How to verify Amazon FPS/SimplePay IPN (Instant Payment Notification), using version 2?

I've looked through the documentation, I've tried downloading various example code, and I've tried hacking various permutations. After a full day's worth of work, I'm spent, and throwing in the towel. So now I'm begging for some help. Can someone please post a PHP class or function, wherein I can simply verify that the ping to my IPN script is legitim开发者_JS百科ate, using signature version 2?

Thank you so much.

Zack

Hard to tell but this might be what you need

http://aws.amazon.com/code/1691

I believe that this supports signature version 2