nRF52840 nRF Connect SDK/Zephyr random number generation

[basvkesteren]

Hi,

Looking for some guidance on how to use the 'cryptographically secure random number generator' in a Zephyr/nRF Connect SDK application on an 52840

Is this a supported combination? I found some older devzone posts about this being in development (https://devzone.nordicsemi.com/f/nordic-q-a/45500/nrf52840-and-cc310-random-number-generator-hanging/179228#179228)

Enabling CSPRNG_GENERATOR_CHOICE requires some other backend/driver options to be enabled. It seems there are multiple options here, are there examples available? What is the advised combination here?

Best regards,

-Bastiaan

[Marte Myrvold]

Hi Bastiaan,

You can use the CC310 entropy driver (entropy_cc310) to generate random numbers.

Best regards,

Marte

[basvkesteren]

Hi Marte,

Thanks! But, one more question, though...

Can you quide me through how to enable/use this? I'm a newbie to both zephyr and it's build-system, so I'm probably missing a lot of stuff that should be obvious here...

The API documentation says "When used on nRF52840, the entropy_cc310 driver gathers entropy by using the CC310 hardware through the nrf_cc310_platform library.". That seems to be the NRF_CC310_PLATFORM config setting, which says 'to use, link with nrfxlib_crypto in CMAKE'. How to i do that?

I did try to implement some entropy-code (with zephyr\samples\drivers\entropy as an example), but sofar I can't get that to work...

device_get_binding("HW_CC310_0");

cannot find the device: The device exists, but the binding fails because dev->driver_api is null in z_impl_device_get_binding

[basvkesteren]

Hi Marte,

Yay, I  have random numbers. Apparently i went into the wrong direction when using the Zephyr entropy stuff, that didn't work. But calling nrf_cc310_platform_init() and then using nrf_cc310_platform_entropy_get() directly gives me random numbers, so that's good enough for me

Next step: encryption.. When I enable CONFIG_NORDIC_SECURITY_BACKEND I run into a compilation trouble, seems to be an existing problem:

https://devzone.nordicsemi.com/f/nordic-q-a/63781/ncs1-3-0----mbedtls_config_file----include-expects-filename-or

I already replied there, but; is there a fix for this?

[Marte Myrvold]

Hi Bastiaan,

Great to hear that you have random numbers now!

The fix for that issue will come in NCS v1.4.0, so unfortunately you will have to use command line for now. There's a guide on how to do this here.

Best regards,

Marte

[basvkesteren]

Hi Marte,

Thanks, I have a working setup now: just performed my first SHA-256 hash  When is NCS 1.4.0 expected?

Thanks,

-Bastiaan