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doc: nrf-bm: app_dev: bootloader_keys: Correct conf BOOT_KEYS_REVOCATION and details on MCUboot image configuration #554

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eivindj-nordic merged 2 commits into from
Dec 9, 2025
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doc: nrf-bm: app_dev: bootloader_keys: Correct conf BOOT_KEYS_REVOCATION and details on MCUboot image configuration #554

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doc: nrf-bm: app_dev: bootloader_keys: Correct conf BOOT_KEYS_REVOCATION
eivindj-nordic Dec 8, 2025
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doc: nrf-bm: app_dev: dfu: Add details on mcuboot image config file
eivindj-nordic Dec 8, 2025
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16 changes: 12 additions & 4 deletions doc/nrf-bm/app_dev/dfu/bootloader_keys.rst
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Expand Up @@ -43,6 +43,8 @@ Using a key in a project
************************

Once a key has been generated, it can be used in a project by setting the :kconfig:option:`SB_CONFIG_BM_BOOTLOADER_MCUBOOT_SIGNATURE_KEY_FILE` sysbuild Kconfig option to the absolute path of the generated ``.pem`` key file.
For most of the samples, you must create a :file:`sysbuild.conf` file in your application directory and add the sysbuild configuration here.
You can also provide the sysbuild Kconfig option during compilation.

.. _ug_bootloader_kmu:

Expand Down Expand Up @@ -74,16 +76,22 @@ Runtime revocation
.. note::
The support for this feature is currently experimental.

MCUboot can invalidate image verification keys through the ``CONFIG_BOOT_KMU_KEYS_REVOCATION`` Kconfig option.
MCUboot can invalidate image verification keys through the ``CONFIG_BOOT_KEYS_REVOCATION`` Kconfig option.
Enable this option during the MCUboot build process if there is a risk that images signed with a compromised key might contain critical vulnerabilities.
The revocation of keys is triggered when both the firmware loader and SoftDevice are using a newer key.

Number of available key slots is set by ``CONFIG_BOOT_SIGNATURE_KMU_SLOTS`` Kconfig option. These slots has to be properly provisioned. For more information refer to `Performing KMU provisioning`_.
The number of available key slots is set by the ``CONFIG_BOOT_SIGNATURE_KMU_SLOTS`` Kconfig option.
These slots have to be properly provisioned.
For more information refer to `Performing KMU provisioning`_.

.. caution::
You must enable the ``CONFIG_BOOT_KMU_KEYS_REVOCATION`` Kconfig option when creating your project.
You must enable the ``CONFIG_BOOT_KEYS_REVOCATION`` Kconfig option when creating your project.
If you have not activated this option initially, you cannot enable it later.
Without the option, this functionality unavailable and potentially exposes your project to security issues.
Without the option, this functionality is unavailable and will potentially expose your project to security issues.

A valid signature verification must precede any key invalidation.
The last remaining key cannot be invalidated.

To enable the Kconfig options for the MCUboot image, edit the :file:`sysbuild/mcuboot.conf` file in your application directory.
For most of the samples, you must create the :file:`sysbuild` folder and the :file:`sysbuild/mcuboot.conf` file.
This file applies to the MCUboot image only and is edited the same way as the :file:`prj.conf` file is used for your application image.