24pay.js

const crypto = require("crypto");
const aesjs = require("aes-js");

module.exports = function (key, iv, text) {
    // http://www.24-pay.sk/wp-content/uploads/24Pay-API-Integration.pdf

    if (!checkParams(key, iv, text)) return;

    // convert string KEY and IV to array of character bytes
    const keyBytes = aesjs.utils.hex.toBytes(key);
    const ivBytes = aesjs.utils.utf8.toBytes(iv);

    // create a hash (in HEX) with SHA1 and cut if from 40 to 32 characters
    const textHashHex = crypto.createHash("sha1").update(text).digest("hex");

    // cut it to 32 characters to make it possible for CBC and bypass padding
    // afterward convert it to an array of character bytes
    const shortHash = textHashHex.substr(0, 32);
    const textHashBytes = aesjs.utils.hex.toBytes(shortHash);

    // create an instance of AES CBC (cipher-block chaining) and convert it to array of chars
    // https://www.npmjs.com/package/aes-js
    const aesCbc = new aesjs.ModeOfOperation.cbc(keyBytes, ivBytes, 16);
    const encryptedBytes = aesCbc.encrypt(textHashBytes);
    const encryptedHex = aesjs.utils.hex.fromBytes(encryptedBytes);

    // requested convention
    return encryptedHex.toUpperCase()
};

const checkParams = function (key, iv, text) {
  if (!key) { throw new Error("24pay: Missing KEY parameter"); return false }
  if (key.length < 3) { throw new Error("24pay: Wrong KEY parameter"); return false }
  if (!iv) { throw new Error("24pay: Missing IV parameter"); return false }
  if (iv.length < 3) { throw new Error("24pay: Wrong IV parameter"); return false }
  if (!text) { throw new Error("24pay: Missing TEXT parameter"); return false }
  if (text.length === 0) { throw new Error("24pay: Wrong TEXT parameter"); return false }
  return true
};