Building a Privacy-Preserving Voting System on Midnight

Overview

This comprehensive guide teaches developers how to create anonymous, verifiable voting applications using Midnight Network's zero-knowledge proof technology. The tutorial covers smart contract development in the Compact language, React frontend integration, testing strategies, and deployment procedures.

Key Concepts

The Privacy Problem

Traditional blockchains create a fundamental conflict: they're transparent by design, yet voting requires privacy. Midnight solves this through zero-knowledge proofs, enabling voters to prove eligibility without revealing identity while maintaining verifiable vote tallies.

Core Features

• Anonymous voting: Prove eligibility without disclosing identity
• Verifiable results: Public verification of vote counts
• Coercion resistance: Impossible to prove how someone voted
• Double-vote prevention: Cryptographic nullifier system prevents duplicate votes

Architecture Components

The system consists of three layers:

• Smart Contract Layer (Compact language): Manages proposal state, vote tallying, and eligibility verification
• SDK Layer: Provides contract interaction methods and state management
• Frontend Layer (React): User interface for voting and results display

State Management

• Public ledger: Proposal details, vote counts, deadlines, used nullifiers
• Private state: Voter eligibility data, vote choices, nullifiers

Prerequisites and Setup

Required tools include Node.js v23+, npm v11+, Docker, and the Compact compiler (v0.27.0). The setup process involves installing Git LFS, the Compact compiler, Lace Wallet, and cloning the starter template.

Contract Implementation

The Compact language enables writing state-changing circuits and pure functions. Key functions include:

• createProposal(): Initialize new voting events
• castVote(): Record votes for valid options
• endVoting(): Finalize voting periods (admin-only)
• resetProposal(): Prepare for new elections (admin-only)

The contract maintains counters for each option (up to 4), tracks total votes, and enforces state transitions through assertions.

Frontend Integration

React components handle voting interface, admin panels, and results visualization. The voting page component allows users to select options, submit votes, and view live participation metrics. The admin panel enables proposal creation, timing control, and voting period management.

Testing Strategy

The testing framework includes unit tests for proposal creation, vote validation, voting period enforcement, and multi-voter scenarios. A simulator class enables local testing without network interactions.

Advanced Patterns

The tutorial explores several extensions:

• Weighted voting: Token-based governance with power proportional to holdings
• Quadratic voting: Cost increases quadratically to reduce wealth concentration
• Delegated voting: Allow vote power transfer to trusted delegates
• Multi-round voting: Implement runoff elections with eliminated options
• Time-locked results: Encrypt votes until deadline passes

Deployment

Local development uses a standalone Midnight node, while Preview Network deployment requires wallet funding via faucet, environment configuration, and contract publishing. The checklist verifies compiler installation, test completion, wallet setup, and successful contract deployment.

Best Practices

The guide emphasizes validating inputs before state changes, maintaining clear state machines, implementing graceful error handling, and testing edge cases including maximum voter scenarios, tied votes, and zero-participation outcomes.

Resources

Official documentation includes Midnight docs, Compact language guides, Lace Wallet information, and community channels including Discord and GitHub repositories.