tornado-nova/circuits/transaction.circom

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include "../node_modules/circomlib/circuits/poseidon.circom";
include "./merkleProof.circom"
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include "./keypair.circom"
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/*
Utxo structure:
{
amount,
blinding, // random number
pubkey,
}
commitment = hash(amount, blinding, pubKey)
nullifier = hash(commitment, privKey, merklePath)
*/
// Universal JoinSplit transaction with nIns inputs and 2 outputs
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template Transaction(levels, nIns, nOuts, zeroLeaf) {
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signal input root;
// extAmount = external amount used for deposits and withdrawals
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// correct extAmount range is enforced on the smart contract
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// publicAmount = extAmount - fee
signal input publicAmount;
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signal input extDataHash;
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// data for transaction inputs
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signal input inputNullifier[nIns];
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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
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signal input outputCommitment[nOuts];
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signal private input outAmount[nOuts];
signal private input outBlinding[nOuts];
signal private input outPubkey[nOuts];
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component inKeypair[nIns];
component inUtxoHasher[nIns];
component nullifierHasher[nIns];
component tree[nIns];
component checkRoot[nIns];
var sumIns = 0;
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// verify correctness of transaction inputs
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for (var tx = 0; tx < nIns; tx++) {
inKeypair[tx] = Keypair();
inKeypair[tx].privateKey <== inPrivateKey[tx];
inUtxoHasher[tx] = Poseidon(3);
inUtxoHasher[tx].inputs[0] <== inAmount[tx];
inUtxoHasher[tx].inputs[1] <== inBlinding[tx];
inUtxoHasher[tx].inputs[2] <== inKeypair[tx].publicKey;
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nullifierHasher[tx] = Poseidon(3);
nullifierHasher[tx].inputs[0] <== inUtxoHasher[tx].out;
nullifierHasher[tx].inputs[1] <== inPathIndices[tx];
nullifierHasher[tx].inputs[2] <== inPrivateKey[tx];
nullifierHasher[tx].out === inputNullifier[tx];
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tree[tx] = MerkleProof(levels);
tree[tx].leaf <== inUtxoHasher[tx].out;
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tree[tx].pathIndices <== inPathIndices[tx];
for (var i = 0; i < levels; i++) {
tree[tx].pathElements[i] <== inPathElements[tx][i];
}
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// 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];
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// We don't need to range check input amounts, since all inputs are valid UTXOs that
// were already checked as outputs in the previous transaction (or zero amount UTXOs that don't
// need to be checked either).
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sumIns += inAmount[tx];
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}
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component outUtxoHasher[nOuts];
component outAmountCheck[nOuts];
var sumOuts = 0;
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// verify correctness of transaction outputs
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for (var tx = 0; tx < nOuts; tx++) {
outUtxoHasher[tx] = Poseidon(3);
outUtxoHasher[tx].inputs[0] <== outAmount[tx];
outUtxoHasher[tx].inputs[1] <== outBlinding[tx];
outUtxoHasher[tx].inputs[2] <== outPubkey[tx];
outUtxoHasher[tx].out === outputCommitment[tx];
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// Check that amount fits into 248 bits to prevent overflow
outAmountCheck[tx] = Num2Bits(248);
outAmountCheck[tx].in <== outAmount[tx];
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sumOuts += outAmount[tx];
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}
// check that there are no same nullifiers among all inputs
component sameNullifiers[nIns * (nIns - 1) / 2];
var index = 0;
for (var i = 0; i < nIns - 1; i++) {
for (var j = i + 1; j < nIns; j++) {
sameNullifiers[index] = IsEqual();
sameNullifiers[index].in[0] <== inputNullifier[i];
sameNullifiers[index].in[1] <== inputNullifier[j];
sameNullifiers[index].out === 0;
index++;
}
}
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// verify amount invariant
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sumIns + publicAmount === sumOuts;
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// optional safety constraint to make sure extDataHash cannot be changed
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signal extDataSquare <== extDataHash * extDataHash;
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}