Bitcoin Notary Guide

In an era of digital information, proving a document existed at a specific point in time can be challenging. File metadata is easily altered, and centralized timestamping services can be compromised or discontinued. The Bitcoin blockchain offers a powerful alternative: a global, decentralized, and immutable ledger that can act as a universal notary.

This guide provides a practical walkthrough of how to embed a document's "fingerprint" into a Bitcoin transaction using the OP_RETURN opcode. This creates a permanent, publicly verifiable record that proves your document existed in its exact form at the time of the transaction.

This is the practical, how-to guide for the concepts discussed in our insight, Chain of Custody for Your Ideas.

The Concept: A Digital Notary

Before proceeding to the steps, it's helpful to understand why this method is so powerful. By embedding a document's hash on the Bitcoin blockchain, you leverage its core properties:

• Immutability: Once data is part of a confirmed block, it is practically impossible to alter or delete. It becomes a permanent part of the global ledger.
• Verifiability: Anyone, anywhere in the world, can look up the transaction and verify the existence of your data at a specific point in time (the block's timestamp).
• Censorship-Resistance: No single company or government can block or prevent your transaction from being processed. As long as you can broadcast it to the network, it will be included.
• Low Cost: The price to store this permanent, globally-verifiable record is simply the cost of a small Bitcoin transaction fee, making it incredibly economical.

Step 1: Generate the Document Hash

First, you need the SHA-256 hash of the file you want to notarize. You can use the command line or our browser-based tool below.

Command-Line Method

On most systems, you can generate the hash from the command line.

shasum -a 256 /path/to/your/document.pdf

sha256sum /path/to/your/document.pdf

Browser-Based Calculator

You can also calculate the hash directly in your browser. Your file is not uploaded and never leaves your computer.

Step 2: Prepare the Transaction Output

To embed your hash onto the blockchain, you need a Bitcoin wallet that supports custom OP_RETURN transactions. For this guide, we will use Electrum Wallet (Version 4 or higher), one of the original non-custodial Bitcoin wallets available for desktop platforms. The following tool will help you create the special multi-line text string needed for Electrum's 'Pay to' field.

Step 3: Broadcast the Transaction in Electrum

With the output from the tool in Step 2 copied to your clipboard, you are ready to create and broadcast the transaction from your Electrum Wallet.

1. Open your wallet and go to the Send tab.
2. Paste the entire multi-line text from the tool above into the "Pay to" field. Electrum will automatically parse this and populate the transaction details.
3. Important: The screenshot below uses the text "Nanar Consulting" as a memo for demonstration purposes. Your transaction will contain the much longer SHA-256 hash you generated in Step 1.

   

4. Click "Pay..." to review the transaction details. Carefully check the transaction fee before signing.
   Warning: Always test this process with a very small amount of money first to ensure you are comfortable with the steps.

   

5. Click "Sign", enter your password if required, and then click "Broadcast" to send the transaction to the Bitcoin network.

Step 4: Verify the Transaction

Once your transaction is confirmed, you can view it on any public Block Explorer to verify that your data was included. Your timestamp is permanently recorded as of the block's confirmation time.

You can see our example transaction here: blockchain.com/explorer/...

From Guide to Implementation

This guide provides the blueprint for digital notarization. However, building a secure, automated, and scalable system for an enterprise requires deep expertise in key management, fee optimization, and system architecture.

Nanar Consulting specializes in developing these robust solutions. If you need to protect high-value intellectual property or integrate blockchain notarization into your business workflow, contact us for a full consultation and custom software development services.