You can enable the nRF Security subsystem using PSA crypto support or Legacy crypto support.

To enable nRF Security, set the CONFIG_NRF_SECURITY Kconfig option along with additional configuration options, as described in Feature configurations and driver support. This includes PSA crypto support by default.

PSA crypto support

PSA crypto support is included by default when you enable nRF Security through the CONFIG_NRF_SECURITY Kconfig option. PSA crypto support is provided through PSA Crypto APIs and is implemented by PSA core. PSA core uses PSA drivers to implement the cryptographic features either in software, or using hardware accelerators.


The PSA Crypto APIs are only thread safe when provided by TF-M.

Legacy crypto support

To enable the legacy crypto support mode of nRF Security, set both the CONFIG_NORDIC_SECURITY_BACKEND and CONFIG_NRF_SECURITY Kconfig options along with additional configuration options, as described in Legacy configurations and supported features. The legacy crypto support allows backwards compatibility for software that requires usage of Mbed TLS crypto toolbox functions prefixed with mbedtls_.

Custom Mbed TLS configuration files

The nRF Security Kconfig options are used to generate an Mbed TLS configuration file.

Although not recommended, it is possible to provide a custom Mbed TLS configuration file by disabling CONFIG_GENERATE_MBEDTLS_CFG_FILE. See User-provided Mbed TLS configuration header.

Building with TF-M

If CONFIG_BUILD_WITH_TFM is enabled together with CONFIG_NRF_SECURITY, the TF-M secure image will enable the use of the hardware acceleration of Arm CryptoCell. In this case, the Kconfig configurations in the nRF Security subsystem control the features enabled in TF-M.