I have unable to do DFU because of my bootloader programmed chip

[Darshan Vyas]

Hi

I have lost my private key for generating my dfu pakage using nrfutil.

I have 2K nrf Modules chips already programmed with bootloader & dfu enabled firmware. However, due to the corruption of the setup I have lost my key.pem file. 

Can you guide me how can i generate private key using earlier app_dfu_package.zip file. As its a complete rework for us to re-program the chips which needs firmware upgrade at project site.

Regards

Darshan

[Einar Thorsrud]

Hi Darshan,

There is no way to generate the private key from an old DFU package. The reason for using cryptographic signing (ECDSA in this case) is precisely to ensure that only the holder of the private key is able to generate valid upgrade images. It is not possible to generate valid DFU packages if the private key is lost.

There are only two possibilities in this situation:

• Either live with the fact that it is impossible to update the devices further,
• or find a way to re-program the bootloader via SWD (which is usually not a realistic option for end products in the field).

Einar

[Darshan Vyas]

Is Possible to recover Public key from the bootloader hex file.

It may help to identify the key.

[Einar Thorsrud]

Yes, it is possible to recover the public key from the bootloader. But no, it will not be possible to derive the private key from the public key.

[Darshan Vyas]

Thank you can guide how to get public key from booloader.

[Einar Thorsrud]

Hi,

The easiest is obviously if you still have the bootloader code, then you can simply read it there. If not, you can find the location if you have the .map file and then read it from the binary. Else you will have to dig into the binary somehow. Since the encryption key does not have a simple pattern it may be difficult to find it without disassembling the binary. That is not something I am experienced with, so I am unable to give any advice.

I do not see why you want to do this, though. The public key will not in any way help you obtain the private key.