As I was working on a custom MP3 player, I wanted to use a web service to search for album arts in order to display them as the corresponding music is played. After a quic Google search I found Amazon Web Services (AWS). Amazon actually provides services to search items in their catalog and therefor you can look for a precise music album and get its cover. This very service is the Product Advertising and is accessible through the Product Advertising API.
But since the 15th of August 2009 AWS requires every request to be signed. It simply means that a "Signature" parameter must be added to each and every request. One might think that the API key should be enough, but this key is inserted in every query URL and can be read by pretty much anyone. The signature is created using the secret AWS password and crypted using the HMAC/SHA256 algorithms so that AWS can be sure the request actually comes from the genuine owner of the API key.
The documentation features a guide to explain the whole signing process step-by-step but as you might have guesses, there is a huge difference between reading it on the documentation and actually implementing it successfully.
Full code right after the jump...