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?

Kevin