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Verify tool known certificate list

The C2PA Verify tool uses a list of known certificates (sometimes referred to as a "trust list") to determine whether a Content Credential was issued by a known source. If an asset's Content Credential was not signed by a known certificate, the Verify tool will display this message:

Conversely, if the Content Credential was signed by a known certificate, the Verify tool will display the name of the certificate owner and time of the claim signature.

note

The C2PA intends to publish an official public list of known certificates. Until then, Verify uses a temporary list. The list is subject to change and will be deprecated when C2PA publishes the official list.

Temporary known certificate list​

The contentcredentials.org site hosts the following files that it uses to validate signing certificates. Together, these files form the temporary known certificate list:

Checking your certificate​

Before requesting to add your signing certificate to the known certificate list, perform a preliminary check to ensure the certificate is configured properly.

Prerequisites​

The preliminary certificate check procedure below requires the following tools. You must install them if you haven't done so already:

  • jq, a lightweight and flexible command-line JSON processor. On macOS, if you have Homebrew, you can install jq by entering brew install jq.
  • OpenSSL, a cryptographic software library and CLI. It's installed on many systems such as macOS (but make sure you have a recent version). If OpenSSL is not installed on your system, see the list of unofficial binary distributions.
  • C2PA Tool, the command line tool for working with C2PA manifests and media assets.

Procedure​

note

In the example commands given below, cert.pem is your certificate file.

Check your certificate by following these steps:

  1. Ensure that signing with the certificate doesn't have any validation errors by using a C2PA Tool command like this:

    c2patool ./image.jpg trust --allowed_list ./cert.pem

    Confirm that the result does not contain a validation_status field, which indicates an error.

  2. Confirm that the signature_info.issuer field in the manifest is correct. This field determines what Verify displays for the organization name after "Issued by ...". Use a C2PA Tool command like this:

    c2patool ./image.jpg trust --allowed_list ./cert.pem \
    | jq --args '.manifests[].signature_info.issuer'

    The response should be something like this:

    "XYZ Inc."

    Where "XYZ Inc." is the name of your organization.

  3. Use openssl to perform basic verification of the certificate you're submitting; for example:

    openssl x509 -noout -text -in 'cert.pem' | grep 'Subject:'

    Example response:

    Subject: organizationIdentifier=XYZ-7155227, C=US, ST=Delaware, L=Dover, O=Whatever Inc., SN=xxx, GN=xxx, CN=xxx

Using the known certificate list​

You can use the C2PA Tool or the CAI JavaScript library to determine whether a certificate is on the temporary known certificate list.

Using with C2PA Tool​

The C2PA Tool documentation explains how to use the temporary known certificate list with the tool.

Using with the JavaScript library​

To load and use these lists with the JavaScript library (c2pa-js), pass them to the read function as shown in the following TypeScript example:

import { createC2pa, type ToolkitSettings } from 'c2pa';
import wasmSrc from 'c2pa/dist/assets/wasm/toolkit_bg.wasm?url';
import workerSrc from 'c2pa/dist/c2pa.worker.min.js?url';

async function loadTrustResource(file: string): Promise<string> {
  const res = await fetch(`https://contentcredentials.org/trust/${file}`);

  return res.text();
}

async function getToolkitSettings(): Promise<ToolkitSettings> {
  const [trustAnchors, allowedList, trustConfig] = await Promise.all(
    ['anchors.pem', 'allowed.sha256.txt', 'store.cfg'].map(loadTrustResource),
  );

  return {
    trust: {
      trustConfig,
      trustAnchors,
      allowedList,
    },
    verify: {
      verifyTrust: true,
    },
  };
}

async function readFile(asset: File) {
  const c2pa = await createC2pa({
    wasmSrc,
    workerSrc,
  });

  return c2pa.read(asset, {
    settings: await getToolkitSettings(),
  });
}
note

This code is for illustration purposes only. To ensure acceptable performance, production code should reuse the c2pa object and cache the output of getToolkitSettings() to avoid making unnecessary network calls.

How to add a certificate to the list​

If you have an application that is in production and publicly available, you can request to add its signing certificate to the temporary known certificate list.

Follow these steps:

  1. Do a preliminary check of your certificate to ensure it meets the requirements for C2PA signing certificates and to be in the Verify temporary certificate list.
  2. Submit your request by emailing verify-tl@c2pa.org. We will review your request, and if it is approved, we'll ask for more details. Once we receive them and deploy the update to the trust list, you will receive a confirmation email.