I have very vey basic skills in cryptography, it's hard for me to explain clearly my problem so I will start with an example. Estimote beacons have a security function called secure UUID, once activated the beacon will change it's UUID randomly and autonomously every 10 min. At any time the server can decrypt the generated UUID to identify the beacon that generated it.
So to summarize, a value changes randomly and it's possible to decrypt it at any time to identify its origin.
I suppose that each beacon has a key and use a function to re-encrypt the last generated UUID and the server use the same function and key to decrypt it ...
I want to understand how this work, did someone have an idea ?