DFU Update: "Upload Failed: Unknown Command" & Signature-less Bootloader

Question

I am trying to package a firmware update and flash it over BLE DFU and I keep getting the following error on the nRF Toolbox app: 
 "Upload Failed: Unknown Command" 
 I cannot figure out why this is happening and I can't find anyone else having this error on here. Here are the commands I used to create the initial bootloader and settings (flashed over J-Link). 
 Generating the Settings hex: 
 nrfutil settings generate --family NRF52 --application ../AKDP/BUILD/AKDP_RevE.hex --application-version 20 --bootloader-version 1 --bl-settings-version 1 akdp_bl_settings.hex

Generated Bootloader DFU settings .hex file and stored it in: akdp_bl_settings.hex

Bootloader DFU Settings:
* File: akdp_bl_settings.hex
* Family: nRF52
* Start Address: 0x0007F000
* CRC: 0x9F32BF67
* Settings Version: 0x00000001 (1)
* App Version: 0x00000014 (20)
* Bootloader Version: 0x00000001 (1)
* Bank Layout: 0x00000000
* Current Bank: 0x00000000
* Application Size: 0x0003EEB8 (257720 bytes)
* Application CRC: 0xD62A0BD6
* Bank0 Bank Code: 0x00000001
 
 Merging the settings hex with the bootloader hex: 
 mergehex -m akdp_bl_settings.hex ./bootloader_secure_ble/pca10040_debug/armgcc/_build/nrf52832_xxaa_s132.hex -o akdp_bl_with_settings.hex

Parsing input hex files.
Merging files.
Storing merged file. 
 After flashing the softdevice and the bootloader, here is what I used to generate the package file: 
 nrfutil pkg generate --application ../AKDP/BUILD/AKDP_RevE.hex --application-version 21 --hw-version 52 --sd-req 0x9D,0xA5 AKDP_RevE_with_BL_pkg.zip 
 Other information: 
 
 Device: nRF52832 
 SDK: 14.2.0 
 Board: Custom 
 
 I cannot understand why this isn't working. It all looks fine to me. The bootloader build completed without any problems. Any help would be greatly appreciated.

Einar Thorsrud · Accepted Answer

You are right, signing is needed even in debug mode. However, in that case the default configuration of the example is to use a example public key that can only be used with the prebuild .zip distributions in the SDK, as we do not provide the private key. You need to replace the public key with your own public key in order to test the bootloader with your own DFU .zip files, even with the debug bootloader. 
 SDK 15 introduced a bootloader which does not use signing (called " open bootloader"). This is intended specifically for the nRF52840 dongle, so the only example we provide uses USB transport. However, it should be possible to replace the transport layer with BLE (though I have not tested). 
 I am a bit unsure about what you mean when you say: 
 
 I would like to not have to sign it with a private key. I need to do this in order to maintain backward compatibility with firmware that was compiled and packaged without key signing. 
 
 I assume this older firmware packages were made for the legacy bootloader (no signature verification)? If so, there are also many other differences, so you cannot use these packages with the new bootloader. You anyway need to re-pack it for use with the new bootloader, therefore I do not see a significant issue with using signed images for the new bootloader and non-signed images for the old. Or am I missing something? I would also like to emphasize the risk of having an open bootloader, as this makes it very easy for an attacker to change the firmware of a device in the field, modifying its behavior or bricking it.

DFU Update: "Upload Failed: Unknown Command" & Signature-less Bootloader

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