DFU 52840

[mijiale]

Hi all

nrf52840 Development board,sdk is nRF5_SDK_15.2.0_9412b96,PC is windows 10

I want to use the DFU to update my file,but I find that only the Init packet is signatured.If the attacker uses the init packet which is signatured and adds his aclicious code,the firmware of ble device will be updated using the aclicious code.Is this a security vulnerablility?

[bjorn-spockeli]

Hi Mijiale, 

you are correct that its only the init packet that contains a signed hash of the firmware, but this does not mean that one can update arbitrary firmware just by using a Init packet from a previous update.  

The init packet signature is actually an encrypted hash of the firmware image, this encrypted hash is de-crypted on the receiver side and compared to the hash of the received data(i.e. firmware). If the  data is modified after the signature is created(i.e. the hash of the data is calculated and encryted), then the hash comparison on the receiver side will fail. 

Hence, this method  ensures three things:

1. Efficiency: Its more efficient to sign the hash instead of 
2. Integrity:  If the data (i.e. the firmware) is changed after the image was signed or the signature is changed, then the post-validation of the data will fail as the hashes will not be identical.
3. Authenticity: The recipient knows that the data is coming from a trusted source.

Best regards
Bjørn

[mijiale]

Thank you very much for your reply！