# Use your zkApp privately

Given a full Recipe and its inputs, [RAILGUN Wallet SDK](/developer-guide/wallet/transactions/cross-contract-calls.md) will generate a [zero-knowledge proof](https://docs.railgun.org/wiki/learn/privacy-system/zero-knowledge-cryptography) and a final serialized transaction for the RAILGUN Relay Adapt contract.

This final transaction can be submitted to the blockchain by any wallet, including a [Broadcaster](/developer-guide/wallet/broadcasters.md).

{% code title="cook-recipe-example.ts" %}

```typescript
import {
  RecipeERC20Info,
  ZeroXSwapRecipe,
  RecipeInput,
  RecipeOutput
} from '@railgun-community/cookbook';
import {
  NetworkName,
} from '@railgun-community/shared-models';

const sellERC20Info: RecipeERC20Info = {
  tokenAddress: '0x6B175474E89094C44Da98b954EedeAC495271d0F', // DAI
  decimals: BigInt(18)
}

const buyERC20Info: RecipeERC20Info = {
  tokenAddress: '0xdac17f958d2ee523a2206206994597c13d831ec7', // USDT
  decimals: BigInt(18)
}

const slippagePercentage = 0.05;

const swap = new ZeroXSwapRecipe(sellERC20Info, buyERC20Info, slippagePercentage);

// Inputs that will be unshielded from private balance.
const unshieldERC20Amounts = [
  { 
    ...sellERC20Info,
    amount: BigInt('0x10'), // hexadecimal amount
  }
];

const recipeInput: RecipeInput = { NetworkName.Ethereum, unshieldERC20Amounts };
const {
  crossContractCalls,
  erc20AmountRecipients,
  nftRecipients,
  feeERC20AmountRecipients,
  minGasLimit,
} = await swap.getRecipeOutput(recipeInput);

// Outputs to re-shield after the Recipe multicall.
const shieldERC20Addresses = erc20AmountRecipients.map(({tokenAddress}) => tokenAddress);

// RAILGUN Wallet will generate a [unshield -> call -> re-shield] 
// transaction enclosing the Recipe multicall.

const { gasEstimate } = await gasEstimateForUnprovenCrossContractCalls(
    ...
    unshieldERC20Amounts,
    ...
    shieldERC20Addresses,
    ...
    crossContractCalls,
    ...
)
await generateCrossContractCallsProof(
    ...
    unshieldERC20Amounts,
    ...
    shieldERC20Addresses,
    ...
    crossContractCalls,
    ...
)
const { transaction } = await populateProvedCrossContractCalls(
    ...
    unshieldERC20Amounts,
    ...
    shieldERC20Addresses,
    ...
    crossContractCalls,
    ...
);

// Submit transaction to RPC.
await wallet.sendTransaction(transaction);

// Note: use @railgun-community/waku-broadcaster-client to submit 
// through a Broadcaster instead of signing with your own wallet.
```

{% endcode %}


---

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