Nordic devices with secure storage supported by Zephry

RE: Nordic devices with secure storage supported by Zephry

Einar Thorsrud — Tue, 19 Jan 2021 11:40:34 GMT

I see. The nRF5340 has more security features than the nRF51840, so it may be sensible. Most importantly the nRF52840 lack a KMU and SPU.

RE: Nordic devices with secure storage supported by Zephry

Nikos Karamolegkos — Tue, 19 Jan 2021 08:14:03 GMT

Thank you. Yes for me is acceptable too. I just want to store the keys securely without maximize the cost. Therefore, compared to this I am looking for the best option. For now, I have some nrf52840-dk devices and I am wondering if it's worth investing in something else (like nrf53) which may offers something more at a reasonable cost

RE: Nordic devices with secure storage supported by Zephry

Einar Thorsrud — Mon, 18 Jan 2021 13:14:22 GMT

Hi,

[quote user="Nikos Karamolegkos"]Help with that " nRF53 does not have secure flash though". So somebody can read the flash.[/quote]

Perhaps I should have been more clear. My point was that unlike secure elements etc. the nRF53 is not a hardened device and do not have tamper protection or similar. If an attacker is willing to pay a good amount of money to decap the IC, he would be able to read out the entire memory content, including KMU. This is outside of the threat model for the nRF53.

[quote user="Nikos Karamolegkos"]what SPU (as part of the Arm TrustZone support) offers?[/quote]

The KMU offer secure key storage in the sense that it can be configured to for instance prevent readout of the key, and only allowing it to be pushed to the CryptoCell peripheral for crypto operations, without ever being part of the system memory. Therefor, there would be no way to access the key via code or debug interface.

The SPU handles separation of memory and peripherals between secure and non-secure region. So that non-secure code will not be able to access anything that is allocated to secure region only. This can be utilized in several ways to reduce the attack surface etc.

[quote user="Nikos Karamolegkos"]For my application I need firstly secure storage of some keys (credentials to connect to a server) and secondly, if possible, to avoid reading the entire flash (the flow of my firmware) from a malicious. [/quote]

There is no such thing as complete security. How secure does your product need to be? The reason I mentioned this is that if it is not acceptable that an attacker willing to spend a good sum of money to pay a lab to decap and extract memory, then it is good to know. But for most products that is an acceptable risk.

RE: Nordic devices with secure storage supported by Zephry

Nikos Karamolegkos — Mon, 18 Jan 2021 12:23:19 GMT

Help with that " nRF53 does not have secure flash though". So somebody can read the flash. Thus, what SPU (as part of the Arm TrustZone support) offers? For my application I need firstly secure storage of some keys (credentials to connect to a server) and secondly, if possible, to avoid reading the entire flash (the flow of my firmware) from a malicious.

RE: Nordic devices with secure storage supported by Zephry

Einar Thorsrud — Thu, 14 Jan 2021 14:02:36 GMT

Yes, all nRF5 devices has a 64 bit DEVICEID in FICR.

RE: Nordic devices with secure storage supported by Zephry

Nikos Karamolegkos — Thu, 14 Jan 2021 13:58:42 GMT

Oh nice. The FICR is really useful. I will check how can read this information by my code. As I can see nr52840 supports this too..

RE: Nordic devices with secure storage supported by Zephry

Einar Thorsrud — Thu, 14 Jan 2021 11:33:44 GMT

[quote user="Nikos Karamolegkos"]So I could just use the KMU to store in a secure way my keys without, let's say, tricks like in nrf52840?[/quote]

Yes, you can. Note that the nRF53 does not have secure flash though, so it would probably be possible to extract the key by decapping and probing directly on the die. You can read more about the KMU features in the KMU chapter in the PS. If that is part of your thread model, then the only option is to use a secure element, but in most products that would be overkill.

[quote user="Nikos Karamolegkos"]Also, does this device have any unique identifier?[/quote]

Yes. The DEVICEID in FICR is a 64 bit random number generated in production. Given the size of the numbers they are unique for all practical purposes.

RE: Nordic devices with secure storage supported by Zephry

Nikos Karamolegkos — Thu, 14 Jan 2021 10:44:43 GMT

So I could just use the KMU to store in a secure way my keys without, let's say, tricks like in nrf52840? Also, does this device have any unique identifier?

RE: Nordic devices with secure storage supported by Zephry

Einar Thorsrud — Wed, 13 Jan 2021 17:47:03 GMT

Hi,

These are all in the same device. The nRF5340 is dual core, so nrf5340dk_nrf5340_cpuapp is the application core (more powerful, more peripherals), and nrf5340dk_nrf5340_cpunet is the network core (more power efficient, less peripherals but it has the radio). You can see more in Working with nRF53 Series.

RE: Nordic devices with secure storage supported by Zephry

Nikos Karamolegkos — Wed, 13 Jan 2021 14:48:27 GMT

Really fast reply. Thanks. As I can see in zephyr rtos documentation there are two types nrf5340dk_nrf5340_cpuapp and nrf5340dk_nrf5340_cpunet. The first mention about SPU but nothing about Radio and the second mention Radio but nothing about SPU. What are the differences? I don't think that these two are different devices.

RE: Nordic devices with secure storage supported by Zephry

Einar Thorsrud — Wed, 13 Jan 2021 13:17:02 GMT

Hi,

The only Nordic device that has both a 80215.4 radio and a key management unit is the nRF5340. This also has a SPU (as part of the Arm TrustZone support).

The nRF52840 has some security features, but no KMU nor an SPU. However, it does have a volatile secure key storage inside the CC310 peripheral, and ability to protect flash using ACL, so it may be good enough depending on your requirements.