Is there another Hardware specific Code / Number / anything which is able to replace UDID?

Question

assume the following :

I created an ipad app on ios6 which uses the UDID of the ipad before the app can be installed. So the consumer types in his UDID and than he can install. In IOS 7 the way I used to get the UDID is not supported anymore, so I search for something else to replace the UDID, if possible.

You may see this question which is somehow related how to find UDID in ios7 without

Answer 1

No there is none, as of iOS 7 you cant even use the MAC address. You should never identify a device but always a user.

You option could be some kind of registration server, where you app will generate a unique number which it will store in the keychain to persist the value.