use drupal's hashing in an external php fil
What you'll need is Drupal's password.inc file, located at: /includes/password.inc

Just copy this file to your project and include it in your custom php file. This way you can use the user_check_password() function (and many others).

here is a good example of something like you are trying to do in Laravel 4. http://www.goodbytes.be/blog/article/create-a-custom-drupal-7-authentication-driver-provider-in-laravel-4