Cannot retrieve hash using img_mgmt_client API

[[email protected]]

Hello,

After I upload a new signed image to my device using MCUboot serial recovery (single image), MCUmgr Img_mgmt_client API

img_mgmt_client_state_read() always fails because there's no hash. I added version number using VERSION file. Is there a similar way to add hash to my image?

Regards,
Chang

[SwRa]

Hi Chang,

As far as I know, the image hash reported by MCUmgr and MCUboot is not a user-configurable value. It is automatically generated as a SHA256 hash of the image header and body. See here: https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/services/device_mgmt/smp_groups/smp_group_1.html#get_state_of_images_response 

It is stated in the documenttion that "This field is optional but only optional when using MCUboot’s serial recovery feature with one pair of image slots, Kconfig CONFIG_BOOT_SERIAL_IMG_GRP_HASH can be disabled to remove support for hashes in this configuration. MCUmgr in applications must support sending hashes."  So, If you need the hash to be present, ensure that hash support is enabled in your MCUboot configuration (check CONFIG_BOOT_SERIAL_IMG_GRP_HASH).

Best Regards,

Swathy

[[email protected]]

Hi Swathy,

Thanks for the info. That makes MCUboot respond to img_mgmt_client_state_read() with hash information. However, the hash length is 64. image_state_res_fn() anticipates strictly 32, so img_mgmt_client_state_read() fails.

For those who ran into the same problem, SB_CONFIG_BOOT_SIGNATURE_TYPE_NONE=y seems to work to make the hash size 32 bytes. Could you please confirm if that is the right way to make it work?

Regards,

Chang