I used to work on a product that was integrating with Honeywell security grade 2-3 panels. These are panels that are used for businesses and airports (grade 4 i

I used to work on a product that was integrating with Honeywell security grade 2-3 panels. These are panels that are used for businesses and airports (grade 4 is the highest). Those panels were using an encoding scheme (s-box at best) to relay data on the peripherals (rs485, rs232) and over the phone line, and if you had a network card (fancy) the same was going on over the network. The user had the option to enable "encryption" from the panel, but his installer could dial in over the phone line supply a 4 digit pin and disable encryption!!!