Crypto backend module used by DFU and Appication

[moon.kim]

Hi.

I am using the oberon crypto backend module to use LESC in the application firmware. (I referred to the GLS example)

And I am trying to add a boot loader to use DFU. However, the boot loader cannot be added because the flash size is insufficient.

So, I want to use the crypto backend module used in DFU and the oberon crypto backend module, which is the backend module used in the application (I am using the micro ecc backend module now in DFU).

It is simply shown in the figure below.

Question 1. Can use the same crypto backend module in bootloader and application?

Question 2. If possible, which cryto backend module should be used for the firmware? 

[Einar Thorsrud]

Hi,

Question 1. Can use the same crypto backend module in bootloader and application?

No, you cannot. The crypto module is part of the binary, and is separate for the bootloader and application. Note that micro-ECC is quite small, so you do not have any other real option for the bootloader.

How does your memory layout look? Would it be possible to compress the application a bit to give room to increase the bootloader sizes? Perhaps by using something other than oberon in the application as well? If you only use crypto for LESC and DFU, then you could use micro-ecc in the app as well (it will not have as good performance, but that only matters when pairing which is not a common task. And you should expect to see a reduction in application size.

[moon.kim]

Hi,

Thank you for reply

I have one question about this.

Does poor performance mean that the connection may not be possible during pairing? Or does it mean that security is weak?

Einar Thorsrud said:

If you only use crypto for LESC and DFU, then you could use micro-ecc in the app as well (it will not have as good performance, but that only matters when pairing which is not a common task. And you should expect to see a reduction in application size.

[Einar Thorsrud]

No, the security will be exactly the same, and the connection will also be established in the exact same way. It is just that the crypto operation done during the Diffie–Hellman key exchange will take slightly more time and consume more power. But this is a one-time operation per pairing so if this is all you use crypto for in your application, it has no practical implications.