Secure iPhone interaction with the server, so that only my application can send data?

I am working on an iPhone application that should host some data on a server, for example. let's say a user votes on a topic. Here's the problem:

I want to implement some form of encryption so that only my iPhone clients can publish voices on the server, no other devices / sources can publish data.

I do not use usernames / passwords, and the server has REST interfaces defined for reading / publishing data.

any ideas? appreciate any / all help.

- MI page