Crypto: Persistent key storage

The persistent key sample shows how to generate a persistent key using the Platform Security Architecture (PSA) APIs. Persistent keys are stored in the Internal Trusted Storage (ITS) of the device and retain their value between resets. The ITS backend is either provided by TF-M, or the Trusted storage library when building applications without TF-M. A persistent key becomes unusable when the psa_destroy_key function is called.

Requirements

The sample supports the following development kits:

Hardware platforms

PCA

Board name

Board target

nRF9161 DK

PCA10153

nrf9161dk

nrf9161dk/nrf9161/ns nrf9161dk/nrf9161

nRF9160 DK

PCA10090

nrf9160dk

nrf9160dk/nrf9160/ns nrf9160dk/nrf9160

nRF9151 DK

PCA10171

nrf9151dk

nrf9151dk/nrf9151/ns nrf9151dk/nrf9151

nRF54L15 PDK

PCA10156

nrf54l15pdk

nrf54l15pdk/nrf54l15/cpuapp/ns nrf54l15pdk/nrf54l15/cpuapp

nRF5340 DK

PCA10095

nrf5340dk

nrf5340dk/nrf5340/cpuapp/ns nrf5340dk/nrf5340/cpuapp

nRF52840 DK

PCA10056

nrf52840dk

nrf52840dk/nrf52840

When built for a board target with the */ns variant, the sample is configured to compile and run as a non-secure application with Cortex-M Security Extensions enabled. Therefore, it automatically includes Trusted Firmware-M that prepares the required peripherals and secure services to be available for the application.

Overview

In this sample, an AES 128-bit key is created. Persistent keys can be of any type supported by the PSA APIs.

The sample performs the following operations:

  1. Initialization of the Platform Security Architecture (PSA) API.

  2. Generation of a persistent AES 128-bit key.

  3. Removal of the key from RAM.

  4. Encryption and decryption of a message using the key.

  5. Cleanup. The AES key is removed from the PSA crypto keystore.

Note

The read-only type of persistent keys cannot be destroyed with the psa_destroy_key function. The PSA_KEY_PERSISTENCE_READ_ONLY macro is used for read-only keys. The key ID of a read-only key is writable again after a full erase of the device memory. Use the west -v flash --erase command for the full erase.

Note

Builds without TF-M and all nRF54L15 builds use the hardware unique key (HUK) to encrypt the key before storing it.

Building and running

This sample can be found under samples/crypto/persistent_key_usage in the nRF Connect SDK folder structure.

When built as firmware image for a board target with the */ns variant, the sample has Cortex-M Security Extensions (CMSE) enabled and separates the firmware between Non-Secure Processing Environment (NSPE) and Secure Processing Environment (SPE). Because of this, it automatically includes the Trusted Firmware-M (TF-M). To read more about CMSE, see Processing environments.

To build the sample, follow the instructions in Configuring and building an application for your preferred building environment. See also Programming an application for programming steps and Testing and optimization for general information about testing and debugging in the nRF Connect SDK.

Note

When building repository applications in the SDK repositories, building with sysbuild is enabled by default. If you work with out-of-tree freestanding applications, you need to manually pass the --sysbuild parameter to every build command or configure west to always use it.

Testing

After programming the sample to your development kit, complete the following steps to test it:

  1. Connect to the kit with a terminal emulator (for example, nRF Connect Serial Terminal). See Testing and optimization for the required settings and steps.

  2. Compile and program the application.

  3. Observe the logs from the application using a terminal emulator.

Dependencies