RNG Functionalities are not working with SOFT DEVICE

RE: RNG Functionalities are not working with SOFT DEVICE

Einar Thorsrud — Tue, 16 Jun 2020 10:39:41 GMT

Hi Srinivas,

[quote user="Srinivas V"][/quote]

1. In back ground how RNG will work like interrupt mode or Polling mode along with SD.

2. SD also using the same RNG peripheral for it's internal use , at that time how it manages with Crypto functionalities.At this time Crypto functions are need to wait until SD releases the RNG peripheral, correct me if i am wrong.

The SoftDevice never releases the RNG, so you have to use the SoftDevice APIs to get random data. This always happens by polling (see the three sd_rand_application_*() functions), and not by interrupts. We also provide several layers of abstraction on top of that:

The RNG driver, which allows you to buffer more RNG data and handles the difference between using a SoftDevice and accessing the RNG directly.
The nrf_crypto RNG module which is integrated with other nrf_crypto functionality. This also allows you to use the RNG together with the mbed TLS CTR-DRBG implementation so that the RNG is used for seeding (you can select if you want Raw NRG data or use the CTR-DRBG algorithm using the NRF_CRYPTO_BACKEND_NRF_HW_RNG_MBEDTLS_CTR_DRBG_ENABLED in sdk_config.h in that case).

[quote user="Srinivas V"]3. Is there any impact on SD if we are going to use the mbedTLS crypto libraries in my application with respect to timing and other aspects.[/quote]

No, not as long as you do your crypto operations in a lower interrupt priority. Typically you will do CPU time consuming operations in a low priority to avoid any issues.

[quote user="Srinivas V"]4. If we want to use the mbed TLS crypto along with RNG,what are the macros we need to enable in sdk_config.h file additionally.[/quote]

If you use the nrf_crypto API (which supports both the RNG as backend and mbed TLS as backend), then you can simply refer to an example. The exact configuration depends on which algorithms and combinations you want to use, as you can see from the nrf_crypto documentation.

Einar

RE: RNG Functionalities are not working with SOFT DEVICE

Srinivas V — Tue, 16 Jun 2020 09:53:16 GMT

HI Einar,

Thanks for your reply, if we are going to use the RNG along with crypto(mbedTLS) as front end,

1. In back ground how RNG will work like interrupt mode or Polling mode along with SD.

3. Is there any impact on SD if we are going to use the mbedTLS crypto libraries in my application with respect to timing and other aspects.

4. If we want to use the mbed TLS crypto along with RNG,what are the macros we need to enable in sdk_config.h file additionally.

Regards,

Srinivas.V

RE: RNG Functionalities are not working with SOFT DEVICE

Einar Thorsrud — Tue, 16 Jun 2020 07:38:23 GMT

Hi Srinivas,

[quote user="Srinivas V"]But it comes to RNG, RNG peripheral is different and CC310 RNG both are different engines.[/quote]

Yes, that is correct.

[quote user="Srinivas V"]If CC310 is available we can use that one only, if not available we can use RNG peripheral with nrf crypto.[/quote]

You can use nrf_crypto as a front end for both the RNG peripheral (all nRF52xxx devices) and the CC310 RNG (only nRF52840).

Einar

RE: RNG Functionalities are not working with SOFT DEVICE

Srinivas V — Mon, 15 Jun 2020 13:45:36 GMT

Hi Einar,

Thanks for your reply. But it comes to RNG, RNG peripheral is different and CC310 RNG both are different engines.

If CC310 is available we can use that one only, if not available we can use RNG peripheral with nrf crypto.

Thanks,

Srinivas.V

RE: RNG Functionalities are not working with SOFT DEVICE

Einar Thorsrud — Mon, 15 Jun 2020 09:21:41 GMT

Hi,

The SoftDevice needs the RNG peripheral, so you cannot use it directly. There are several options, though:

Use the SoftDevice RNG API: sd_rand_application_vector_get()
Use the RNG driver
nrf_crypto RNG module (recommended in most cases)

All of the above use the RNG peripheral (by adding more layers of abstractions). The nrf_crypto RNG module can also use the CC310 RNG on the nRF52840, depending on how you configure the module in sdk_config.h.

RE: RNG Functionalities are not working with SOFT DEVICE

hmolesworth — Sun, 14 Jun 2020 17:21:48 GMT

I just answered a similar question here, so my notes might help; maybe look at something like nrf_crypto_rng_init() in nrf_crypto_rng.c tosee if that makes clear the restrictions

// Access type Definition
// ======================
// Restricted
//   The hardware peripheral is used by the SoftDevice and is outside
//   the application sandbox. When the SoftDevice is enabled, it shall
//   only be accessed through the SoftDevice API. Through this API, the
//   application has limited access.
// Blocked
//   The hardware peripheral is used by the SoftDevice and is outside the
//   application sandbox.
//   The application has no access. Interrupts from blocked peripherals
//   are forwarded to the SoftDevice by the MBR and are not available to
//   the application, even inside a Radio Timeslot API timeslot.
// Open
//   The hardware peripheral is not used by the SoftDevice.
//   The application has full access.
//
// Table 3: Hardware access type definitions
//
// Instance SD Enabled  SD Disabled Restrictions
// ======== ==========  =========== ======================================================
// CLOCK    Restricted    Open
// POWER    Restricted    Open
// BPROT    Restricted    Open
// RADIO    Blocked       Open      Available through the Radio Timeslot API
// TIMER0   Blocked       Open      Available through the Radio Timeslot API
// RTC0     Blocked       Open
// TEMP     Restricted    Open
// RNG      Restricted    Open
// ECB      Restricted    Open
// CCM      Blocked       Open      Available during a Radio Timeslot API
// AAR      Blocked       Open      Available during a Radio Timeslot API
// EGU/SWI1 Restricted    Open      Blocked only when Radio Notification signal is enabled
// Radio    Restricted    Open      Blocked only when Radio Notification signal is enabled
// EGU/SWI5 Blocked       Open
// NVMC     Restricted    Open
// MWU      Restricted    Open      Limitations on use of MWU when SoftDevice is enabled
// FICR     Blocked       Blocked
// UICR     Restricted    Open
// NVIC     Restricted    Open      Use SoftDevice NVIC API for configuration when SoftDevice enable