Skip to main content

Deposit circuit

The Deposit circuit proves a deposit is well-formed: the depositor knows a (noteSecret, depositSecret) pair that produces a specific commitment for a specific value of a specific asset.

Public signals​

The Deposit circuit exposes four public signals (one output and three inputs). The contract reads them in this order:

  • outputCommitment: the full note commitment, and the only public output of the circuit.
  • tokenId: the asset address (20-byte hex).
  • value: the value in the asset's smallest unit.
  • context: the deposit context, computed on-chain as uint256(keccak256(abi.encode(noteData))) % SNARK_SCALAR_FIELD, which binds the proof to the supplied note data. (The transact circuit binds keccak256(abi.encode(transactParams, noteData)) instead.)

precommitment and label are computed in-circuit from the private inputs and are not public signals.

Private inputs​

The circuit has exactly two private inputs:

  • depositSecret: an SDK-generated 32-byte scalar in the BN254 field (produced by generateSecret, not raw random bytes), used only by this circuit to compute the label. It is not an input to the ragequit or transact circuits.
  • noteAddressHash: Poseidon(ownerAddress, noteSecret), computed outside the circuit and supplied as a private input. The noteSecret folded into it never enters the circuit directly, though it is required again to spend the note (transact, withdraw) or to ragequit it.

Constraints (high level)​

  1. precommitment = Poseidon(noteAddressHash, tokenId, value, 0) (metadata is hard-coded to 0 in v2.0).
  2. label = Poseidon(precommitment, depositSecret)
  3. outputCommitment = Poseidon(precommitment, label)
  4. Range checks ensure that tokenId fits in 160 bits and value fits in 128 bits.

Verifier​

Each deployment has its own DepositGroth16Verifier contract, and the verification key is locked in at deploy time. If your local zkey comes from a different deployment set, the proof is rejected with PoolVault_InvalidDepositProof.

Source: v2-monorepo/packages/circuits/circuits/main/deposit.circom