DFU Signing

[Freddy Sørensen]

I have had a look at you experimental implementation of DFU signing. I'm very concerned about the code size. The old Bootloader used about 13KB and the new one with signing has allocated 25KB. Let's assume we use 4KB for MBR and 4KB for App-data, this leaves us with 248KB. In order to update the SoftDevice+Bootloader, their maximum combined size is 124KB (248/2KB). The S130 is using 108KB, which leaves us with 16KB for the Bootloader. Please consider to integrate the nrf_sec_module into the Bootloader, in order to reduce the size and see if it's possible to keep the size below 16KB? Clem Taylor managed to implement a SHA1 + RSA512 within 1KB of code. Have a look here: devzone.nordicsemi.com/.../

[Stefan Birnir Sverrisson]

Hi Freddy

Thank you for your feedback. I acknowledge your concern about the size when using bootloader with S130 softdevice. We will try for future development to decrease the size of the bootloader with signing. As I understand it, there is a size/speed tradeoff when doing the signing, where we have prioritized speed apparently. This experimental implementation of DFU signing has primarily been intended for application updates. Is it possible for you to update the softdevice and bootloader separately, in order to make everything fit within the 256k?

[Lucas]

The size has blown my bootloader start address estimation. If I understand correctly bootloader start address cannot be changed after the bootloader has been flashed. code size reduction would be nice for me as well.