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 Node.js server 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

There are two ways to install C2PA Tool:

• Using a pre-built binary executable: This is the quickest way to install the tool. If you just want to try C2PA Tool quickly, use this method.
• Using Cargo Binstall, a low-complexity way to install Rust binaries. This method is preferable for long-term use. If you know you want to use C2PA Tool for development, use this method.

Installing a pre-built binary

The quickest way to install the tool is to use the binary executable builds. If you just want to try C2PA Tool quickly:

1. Go to the c2patool repository releases page.
2. Under the latest release, click Assets.
3. Download the archive for your operating system (Linux, macOS, or Windows).
4. Copy the executable file to a location on your PATH.

Confirm that you can run the tool by entering a command such as:

c2patool -h

NOTE: You also may want to get some of the example files provided in the repository sample directory. To do so, clone the repository with git clone https://github.com/contentauth/c2patool.git.

Using Cargo Binstall

Installing C2PA Tool using Cargo Binstall is recommended because it makes it easier to:

• Automatically select the correct installation package for your platform/architecture.
• Update the tool when a new version is released.
• Maintain, since you don't have to manually keep track of random binaries on your system.
• Integrate into CI or other scripting environments.

Additionally, using Binstall enables you to automate code signing to ensure package integrity.

Process

PREREQUISITE: Install Rust.

To install by using Binstall:

1. Install cargo-binstall by following the quick install method for your OS, or by building from source by running cargo install cargo-binstall
2. Run cargo binstall c2patool.

Upgrading

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.

If you need to upgrade, simply run cargo binstall c2patool again, or use cargo-update.

Building from source

NOTE: Please use one of the installation methods described above unless you are doing active development work on C2PA Tool, or if a pre-built binary is not available for your system.

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

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:

• trust is an optional subcommand to enable trust support for certificates on a "known certificate list." With this sub-command, several additional options are available.
• PATH is the (relative or absolute) file path to the asset to read or embed a manifest into.
• OPTIONS is one or more of the command-line options described in following table.

CLI option	Short version	Argument	Description
--certs		N/A	Extract a certificate chain to standard output (stdout).
--config	-c	<config>	Specify 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	Create an Ingredient definition in --output folder.
--output	-o	<output_file>	Path to output folder or file. See Adding a manifest to an asset file.
--manifest	-m	<manifest_file>	Specify a manifest file to add to an asset file. See Adding a manifest to an asset file.
--no_signing_verify	None	N/A	Do not validate the signature after signing an asset, which speeds up signing. See Speeding up signing
--parent	-p	<parent_file>	Path to parent file. See Specifying a parent file.
--remote	-r	<manifest_url>	URL for remote manifest available over HTTP. See Generating a remote manifest
--reserve-size	N/A	Only valid with --signer-path argument. The amount of memory to reserve for signing. Default: 20000. For more information, see CLI help.
--sidecar	-s	N/A	Put manifest in external "sidecar" file with .c2pa extension. See Generating an external manifest.
--signer-path	N/A	Specify path to command-line executable for signing. See Signing claim bytes with your own signer.
--tree		N/A	Create a tree diagram of the manifest store.
--version	-V	N/A	Display version information.

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).

Use the --output argument to write the contents of the manifest, (including the manifest's assertion and ingredient thumbnails) to the specified directory.

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

Detailed manifest report

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

c2patool sample/C.jpg -d

By default, the tool displays the detailed report to standard output (stdout). If you specify an output folder, the tool saves it to a file named detailed.json in that folder.

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 creates an ingredient report. When used with the --output folder, it extracts or creates 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

Use the --manifest / -m option to add the C2PA manifest definition file specified in the argument 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.

If the manifest definition file has private_key and sign_cert fields, then the tool signs the manifest using the private key and certificate they specify, respectively. Otherwise, the tool uses the built-in test certificate and key, which is suitable for development and testing. You can also specify the private key and certificate using environment variables; for more information, see Creating and using an X.509 certificate.

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 sample/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

When generating a manifest, if the private key is not accessible on the system on which you are running the tool, use the --signer-path argument to specify the path to an executable that performs signing. This executable receives the claim bytes (the bytes to be signed) from standard input (stdin) and outputs the signature bytes to standard output (stdout).

For example, the following command signs the asset's claim bytes by using an executable named custom-signer:

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

For information on calculating the value of the --reserve-size argument, see c2patool --help.

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 subcommand, as follows:

c2patool [path] trust [OPTIONS]

Several additional CLI options are available with the trust sub-command to specify the location of files containing the trust anchors list or known certificate list, as described in the following table. You can also use environment variables to specify these values.

Option	Environment variable	Description
--trust_anchors	C2PATOOL_TRUST_ANCHORS	URL or relative path to a file containing 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.
--allowed_list	C2PATOOL_ALLOWED_LIST	URL or relative path to a file containing a list of end-entity certificates (in PEM format) to trust. These certificates are used to sign the manifest. Supersedes the trust_anchors setting. The list must NOT contain certificates with the Basic Constraints extension with the CA attribute True.
--trust_config	C2PATOOL_TRUST_CONFIG	URL or relative path to a file containing the allowed set of custom certificate extended key usages (EKUs). Each entry in the list is an object identifiers in OID dot notation format.

For example:

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

Another example with URL argument values:

c2patool sample/C.jpg trust \
  --trust_anchors https://server.com/anchors.pem \
  --trust_config https://server.com/store.cfg

Using the Verify known certificate list

IMPORTANT: The C2PA intends to publish an official trust list. Until that time, the C2PA Verify tool uses a temporary known certificate list. These lists are subject to change, and will be deprecated when C2PA publishes its trust list.

To configure C2PA tool to use the Verify temporary known certificate list, set the following environment variables on your system:

export C2PATOOL_TRUST_ANCHORS='https://contentcredentials.org/trust/anchors.pem'
export C2PATOOL_ALLOWED_LIST='https://contentcredentials.org/trust/allowed.sha256.txt'
export C2PATOOL_TRUST_CONFIG='https://contentcredentials.org/trust/store.cfg'

Note: When these environment variables are set, C2PA Tool will make several HTTP requests each time it runs. Since these lists may change without notice (and the allowed list may change quite often), check these lists frequently to stay in sync with the Verify site. However, when performing bulk operations, you may want to cache these files locally to avoid a large number of network calls that might affect performance.

You can then run:

c2patool sample/C.jpg trust

You can also specify these values as CLI arguments instead:

c2patool sample/C.jpg trust \
  --trust_anchors='https://contentcredentials.org/trust/anchors.pem' \
  --allowed_list='https://contentcredentials.org/trust/allowed.sha256.txt' \
  --trust_config='https://contentcredentials.org/trust/store.cfg'

Note: This sample image should show a signingCredential.untrusted validation status since the test signing certificate used to sign them is not contained on the trust lists above.

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.