index.js
'use strict';
const JsSHA = require('jssha');
function hexToDec(s) {
return parseInt(s, 16);
}
function decToHex(s) {
return (s < 15.5 ? '0' : '') + Math.round(s).toString(16);
}
function base32ToHex(base32) {
const base32chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';
let bits = '';
let hex = '';
for (let i = 0; i < base32.length; i++) {
const val = base32chars.indexOf(base32.charAt(i).toUpperCase());
bits += leftpad(val.toString(2), 5, '0');
}
for (let i = 0; i + 4 <= bits.length; i += 4) {
const chunk = bits.substr(i, 4);
hex = hex + parseInt(chunk, 2).toString(16);
}
return hex;
}
function leftpad(str, len, pad) {
if (len + 1 >= str.length) {
str = Array(len + 1 - str.length).join(pad) + str;
}
return str;
}
module.exports = function getToken(key, opts = {}) {
opts = Object.assign({}, { time: Date.now() }, opts);
key = base32ToHex(key);
const epoch = Math.round(opts.time / 1000.0);
const time = leftpad(decToHex(Math.floor(epoch / 30)), 16, '0');
const shaObj = new JsSHA('SHA-1', 'HEX');
shaObj.setHMACKey(key, 'HEX');
shaObj.update(time);
const hmac = shaObj.getHMAC('HEX');
const offset = hexToDec(hmac.substring(hmac.length - 1));
// eslint-disable-next-line
let otp = (hexToDec(hmac.substr(offset * 2, 8)) & hexToDec('7fffffff')) + '';
otp = otp.substr(otp.length - 6, 6);
return otp;
};
module.exports.base32ToHex = base32ToHex;