NRF9160-SICA-R7 datasheet(141/400 Pages) NORDIC

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Peripherals

Access type

Key headers

Key values

Read

Allowed

Restricted

Write

Restricted

Table 50: Access control

Any restricted access requires an explicit key slot selection through the KMU register interface. Any illegal

access to restricted key slot registers will be blocked and word

0xDEADDEAD will be returned on the AHB.

The OTP region has individual access control behavior, while access control to the key storage region is

configured on a per key slot basis. The KMU FSM operates on only one key slot instance at a time, and

the permissions and the usage restriction for a key value associated with a key slot can be configured

individually.

Note: Even if the KMU can be configured as non-secure, all non-secure transactions will be

blocked.

6.8.3 Protecting the UICR content

The UICR content can be protected against device-internal NVMC.ERASEALL requests, in addition to

device-external ERASEALL requests, through the CTRL-AP interface. This feature is useful if the firmware

designers want to prevent the OTP region from being erased.

Since enabling this step will permanently disable erase for the UICR, the procedure requires an

implementation defined 32-bit word to be written into the UICR's ERASEPROTECT register.

In case of a field return handling, it is still possible to erase the UICR even if the ERASEPROTECT is set. If

this functionality is desired, the secure boot code must implement a secure communication channel over

the CTRL-AP mailbox interface. Upon successful authentication of the external party, the secure boot code

can temporarily re-enable the CTRL-AP ERASEALL functionality.

6.8.4 Usage

This section describes the specific KMU and UICR behavior in more detail, to help the reader get a better

overview of KMU's features and the intended usage.

6.8.4.1 OTP

The OTP region of the UICR contains a user-defined static configuration of the device. The KMU emulates

the OTP functionality by placing a write-once per halfword limitation of registers defined in this region, i.e.

only halfwords containing all '1's can be written.

An OTP write transaction must consist of a full 32-bit word. Both halfwords can either be written

simultaneously or one at a time. The KMU FSM will block any write to a halfword in the OTP region, if the

initial value of this halfword is not 0xFFFF. When writing halfwords one at a time, the non-active halfword

must be masked as 0xFFFF, otherwise the request will be blocked. For example, writing 0x1234XXXX to an

OTP destination address which already contains the value 0xFFFFAABB, must be configured as 0x1234FFFF.

The OTP destination address will contain the value 0x1234AABB after both write transactions have been

processed.

The KMU will also only allow secure AHB write transactions into the OTP region of the UICR. Any AHB

write transaction to this region that does not satisfy the above requirements will be ignored, and the

STATUS.BLOCKED register will be set to '1'.

6.8.4.2 Key storage

The key storage region of the UICR can contain multiple keys of different type, including symmetrical keys,

hashes, public/private key pairs and other device secrets. One of the key features of the KMU, is that these

4418_1315 v2.0

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