Private Voting
🟡 Intermediate | 🚀 Advanced
Encrypted voting system with private ballots and verifiable tallying
Overview
A private voting system where each vote is encrypted and no one can see individual votes. Vote counts are tallied homomorphically - addition happens on encrypted values. Demonstrates FHE.add for accumulating encrypted votes and proper ACL for vote privacy. Essential pattern for DAOs and governance systems.
Quick Start
# Create new project from this template
npx labz create voting my-project
# Navigate and install
cd my-project
npm install
# Run tests
npx hardhat testContract
// SPDX-License-Identifier: BSD-3-Clause-Clear
pragma solidity ^0.8.24;
import { FHE, euint64, euint8, ebool, eaddress, externalEuint64, externalEuint8, externalEbool, externalEaddress } from "@fhevm/solidity/lib/FHE.sol";
import { ZamaEthereumConfig } from "@fhevm/solidity/config/ZamaConfig.sol";
/// @title Voting - Encrypted Voting
/// @notice Private voting system using FHE - votes are encrypted and tallied homomorphically
/// @dev Generated with Lab-Z Composable Templates
contract Voting is ZamaEthereumConfig {
// ============ Errors ============
/// @dev Proposal does not exist
error ProposalNotFound(uint256 proposalId);
/// @dev Voting period has ended
error VotingEnded(uint256 proposalId);
/// @dev Voting period has not ended yet
error VotingNotEnded(uint256 proposalId);
/// @dev User has already voted
error AlreadyVoted(address voter, uint256 proposalId);
/// @dev Invalid vote value
error InvalidVote();
// ============ Events ============
/// @notice Emitted when a new proposal is created
event ProposalCreated(uint256 indexed proposalId, string description, uint256 endTime);
/// @notice Emitted when a vote is cast
event VoteCast(address indexed voter, uint256 indexed proposalId);
// ============ Structs ============
struct Proposal {
string description;
uint256 endTime;
euint64 yesVotes;
euint64 noVotes;
bool exists;
bool finalized;
}
// ============ State Variables ============
/// @dev Proposal storage
mapping(uint256 => Proposal) private _proposals;
/// @dev Track if user has voted on a proposal
mapping(uint256 => mapping(address => bool)) private _hasVoted;
/// @dev Next proposal ID
uint256 private _nextProposalId;
// ============ Modifiers ============
// ============ Constructor ============
constructor() {
_nextProposalId = 1;
}
// ============ External Functions ============
/// @notice Create a new proposal
/// @param description The proposal description
/// @param durationSeconds How long the voting period lasts
/// @return proposalId The ID of the created proposal
function createProposal(
string calldata description,
uint256 durationSeconds
) external returns (uint256 proposalId) {
proposalId = _nextProposalId++;
Proposal storage proposal = _proposals[proposalId];
proposal.description = description;
proposal.endTime = block.timestamp + durationSeconds;
proposal.yesVotes = FHE.asEuint64(0);
proposal.noVotes = FHE.asEuint64(0);
proposal.exists = true;
// Set ACL for vote counts
FHE.allowThis(proposal.yesVotes);
FHE.allowThis(proposal.noVotes);
emit ProposalCreated(proposalId, description, proposal.endTime);
}
/// @notice Cast an encrypted vote
/// @param proposalId The proposal to vote on
/// @param encryptedVote Encrypted vote (1 = yes, 0 = no)
/// @param inputProof Zero-knowledge proof for the input
function vote(
uint256 proposalId,
externalEuint64 encryptedVote,
bytes calldata inputProof
) external {
Proposal storage proposal = _proposals[proposalId];
if (!proposal.exists) {
revert ProposalNotFound(proposalId);
}
if (block.timestamp > proposal.endTime) {
revert VotingEnded(proposalId);
}
if (_hasVoted[proposalId][msg.sender]) {
revert AlreadyVoted(msg.sender, proposalId);
}
// Convert external input to internal encrypted value
euint64 eVote = FHE.fromExternal(encryptedVote, inputProof);
// Encrypted vote: if vote > 0, it's a yes vote
ebool isYes = FHE.gt(eVote, FHE.asEuint64(0));
// Homomorphic conditional addition
// yesVotes += isYes ? 1 : 0
// noVotes += isYes ? 0 : 1
euint64 one = FHE.asEuint64(1);
euint64 zero = FHE.asEuint64(0);
proposal.yesVotes = FHE.add(proposal.yesVotes, FHE.select(isYes, one, zero));
proposal.noVotes = FHE.add(proposal.noVotes, FHE.select(isYes, zero, one));
// Mark as voted
_hasVoted[proposalId][msg.sender] = true;
// Set ACL permissions
FHE.allowThis(proposal.yesVotes);
FHE.allowThis(proposal.noVotes);
emit VoteCast(msg.sender, proposalId);
}
// ============ View Functions ============
/// @notice Get proposal details (without encrypted vote counts)
/// @param proposalId The proposal ID
/// @return description The proposal description
/// @return endTime When voting ends
/// @return exists Whether the proposal exists
/// @return finalized Whether the proposal has been finalized
function getProposal(uint256 proposalId) external view returns (
string memory description,
uint256 endTime,
bool exists,
bool finalized
) {
Proposal storage proposal = _proposals[proposalId];
return (proposal.description, proposal.endTime, proposal.exists, proposal.finalized);
}
/// @notice Check if an address has voted on a proposal
/// @param proposalId The proposal ID
/// @param voter The voter address
/// @return Whether the voter has voted
function hasVoted(uint256 proposalId, address voter) external view returns (bool) {
return _hasVoted[proposalId][voter];
}
/// @notice Get the encrypted vote counts (requires ACL permission)
/// @param proposalId The proposal ID
/// @return yesVotes Encrypted yes vote count
/// @return noVotes Encrypted no vote count
function getVoteCounts(uint256 proposalId) external view returns (
euint64 yesVotes,
euint64 noVotes
) {
Proposal storage proposal = _proposals[proposalId];
if (!proposal.exists) {
revert ProposalNotFound(proposalId);
}
return (proposal.yesVotes, proposal.noVotes);
}
/// @notice Get the next proposal ID
/// @return The next proposal ID that will be assigned
function nextProposalId() external view returns (uint256) {
return _nextProposalId;
}
// ============ Internal Functions ============
}
FHE Operations Used
FHE.add()FHE.allowThis()FHE.allow()FHE.fromExternal()FHE.asEuint32()
FHE Types Used
euint32externalEuint32ebool
Tags
voting governance dao privacy elections
Related Examples
Prerequisites
Before this example, you should understand:
Next Steps
After this example, check out:
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