Introduction
Relai users can buy bitcoin directly to their hardware wallet, potentially saving on future transaction fees by avoiding a later transfer from the Relai self-custodial wallet.
Since at Relai we cover the on-chain fees for transferring the bitcoin you purchase to your wallet, it makes sense to take advantage of this feature.
During the order creation process, you are prompted to use an external address that you can provide. This tutorial will walk you through the process of buying bitcoin to an external wallet using the BitBox02 hardware wallet and the Sparrow Wallet desktop application. You’ll learn how to manage your cold storage wallet and complete the signature process step by step.
Prerequisites
Before starting, ensure you have the following:
A BitBox02 hardware wallet (initialized and set up via the BitBox Desktop App).
The BitBox application installed on your computer (for firmware updates and device management)
Sparrow Wallet installed on your computer. Download it here.
Step 1: Prepare Your BitBox02
Open the BitBox application, connect your BitBox02, unlock it with your PIN, and update it to the latest firmware if necessary.
Step 2: Create a wallet with Sparrow Wallet
Launch Sparrow wallet.
On the home screen, click 'File' → 'New Wallet'.
Choose a wallet name and click 'Create Wallet'.
In the next window, go to Settings, and in the 'Keystores' tab, click on 'Connected Hardware Wallet'.
Click on the 'Scan' button in the window that appears. Please note that you have to close the BitBox application before doing so, otherwise you will be prompted with an error.
Click the 'Import Keystore' button next to the newly detected BitBox02.
Leave everything at the default settings and click on 'Apply' at the bottom right. It is recommended to add a password for the wallet.
At this stage, you have successfully connected Sparrow Wallet to the BitBox02. Sparrow Wallet acts as an interface, while the private keys remain securely stored inside the BitBox02. This ensures that transactions cannot be signed without physically interacting with the hardware device.
Since the private keys never leave the BitBox02, Sparrow Wallet alone cannot authorize transactions. To spend bitcoin or sign a message, you must have the BitBox02 physically connected and interact with it.
Step 3: Creating an Order in the Relai App
Open the Relai app, tap the plus ( + ) button in the menu on the landing page, and select 'Buy'.
Select an amount and then click on 'Continue'.
Choose the frequency for your purchase.
Select your payment method.
On the 'Order Summary' page, you will see a recap of your order. To use an external wallet, toggle the switch for 'Use an external wallet' and click 'Confirm external wallet'. This will open the camera for scanning your wallet address.
In Sparrow Wallet, select the 'Receive' tab. You will be shown an unused Bitcoin address along with its QR-code representation. Scan this QR-code with the camera in your Relai app to add this Bitcoin address as the receiving address in your Relai app.
Step 4: Signing the message
At this point, the Relai app will generate a message that needs to be cryptographically signed with the private key of your BitBox.
Copy the text by clicking the designated button and send it to your computer, where you have access to Sparrow Wallet. You can use services like WhatsApp Web, Telegram Web, email, or your phone’s notes app to transfer the message.
Click on 'Continue'.
In the Sparrow wallet application, click on 'Tools' → 'Sign/Verify Message' and paste the message copied from the Relai app into the 'Message' box, paying attention to not include any spaces or extra characters.
Enter the previously selected receiving Bitcoin address (bc1q…) in the 'Address' field.Click on 'Sign' and then on 'Sign Message' in the next window, next to the BitBox02 logo.
The BitBox02 will light up and display instructions on its screen. Follow the prompts to sign the message. Once completed, the 'Signature' field in Sparrow Wallet will be automatically filled.
Copy this 'Signature' string, send it to your smartphone and paste it into the Relai app, in the 'Add your signature' field. Click 'Done' to confirm.
Tap 'Buy Now' to create the order.
If bank transfer was selected as the payment method, the payment details will be displayed. You need to manually initiate the transfer using the provided bank details.
A payment reference is not required. As long as IBAN, amount, and currency match, the payment will be automatically assigned correctly.
Once the transfer is processed, the bitcoin will be sent to your external Bitcoin address.
Conclusion
By signing a message with Sparrow Wallet and BitBox02, you verify ownership of the external Bitcoin address where Relai will send your bitcoin. This ensures that only you control the address and have access to the funds.
The same process can also be used with other hardware wallets.
For further assistance, check out: