C2PATool

Introduction

This is a PHP wrapper for the c2patool command line binary provided by the Content Authenticity Initiative. The intent is to make it easier to add signed manifests to media assets as well as reading/validating those signed manifests.

Usage

The Tool class

The tool class is the actual wrapper would the c2patool excutable. This Class will pass commands off to the exceutable and return any output.

Creating the Tool

$tool = new \Jrglasgow\C2paTool\Tool(Psr\Log\LoggerInterface $logger);

By default the Tool constructor will search the $PATH for the c2patool executable. If it can be found it will be used...if you wish for a different version of the utility to be used you can specify

$tool->setBinary('/path/to/bin/c2patool');

The Signer class

The Signer class will handle all things certificate and will sign the media asset manifests.

Validating the cert can be used for Content Authenticity

You can validate that the certificate can be used for Content Credential signing by passing the certificate/key locations into the Signer::validateCert() method. If you pass in a stdClass object information about the certificate will be placed in the object for later use. Certificate MUST follow the specification in the Content Authenticity Initiative documentation for Signing Manifests.

$is_valid = \Jrglasgow\c2patool\Signer::validateCert($cert_file_path, $key_file_path, $cert_file);

If $cert_file_path = 'ENVIRONMENT_VARIABLE'; and $key_file_path = ''ENVIRONMENT_VARIABLE'; then instead of looking for the key and cert files on the file shystem the environment variables C2PA_PRIVATE_KEY and C2PA_SIGN_CERT variables will be used instead as allowed in the c2patool documentation.

Creating a new Signer

As with certificate validation if $cert_file_path = 'ENVIRONMENT_VARIABLE'; and $key_file_path = ''ENVIRONMENT_VARIABLE'; then instead of looking for the key and cert files on the file shystem the environment variables C2PA_PRIVATE_KEY and C2PA_SIGN_CERT variables will be used instead as allowed in the c2patool documentation.

$signer = new Jrglasgow\C2paToolSigner($tool, $cert_file_path, $key_file_path);

Signing and embedding a manifest

Creating a Manifest

Create your manifest as a JSON string or an Array using the examples as a reference. The manifest will be modified and converted to a string afterwards.. The signature algorithm (alg), Private Key (private_key) and Sign Certificate (sign_cert) need not be included as they will be replaced with the information from the certificate when creating the Signer object. If the Claim Generator (claim_generator) is left empty one will be inserted automatically. Likewise if the Time Authority (ta_url) is left empty one will be inserted as well.

Invoke the sign method

$success = $signer->sign($source_file, $destination_file, $manifest);