Hi Kevin,
Recently there are two major change in TF-M MCUBoot: - images signed separately with different keys and concatenated after to make one blob. It drives by MCUBOOT_IMAGE_NUMBER (default is 2 on AN521) - It's possible to use keys from HW and not hard-code the public key to the MCUBoot code at compile time. It derives by MCUBOOT_HW_KEY (default is True on AN521) - You can check the bl2/ext/mcuboot/MCUBoot.cmake two see how the scripts are invoked, which order, what kind of attributes. Additional info is in docs/user_guide/tfm_secure_boot.rst
You can revert back to previous behaviour, single(S+NS) signed image(key is: *3072.pem) and public-key is embedded in MCUBoot code base with setting MCUBOOT_IMAGE_NUMBER=1 and MCUBOOT_HW_KEY=False
Tamas
-----Original Message----- From: TF-M tf-m-bounces@lists.trustedfirmware.org On Behalf Of Kevin Townsend via TF-M Sent: 13 September 2019 11:48 To: Thomas Törnblom via TF-M tf-m@lists.trustedfirmware.org Subject: [TF-M] Signing merged single image with dual keys
Hi,
Updating to the latest code in the TF-M repo, I noticed that there are now two separates keys for signing images:
- *3072.pem for the S image - *3072_1.pem for the NS image
It's not clear to me how to make this work with a single merged image, which is what we generally need, with an IPC-based system where the S image is generated via the TF-M repo and the NS image in Zephyr, making calls to the S services via the PSA APIs.
Previously, we used the ASSEMBLE.PY tool in BL2 to merge the TF-M S and Zephyr NS images, outputting a single binary that we then signed via IMGTOOL.PY using the default or user-defined .pem file. This no longer works, and any attempt to use a binary generated via this method results in:
[INF] Starting bootloader [INF] Swap type: none [INF] Swap type: none [ERR] Authentication failed! Image in the primary slot is not valid. [ERR] Unable to find bootable image
With the latest dual-key TF-M code, when we build the TF-M repo, we get an S image that is signed using the 3072.pem key, but after a bit of trial and error I haven't found the secret handshake on how to sign the NS image and merge them into a single binary and then copy them over to the MPS2+ (or other HW) and have the BL accept them at startup.
Any pointers on how to generate a single merged image with both parts signed using the different keys, or am I going about this the wrong way?
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