c2patool - C2PA command line tool

c2patool is a command line tool for working with C2PA manifests and media assets (audio, image or video files).

Use the tool on a file in one of the supported file formats to:

• Read a summary JSON report of C2PA manifests.
• Read a low-level report of C2PA manifest data.
• Add a C2PA manifest to the file.

For a simple example of calling c2patool from a server-based application, see the c2pa-service-example repository.

Contents:

• Installation
• Supported file formats
• Usage
• Configuring trust support

Additional documentation:

• Manifest definition file
• Creating and using an X.509 certificate
• Release notes

Installation

Prebuilt versions of the tool are available for download.

PREREQUISITE: Install Rust.

Enter this command to install or update the tool:

cargo install c2patool

To build the tool on a Windows machine, you need to install the 7zip tool.

NOTE: If you encounter errors installing, you may need to update your Rust installation by entering this command:

rustup update

Updating

To ensure you have the latest version, enter this command:

c2patool -V

The tool will display the version installed. Compare the version number displayed with the latest release version shown in the repository releases page. To update to the latest version, use the installation command shown above.

Supported file formats

Extensions	MIME type
avi	video/msvideo, video/avi, application-msvideo
avif	image/avif
c2pa	application/x-c2pa-manifest-store
dng	image/x-adobe-dng
heic	image/heic
heif	image/heif
jpg, jpeg	image/jpeg
m4a	audio/mp4
mp3	"audio/mpeg"
mp4	video/mp4, application/mp4 *
mov	video/quicktime
pdf	application/pdf **
png	image/png
svg	image/svg+xml
tif,tiff	image/tiff
wav	audio/x-wav
webp	image/webp

^* Fragmented MP4 is not yet supported.

^** Read only

Usage

The tool's command-line syntax is:

c2patool [trust] [PATH] [OPTIONS]

Where PATH is the (relative or absolute) file path to the asset to read or embed a manifest into.

The following table describes the command-line options.

CLI option	Short version	Argument	Description
--certs		N/A	Extract a certificate chain to stdout.
--config	-c	<config>	Specifies a manifest definition as a JSON string. See Providing a manifest definition on the command line.
--detailed	-d	N/A	Display detailed C2PA-formatted manifest data. See Displaying a detailed manifest report.
--force	-f	N/A	Force overwriting output file. See Forced overwrite.
--help	-h	N/A	Display CLI help information.
--info		N/A	Display brief information about the file.
--ingredient	-i	N/A	Creates an Ingredient definition in --output folder.
--output	-o	<output_file>	Specifies path to output folder or file. See Adding a manifest to an asset file.
--manifest	-m	<manifest_file>	Specifies a manifest file to add to an asset file. See Adding a manifest to an asset file.
--no_signing_verify	None	N/A	Does not validate the signature after signing an asset, which speeds up signing. See Speeding up signing
--parent	-p	<parent_file>	Specifies path to parent file. See Specifying a parent file.
--remote	-r	<manifest_url>	Specify URL for remote manifest available over HTTP. See Generating a remote manifest
--sidecar	-s	N/A	Put manifest in external "sidecar" file with .c2pa extension. See Generating an external manifest.
--tree		N/A	Create a tree diagram of the manifest store.
--version	-V	N/A	Display version information.

Use the optional trust sub-command to enable and configure trust support. When you use this sub-command, several other options are available; see Configuring trust support for details.

Displaying manifest data

To display the manifest associated with an asset file, provide the path to the file as the argument; for example:

c2patool sample/C.jpg

The tool displays the manifest JSON to standard output (stdout).

You may include an --output argument to write the contents of the manifest, including the manifest's assertion and ingredient thumbnails, to the provided output directory.

c2patool sample/C.jpg --output ./report

Detailed manifest report

To display a detailed report describing the internal C2PA format of manifests contained in the asset, use the -d option; for example, using one of the example images in the sample directory:

c2patool sample/C.jpg -d

The tool displays the detailed report to standard output (stdout) or will add a detailed.json if an output folder is supplied.

Displaying an information report

Use the --info option to print a high-level report about the asset file and related C2PA data. For a cloud manifest the tool displays the URL to the manifest. Displays the size of the manifest store and number of manifests. It will report if the manifest validated or show any errors encountered in validation.

c2patool sample/C.jpg --info

The tool displays the report to standard output (stdout).

Creating an ingredient from a file

The --ingredient option will create an ingredient report. When used with the --output folder, it will extract or create a thumbnail image and a binary .c2pa manifest store containing the c2pa data from the file. The JSON ingredient this produces can be added to a manifest definition to carry the full history and validation record of that asset into a newly created manifest. Provide the path to the file as the argument; for example:

c2patool sample/C.jpg --ingredient --output ./ingredient

Adding a manifest to an asset file

To add C2PA manifest data to a file, use the --manifest / -m option with a manifest JSON file as the option argument and the path to the asset file to be signed. Specify the output file as the argument to the --output / -o option. The output extension type must match the source. The tool will not convert between file types. For example:

c2patool sample/image.jpg -m sample/test.json -o signed_image.jpg

The tool generates a new manifest using the values given in the file and displays the manifest store to standard output (stdout).

CAUTION: If the output file is the same as the source file, the tool will overwrite the source file.

Specifying a parent file

A parent file represents the state of the image before the current edits were made.

Specify a parent file as the argument to the --parent / -p option; for example:

c2patool sample/image.jpg -m sample/test.json -p sample/c.jpg -o signed_image.jpg

You can pass an ingredient generated with the --ingredient option by giving the folder or ingredient.json file.

c2patool sample/C.jpg --ingredient --output ./ingredient

c2patool sample/image.jpg -m sample/test.json -p ./ingredient -o signed_image.jpg

Forced overwrite

The tool will return an error if the output file already exists. Use the --force / -f option to force overwriting the output file. For example:

c2patool sample/image.jpg -m sample/test.json -f -o signed_image.jpg

Generating an external manifest

Use the --sidecar / -s option to put the manifest in an external sidecar file in the same location as the output file. The manifest will have the same output filename but with a .c2pa extension. The tool will copy the output file but the original will be untouched.

c2patool image.jpg -s -m sample/test.json -o signed_image.jpg

Generating a remote manifest

Use the --remote / -r option to place an HTTP reference to the manifest in the output file. The manifest is returned as an external sidecar file in the same location as the output file with the same filename but with a .c2pa extension. Place the manifest at the location specified by the -r option. When using remote manifests the remote URL should be publicly accessible to be most useful to users. When verifying an asset, remote manifests are automatically fetched.

c2patool sample/image.jpg -r http://my_server/myasset.c2pa -m sample/test.json -o signed_image.jpg

In the example above, the tool will embed the URL http://my_server/myasset.c2pa in signed_image.jpg then fetch the manifest from that URL and save it to signed_image.c2pa.

If you use both the -s and -r options, the tool embeds a manifest in the output file and also adds the remote reference.

Signing Claim Bytes With Your Own Signer

You may be unable to provide c2patool with a private key when generating a manifest because the private key is not accessible on the system on which you are executing c2patool. We provide the --signer-path argument for this case. --signer-path takes a path to a command-line executable. This executable will receive the claim bytes (the bytes to be signed) via stdin, along with a few CLI arguments, and should output, via stdout the signature bytes. For example, the following command will use an external signer to sign the asset's claim bytes:

c2patool sample/image.jpg            \
    --manifest sample/test.json      \
    --output sample/signed-image.jpg \
    --signer-path ./custom-signer    \
    --reserve-size 20248             \
    -f

You can see an example external signer here: signer-path-success.rs.

Please see c2patool --help for how to calculate the --reserve-size argument.

Providing a manifest definition on the command line

To provide the manifest definition in a command line argument instead of a file, use the --config / -c option.

For example, the following command adds a custom assertion called "org.contentauth.test".

c2patool sample/image.jpg \
  -c '{"assertions": \
    [{"label": "org.contentauth.test", \
      "data": {"my_key": "whatever I want"}}]}'

Speeding up signing

By default, c2patool validates the signature immediately after signing a manifest. To disable this and speed up the validation process, use the --no_signing_verify option.

Configuring trust support

Enable trust support by using the trust sub-command, as follows:

c2patool trust [path] [OPTIONS]

The following additional CLI options are available with the trust sub-command:

Option option	Description	Example
--trust_anchors	Specifies a list of trust anchors (in PEM format) used to validate the manifest certificate chain. To be valid, the manifest certificate chain must lead to a certificate on the trust list. All certificates in the trust anchor list must have the Basic Constraints extension and the CA attribute of this extension must be True.	sample/trust_anchors.pem
--allowed_list	Supersedes the trust_anchors check and specifies a list of end-entity certificates (in PEM format) to trust. These certificates are used to sign the manifest. The allowed list must NOT contain certificates with the Basic Constraints extension with the CA attribute True.	sample/allowed_list.pem
--trust_config	Specifies a set of custom certificate extended key usages (EKUs) to allow. Format is a list with object identifiers in OID dot notation format.	sample/store.cfg

For example:

c2patool sample/C.jpg trust \
  --allowed_list sample/allowed_list.pem \
  --trust_config sample/store.cfg

Nightly builds

Interim binaries are generated every day around 05:30 UTC (overnight for our US-based team) and are available for roughly two weeks thereafter. These can be helpful for testing purposes. For more information, see the documentation on nightly builds.