Ethereum: How to get xpriv and xpub from keyPair with bitcoinjs-lib

Here is an article explaining how to extract “xpriv” and “xpub” from a key pair using the BitcoinJS library:

Extracting X-Public and X-Private Keys from a Key Pair

In this article, we will explore how to obtain the “xpriv” and “xpub” keys from a Bitcoin public/private key pair generated using the “bitcoinjs-lib” library.

Prerequisites

Before proceeding, make sure you have the following installed:

  • bitcoinjs-lib: A Node.js library for interacting with the Bitcoin blockchain.
  • A Bitcoin private key pair (generated by bitcoinjs-lib)

Sample Code

const bitcoin = require('bitcoinjs-lib');

const keyPair = bitcoin.ECPair.makeRandom({});

// Get the private key

const privateKey = keyPair.private;

// Convert the private key to PEM format for easier manipulation

const privateKeyPem = bitcoin.privateKeyToPem(privateKey);

console.log(Private Key (PEM): ${privateKeyPem});

// Extract the X-Public and X-Private keys from the private key

const xpub = keypair.xpub;

const xpriv = keyPair.xpriv;

console.log(Public Key X: ${xpub});

console.log(Private Key X: ${xpriv});

Explanation

In this example:

  • We create a new ECPair instance using bitcoinjs-lib.
  • Generate a random private key using makeRandom(). This function returns an ECPair object.
  • We convert the generated private key to PEM format for easier manipulation by calling privateKeyToPem() on our private key object.
  • We extract the X-Public and X-Private keys from the private key using xpub and xpriv respectively and log them to the console.

Tips and Variations

  • If you are working with a specific key pair or a large number of keys, consider caching the private key before converting it to PEM format to avoid redundant conversions.
  • You can also use ECPair.fromPrivateKey() instead of makeRandom() if you already have a trusted private key.
  • If you are dealing with large files or need more advanced cryptographic operations, consider using other Bitcoin libraries such as bitcoinjs-core or ethers.js.

By following these steps and understanding the process, you should be able to extract the “xpriv” and “xpub” keys from the generated key pair. Happy coding!

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