imgtool

imgtool [GLOBAL_OPTIONS] COMMAND [COMMAND_OPTIONS] [ARGS]

Common commands:
imgtool sign INPUT_FILE OUTPUT_FILE --key KEY_FILE [OPTIONS]
imgtool gen INPUT_FILE OUTPUT_FILE --key KEY_FILE [OPTIONS]
imgtool verify IMAGE_FILE
imgtool getpub --key KEY_FILE --PEM_OUTPUT_FILE
imgtool manifest SUBCOMMAND [ARGS]

--help
    Display help message and exit for imgtool or a specific subcommand.

--version
    Show program's version number and exit.

COMMAND
    The subcommand to execute (e.g., sign, gen, verify, getpub, manifest, key).

--key KEY_FILE
    Specify the private key file (PEM or raw) used for signing or generating images.

--header-size SIZE
    Size of the image header in bytes (e.g., 0x200). Used by sign/gen.

--align ALIGNMENT
    Image alignment requirement in bytes (e.g., 1, 2, 4, 8, 16). Used by sign/gen.

--pad
    Pad the image to fill the image header. Used with --header-size for sign/gen.

--max-pad SIZE
    Pad the image to a maximum size if it's smaller. Used by sign/gen.

--version MAJOR.MINOR.REVISION+BUILD
    Specify the firmware version string for the image. Used by sign/gen.

--dependencies DEPS_FILE
    Provide a file specifying image dependencies for multi-image updates. Used by sign/gen.

--boot-record SIZE
    Size of the boot record in bytes. Used for bootloader-specific padding by sign/gen.

--erase-value VALUE
    Value to use for erased flash (e.g., 0xff). Used by sign/gen.

The imgtool is a specialized command-line utility primarily used within the Zephyr RTOS ecosystem for manipulating firmware images. Its core functionality revolves around creating, signing, and verifying bootable images, essential for secure boot and over-the-air (OTA) update mechanisms in embedded systems. It integrates tightly with bootloaders like MCUboot, ensuring the integrity and authenticity of firmware by applying cryptographic signatures using private keys.

The tool can generate images from compiled binaries, embed version information, dependencies, and pad images to specific sizes or alignments. It also supports various manifest operations and key management functionalities, making it a critical component for deploying secure and verifiable firmware.

imgtool is a specialized Python-based utility primarily developed for use with the Zephyr RTOS and its associated secure bootloader, MCUboot. It is not a general-purpose Linux disk imaging tool. Its effective use requires an understanding of embedded firmware development, secure boot concepts, and cryptographic key management. Mismanagement of private keys can compromise the security of your embedded devices.

The tool's functionality and options can vary slightly between different versions and specific Zephyr releases. Users should always consult the official Zephyr documentation for the most accurate and up-to-date information pertaining to their specific development environment.

imgtool is specifically designed to generate images compatible with the MCUboot secure bootloader. It adds the necessary header and signature information that MCUboot verifies before booting new firmware, preventing unauthorized or corrupted updates.

The typical workflow involves compiling application code, then using imgtool to sign the resulting binary with a private key. The public key counterpart is embedded in the bootloader. During device startup, the bootloader uses this public key to verify the signature of the new firmware image, only proceeding if the signature is valid.

imgtool emerged from the need for robust and secure firmware update mechanisms in embedded systems, particularly in the context of the Zephyr RTOS and the MCUboot bootloader. Its development is tightly coupled with the evolution of secure boot practices for microcontrollers. It provides a standardized way to sign firmware images, ensuring their authenticity and integrity before they are loaded onto a device.

This functionality has become increasingly vital as IoT and embedded devices face growing security threats, making imgtool a foundational component for secure product development using Zephyr.

objcopy(1) (Manipulate object file formats, often used to convert binaries), openssl(1) (Cryptographic toolkit for key generation and certificate management), dd(1) (Convert and copy a file, can be used for raw image manipulation), west(1) (Meta-tool for Zephyr development, often invokes imgtool during the build process)