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---
title: Image
---
# Image
## Image selection
The boot process shall be uninterruptible and shall irrevocably boot the image
as specified in the boot environment.
In U-Boot set the "_bootdelay_" environment variable and/or define
`CONFIG_BOOTDELAY` to _-2_.
<!-- section-config -->
Domain | _Variable_ / `Config` name | `Value`
---------------------- | -------------------------- | -------
Boot-Image-Selection-1 | `CONFIG_BOOTDELAY` | `-2`
Boot-Image-Selection-2 | _bootdelay_ | `-2`
<!-- end-section-config -->
--------------------------------------------------------------------------------
## Image authenticity
It shall not be possible to boot from an unverified image. The secure boot
feature in U-Boot shall be enabled. The secure boot feature is available from
U-Boot 2013.07 version. To enable the secure boot feature, enable the following
features:
```
CONFIG_FIT: Enables support for Flat Image Tree (FIT) uImage format.
CONFIG_FIT_SIGNATURE: Enables signature verification of FIT images.
CONFIG_RSA: Enables RSA algorithm used for FIT image verification.
CONFIG_OF_CONTROL: Enables Flattened Device Tree (FDT) configuration.
CONFIG_OF_SEPARATE: Enables separate build of u-Boot from the device tree.
CONFIG_DEFAULT_DEVICE_TREE: Specifies the default Device Tree used for the run-time configuration of U-Boot.
```
Generate the U-Boot image with public keys to validate and load the image. It
shall use RSA2048 and SHA256 for authentication.
<!-- section-config -->
Domain | `Config` name | _State_
------------------------- | ---------------------------- | --------
Boot-Image-Authenticity-1 | `CONFIG_FIT` | _Enable_
Boot-Image-Authenticity-2 | `CONFIG_FIT_SIGNATURE` | _Enable_
Boot-Image-Authenticity-3 | `CONFIG_RSA` | _Enable_
Boot-Image-Authenticity-4 | `CONFIG_OF_CONTROL` | _Enable_
Boot-Image-Authenticity-5 | `CONFIG_OF_SEPARATE` | _Enable_
Boot-Image-Authenticity-6 | `CONFIG_DEFAULT_DEVICE_TREE` | _Enable_
<!-- end-section-config -->
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