Preventing reprogramming an nrf52832

[Rolf]

I can see that we can use APPROTECT to disable reading of the flash.   

This seems to be reversible using: nrfjprog -f NRF52 --recover, which will erase the flash and allow reprogramming.

This protects the original code from being discovered but does not prevent malicious reprogramming.

Is there no way to prevent reprogramming the device with arbitrary code once in the field?

[Edvin]

Hello,

There is no way in software to prevent an erase and reprogramming of the nRF if they have physical access to the programming pins of the nRF, but as you say, there is readback protection, to prevent them from reading the .hex file programmed to the chip.

What you could do, is to pre-program the chip, before soldering it on to the PCB. Then, on the PCB, you can ground the SWDIO and SWDCLK. This will make it impossible to program the chip unless you desolder the chip. In my opinion, if someone is able to desolder the chip, they might as well change the entire PCB with their own chip and firmware.

BR,

Edvin

[Matt]

The Decepticons are working on it... any "Transformer 6" fans here? :)

[karthikeyan]

hi edwin,

     similar question to me. but i am programming the chip after soldering in my custom pcb. so after that how can i give protection. i need suggestion from hardware not in software.

[Matt]

If folks are desperate to reprogram your chip they'll always find a "way". You have to think system protection then i.e. how would the "other" side verify the identity of your chip.

[Edvin]

Well. If the SWDIO and SWCLK are shorted to GND, there is no way to program it. The only way to program it then would be through a bootloader, but this would have to be programmed in before the chip is soldered to the pcb, or at least before the SWDIO and SWCLK are grounded.

[karthikeyan]

thanks edvin