使用UDID创建唯一的用户标识

I am working on an iPhone App which communicates with a Server to store and exchange data. Since I would like to make it as simple as possible, I want to avoid registration (or mybe also the using of a password) for the user account. Is it possible (and allowed?) to get the UDID of the iPhone device and make eg. an MD5-hash of it, which I transfer to the server and use it for authentification? Since this ID is unique I could simply use it to login and get the user specified data from the server, without any need of creating login data.I am working on an iPhone App which communicate