tornado-nova/circuits/transaction.circom
2021-06-09 13:58:57 +03:00

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include "./merkleTree.circom"
include "./treeUpdater.circom"
include "./utils.circom"
/*
Utxo structure:
{
amount,
blinding, // random number
pubkey,
}
commitment = hash(amount, blinding, pubKey)
nullifier = hash(commitment, privKey, merklePath)
*/
// Universal JoinSplit transaction with 2 inputs and 2 outputs
template Transaction(levels, nIns, nOuts, zeroLeaf) {
signal input root;
signal input newRoot;
signal input inputNullifier[nIns];
signal input outputCommitment[nOuts];
// external amount used for deposits and withdrawals
// correct extAmount range is enforced on the smart contract
signal input extAmount;
signal input fee;
signal input extDataHash;
// data for transaction inputs
signal private input inAmount[nIns];
signal private input inBlinding[nIns];
signal private input inPrivateKey[nIns];
signal private input inPathIndices[nIns];
signal private input inPathElements[nIns][levels];
// data for transaction outputs
signal private input outAmount[nOuts];
signal private input outBlinding[nOuts];
signal private input outPubkey[nOuts];
signal private input outPathIndices;
signal private input outPathElements[levels - 1];
component inKeypair[nIns];
component inUtxoHasher[nIns];
component nullifierHasher[nIns];
component inAmountCheck[nIns];
component tree[nIns];
component checkRoot[nIns];
var sumIns = 0;
// verify correctness of transaction inputs
for (var tx = 0; tx < nIns; tx++) {
inKeypair[tx] = Keypair();
inKeypair[tx].privateKey <== inPrivateKey[tx];
inUtxoHasher[tx] = TransactionHasher();
inUtxoHasher[tx].amount <== inAmount[tx];
inUtxoHasher[tx].blinding <== inBlinding[tx];
inUtxoHasher[tx].publicKey <== inKeypair[tx].publicKey;
nullifierHasher[tx] = NullifierHasher();
nullifierHasher[tx].commitment <== inUtxoHasher[tx].commitment;
nullifierHasher[tx].merklePath <== inPathIndices[tx];
nullifierHasher[tx].privateKey <== inPrivateKey[tx];
nullifierHasher[tx].nullifier === inputNullifier[tx];
tree[tx] = MerkleTree(levels);
tree[tx].leaf <== inUtxoHasher[tx].commitment;
tree[tx].pathIndices <== inPathIndices[tx];
for (var i = 0; i < levels; i++) {
tree[tx].pathElements[i] <== inPathElements[tx][i];
}
// check merkle proof only if amount is non-zero
checkRoot[tx] = ForceEqualIfEnabled();
checkRoot[tx].in[0] <== root;
checkRoot[tx].in[1] <== tree[tx].root;
checkRoot[tx].enabled <== inAmount[tx];
// Check that amount fits into 248 bits to prevent overflow
inAmountCheck[tx] = Num2Bits(248);
inAmountCheck[tx].in <== inAmount[tx];
sumIns += inAmount[tx];
}
component outUtxoHasher[nOuts];
component outAmountCheck[nOuts];
var sumOuts = 0;
// verify correctness of transaction outputs
for (var tx = 0; tx < nOuts; tx++) {
outUtxoHasher[tx] = TransactionHasher();
outUtxoHasher[tx].amount <== outAmount[tx];
outUtxoHasher[tx].blinding <== outBlinding[tx];
outUtxoHasher[tx].publicKey <== outPubkey[tx];
outUtxoHasher[tx].commitment === outputCommitment[tx];
// Check that amount fits into 248 bits to prevent overflow
outAmountCheck[tx] = Num2Bits(248);
outAmountCheck[tx].in <== outAmount[tx];
sumOuts += outAmount[tx];
}
// Check that fee fits into 248 bits to prevent overflow
component feeCheck = Num2Bits(248);
feeCheck.in <== fee;
component sameNullifiers = IsEqual();
sameNullifiers.in[0] <== inputNullifier[0];
sameNullifiers.in[1] <== inputNullifier[1];
sameNullifiers.out === 0;
// verify amount invariant
sumIns + extAmount === sumOuts + fee;
// Check merkle tree update with inserted transaction outputs
component treeUpdater = TreeUpdater(levels, zeroLeaf);
treeUpdater.oldRoot <== root;
treeUpdater.newRoot <== newRoot;
treeUpdater.leaf[0] <== outputCommitment[0];
treeUpdater.leaf[1] <== outputCommitment[1];
treeUpdater.pathIndices <== outPathIndices;
for (var i = 0; i < levels - 1; i++) {
treeUpdater.pathElements[i] <== outPathElements[i];
}
}