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PSA Protected Storage

Overview

This sample demonstrates how the Protected Storage (PS) API can be used for storing data.

Protected storage provides a key/value storage interface where data is (by default) encrypted, with optional authentication and rollback protection. The default crypto algorithm is AES-128-GCM. The encryption key is derived from the Hardware Unique Key (HUK), which is often set via device fuses, etc.

Using the PS API, this sample stores data to non-volatile storage. The sample shows how data can be stored to and read from UIDs, and how overwrite protection can be enabled using flags.

TF-M includes a maximum number of PS records, set via PS_NUM_ASSETS (default 10 as of TF-M 1.3), and a maximum record size, set via PS_MAX_ASSET_SIZE (default of 2048 as of TF-M 1.3.0). These defaults may be different depending on the platform being used, the current value will be printed by the build system during the TF-M compilation step.

More information about Protected Storage can be found in the Platform Security Architecture (PSA) Secure Storage API: https://developer.arm.com/architectures/architecture-security-features/platform-security

This sample is available for platforms that are supported in the trusted-firmware-m repo: https://git.trustedfirmware.org/TF-M/trusted-firmware-m.git/ See sample.yaml for a list of supported platforms.

Building and Running

On Target

Refer to TF-M PSA crypto for detailed instructions.

Note that the board needs to be completely erased before programming the sample, as the flash area used might contain data from before. The board must also be erased between each time the sample is run as the overwrite protection will not be removed with a power reset.

On QEMU

Refer to TF-M IPC for detailed instructions. Following is an example based on west build

$ west build samples/tfm_integration/psa_protected_storage/ -p -b mps2_an521_nonsecure -t run

Sample Output

*** Booting Zephyr OS build zephyr-v2.5.0-2791-g5585355dde0c  ***
TF-M Protected Storage sample started. PSA Protected Storage API Version 1.0
Writing data to UID1: The quick brown fox jumps over the lazy dog
Info on data stored in UID1:
- Size: 16
- Capacity: 0x42
- Flags: 0x 0
Read and compare data stored in UID1
Data stored in UID1: The quick brown fox jumps over the lazy dog
Overwriting data stored in UID1 with: Lorem ipsum dolor sit amet
Writing data to UID2 with overwrite protection: The quick brown fox jumps over the lazy dog
Attempting to write 'The quick brown fox jumps over the lazy dog' to UID2
Got expected error (PSA_ERROR_NOT_PERMITTED) when writing to protected UID
Removing UID1