Encrypting a Message with a Bitcoin Public and Private Key

In this article, we will explore how to use a Bitcoin public key and corresponding private key to encrypt and decrypt messages. We will focus on Ethereum as an example, but similar techniques can be applied to other blockchain networks.

Public Key Cryptography

A public key, in the context of cryptography, refers to a pair of keys: a public key (usually represented by the hexadecimal string “xpub”) and a corresponding private key (usually represented by “y”). In this scenario, we use the Ethereum Public Key (EPK) format, which is commonly used for public-key cryptography.

To encrypt a message with a Bitcoin EPK:

• 
  Generate the Private Key: First, generate a private key for your Bitcoin wallet. You can do this on the Bitcoin website or through the Electrum wallet software.

• 
  Create message: Create a string of text that you want to encrypt with your public key and the corresponding private key.

Decrypt with private key

To decrypt the message with the private key:

• 
  Convert EPK to JSON Web Token (JWT)
  
  
  
  
  : Convert the Bitcoin EPK to a JSON Web Token (JWT) using the ethers.js library.

• 
  Decrypt with public key: Use the decrypted JWT as input to the public key in xpub format.

• 
  Convert JWT back to message: Finally, convert the decrypted message from the public key back to its original text format.

Sample code

Here is a sample code snippet using the ethers.js library:

const ethers = require('ethers');
// Set private key and message
const privateKey = 'your_private_key_here';
const message = 'This is a test message.';
const encryptedMessage = 'encrypted_message';
// Convert EPK to JWT
async function convertEPKtoJWT(epk) {
const jwt = await ethers.utils.fromJsonWebToken(epk);
return jwt;
}
// Decrypt with public key
function decryptWithPublicKey(jwt, publicKey) {
// Convert JWT back to message
const messageFromJwt = await ethers.utils.recoverMessage(jwt, publicKey);
return messageFromJwt;
}
// Example application:
async function main() {
const epk = '0x... your_EPK_here ...';
const jwt = await convertEPKtoJWT(epk);
const decryptedMessage = await decryptWithPublicKey(jwt, epk);
console.log(decryptedmessage); // This should print the original message
}
Main();

Note



: Make sure to replace your_private_key_here and 0x... your_EPK_here ... with the actual values ​​for your Ethereum private key and public key. Also, make sure you have the required libraries (ethers.js) installed before running this code.

In conclusion, using a Bitcoin EPK and the corresponding private key to encrypt and decrypt messages is a secure method in the context of blockchain cryptography. The provided example shows how to convert an encrypted message from an Ethereum public key format to a JSON Web Token (JWT) and then back to a message that can be decrypted using the same public key.

Ethereum Extended Public