Skip to content

A small wrapper around the sign_file function from the c2pa-python library that helps generate the manifest JSON necessary before signing and attaching the manifest to a media file.

Notifications You must be signed in to change notification settings

rob/c2pa-helper

Folders and files

NameName
Last commit message
Last commit date

Latest commit

 

History

16 Commits
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Repository files navigation

c2pa-helper

This Python script is a small wrapper around the sign_file function from the c2pa-python library that helps generate the manifest JSON necessary before signing and attaching the manifest to a media file.

More information

Overview

This script extracts metadata from a media file (e.g., EXIF, IPTC, and XMP) and generates the manifest JSON with C2PA's assertions and actions. It uses this generated manifest JSON to sign and attach the manifest to a media file, optionally using your own certificate.

Once the media file is signed, end users can use something like the C2PA's online Verify tool to upload the media file and view its signed content credentials (i.e., the manifests.) There's also a command line tool called c2patool available.

Important

This script was designed to be modified to fit your individual needs. It includes support for the metadata below and assumes certain things — like your media file never being signed before (see Considerations).

For example, you might need to support custom IPTC fields not handled below, change the order in how you search for the "author" field, or want to remove the GPS data assertion from being included for privacy reasons.

Out of the box, this script handles a lot of the actions, assertions, and organizational information (i.e., website and social networks) that are displayed on the C2PA's online Verify tool when uploading and validating content credentials found inside a media file.

Metadata included

If any of the following metadata is found in the media file, it's included in the generated manifest:

Metadata Description
Title Extracted from XMP:Title
(or defaults to filename)
Author First occurance of EXIF:Artist, XMP:Creator, or XMP:Credit
(in that order)
Camera make and model Extracted from EXIF:Make and EXIF:Model
GPS information Extracted from EXIF:GPS* fields
Original date and time Extracted from EXIF:DateTimeOriginal

Extra metadata included

In addition to the above, the following is also included in the manifest:

Installation

Dependencies

Note

Depending on your OS and environment, you may need to modify some of these commands.

git clone https://github.com/rob/c2pa-helper.git && \
cd c2pa-helper && \
python3 -m venv .venv && \
source .venv/bin/activate && \
pip install -r requirements.txt

Configuration

Copy .env.sample to .env and modify the variable values.

Note

All of the variables found in .env are optional — remove any that you don't need.

Variable Description
CLAIM_GENERATOR Specifies the generator of the claim (e.g., "org-name/0.1.0") (docs)
CERT_TYPE The type of certificate, e.g., "ps256" (docs)
CERT Path to the certificate file (docs)
CERT_PRIVATE_KEY Path to the certificate's private key file (docs)
CERT_TIMESTAMP_URL URL for the certificate timestamping service (docs)
(You shouldn't need to modify this in most cases.)
ORGANIZATION_URL The URL of the organization's homepage (docs)
LINKEDIN_NAME The name of the organization on LinkedIn (docs)
LINKEDIN_URL URL to the organization's LinkedIn page (docs)
INSTAGRAM_NAME The organization's Instagram username (docs)
INSTAGRAM_URL URL to the organization's Instagram page (docs)

Important

If you don't have your own certificate, remove all of the CERT variables and sign_file will use the built-in certificate found in certs/sample. This certificate is pulled directly from the C2PA repository and will show as "C2PA Test Signing Cert" in the C2PA's online Verify tool.

Modifying

Assertions are functions stored in lib/assertions.py that return a Dict if they're valid, or None if the assertion isn't valid (e.g., you're looking for the EXIF:DateTimeOriginal field but it isn't found in the metadata.)

You can modify these assertion functions or add new ones.

These assertion functions are called from lib/manifest.py in the potential_assertions List in the order you specify. They're only included in the final manifest JSON if they return a Dict (i.e., not None.)

Usage

Assuming your .env is set up and the potential_assertions List in lib/manifest.py contains all of the assertions you want to include, you can run the script via cli.py (for a single file) or batch.py (to batch process multiple files inside a directory.)

cli.py

python cli.py /path/to/original_file /path/to/signed_file

batch.py

[...]

Considerations

c2pa.published action

Right now, this script assumes you are generating a manifest and signing a media file for the first time, so everything signed gets the c2pa.published action included in its manifest.

This might not make sense if you're trying to re-sign a media file after making changes to it and have already signed it previously. You would want to use a different action, most likely.

For example, you might want to use c2pa.resized, c2pa.filtered, or c2pa.color_adjustments instead.

About

A small wrapper around the sign_file function from the c2pa-python library that helps generate the manifest JSON necessary before signing and attaching the manifest to a media file.

Topics

Resources

Stars

Watchers

Forks

Languages