Some services, like cryptocurrency exchanges, may ask you to "sign a message" before you can withdraw bitcoin to an address you control. This is a common security step that lets you prove you are the true owner of the address. This guide shows you how to do this safely using your BitBox02 with Sparrow Wallet.

Before you start

To ensure everything goes smoothly, please check the following first:

• Prepare your BitBox02: Your device should already be initialized using the BitBoxApp and updated to the latest firmware. You can find instructions on our guide: How to update the BitBox02 firmware
• Install Sparrow Wallet: Make sure you have the latest version of Sparrow Wallet installed from their official website.
• Close the BitBoxApp: It is essential that the BitBoxApp is completely closed. If it is running, Sparrow will not be able to communicate with your BitBox02.
• Connect to Sparrow: Your BitBox02 must already be connected to Sparrow Wallet. If you haven't done this yet, please follow our connection guide first.
• Have your BitBox02 handy: Keep your device nearby, as you will need it to securely verify the address on its screen.

For this guide, we will use the following example details:

• Address: bc1qzp932aaf3y7edfdxj2h80728aagpasqe24q3sy
• Message: I confirm that I am the sole owner of this Bitcoin address. Order reference 1bd973455f.

Step 1: Open the message signing tool

You can open the tool in Sparrow Wallet in two ways.

Method 1: Using the top menu

1. Open Sparrow Wallet.
2. In the top menu bar, click on Tools → Sign/Verify Message (or press the shortcut shown).

Method 2: From the Addresses tab

1. In the left sidebar, go to the Addresses tab.

2. From the list, find the specific address you need to use. Always use a receiving address, not a change address.
3. Right-click on the address (or click the pen icon) and choose Sign/Verify Message. The address will be automatically filled in for you.

Step 2: Enter the message details

A "Sign/Verify Message" window will now be open.

4. If the Address field isn't already filled, paste your Bitcoin address into it.
5. Carefully copy the exact message provided by the service and paste it into the Message field.
6. Ensure Format is set to Standard (Electrum) unless the service asks for another format.
7. Click the Sign button. 

8. Sparrow will now ask for your BitBox02 to be connected.

Step 3: Confirm on your BitBox02

Now it's time to use your hardware wallet to securely create the signature.

9. Connect your BitBox02 to your computer.
10. Unlock the BitBox02 with your device password. If you see an error in Sparrow, ensure the BitBoxApp is closed and click Rescan.
11. Once unlocked, the signing prompt will appear on your BitBox02 screen. The device will show:

9. The device shows on the BitBox display:
   1. Coin: Bitcoin
   2. The address you are verifying
   3. The message to be signed.
10. Check every detail carefully on the BitBox02 screen. It must exactly match the information from the service.
11. If everything is correct, confirm on the BitBox02.

Step 4: Copy and share the signature

Sparrow now fills the Signature field with a long string of characters.

12. You can click Verify to check that Sparrow shows “Verification succeeded”.

13. Then click OK

14. Right-click inside the Signature field and choose Copy.

15. Send this signature unchanged to the service that requested it.

Frequently Asked Questions (FAQ)

What is the purpose of signing a message?

It is a secure way to prove you control the private keys for a Bitcoin address. Since only the true owner can create a valid signature for a specific message and address, it serves as a proof of ownership for third parties like exchanges.

Is signing a message safe? Can I lose my bitcoin?

Yes, it is completely safe. Signing a message is a read-only operation that does not authorize the spending of any funds.  It simply creates a mathematical proof. You cannot lose bitcoin by signing a message, as long as you verify the content of the message on your BitBox02 is not a transaction confirmation.

What does the "Verification succeeded" message in Sparrow mean?

This is a local check to confirm that the signature you just generated is mathematically correct for the specific address and message you used. It confirms the process worked as expected before you send the signature to a third party.