DFU firmware encryption

[Jonathan]

Hi,

I would like to implement DFU with firmware encryption. I'm aware this isn't present in SDK 12 and would like to modify the secured bootloader to implement it.

As far as I understand, a DFU package is a zip file containing a manifest, and sets of 2 files, a .dat and a .bin . Is it right that the .bin is pure image, and .dat is the header/init packet?

My plan was to encrypt the .bin file, then, in the DFU bootloader, decrypt just before writing to flash. Does this sound like a good approach?

Thanks for your help!

[Hung Bui]

I don't see any problem with this.

And you are correct, .bin file is the pure image, and .data is the init packet.

If you going to encrypt the .bin file and decrypt it after you receive it on the bootloader, you need to modify the bootloader so that hash and signature is only validated after the image is decrypted.

[Jonathan]

I didn't do anything that would affect the bin file size. You can try but you may need to apply more changes for it to work [unsure]. One thing to keep in mind also is the transfer can be resumed, so unless you want to kill that feature, you'll need an encryption that makes this possible [my XOR one does, but it's not a proper encryption]. I did keep the private key signature, having it means during transfer I don't have to worry about malleability of the chosen encryption algorithm as any tampering will be detected at signature checking.