Using Certificates Encryption and Decryption hash with Node.js crypto Package

hash_and_certEncrypt.js

const fs      =  require('fs'),
      crypto  =  require('crypto');

function loadKey(file) {
    return fs.readFileSync(file, 'utf8');
}

let
    prvKey   =  loadKey('./privateKey.pem'),
    pubKey   =  loadKey('./publicKey.pem'),
    message  =  crypto.createHash('sha512').update('Hello').digest('base64');

console.log('message: ' + message);

const encryptOptions = {
    key: prvKey,
    padding: crypto.constants.RSA_PKCS1_PADDING
}
let enc_by_prv = crypto.privateEncrypt(encryptOptions, Buffer.from(message, 'base64'));
console.log('encrypted by private key: ' + enc_by_prv.toString('base64'));

const decryptOptions = {
    key: pubKey,
    padding: crypto.constants.RSA_PKCS1_PADDING
}
let dec_by_pub = crypto.publicDecrypt(decryptOptions, Buffer.from(enc_by_prv, 'base64'));
console.log('decrypted by public key: ' + dec_by_pub.toString('base64'));