암호화 예시
shiftBy('test', 2) // =>'sdfewdf'
shiftBy('sdfewdf', -2) // => 'test'
const crypto = require('crypto');
const secret = 'abcdefg';
const hash = crypto.createHmac('sha256', secret)
.update('I love cupcakes')
.digest('hex');
console.log(hash);
// Prints:
// c0fa1bc00531bd78ef38c628