I am currently implementing a fairly simple signing library (for my personal use) to verify the identity of packets sent with the RF24Mesh library (using NRF24L01+) radios. Never made a flowchart but I've added one to clarify my current implementation. I'm using Atmel's ATMega328P to do all the calculations.
All devices have a list of unique MAC addresses of other nodes programmed in them. Then before sending the message the device just checks if it has a nonce that can be used to send the message. If not then it's requested. When there's nonce, HMAC-SHA256 library/implementation is used to include a hash of the data(+hmac+nonce) sent in the payload.
Now my question is, is my implementation secure in the way that it would be the only way to hit me with a wrench to turn on my TV than to forge packets to do the same?
Do ask if something was left unclear.