I am using ECDH key exchange protocol for establishing shared secret between Arduino Uno and Android device. For this purpose I am using this library and more specifically Curve25519. This is the confidentiality part of the secure communication I want to establish.
Now, before establishing shared secret between Arduino Uno and Android device, I want to have both ways authentication. It would be nice to have some sort of session IDs in order to be able to communicate with multiple Arduino Uno devices from single Android device.
What do you suggest? Please consider the memory size of Arduino Uno.