nRF5340 w/ 'Crypto: RNG', true or pseudo random numbers?

[esmart-engineering]

I am working w/ the nRF5340DK, and the project mentioned here (NCS v2.5.0, nrf/samples/crypto/rng). I was able to build/flash the project.

I wanted to verify whether the random numbers generated are pseudo random or true random. It appears to be true random (I get different numbers when I reset the board), but I wanted to double check.

What parameters, hardware, etc. would change whether it's pseudo or true? For example, does enabling/disabling something in KConfig, switching the hardware to nRF52840, etc. affect the result?

[esmart-engineering]

Okay this makes sense. I went ahead and tested adding the breakpoint, and confirmed it does get called.

Just to confirm, it looks like this TrustedZone call also similarly uses PRNG  seeded by TRNG, just like what the non-TrustedZone does? I saw a description of the TrustedZone call in nrfxlib/crypto/nrf_cc312_platform/include that claims "This function will calculate PRNG using HW accelerated AES CTR_DRBG with a 16-byte key and reseed with TRNG using ARM CryptoCell cc3xx HW according to a reseed interval."

[Vidar Berg]

Yes, TF-M uses the same crypto backend as the app does when not using Trustzone (Enabling secure services).