How to identify each iOS device?

As per my title suggest and my game requirement, I want to identify each ios device uniquely.
Because I want to pass data over server for this and want to manage data related to that.

So I want to detect my iphone is different than my friends have.
How to do this? Is there any way exist to access iphone UDID?

EDIT: If I uninstall and install same game again then it will generating different uniqueDeviceIdentified. I want per device some unique thing. So what I need to do?