When I want to use encryption only for challenge-response exchange and not for hiding the contents of an encrypted message, is it still a threat to me not changing IV for new encryption?
For easier understanding why I ask this here is my situation:
I'm using two Arduinos with LoRa transceivers to communicate with each other. One is a bridge connected to the internet and the other is connected to servos and sensors.
I don't care if the potential attacker knows that some packet is for example rotating servo to right and another packet is sending data from the humidity sensor to the bridge.
The only thing I care for is that attacker cannot imitate any of these commands so he can't spin my servos and send bad values that don't come from my humidity sensor.
That's why I use challenge-response exchange so that I can verify if my bridge sent the packet and etc.
But there is no way (at least one I know of) for me to exchange IV to the other Arduino, so it can decode the challenge.
My questions are:
Can not changing the IV be in my case somehow exploited? If yes. How and what it means for me?
Is there any better way to do it?