android - Unique device fingerprint

How do we generate a unique device fingerprint, for each and every android device?

Criteria,

1. It should be unique for each and every device.


2. Should not change when user upgrades the OS.


3. Should not be predictable, for security reasons.

I have already tried various permutation and combination. I see that generating a random, and storing is the easiest alternative.

I am not very comfortable with the "storing" part.