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.

[Hung Bui]

CRC is calculated and checked after each object is received. Have a look here. You can consider to check CRC for the encrypted packet instead of decrypted packet. This is to ensure the object is received properly over the air. Also, doing this you don't have to modify the bootloader on that part.

You can use the hash of the decrypted image to do the final validation of the image integrity.