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MACI.sol
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MACI.sol
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// SPDX-License-Identifier: MIT
pragma experimental ABIEncoderV2;
pragma solidity ^0.6.12;
import { DomainObjs } from './DomainObjs.sol';
import { IncrementalQuinTree } from "./IncrementalQuinTree.sol";
import { IncrementalMerkleTree } from "./IncrementalMerkleTree.sol";
import { SignUpGatekeeper } from "./gatekeepers/SignUpGatekeeper.sol";
import { InitialVoiceCreditProxy } from './initialVoiceCreditProxy/InitialVoiceCreditProxy.sol';
import { SnarkConstants } from './SnarkConstants.sol';
import { ComputeRoot } from './ComputeRoot.sol';
import { MACIParameters } from './MACIParameters.sol';
import { VerifyTally } from './VerifyTally.sol';
interface SnarkVerifier {
function verifyProof(
uint256[2] calldata a,
uint256[2][2] calldata b,
uint256[2] calldata c,
uint256[] calldata input
) external view returns (bool);
}
contract MACI is DomainObjs, ComputeRoot, MACIParameters, VerifyTally {
// A nothing-up-my-sleeve zero value
// Should be equal to 8370432830353022751713833565135785980866757267633941821328460903436894336785
uint256 ZERO_VALUE = uint256(keccak256(abi.encodePacked('Maci'))) % SNARK_SCALAR_FIELD;
// Verifier Contracts
SnarkVerifier internal batchUstVerifier;
SnarkVerifier internal qvtVerifier;
// The number of messages which the batch update state tree snark can
// process per batch
uint8 public messageBatchSize;
// The number of state leaves to tally per batch via the vote tally snark
uint8 public tallyBatchSize;
// The tree that tracks the sign-up messages.
IncrementalMerkleTree public messageTree;
// The tree that tracks each user's public key and votes
IncrementalMerkleTree public stateTree;
uint256 public originalSpentVoiceCreditsCommitment = hashLeftRight(0, 0);
uint256 public originalCurrentResultsCommitment;
// To store the Merkle root of a tree with 5 **
// _treeDepths.voteOptionTreeDepth leaves of value 0
uint256 public emptyVoteOptionTreeRoot;
// The maximum number of leaves, minus one, of meaningful vote options.
uint256 public voteOptionsMaxLeafIndex;
// The total sum of votes
uint256 public totalVotes;
// Cached results of 2 ** depth - 1 where depth is the state tree depth and
// message tree depth
uint256 public messageTreeMaxLeafIndex;
// The maximum number of signups allowed
uint256 public maxUsers;
// The maximum number of messages allowed
uint256 public maxMessages;
// When the contract was deployed. We assume that the signup period starts
// immediately upon deployment.
uint256 public signUpTimestamp;
// Duration of the sign-up and voting periods, in seconds. If these values
// are set to 0, the contract will be in debug mode - that is, only the
// coordinator may sign up and publish messages. This makes it possible to
// submit a large number of signups and messages without having to do so
// before the signup and voting deadlines.
uint256 public signUpDurationSeconds;
uint256 public votingDurationSeconds;
// Address of the SignUpGatekeeper, a contract which determines whether a
// user may sign up to vote
SignUpGatekeeper public signUpGatekeeper;
// The contract which provides the values of the initial voice credit
// balance per user
InitialVoiceCreditProxy public initialVoiceCreditProxy;
// The coordinator's public key
PubKey public coordinatorPubKey;
uint256 public numSignUps = 0;
uint256 public numMessages = 0;
TreeDepths public treeDepths;
bool public hasUnprocessedMessages = true;
address public coordinatorAddress;
//----------------------
// Storage variables that can be reset by coordinatorReset()
// The Merkle root of the state tree after each signup. Note that
// batchProcessMessage() will not update the state tree. Rather, it will
// directly update stateRoot if given a valid proof and public signals.
uint256 public stateRoot;
uint256 public stateRootBeforeProcessing;
// The current message batch index
uint256 public currentMessageBatchIndex;
// The batch # for proveVoteTallyBatch
uint256 public currentQvtBatchNum;
// To store hashLeftRight(Merkle root of 5 ** voteOptionTreeDepth zeros, 0)
uint256 public currentResultsCommitment;
// To store hashLeftRight(0, 0). We precompute it here to save gas.
uint256 public currentSpentVoiceCreditsCommitment;
// To store hashLeftRight(Merkle root of 5 ** voteOptionTreeDepth zeros, 0)
uint256 public currentPerVOSpentVoiceCreditsCommitment;
//----------------------
string constant ERROR_PUBLIC_SIGNAL_TOO_LARGE = "E01";
string constant ERROR_INVALID_BATCH_UST_PROOF = "E02";
string constant ERROR_INVALID_TALLY_PROOF = "E03";
string constant ERROR_ONLY_COORDINATOR = "E04";
string constant ERROR_ALL_BATCHES_TALLIED = "E05";
string constant ERROR_CURRENT_MESSAGE_BATCH_OUT_OF_RANGE = "E06";
string constant ERROR_NO_SIGNUPS = "E07";
string constant ERROR_INVALID_ECDH_PUBKEYS_LENGTH = "E08";
string constant ERROR_NO_MORE_MESSAGES = "E09";
string constant ERROR_INVALID_MAX_USERS_OR_MESSAGES = "E10";
string constant ERROR_SIGNUP_PERIOD_PASSED = "E11";
string constant ERROR_SIGNUP_PERIOD_NOT_OVER = "E12";
string constant ERROR_VOTING_PERIOD_PASSED = "E13";
string constant ERROR_VOTING_PERIOD_NOT_OVER = "E14";
// Events
event SignUp(
PubKey _userPubKey,
uint256 _stateIndex,
uint256 _voiceCreditBalance
);
event PublishMessage(
Message _message,
PubKey _encPubKey
);
constructor(
TreeDepths memory _treeDepths,
BatchSizes memory _batchSizes,
MaxValues memory _maxValues,
SignUpGatekeeper _signUpGatekeeper,
SnarkVerifier _batchUstVerifier,
SnarkVerifier _qvtVerifier,
uint256 _signUpDurationSeconds,
uint256 _votingDurationSeconds,
InitialVoiceCreditProxy _initialVoiceCreditProxy,
PubKey memory _coordinatorPubKey,
address _coordinatorAddress
) public {
coordinatorAddress = _coordinatorAddress;
treeDepths = _treeDepths;
tallyBatchSize = _batchSizes.tallyBatchSize;
messageBatchSize = _batchSizes.messageBatchSize;
// Set the verifier contracts
batchUstVerifier = _batchUstVerifier;
qvtVerifier = _qvtVerifier;
// Set the sign-up duration
signUpTimestamp = block.timestamp;
signUpDurationSeconds = _signUpDurationSeconds;
votingDurationSeconds = _votingDurationSeconds;
// Set the sign-up gatekeeper contract
signUpGatekeeper = _signUpGatekeeper;
// Set the initial voice credit balance proxy
initialVoiceCreditProxy = _initialVoiceCreditProxy;
// Set the coordinator's public key
coordinatorPubKey = _coordinatorPubKey;
// Calculate and cache the max number of leaves for each tree.
// They are used as public inputs to the batch update state tree snark.
messageTreeMaxLeafIndex = uint256(2) ** _treeDepths.messageTreeDepth - 1;
// Check and store the maximum number of signups
// It is the user's responsibility to ensure that the state tree depth
// is just large enough and not more, or they will waste gas.
uint256 stateTreeMaxLeafIndex = uint256(2) ** _treeDepths.stateTreeDepth - 1;
maxUsers = _maxValues.maxUsers;
// The maximum number of messages
require(
_maxValues.maxUsers <= stateTreeMaxLeafIndex ||
_maxValues.maxMessages <= messageTreeMaxLeafIndex,
ERROR_INVALID_MAX_USERS_OR_MESSAGES
);
maxMessages = _maxValues.maxMessages;
// The maximum number of leaves, minus one, of meaningful vote options.
// This allows the snark to do a no-op if the user votes for an option
// which has no meaning attached to it
voteOptionsMaxLeafIndex = _maxValues.maxVoteOptions;
// Create the message tree
messageTree = new IncrementalMerkleTree(_treeDepths.messageTreeDepth, ZERO_VALUE, true);
// Calculate and store the empty vote option tree root. This value must
// be set before we call hashedBlankStateLeaf() later
emptyVoteOptionTreeRoot = calcEmptyVoteOptionTreeRoot(_treeDepths.voteOptionTreeDepth);
// Calculate and store a commitment to 5 ** voteOptionTreeDepth zeros,
// and a salt of 0.
originalCurrentResultsCommitment = hashLeftRight(emptyVoteOptionTreeRoot, 0);
currentResultsCommitment = originalCurrentResultsCommitment;
currentSpentVoiceCreditsCommitment = originalSpentVoiceCreditsCommitment;
currentPerVOSpentVoiceCreditsCommitment = originalCurrentResultsCommitment;
// Compute the hash of a blank state leaf
uint256 h = hashedBlankStateLeaf();
// Create the state tree
stateTree = new IncrementalMerkleTree(_treeDepths.stateTreeDepth, h, false);
// Make subsequent insertions start from leaf #1, as leaf #0 is only
// updated with random data if a command is invalid.
stateTree.insertLeaf(h);
}
/*
* Returns the deadline to sign up.
*/
function calcSignUpDeadline() public view returns (uint256) {
return signUpTimestamp + signUpDurationSeconds;
}
/*
* Ensures that the calling function only continues execution if the
* current block time is before the sign-up deadline.
*/
modifier isBeforeSignUpDeadline() {
if (signUpDurationSeconds != 0) {
require(block.timestamp < calcSignUpDeadline(), ERROR_SIGNUP_PERIOD_PASSED);
}
_;
}
/*
* Ensures that the calling function only continues execution if the
* current block time is after or equal to the sign-up deadline.
*/
modifier isAfterSignUpDeadline() {
if (signUpDurationSeconds != 0) {
require(block.timestamp >= calcSignUpDeadline(), ERROR_SIGNUP_PERIOD_NOT_OVER);
}
_;
}
/*
* Returns the deadline to vote
*/
function calcVotingDeadline() public view returns (uint256) {
return calcSignUpDeadline() + votingDurationSeconds;
}
/*
* Ensures that the calling function only continues execution if the
* current block time is before the voting deadline.
*/
modifier isBeforeVotingDeadline() {
if (votingDurationSeconds != 0) {
require(block.timestamp < calcVotingDeadline(), ERROR_VOTING_PERIOD_PASSED);
}
_;
}
/*
* Ensures that the calling function only continues execution if the
* current block time is after or equal to the voting deadline.
*/
modifier isAfterVotingDeadline() {
if (votingDurationSeconds != 0) {
require(block.timestamp >= calcVotingDeadline(), ERROR_VOTING_PERIOD_NOT_OVER);
}
_;
}
/*
* Allows a user who is eligible to sign up to do so. The sign-up
* gatekeeper will prevent double sign-ups or ineligible users from signing
* up. This function will only succeed if the sign-up deadline has not
* passed. It also inserts a fresh state leaf into the state tree.
* @param _userPubKey The user's desired public key.
* @param _signUpGatekeeperData Data to pass to the sign-up gatekeeper's
* register() function. For instance, the POAPGatekeeper or
* SignUpTokenGatekeeper requires this value to be the ABI-encoded
* token ID.
*/
function signUp(
PubKey memory _userPubKey,
bytes memory _signUpGatekeeperData,
bytes memory _initialVoiceCreditProxyData
)
isBeforeSignUpDeadline
public {
if (signUpDurationSeconds == 0) {
require(
msg.sender == coordinatorAddress,
"MACI: only the coordinator can submit signups in debug mode"
);
}
require(numSignUps < maxUsers, "MACI: maximum number of signups reached");
// Register the user via the sign-up gatekeeper. This function should
// throw if the user has already registered or if ineligible to do so.
signUpGatekeeper.register(msg.sender, _signUpGatekeeperData);
uint256 voiceCreditBalance = initialVoiceCreditProxy.getVoiceCredits(
msg.sender,
_initialVoiceCreditProxyData
);
// The limit on voice credits is 2 ^ 32 which is hardcoded into the
// UpdateStateTree circuit, specifically at check that there are
// sufficient voice credits (using GreaterEqThan(32)).
require(voiceCreditBalance <= 4294967296, "MACI: too many voice credits");
// Create, hash, and insert a fresh state leaf
StateLeaf memory stateLeaf = StateLeaf({
pubKey: _userPubKey,
voteOptionTreeRoot: emptyVoteOptionTreeRoot,
voiceCreditBalance: voiceCreditBalance,
nonce: 0
});
uint256 hashedLeaf = hashStateLeaf(stateLeaf);
// Insert the leaf
stateTree.insertLeaf(hashedLeaf);
// Update a copy of the state tree root
stateRoot = getStateTreeRoot();
numSignUps ++;
// numSignUps is equal to the state index of the leaf which was just
// added to the state tree above
emit SignUp(_userPubKey, numSignUps, voiceCreditBalance);
}
/*
* Allows anyone to publish a message (an encrypted command and signature).
* This function also inserts it into the message tree.
* @param _message The message to publish
* @param _encPubKey An epheremal public key which can be combined with the
* coordinator's private key to generate an ECDH shared key which which was
* used to encrypt the message.
*/
function publishMessage(
Message memory _message,
PubKey memory _encPubKey
)
isBeforeVotingDeadline
public {
if (signUpDurationSeconds == 0) {
require(
msg.sender == coordinatorAddress,
"MACI: only the coordinator can publish messages in debug mode"
);
}
require(numMessages < maxMessages, "MACI: message limit reached");
// Calculate leaf value
uint256 leaf = hashMessage(_message);
// Insert the new leaf into the message tree
messageTree.insertLeaf(leaf);
currentMessageBatchIndex = (numMessages / messageBatchSize) * messageBatchSize;
numMessages ++;
emit PublishMessage(_message, _encPubKey);
}
/*
* A helper function to convert an array of 8 uint256 values into the a, b,
* and c array values that the zk-SNARK verifier's verifyProof accepts.
*/
function unpackProof(
uint256[8] memory _proof
) public pure returns (
uint256[2] memory,
uint256[2][2] memory,
uint256[2] memory
) {
return (
[_proof[0], _proof[1]],
[
[_proof[2], _proof[3]],
[_proof[4], _proof[5]]
],
[_proof[6], _proof[7]]
);
}
/*
* A helper function to create the publicSignals array from meaningful
* parameters.
* @param _newStateRoot The new state root after all messages are processed
* @param _ecdhPubKeys The public key used to generated the ECDH shared key
* to decrypt the message
*/
function genBatchUstPublicSignals(
uint256 _newStateRoot,
PubKey[] memory _ecdhPubKeys
) public view returns (uint256[] memory) {
uint256 messageBatchEndIndex;
if (currentMessageBatchIndex + messageBatchSize <= numMessages) {
messageBatchEndIndex = currentMessageBatchIndex + messageBatchSize - 1;
} else {
messageBatchEndIndex = numMessages - 1;
}
uint256[] memory publicSignals = new uint256[](12 + messageBatchSize * 3);
publicSignals[0] = _newStateRoot;
publicSignals[1] = coordinatorPubKey.x;
publicSignals[2] = coordinatorPubKey.y;
publicSignals[3] = voteOptionsMaxLeafIndex;
publicSignals[4] = messageTree.root();
publicSignals[5] = currentMessageBatchIndex;
publicSignals[6] = messageBatchEndIndex;
publicSignals[7] = numSignUps;
for (uint8 i = 0; i < messageBatchSize; i++) {
uint8 x = 8 + i * 2;
uint8 y = x + 1;
publicSignals[x] = _ecdhPubKeys[i].x;
publicSignals[y] = _ecdhPubKeys[i].y;
}
return publicSignals;
}
/*
* Update the stateRoot if the batch update state root proof is
* valid.
* @param _newStateRoot The new state root after all messages are processed
* @param _ecdhPubKeys The public key used to generated the ECDH shared key
* to decrypt the message
* @param _proof The zk-SNARK proof
*/
function batchProcessMessage(
uint256 _newStateRoot,
PubKey[] memory _ecdhPubKeys,
uint256[8] memory _proof
)
isAfterVotingDeadline
public {
// Ensure that the current batch index is within range
require(
hasUnprocessedMessages,
ERROR_NO_MORE_MESSAGES
);
require(
_ecdhPubKeys.length == messageBatchSize,
ERROR_INVALID_ECDH_PUBKEYS_LENGTH
);
// Ensure that currentMessageBatchIndex is within range
require(
currentMessageBatchIndex <= messageTreeMaxLeafIndex,
ERROR_CURRENT_MESSAGE_BATCH_OUT_OF_RANGE
);
// Assemble the public inputs to the snark
uint256[] memory publicSignals = genBatchUstPublicSignals(
_newStateRoot,
_ecdhPubKeys
);
// Ensure that each public input is within range of the snark scalar
// field.
// TODO: consider having more granular revert reasons
// TODO: this check is already performed in the verifier contract
for (uint8 i = 0; i < publicSignals.length; i++) {
require(
publicSignals[i] < SNARK_SCALAR_FIELD,
ERROR_PUBLIC_SIGNAL_TOO_LARGE
);
}
// Unpack the snark proof
(
uint256[2] memory a,
uint256[2][2] memory b,
uint256[2] memory c
) = unpackProof(_proof);
// Verify the proof
require(
batchUstVerifier.verifyProof(a, b, c, publicSignals),
ERROR_INVALID_BATCH_UST_PROOF
);
// Increase the message batch start index to ensure that each message
// batch is processed in order
if (currentMessageBatchIndex == 0) {
hasUnprocessedMessages = false;
} else {
currentMessageBatchIndex -= messageBatchSize;
}
// Update the state root
stateRoot = _newStateRoot;
if (stateRootBeforeProcessing == 0) {
stateRootBeforeProcessing = stateRoot;
}
}
/*
* Returns the public signals required to verify a quadratic vote tally
* snark.
*/
function genQvtPublicSignals(
uint256 _intermediateStateRoot,
uint256 _newResultsCommitment,
uint256 _newSpentVoiceCreditsCommitment,
uint256 _newPerVOSpentVoiceCreditsCommitment,
uint256 _totalVotes
) public view returns (uint256[] memory) {
uint256[] memory publicSignals = new uint256[](10);
publicSignals[0] = _newResultsCommitment;
publicSignals[1] = _newSpentVoiceCreditsCommitment;
publicSignals[2] = _newPerVOSpentVoiceCreditsCommitment;
publicSignals[3] = _totalVotes;
publicSignals[4] = stateRoot;
publicSignals[5] = currentQvtBatchNum;
publicSignals[6] = _intermediateStateRoot;
publicSignals[7] = currentResultsCommitment;
publicSignals[8] = currentSpentVoiceCreditsCommitment;
publicSignals[9] = currentPerVOSpentVoiceCreditsCommitment;
return publicSignals;
}
function hashedBlankStateLeaf() public view returns (uint256) {
// The pubkey is the first Pedersen base point from iden3's circomlib
StateLeaf memory stateLeaf = StateLeaf({
pubKey: PubKey({
x: 10457101036533406547632367118273992217979173478358440826365724437999023779287,
y: 19824078218392094440610104313265183977899662750282163392862422243483260492317
}),
voteOptionTreeRoot: emptyVoteOptionTreeRoot,
voiceCreditBalance: 0,
nonce: 0
});
return hashStateLeaf(stateLeaf);
}
function hasUntalliedStateLeaves() public view returns (bool) {
return currentQvtBatchNum < (1 + (numSignUps / tallyBatchSize));
}
/*
* Tally the next batch of state leaves.
* @param _intermediateStateRoot The intermediate state root, which is
* generated from the current batch of state leaves
* @param _newResultsCommitment A hash of the tallied results so far
* (cumulative)
* @param _proof The zk-SNARK proof
*/
function proveVoteTallyBatch(
uint256 _intermediateStateRoot,
uint256 _newResultsCommitment,
uint256 _newSpentVoiceCreditsCommitment,
uint256 _newPerVOSpentVoiceCreditsCommitment,
uint256 _totalVotes,
uint256[8] memory _proof
)
public {
require(numSignUps > 0, ERROR_NO_SIGNUPS);
uint256 totalBatches = 1 + (numSignUps / tallyBatchSize);
// Ensure that the batch # is within range
require(
currentQvtBatchNum < totalBatches,
ERROR_ALL_BATCHES_TALLIED
);
// Generate the public signals
// public 'input' signals = [output signals, public inputs]
uint256[] memory publicSignals = genQvtPublicSignals(
_intermediateStateRoot,
_newResultsCommitment,
_newSpentVoiceCreditsCommitment,
_newPerVOSpentVoiceCreditsCommitment,
_totalVotes
);
// Ensure that each public input is within range of the snark scalar
// field.
// TODO: consider having more granular revert reasons
for (uint8 i = 0; i < publicSignals.length; i++) {
require(
publicSignals[i] < SNARK_SCALAR_FIELD,
ERROR_PUBLIC_SIGNAL_TOO_LARGE
);
}
// Unpack the snark proof
(
uint256[2] memory a,
uint256[2][2] memory b,
uint256[2] memory c
) = unpackProof(_proof);
// Verify the proof
bool isValid = qvtVerifier.verifyProof(a, b, c, publicSignals);
require(isValid == true, ERROR_INVALID_TALLY_PROOF);
// Save the commitment to the new results for the next batch
currentResultsCommitment = _newResultsCommitment;
// Save the commitment to the total spent voice credits for the next batch
currentSpentVoiceCreditsCommitment = _newSpentVoiceCreditsCommitment;
// Save the commitment to the per voice credit spent voice credits for the next batch
currentPerVOSpentVoiceCreditsCommitment = _newPerVOSpentVoiceCreditsCommitment;
// Save the total votes
totalVotes = _totalVotes;
// Increment the batch #
currentQvtBatchNum ++;
}
/*
* Reset the storage variables which change during message processing and
* vote tallying. Does not affect any signups or messages. This is useful
* if the client-side process/tally code has a bug that causes an invalid
* state transition.
*/
function coordinatorReset() public {
require(msg.sender == coordinatorAddress, ERROR_ONLY_COORDINATOR);
hasUnprocessedMessages = true;
stateRoot = stateRootBeforeProcessing;
if (numMessages % messageBatchSize == 0) {
currentMessageBatchIndex = numMessages - messageBatchSize;
} else {
currentMessageBatchIndex = (numMessages / messageBatchSize) * messageBatchSize;
}
currentQvtBatchNum = 0;
currentResultsCommitment = originalCurrentResultsCommitment;
currentSpentVoiceCreditsCommitment = originalSpentVoiceCreditsCommitment;
currentPerVOSpentVoiceCreditsCommitment = originalCurrentResultsCommitment;
totalVotes = 0;
}
/*
* Verify the result of the vote tally using a Merkle proof and the salt.
*/
function verifyTallyResult(
uint8 _depth,
uint256 _index,
uint256 _leaf,
uint256[][] memory _pathElements,
uint256 _salt
) public view returns (bool) {
uint256 computedRoot = computeMerkleRootFromPath(
_depth,
_index,
_leaf,
_pathElements
);
uint256 computedCommitment = hashLeftRight(computedRoot, _salt);
return computedCommitment == currentResultsCommitment;
}
/*
* Verify the number of voice credits spent for a particular vote option
* using a Merkle proof and the salt.
*/
function verifyPerVOSpentVoiceCredits(
uint8 _depth,
uint256 _index,
uint256 _leaf,
uint256[][] memory _pathElements,
uint256 _salt
) public view returns (bool) {
uint256 computedRoot = computeMerkleRootFromPath(
_depth,
_index,
_leaf,
_pathElements
);
uint256 computedCommitment = hashLeftRight(computedRoot, _salt);
return computedCommitment == currentPerVOSpentVoiceCreditsCommitment;
}
/*
* Verify the total number of spent voice credits.
* @param _spent The value to verify
* @param _salt The salt which is hashed with the value to generate the
* commitment to the spent voice credits.
*/
function verifySpentVoiceCredits(
uint256 _spent,
uint256 _salt
) public view returns (bool) {
uint256 computedCommitment = hashLeftRight(_spent, _salt);
return computedCommitment == currentSpentVoiceCreditsCommitment;
}
function calcEmptyVoteOptionTreeRoot(uint8 _levels) public pure returns (uint256) {
return computeEmptyQuinRoot(_levels, 0);
}
function getMessageTreeRoot() public view returns (uint256) {
return messageTree.root();
}
function getStateTreeRoot() public view returns (uint256) {
return stateTree.root();
}
}