jwk-39.ts

import { base64url } from '@scure/base';
import { entropyToMnemonic } from '@scure/bip39';
import { wordlist } from '@scure/bip39/wordlists/english';

// Function to convert Base64URL string to Uint8Array
function base64UrlToUint8Array(b64url: string): Uint8Array {
  return base64url.decode(b64url + '='.repeat((4 - (b64url.length % 4)) % 4));
}

// Function to convert the private key to a BIP39 mnemonic
function privateKeysToMnemonic(combinedPrivKey: string): { privateKey: string, mnemonic: string } {
  // Split the combined private key into two Base64URL strings
  const b64urlpks = combinedPrivKey.split(':');
  // Decode the two Base64URL strings to Uint8Arrays
  const b64urlpk1 = b64urlpks[0];
  const b64urlpk2 = b64urlpks[1];
  // Convert the two Base64URL strings to Uint8Arrays
  const privateKey1 = base64UrlToUint8Array(b64urlpk1);
  const privateKey2 = base64UrlToUint8Array(b64urlpk2);
  // Check if the private keys are 32 bytes each
  if (privateKey1.length === 32 && privateKey2.length === 32) {
    // Convert the each 32-byte private key to a 24-word mnemonic
    const m1 = entropyToMnemonic(privateKey1, wordlist);
    const m2 = entropyToMnemonic(privateKey2, wordlist);
    // Combine the two mnemonics and return 48-word mnemonic
    return { privateKey: combinedPrivKey, mnemonic: `${m1} ${m2}` };
  } else {
    throw new Error('Unexpected private key length. Expected 32 bytes.');
  }
}

try {
  const privKey0 = {}; // Insert the #0 private key here
  const privKeySig = {}; // Insert the #sig private key here
  const { privateKey, mnemonic } = privateKeysToMnemonic(`${privKey0}:${privKeySig}`);
  console.log('combined privateKeys', privateKey);
  console.log('combined mnemonics', mnemonic);
} catch (error) {
  console.error('Error:', error);
}