[Nexxxeh]

Parent-poster said tamper-resistance wasn't an issue in their usage case.

But are you sure it'll DFU over USB?

If so, for avoiding DFU, could you use some simple hardware to disable the data lines on the OTG port until the Pi had finished booting?

Could one use an i2c or spi based crypto chip for key storage?

[drdaeman]

Actually, no. I think I have confused RPi with some other board.

Don't have Pi at hand to test for sure, but searching online can't find mentions of USB DFU. I think I may be mistaken.