Legal ways to identify ios devices?

Question

iOS

Guys, the task was to write our own analytics system for a mobile ios application without resorting to using existing ones.
Question: What are the allowed and not allowed ways to identify the device?
If earlier everything was simple with UDID, now the situation has become more complicated.
It is desirable that the solution is also integrated into the android application, which will appear later.
One option is to create a cookie the first time the app is launched. Some identifier and use it for tracking. Is this option allowed?
Some news reports say that Apple is banning apps for using tracking cookies, and some write that it's not so bad, so everything is ambiguous.
IOS application is being developed on Air.

Answer 1

Now, the MAC address is usually used to identify the device.

Answer 2

SecureUDID

Answer 3

CFUUID+KeyChain.

Answer 4

The MAC address after updating iOS to version 7 will no longer be able to be used.
Now use only view ID:
A3C2C08C-FF3A-4CFA-ABB4-0A1AC3A0D14E

Answer 5

tell me did you find a solution?
i need id for ios too