Amazon S3 provides a great place to store all sorts of files but sometimes managing permissions can be a bit of a pain. Built-in to S3 is the ability to generate links to private files that expire after a set period of time. This tool generates those for you so you don't have to fiddle with the command line or install any 3rd party tools.
Your secret key is safe, all code runs client side. The code is also available in case you don't trust me.