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]

Thank you very much for the suggestion! I'm now looking at changing the CRC in my update package, but something puzzles me... I can't find the CRC inside the DAT file. I was under the impression it would follow struct dfu_init_command_t (or dfu-cc.proto). The first 16 bytes are 12 84 01 0A 3E 08 01 12 3A 08 01 10 33 1A 02 87, 87 could match with SD requirement, but 12 (first one) certainly doesn't look like a boolean!