I'm not even sure of the correct term to use.
I want to build some security into a product that uses a pair of controllers communicating by RS-232. I'd like the "slave" controller to require the "master" controller to perform some sort of validation before the slave will respond with any but the most basic of keep-alive messages.
This whole thing doesn't need to be perfect: it just needs to discourage all but the serious hackers from breaking into the link.
I'm pretty sure that the best way to do this is to have the slave send a challenge to the master, and only open up if it gets the correct response.
What's the right place to go to find a good method, or do you have any suggestions?