crypto.pbkdf2(pass, salt, 1000000, 128, 'sha512', () => {
  console.log('5:', Date.now() - start);
});

crypto.pbkdf2(pass, salt, 1000000, 128, 'sha512', () => {
  console.log('6:', Date.now() - start);
});

crypto.pbkdf2(pass, salt, 1000000, 128, 'sha512', () => {
  console.log('7:', Date.now() - start);
});

crypto.pbkdf2(pass, salt, 1000000, 128, 'sha512', () => {
  console.log('8:', Date.now() - start);
});