ble_sm_alg: Replace use of CTR DRBG with mbedtls_esp_random

[rojer]

Description

ESP has a HW TRNG that produces good quality random numbers without the need to pass them through a PRNG such as CTR DRBG.

mbedtls_esp_random is the RNG function providing access to ESP's HW TRNG.

Dropping usage of CTR DRBG by nimble eliminates it from the firnmware, saving a few K of space.

Related

This PR is similar to the change previously made to wpa_sucpplicant.

Testing

Been using this patch for a while internally.

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

[rahult-github]

Thanks for this. Will work to get this merged.

[rahult-github]

@rojer , current IDF master and release/v6.0 code have migrated to mbedTLS v4.0 which uses PSA crypto and would now not fallback to older code. So the change is not applicable for these branches anymore. However, we will take the change and backport it to relevant branches