The LonTalk protocol does not implement data encryption but it does implement Sender Authentication.
Sender Authentication uses an authentication key. The authentication key cannot be read out of the Neuron and cannot be changed without already having the key.
When a device receives data, it sees an Authenticated message. The device responds to the Authenticated message by sending back a challenge with a 64 bit random number. The sending device receives the random number and performs an authentication transform on it and returns the transform back to the original device and if it matches the response from the sender, then the message will be processed.