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

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

Einar Thorsrud — Thu, 06 Feb 2020 10:12:08 GMT

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.

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

Darshan Vyas — Thu, 06 Feb 2020 05:37:06 GMT

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

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

Einar Thorsrud — Wed, 05 Feb 2020 06:09:44 GMT

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.

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

Darshan Vyas — Wed, 05 Feb 2020 05:37:34 GMT

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

It may help to identify the key.

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

Einar Thorsrud — Tue, 04 Feb 2020 19:20:23 GMT

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