Ergonomic update

[coolaj86]

This just cleans up the API:

• makes it possible to have multiple instances
• removes the 'bespoke' prefix (no standards for encoding exist, AFAIK, so it's all 'bespoke')
• places IV before and after the data (the backup is small, and without the IV, the data is unrecoverable)

"use strict";

let Crypto = require("crypto");

let Cipher = module.exports;

const ALG = "aes-128-cbc";
const IV_SIZE = 16;

/**
 * @param {Buffer} key128
 */
Cipher.create = function (key128) {
  //let sharedSecret = Buffer.from(key128, "base64");

  let cipher = {};

  /**
   * @param {String} plaintext
   */
  cipher.encrypt = function (plaintext) {
    let initializationVector = Crypto.randomBytes(IV_SIZE); // IV is always 16-bytes
    let encrypted = "";

    let _cipher = Crypto.createCipheriv(ALG, key128, initializationVector);
    encrypted += _cipher.update(plaintext, "utf8", "base64");
    encrypted += _cipher.final("base64");

    let iv64 = toWeb64(initializationVector.toString("base64"));
    let enc64 = toWeb64(encrypted);
    // store iv64 twice, as a backup
    return `${iv64}:${enc64}:${iv64}`;
  };

  /**
   * @param {String} parts
   */
  cipher.decrypt = function (parts) {
    let [initializationVector, encrypted, initializationVectorBak] =
      parts.split(":");
    let plaintext = "";
    if (initializationVector !== initializationVectorBak) {
      console.error("corrupt (but possibly recoverable) initialization vector");
    }

    let iv = Buffer.from(initializationVector, "base64");
    let _cipher = Crypto.createDecipheriv(ALG, key128, iv);
    plaintext += _cipher.update(encrypted, "base64", "utf8");
    plaintext += _cipher.final("utf8");

    return plaintext;
  };

  return cipher;
};

/**
 * @param {String} x
 */
function toWeb64(x) {
  return x.replace(/\+/g, "-").replace(/\//g, "_").replace(/=/g, "");
}