Issue running ECDSA with a different backend

[cdugue]

Hello,

I am trying to benchmark the CC310 cryptocell on the nRF52840. I am testing the ECDSA example (examples/crypto/nrf_crypto/ecdsa). I can run the code fine with the CC310 backend. However, if I change the backend to mbed tls in the sdk_config then there is an error when running the code on the nRF52840 (0x8503)

"Error 0x8503: The function was called with a feature that is unavailable
<error> app: Fatal error"

The same issue happens with Oberon and also with other examples such as ECDH.

Do you know what could be the issue?

[Vidar Berg]

Hello, 

Please make sure that you're using a curve supported by both cc310 and Oberon. The ecdsa project for pca10040 (nrf52832) uses the Oberon backend. 

[cdugue]

Hello,

I am attempting to use secp256r1 which is supported by the three backends on the nRF52840 but I get the error mentioned above at runtime.

[Vidar Berg]

Hello,

I got the same error. Turns out that you need to enable the nrf RNG since you're not using the RNG in CC310. Set NRF_CRYPTO_BACKEND_NRF_HW_RNG_ENABLED to '1' in sdk_config.h to enable it. 

[cdugue]

That fixed it, thanks!