maci-core

This submodule assists with handling key business logic functions and processes.

Overview

One may conceive of MACI as a state machine with 1) data and 2) functions which transform said data. This makes it easier to reason about the system, write tests, and implement functionality. It also allows us to implement the smart contracts in discrete components which are easy to test.

To this end, this submodule exposes a MaciState class and a Poll class. Developers should instantiate objects from these classes to test MACI. For instance, MACI.test.ts creates a MaciState object and every time it interacts with the MACI smart contract, it mirrors said interaction on the MaciState and Poll. As such, the developer can then use their helper functions like maciState.signUp(), poll.publishMessage, poll.processMessages(), and poll.tallyVotes() to step through the various stages of the MACI flow.

MaciState

Key functions

signUp

Accepts a user's public key and creates a new state leaf and ballot leaf.

In testing, whenever a test suite submits a signUp() transaction, it should call maciState.signUp() as well, so that the off-chain representation of MACI is kept up to date.

In production, genMaciStateFromContract() in genMaciState.ts uses this function when it scans a MACI contract's event log for signups, so as to bring its MaciState instance up to date.

deployPoll

Creates a new Poll. This should be done whenever the MACI contract's deployPoll() function is called.

Helper functions

copy

A function that deep-copies an object.

Key data structures

stateTree

stateTree is a quinary Merkle tree, chosen over a binary tree due to the gas and circuit constraints associated with the Poseidon hash function (details here). Each leaf in this tree represents a participant's public key, their voice credit balance and the block timestamp at which they signed up. The tree features a configurable depth and an arity of five, with insertions starting at index 1. The zeroth leaf is reserved as a security measure against denial-of-service attacks.

Poll

A Poll is an off-chain representation of a Poll. In testing, Poll instances should mirror their on-chain counterparts.

Key functions

publishMessage

Publishes a message by updating the message tree and message accumulation queue.

processMessages

Processes a batch of messages and returns the inputs to the processMessages circuit which can be used to prove correct execution.

tallyVotes

Tallies a batch of votes and returns the inputs to the tallyVotes circuit which can be used to prove correct execution.

Helper functions

copy

Deep-copies and returns this object.

Key data structures

messageTree

messageTree is also a quinary Merkle tree. Each message in this tree represents an encrypted command, such as a user casting a vote in a poll or changing their public key.

Testing

For more details about testing please refer to the tests documentation.

Directory Structure

• ts/: The home for our core classes, MaciState and Poll
• ts/utls/: Contains supporting utilities
• ts/__tests__/: A dedicated test suite directory