[Cryptech Tech] road to berlin

[Fredrik Thulin]

On Monday, May 02, 2016 12:37:50 AM Paul Selkirk wrote:
...
> The AVR has to do approximately the following:
> - receive a tamper interrupt from an external circuit (currently a panic
> button)
> - wipe the MKM
> - raise an interrupt on the ARM, so it can do whatever it needs to do
> - light an LED (red, of course)
> 
> If we get that right, we might never have to upgrade the AVR.

I agree. I would consider it nice to have (or harmful =) ) to have a software 
upgrade path for the AVR before Berlin. We could absolutely make a way to 
transfer firmware to the AVR from the FPGA using GPIOs, but with close to zero 
benefit at this stage.

My reasoning:

The whole tamper circuitry is currently a development module. It is nice to 
have a way to erase any keys in the device when re-purposing it or similar, 
but it currently requires pressing a button on the bottom side of the PCB. If 
someone wants to actually add tamper protection to the Alpha using the AVR 
GPIOs, it is not unreasonable to expect them to program the AVR using an ISP 
programmer connected to the programming header.

So the main reason to make DFU for the AVR I can see would be to streamline 
manufacturing, and I think we have other things to focus on first.

/Fredrik
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