c2pa-python 0.4.0

Python bindings for the C2PA Content Authenticity Initiative (CAI) library

C2PA Python

Python bindings for the C2PA Content Authenticity Initiative (CAI) library.

This library enables you to read and validate C2PA data in supported media files and add signed manifests to supported media files.

WARNING: This is an early prerelease version of this library. There may be bugs and unimplemented features, and the API is subject to change.

Installation

Install from PyPI by entering this command:

pip install -U c2pa-python

This is a platform wheel built with Rust. If your platform is not already supported, see the development section for info on how to build from source.

## Usage

### Import

Import the C2PA module as follows:

```py
import c2pa

Read and validate C2PA data in a file

Use the read_file function to read C2PA data from the specified file:

json_store = c2pa.read_file("path/to/media_file.jpg", "path/to/data_dir")

This function examines the specified media file for C2PA data and generates a JSON report of any data it finds. If there are validation errors, the report includes a validation_status field. For a summary of supported media types, see Supported file formats.

A media file may contain many manifests in a manifest store. The most recent manifest is identified by the value of the active_manifest field in the manifests map.

If the optional data_dir is provided, the function extracts any binary resources, such as thumbnails, icons, and C2PA data into that directory. These files are referenced by the identifier fields in the manifest store report.

NOTE: For a comprehensive reference to the JSON manifest structure, see the CAI manifest store reference.

Add a signed manifest to a media file

Use the sign_file function to add a signed manifest to a media file.

result = c2pa.sign_file("path/to/source.jpg", 
                                        "path/to/dest.jpg", 
                                        manifest_json, 
                                        sign_info, 
                                        data_dir)

The parameters (in order) are:

• The source (original) media file.
• The destination file that will contain a copy of the source file with the manifest data added.
• manifest_json, a JSON-formatted string containing the manifest data you want to add; see Creating a manifest JSON definition file below.
• sign_info, a SignerInfo object instance; see Generating SignerInfo below.
• data_dir optionally specifies a directory path from which to load resource files referenced in the manifest JSON identifier fields; for example, thumbnails, icons, and manifest data for ingredients.

Create a SignerInfo Instance

A SignerInfo object contains information about a signature. To create an instance of SignerInfo, first set up the signer information from the public and private key .pem files as follows:

certs = open("path/to/public_certs.pem","rb").read()
prv_key = open("path/to/private_key.pem","rb").read()

Then create a new SignerInfo instance using the keys as follows, specifying the signing algorithm used and optionally a time stamp authority URL:

sign_info = c2pa.SignerInfo("es256", certs, priv_key, "http://timestamp.digicert.com")

For the list of supported signing algorithms, see Creating and using an X.509 certificate.

Creating a manifest JSON definition file

The manifest JSON string defines the C2PA manifest to add to the file.

manifest_json = json.dumps({
    "claim_generator": "python_test/0.1",
    "assertions": [
    {
      "label": "c2pa.training-mining",
      "data": {
        "entries": {
          "c2pa.ai_generative_training": { "use": "notAllowed" },
          "c2pa.ai_inference": { "use": "notAllowed" },
          "c2pa.ai_training": { "use": "notAllowed" },
          "c2pa.data_mining": { "use": "notAllowed" }
        }
      }
    }
  ]
 })

Development

It is best to set up a virtual environment for development and testing.

To build from source on Linux, install curl and rustup and set up python

First update apt

apt update

Install Rust

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
source "$HOME/.cargo/env"

Install Python, pip and venv

apt install python3
apt install pip
apt install python3.11-venv
python3 -m venv .venv

Build the wheel for your platform

source .venv/bin/activate
pip install maturin
pip install uniffi-bindgen
python3 -m pip install build
pip install -U pytest

python3 -m build --wheel

ManyLinux build

docker run -it quay.io/pypa/manylinux_2_28_aarch64 bash
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
source "$HOME/.cargo/env"
export PATH=/opt/python/cp312-cp312/bin:$PATH
pip install maturin
pip install venv
pip install build
pip install -U pytest

cd home
git clone https://github.com/contentauth/c2pa-python.git 
cd c2pa-python
python3 -m build --wheel
auditwheel repair target/wheels/c2pa_python-0.4.0-py3-none-linux_aarch64.whl 

Testing

We use PyTest for testing.

Run tests by entering this command:

source .venv/bin/activate
maturin develop
pytest
deactivate

Example

Run the example code like this:

source .venv/bin/activate
maturin develop
python3 tests/training.py
deactivate

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
mp4	video/mp4, application/mp4
mov	video/quicktime
png	image/png
svg	image/svg+xml
tif,tiff	image/tiff
wav	audio/x-wav
webp	image/webp

Change Notes:

Version 0.3.0 changes: There are some breaking changes to align with future APIs:

• C2paSignerInfo moves the alg to the first parameter from the 3rd.
• c2pa.verify_from_file_json is now c2pa.read_file.
• c2pa.ingredient_from_file_json is now c2pa.read_ingredient_file.
• c2pa.add_manifest_to_file_json is now c2pa.sign_file.
• There are many more specific errors types now, and Error messages always start with the name of the error i.e (str(err.value).startswith("ManifestNotFound")).
• The ingredient thumbnail identifier may be jumbf uri reference if a valid thumb already exists in the active manifest.
• Extracted file paths for read_file now use a folder structure and different naming conventions.

License

This package is distributed under the terms of both the MIT license and the Apache License (Version 2.0).

Note that some components and dependent crates are licensed under different terms; please check the license terms for each crate and component for details.

Contributions and feedback

We welcome contributions to this project. For information on contributing, providing feedback, and about ongoing work, see Contributing.