Private Transfer

Transferring tokens inside the shielded pool is completely private — amounts, senders, and receivers are hidden.

How it works

import { transfer, waitForTransfer } from '@shroud/sdk';

const { tx, recipientNote, changeNote } = await transfer({
  signer,
  provider,
  poolAddress: "0x91c912eac...",
  inputNote: myNote,           // note to spend
  transferAmount: 50n,         // amount to send
  recipientPublicKey: bobPk,   // Bob's Baby Jubjub public key
  senderPublicKey: myPk,
  senderPrivateKey: myPrivKey,
  wasmPath: "/transfer.wasm",
  zkeyPath: "/transfer_final.zkey",
});

const { recipient, change } = await waitForTransfer(tx, recipientNote, changeNote, provider, poolAddress);

Transfer flow

1. Select input note — choose an unspent note with sufficient balance
2. Compute outputs:
   • Recipient note: amount = transferAmount
   • Change note: amount = inputNote.amount - transferAmount
   • Blinding conservation: changeBlinding = inputNote.blinding - recipientBlinding
3. Generate random values for both output notes (secrets, nullifier preimages)
4. Compute commitments — Pedersen + Poseidon for both outputs
5. Sync Merkle tree — fetch events and reconstruct tree locally
6. Generate Groth16 proof — snarkjs in browser (~1 second)
7. Encrypt memos — ECDH + AES-256-GCM for each recipient
8. Submit transaction — proof, nullifier, 2 new commitments, 2 encrypted memos

What the contract sees

Only 4 public signals from the proof:

Signal	Contains
merkle_root	Which tree state the proof is against
nullifier_hash	Prevents double-spend (unlinkable to note without secret)
new_commitment_1	Opaque hash — hides amount, recipient, everything
new_commitment_2	Opaque hash — hides amount, recipient, everything

The contract verifies the Groth16 proof, marks the nullifier as spent, and inserts both new commitments. It learns nothing about amounts, senders, or receivers.

Relayed transfer

Transfers can also be submitted via the relay API to avoid linking your EVM address to the transaction:

import { relayTransfer } from '@shroud/sdk';

const result = await relayTransfer({
  provider,
  poolAddress: "0x91c912eac...",
  inputNote: myNote,
  transferAmount: 50n,
  recipientPublicKey: bobPk,
  senderPublicKey: myPk,
  senderPrivateKey: myPrivKey,
  wasmPath: "/transfer.wasm",
  zkeyPath: "/transfer_final.zkey",
  relayUrl: "/api/relay",
  paymasterAddress: "0x102C04f39...",
});

The relay wallet submits the transaction — your EVM address never appears on-chain.