GITBOOK-114: feat: Hinkal Private Payments

Author: MantisClone

docs/SUMMARY.md

@@ -69,6 +69,7 @@
   * [Escrow Payment](sdk-guides/payment/escrow-request.md)
   * [Streaming Payment](sdk-guides/payment/streaming-request.md)
   * [Pay through a proxy-contract with a multisig](sdk-guides/payment/pay-through-a-proxy-contract-with-a-multisig.md)
+  * [Hinkal Private Payments](sdk-guides/payment/hinkal-private-payments.md)
 
 ## Learn Request Network
 

docs/sdk-guides/payment/hinkal-private-payments.md

@@ -0,0 +1,88 @@
+# Hinkal Private Payments
+
+The Request Network SDK supports Hinkal Private Payments using ERC-20 tokens.  Hinkal is a middleware and suite of smart contracts on EVM-compatible chains that leverage zero-knowledge proofs and shielded addresses to facilitate compliant and private transactions. 
+
+Each public address has exactly one Hinkal shielded address.
+
+The `@requestnetwork/payment-processor` package provides functions to:
+
+* **Pay a request from a Hinkal shielded address to a public address:** such that the payment sender's public address never appears on-chain.
+* **Deposit to a Hinkal shielded address from a public address**: such that the payment recipient's public address never appears on-chain. Callers can choose to deposit to their own shielded address or someone else's shielded address.
+
+{% hint style="info" %}
+Paying a request where the payment recipient address is a Hinkal shielded address is not supported because the Request Network payment proxy smart contracts can only send funds to public addresses. Consider using [declarative-request.md](declarative-request.md "mention") instead.
+{% endhint %}
+
+## Benefits
+
+* **Privacy**: Obfuscates payer address when paying a request.
+* **Compliance**: Ensures transactions adhere to regulatory requirements. See [Hinkal Compliance](https://hinkal-team.gitbook.io/hinkal/hinkal-wallet/compliance) for details
+
+## Installation
+
+To use the Hinkal Private Payments feature, install the necessary package:
+
+```bash
+npm install @requestnetwork/payment-processor
+npm install @requestnetwork/request-client.js
+```
+
+## Usage
+
+### **Pay a request from a Hinkal shielded address**
+
+To pay a request from a Hinkal shielded address to a public address, where only the payment sender's address is obfuscated, use the \``` payErc20FeeProxyRequestFromHinkalShieldedAddress()` `` function. Ensure the payment sender's Hinkal shielded address has a positive balance.
+
+{% hint style="warning" %}
+Strongly consider using [encryption-and-decryption](../encryption-and-decryption/ "mention")to keep the request contents private, including the payer and payee identity addresses, when paying requests from a Hinkal shielded address!
+{% endhint %}
+
+```typescript
+import { payErc20FeeProxyRequestFromHinkalShieldedAddress } from '@requestnetwork/payment-processor';
+
+// Instantiation of `RequestNetwork` and `Signer` omitted for brevity
+
+const request = await requestClient.fromRequestId('insert request id');
+const requestData = request.getData();
+
+const paymentResult = await payErc20FeeProxyRequestFromHinkalShieldedAddress(requestData, signer);
+```
+
+{% hint style="info" %}
+See [quickstart-browser.md](../../get-started/quickstart-browser.md "mention") for how to instantiate a `RequestNetwork` and `Signer`
+{% endhint %}
+
+### Deposit to a Hinkal shielded address
+
+To deposit funds to a Hinkal shielded address from a public address, where only the payment recipient's address is obfuscated, use the `sendToHinkalShieldedAddressFromPublic()` function.  
+
+* Deposit to own Hinkal shielded address: omit the `recipientInfo`argument
+* Deposit to someone else's Hinkal shielded address: set `recipientInfo` to the shielded address of the payment recipient.
+
+{% hint style="info" %}
+Hinkal shielded addresses must be shared out-of-band. This SDK doesn't offer functions for sharing Hinkal shielded addresses.
+{% endhint %}
+
+{% code overflow="wrap" %}
+```typescript
+import { sendToHinkalShieldedAddressFromPublic } from '@requestnetwork/payment-processor';
+
+// Instantiation of `Signer` omitted for brevity
+
+const recipientShieldedAddress = '142590100039484718476239190022599206250779986428210948946438848754146776167,0x096d6d5d8b2292aa52e57123a58fc4d5f3d66171acd895f22ce1a5b16ac51b9e,0xc025ccc6ef46399da52763a866a3a10d2eade509af27eb8411c5d251eb8cd34d'
+await sendToHinkalShieldedAddressFromPublic({
+    signerOrProvider: paymentSender,
+    tokenAddress: '0x833589fcd6edb6e08f4c7c32d4f71b54bda02913', // USDC on Base
+    amount: '1000000', // 1 USDC
+    recipientInfo: recipientShieldedAddress, // omit to deposit to own Hinkal shielded address
+})
+```
+{% endcode %}
+
+{% hint style="info" %}
+See [quickstart-browser.md](../../get-started/quickstart-browser.md "mention") for how to instantiate a `Signer`
+{% endhint %}
+
+## Details
+
+For more details, refer to the [Pull Request #1482](https://github.com/RequestNetwork/requestNetwork/pull/1482) on GitHub.