Master Key - A stateless password manager

index.js

import scrypt from 'scrypt-js';

const ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz01233456789~!@#$%^&*_-+=`|(){}[]:;"\'<>,.?/';
/**
 * Checks for presence of lowercase letters, uppercase letters, digits, and special characters
 */
const VALIDATION_REGEX = /^(?=.*[a-z]+)(?=.*[A-Z]+)(?=.*[0-9]+)(?=.*[\W]+).*$/;

/**
 * Takes an array of bytes and converts it to a string of substituted characters.
 * 
 * @param {Uint8Array|Array} array - An array of byte values 
 * @param {String} alphabet - The alphabet to use for substitution
 */
function substitute(array, alphabet) {
  const limit = alphabet.length - 1;
  return Array.from(array).map(int => alphabet[int % limit]).join('');
}

/**
 * Generates a unique password based on the parameters.
 * It does this by using Scrypt, with the private info(i.e. password, nonce, etc)
 * being the main input, and the public info(domain, user id) as the salt.
 * 
 * @param {String} domain 
 * @param {String} userId 
 * @param {String} password 
 * @param {Number} nonce 
 * @param {Number} numCharacters 
 * @param {String} alphabet 
 * @param {RegExp} validationRegex
 * @yields {Promise<String|null>}
 */
function* generatePassword(domain, userId, password, nonce, numCharacters, alphabet, validationRegex) {
  let attempt = 0;
  while (true) {
    yield new Promise(async resolve => {
      const digest = await scrypt.scrypt(Buffer.from(`${password}:${nonce}:${attempt}`), Buffer.from(`${domain}:${userId}`), 16384, 8, 1, numCharacters);
      const output = substitute(digest, alphabet);
      if (validationRegex.test(output)) return resolve(output);
      attempt++;
      resolve(null);
    });
  }
}

/**
 * @param {String} params.domain
 * @param {String} params.userId
 * @param {String} params.password
 * @param {Number=1} params.nonce
 * @param {String} params.alphabet
 * @param {Number=8} params.numCharacters
 * @param {RegExp} params.validationRegex
 * @returns {Promise<String>}
 */
export default async function masterKey({ 
  domain,
  userId,
  password,
  nonce=1,
  alphabet=ALPHABET,
  numCharacters=8,
  validationRegex=VALIDATION_REGEX
}) {
  for (const promise of generatePassword(domain, userId, password, nonce, numCharacters, alphabet, validationRegex)) {
    const password = await promise;
    if (password) return password;
  }
}