How to sign Bitcoin transactions on air-isolated computers?

For increased security against malicious actors, air-gapped setups isolate the computer used for signing Bitcoin transactions, preventing unauthorized access to private keys.

Feb 20, 2025 at 07:54 am

Air-Gapped Transactions: A Comprehensive Guide to Signing Bitcoin Transactions on Isolated Computers

Key Points:

• Understanding air gaps: Why they are crucial for Bitcoin transaction security
• Creating an air-gapped signing setup: Hardware and software requirements
• Generating a transaction on an online computer
• Transferring the unsigned transaction to the air-gapped computer
• Signing the transaction on the air-gapped computer
• Broadcasting the signed transaction back to the online computer

Creating an Air-Gapped Signing Setup

1. Hardware Requirements:

Obtain two separate computers: one to create and broadcast transactions, and the other to sign transactions. The air-gapped computer should be kept isolated from the internet and any potentially compromised networks.

2. Software Requirements:

• Install a Bitcoin wallet on the online computer.
• Install a Bitcoin signing software (e.g., Electrum, Armory) on the air-gapped computer.

Generating an Unsigned Transaction

3. Create a New Transaction:

On the online computer, use the Bitcoin wallet to create a new transaction, specifying the recipient's address and transaction amount. Do not sign the transaction at this stage.

4. Export the Unsigned Transaction:

Right-click on the unsigned transaction in the wallet and select "Export" or "Save As." This will save the transaction details in a file (usually with a .tx extension).

Transferring the Unsigned Transaction

5. Physical Transfer:

Remove the USB drive or other removable storage device from the online computer. Insert it into the air-gapped computer.

6. Copy the File:

On the air-gapped computer, copy the unsigned transaction file from the USB drive to a secure location on the hard drive.

Signing the Transaction

7. Open the Signing Software:

Launch the Bitcoin signing software on the air-gapped computer. Import the unsigned transaction file into the software.

8. Check Transaction Details:

Carefully review the transaction details to ensure they are what you intended.

9. Sign the Transaction:

Use the signing software to sign the transaction with the private key stored on the air-gapped computer. This creates a digitally signed transaction.

Broadcasting the Signed Transaction

10. Transfer the Signed Transaction:

Remove the USB drive from the air-gapped computer and insert it into the online computer.

11. Copy the File:

On the online computer, copy the signed transaction file from the USB drive to the location where the wallet stores other transactions.

12. Broadcast the Transaction:

Open the Bitcoin wallet on the online computer. The signed transaction will be automatically detected and broadcast to the Bitcoin network for confirmation.

Frequently Asked Questions (FAQs)

Q: Why is it important to use an air gap for signing Bitcoin transactions?

A: Air gapping prevents malicious actors from accessing the private keys used to sign transactions. This mitigates the risk of unauthorized transactions being sent or funds being stolen.

Q: What are the different methods for creating an air-gapped signing setup?

A: There are multiple approaches, including using a dedicated air-gapped computer, a virtual air-gapped environment, or a hardware device specifically designed for air-gapped signing.

Q: Can I use an air-gapped signing setup with multi-signature wallets?

A: Yes, you can use an air gap for signing multi-signature transactions. This requires coordinating with all co-signers to ensure they follow the same air-gapped signing procedure.

Q: Is it possible to sign Bitcoin transactions offline without an air gap?

A: Yes, there are offline signing tools that allow you to sign transactions on a computer that is not connected to the internet. However, these methods still require a level of trust in the software and hardware used, as they are not completely isolated from potential vulnerabilities.

Q: How often should I create a new air-gap signing setup?

A: The frequency depends on the security requirements and threat level. It is recommended to create a new setup periodically, especially if you suspect any compromise to your previous setup.