Is it possible to use the KMU (or other secure area??) in the nRF9160 to store encryption keys?

[Spi]

I recently had a question about AES encryption on the nRF9160 and about how to store 32-byte encryption keys.   The ticket was closed after I got the following answer: "we don't have support for keys stored in the KMU using PSA Crypto on 91-series".  I should have followed-up to that with this more specific question:

Is it possible to store keys in the KMU (or similar?), then read them into RAM, then use psa_import_key() for subsequent use with psa_aead_encrypt()?

If it is possible, what are the API functions I should use to

a) write key(s) to KMU (presumably from RAM)

b) read key(s) from KMU into RAM

If that's not possible, what is the recommended way to store 32-byte encryption keys on the nRF9160?

[Michal]

Hello,

So in general, KMU has only support for 128-bit keys, which is 16-byte.

Also, you should be able to reopen that ticket and continue there I think?

Best regards,

Michal

[Spi]

Thank you for your response.  How many KMU keys are there? I can combine two 16-byte keys to make one 32-byte key.  What are the API functions to read/write the KMU keys?

[Michal]

Sorry, I just saw that yes, you should be able to combine the KMU keys, as said on top here:

https://docs.nordicsemi.com/bundle/ps_nrf9160/page/kmu.html

To my knowledge you can use ARM CryptoCell 310 included in the nRF9160, so please take a look at its capabilities here:

https://docs.nordicsemi.com/bundle/ps_nrf9160/page/cryptocell.html

The catch is that you may possibly have to implement drivers for whatever you need specifically on your own.

I'll double check that and get back to you.

Could you also tell me more about your use case?

Best regards,

Michal

[Michal]

Hello again,

If using TF-M with ITS is an option, then we can recommend using it instead.

Here is a sample that showcases it: https://docs.nordicsemi.com/bundle/ncs-3.2.2/page/nrf/samples/crypto/persistent_key_usage/README.html

Best regards,

Michal

[Spi]

For use-case, our application has to encrypt using AES-GCM with 256-bit keys. We have the prototype functionality working using a key stored in I2C EEPROM that we read into RAM and then call psa_import_key(). We would prefer to store the keys in a more secure manner.