Why does the CC312 appear to be disabled for B0 on the nRF5340DK?

[hyper]

This commit to the sdk-nrf repo: https://github.com/nrfconnect/sdk-nrf/commit/fdd7a24857a6e762055a0192293fc85165246e7f appears to me to indicate that hardware crypto support is disabled when compiling B0 for the nRF5340 DK "since it is not used".

If I have interpreted that correctly, does anyone know why this is the case, and why it appears to be specifically disabled for the DK but not for other nRF5340 based boards?

Is it just that there isn't code yet to support the use of the CC312 in the Nordic secure bootloader?

Does this commit mean that software crypto is the only option for B0 (and by extension MCUBoot when external crypto support is enabled?) on nRF5340 based boards?

Is this something we should be concerned about (eg negative affect on flash usage and/or boot time)?

Thanks.

[Sigurd]

Hi,

Is it just that there isn't code yet to support the use of the CC312 in the Nordic secure bootloader?

We are missing the bootloader-specific C312 libraries. We currently only have it for C310. http://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.8.0/nrfxlib/crypto/doc/nrf_cc310_bl.html

So adding C312 non-specific-bootloader libraries increases the flash over the SPU limit. (The MCUBoot partition size is set specific to lockable regions in SPU. For nRF5340 it's 16KB.)

[hyper]

Thanks for looking into this for us.

Are there plans to add the bootloader-specific CC312 libraries to nrfxlib in the next few months?

[Sigurd]

hyper said:

Are there plans to add the bootloader-specific CC312 libraries to nrfxlib in the next few months

No immediate plans as far as I know. Updates of MCUboot itself is currently only fully supported through HTTP/AWS, so benefit of using C312 in B0 has limited value right now.