Arduino wireless encrypted data project

Hi there I’m wonder if someone could help me please, I have a project which I need to complete which has two arduino’s that transmits encrypted data between eachother wirelessly. Could someone please give me some details on what they recommend and how I should go about making it function. I wish to create something like the image below could someone please guide me on what i would need to do? 

My plan would be to have an RFID tag which is then encryped and sent wirelessly to the receiver, which will be decrypted to allow for secure authentication.