Shielding Tokens

The shield(...) method allows a user to privately deposit (a.k.a. “shield”) tokens into their Shielder account. This is the entry point to private asset management.

When to Use

Call shield() when a user wants to move tokens from a public wallet to a private Shielder account. This works for both native tokens and supported ERC-20s.

Method Signature

async shield(
  token: Token, // either native or ERC-20 token
  amount: bigint, // in wei
  sendShielderTransaction: SendShielderTransaction,
  from: `0x${string}` // public wallet address
): Promise<`0x${string}`> // tx hash

What it does

• Computes and generates a zero-knowledge proof of deposit.

• Sends a deposit transaction to the Shielder smart contract.

• Stores your shielded note client-side and syncs local state.

• Emits SDK callbacks like onCalldataGenerated, onCalldataSent , onNewTransaction etc.

Example: Shielding Native Token:

src/App.tsx

src/App.tsx

...

import { initializeShielderClient } from "./shielder";
import { nativeToken } from "@cardinal-cryptography/shielder-sdk";
import { userAddress, walletClient } from "./wallet";

const amountToShield = 1_000_000_000_000_000n; // 0.001 ETH in wei

(async () => {
  const shielder = await initializeShielderClient();
  const token = nativeToken();

  const txHash = await shielder.shield(
    token,
    amountToShield,
    async (txRequest) => {
      // send transaction via viem or wagmi
      return walletClient.sendTransaction(txRequest);
    },
    userAddress
  );

  console.log("Shield tx hash:", txHash);
})();

...

src/wallet.ts

src/wallet.ts

import { createWalletClient, http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { baseSepolia } from "viem/chains";

const account = privateKeyToAccount(
  import.meta.env.VITE_PRIVATE_KEY as `0x${string}` // Replace with your private key
);

export const walletClient = createWalletClient({
  chain: baseSepolia,
  transport: http(),
  account,
});

export const userAddress = account.address;

What Happens Under the Hood

1. Shielder SDK checks if user has an account (creates one if needed).

2. Generates ZK proof client-side using WASM cryptography engine.

3. Encodes and sends a deposit() transaction to the smart contract.

4. Stores new private note in local app storage (or your custom store).

5. Triggers callbacks like onNewTransaction.

Tips

• Ensure the user approves token spending if shielding ERC-20s.

• Always call await shielder.syncShielder() before or after to stay up to date.

• Handle errors and show transaction progress in the UI via SDK callbacks.