Rolling Codes & CAN?

Projects General Guidance
1

Hi,
I'm working on a project where I use two Arduinos together, one gathering sensor data and sending it to the other, which sends data packets out over a CAN network.

I'm wondering if anyone has suggestions - or an application note, or anything, for that matter - on how to use rolling codes to ensure that the devices are not tampered with. I want to use CAN ultimately (using a CAN shield on a Duemilanove), but uart would work for now, so I can get a feel for how it works.

I know I will need a button on each device to synchronize the seed, but I am not sure on what type of algorithm the code must take. I understand most devices use a common seed and a formula programmed into both devices, with the device that does the "reading" of the code storing the next ~3-5 codes in memory (so if it misses due to network traffic/interference, it still responds for a bit). If the devices become disconnected for more than those 3-5 expected responses, it sets a bit (turns on a buzzer or a light, in my case) and lets the operator know that the devices are no longer synchronized.

I'm concerned about the rolling code algorithm lagging the Arduino. I want this "secure" functionality, but it is secondary to gathering and logging the data from my sensors. Is this feasible?

Secondly, I tried a quick search but couldn't find anything - does the Arduino have a "code fuse" to prevent reflashing?

Thank you!

2

What kind of tampering are you trying to detect?

3

I'm trying to figure out if the device is disconnected from the sensor, even for a second. Unfortunately, a check for a zero value is not a good enough solution in my eyes. What I'm envisioning, is a CAN sensor hooked to one Arduino and that Arduino talking to a second Arduino, also over CAN. If the the first Arduino is disconnected from the sensor, the second Arduino would then (using a rolling code or similar) be able to tell that the first Arduino was missing, a set some sort of flag.

4

If you only want to detect a disconnection (a dropped frame), a simple sequence number will work.