Dear Simon Glass,
Normally, multiple public keys can be provided and U-Boot is not required to use all of them for verification. This is because some images may not be signed, or may be optionally signed.
But we still need a mechanism to determine when a key must be used. This feature cannot be implemented in the FIT itself, since anyone could change it to mark a key as optional. The requirement for key verification must go in with the public keys, in a place that is protected from modification.
Add a -r option which tells mkimage to mark all keys that it uses for signing as 'required'.
If some keys are optional and some are required, run mkimage several times (perhaps with different key directories if some keys are very secret) using the -F flag to update an existing FIT.
Signed-off-by: Simon Glass sjg@chromium.org
Reviewed-by: Marek Vasut marex@denx.de
Best regards, Marek Vasut