Hi Tuan,
[quote user="Tuan Pham"]But my question #3 is: If the link is encrypted, is there any chance that the 3rd person can listen and trick/fake to become 1 of 2 connected device and talk to other?[/quote]
Only if the 3rd person was eavesdropping during pairing process and performed man in the middle attack.
[quote user="Tuan Pham"]So it's very easy for anyone else to connect to my central device and destroy my system.[/quote]
Then have a check at the application level if the connected device can be trusted, by for example having a unique number stored in a characteristic. You can also check IEEE address (if it's known).
Best Regards
