How to ensure/determine that a post is coming from an specific application running on an iPhone/iTouch?

Question

Building an iPhone OS application that will allow users to anonymously post information to a web application (in my particular case it will be a Rails based site) ... and I

Answer 1

Encrypt or sign something using the public key of a key pair, then decrypt or verify it on the server with the private key. Ultimately, anything that can be sent can be duplicated, be it a spoofed html header or an encrypted block. The app has to know the secret handshake, and anyone with access to it (and sufficient technical skills) can figure out the secret handshake.