident this tooling will accelerate community adoption by offloading the technical overhead and domain knowledge currently required to use this technology stack. More details to come on this soon!

🎯 MACI Core Protocol Improvements​

After our thorough refactor of MACI's code, which led to the release of v1.2, we're now in position to add new features and improvements to the core protocol. As always, we are open to suggestions from the community, so please let us know what ideas and feature requests you have!

Currently, we have a couple of focus areas:

Unconditional Privacy

As of now, MACI's coordinator can track user key changes, which allows them to associate voters with their respective votes, and thus potentially collude with bribers to deanonymize users. We're investigating ways to prevent this possibility. The 3227 team implemented a proof of concept using El-Gamal to remove the link between a new MACI key and their original key. Furthermore, there is a proposal under discussion on how to implement anonymous poll signups, which would provide the same benefits of the El-Gamal protocol, though with a much better user experience.

Deployment Improvements

MACI's deployment process can certainly be made easier and more efficient. We will explore ways to improve this, for instance making it cheaper to deploy MACI by implementing patterns to only deploy contracts once if they can be reused across MACI instances. We aim to make it more user-friendly as well by providing a better interface to deploy MACI instances.

🎯 Support Gitcoin Allo protocol integration​

In our initial 2024 roadmap we outlined our plans to engage more with the broader Ethereum ecosystem in order to validate the value of MACI by exploring integrations and gathering input from community developers. Gitcoin is a great example: we've been in discussions with them to explore a MACI integration into their Allo protocol - the smart contracts that power Gitcoin Grants Stack - in order to increase user privacy and bribery resistance in their public good funding infrastructure.

We're already in the process of supporting this integration, thanks to Nick Lionis and Tse Lao and their ETHDam hackathon project. We're excited to see this integration come to life in production and to support Gitcoin in their efforts to improve public goods funding on Ethereum!

🎯 Support ETHDam hackathon QV round​

Given the privacy focus of ETHDam, we're excited to support a private quadratic voting (QV) round for the hackathon, powered by MACI. Conference attendees will use clr.fund to vote on their favorite hackathon projects in order to allocate $10,000 to hackathon projects building novel privacy and security solutions in the ecosystem. The round is live at ethdamqf.com, so stay tuned for results!

🎯 MACI starter kit​

We're teaming up with Buidl Guild and the Scaffold-ETH team to build a MACI starter kit: a web app that integrates MACI in order to run polls. We expect this to be a useful template for any developer prototyping on MACI or just looking for a simple reference implementation. Whether you're a dev that prefers reading through code vs. documentation, or you're a builder who merely wants to understand how the MACI user flow works, we hope this will be a great resource for you!

How does that sound?​

Questions? Concerns? Ideas? We’d love to hear from you!

If there is a feature you think we should work on, or an initiative you'd like to collaborate with us on, please let us know! We welcome input from anyone in the community. The best ways to get in touch are to hop in our Discord (#🗳️-maci channel), tag us on X or create an issue on GitHub.

Onward and upward 🚀