# Credentio

C++ libraries to support validation and generation of C2PA Content Credentials
(https://c2pa.org/).

NOTE: We are actively developing this project and may introduce breaking changes
without notice.

## Supported Media Formats

The library supports C2PA provenance validation (extracting and verifying an
embedded C2PA manifest store) and generation (embedding a newly generated and
signed C2PA manifest store) for the following container formats:

<!-- mdformat off(no multiline table cells) -->

Format                      | Extensions                | Validation | Generation
:-------------------------- | :------------------------ | :--------- | :---------
JPEG                        | `.jpg`, `.jpeg`           | Yes        | [Yes](formats/jpeg/writer.h)
PNG                         | `.png`                    | Yes        | [Yes](formats/png/writer.h)
MP4                         | `.mp4`                    | Yes        | [Yes](formats/bmff/writer.h)
fMP4 (fragmented MP4)       |                           | No         | No
RIFF (e.g., WebP, WAV, AVI) | `.webp`, `.wav`, `.avi`   | Yes        | [Yes](formats/riff/writer.h)
TIFF (e.g., TIFF, DNG)      | `.tif`, `.tiff`, `.dng`   | Yes        | [Yes](formats/tiff/writer.h)
AVIF                        | `.avif`                   | Yes        | [Yes](formats/bmff/writer.h)
M4A                         | `.m4a`                    | Yes        | [Yes](formats/bmff/writer.h)
HEIF, HEIC                  | `.heif`, `.heic`          | Yes        | [Yes](formats/bmff/writer.h)
MOV                         | `.mov`                    | Yes        | [Yes](formats/bmff/writer.h)
GIF                         | `.gif`                    | Yes        | [Yes](formats/gif/writer.h)
MP3                         | `.mp3`                    | Yes        | [Yes](formats/id3/writer.h)
FLAC                        | `.flac`                   | Yes        | [Yes](formats/id3/writer.h)
PDF                         | `.pdf`                    | Yes        | [Yes](formats/pdf/writer.h)
SVG                         |                           | No         | No
OGG Vorbis                  |                           | No         | No
Text                        |                           | No         | No
Live stream video           |                           | No         | No
ZIP-based containers        | `.docx`, `.pptx`, `.xlsx` | Yes        | [Yes](formats/zip/writer.h)
Fonts                       |                           | No         | No

<!-- mdformat on -->

## Prerequisites

*   Clang with libc++ (tested with Clang 19). `.bazelrc` builds with `clang` and
    `clang++` against libc++, so both must be on `PATH` and the libc++
    development packages must be installed.
*   [Bazelisk](https://github.com/bazelbuild/bazelisk), installed as `bazel`. It
    downloads the Bazel version pinned in `.bazelversion`.
*   Git

On Ubuntu, CI sets these up as follows:

```shell
# Clang 19, including libc++, from the LLVM apt repository.
sudo apt-get install -y lsb-release wget software-properties-common gnupg
wget https://apt.llvm.org/llvm.sh
chmod +x llvm.sh
sudo ./llvm.sh 19 all
sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-19 100
sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-19 100

# Bazelisk.
curl -sLO https://github.com/bazelbuild/bazelisk/releases/latest/download/bazelisk-linux-amd64
chmod +x bazelisk-linux-amd64
sudo mv bazelisk-linux-amd64 /usr/local/bin/bazel
```

Bazel caches the detected C++ toolchain, so after installing or changing the
compiler or libc++, run `bazel clean --expunge` before building again.

## Dependencies

*   [Abseil (`abseil-cpp`)](https://abseil.io/)
*   [Riegeli](https://github.com/google/riegeli)
*   [BoringSSL](https://github.com/google/boringssl)
*   [GoogleTest (`googletest`)](https://github.com/google/googletest)
*   [Google Tink (`tink_cc`)](https://github.com/tink-crypto/tink-cc)
*   [LibCppBor](https://android.googlesource.com/platform/system/libcppbor/)
*   [nlohmann_json](https://github.com/nlohmann/json)
*   [Protocol Buffers (`protobuf`)](https://github.com/protocolbuffers/protobuf)

## Quickstart

Credentio includes fast standalone command-line tools for inspecting, verifying,
and writing C2PA metadata embedded in media assets.

### Building the CLIs

Build the tools once:

```bash
bazel build tools:c2pa_validate tools:asset_write
```

The binaries are written to `bazel-bin/tools/c2pa_validate` and
`bazel-bin/tools/asset_write`.

### Validating C2PA Metadata

#### Validating with Trust Anchors

You can validate assets against specific PEM-encoded trust anchors for claim
signers and Time Stamping Authorities (TSA):

```bash
bazel-bin/tools/c2pa_validate \
  --asset=/path/to/asset.jpg \
  --claim_signer_trust=/path/to/claim_signer_trust_anchors.pem \
  --tsa_trust=/path/to/tsa_trust_anchors.pem
```

> **Note on Trust Lists:** Credentio does not distribute or provide trust anchor
> lists. You can obtain the latest official C2PA trust lists from the C2PA
> organization on GitHub
> ([https://github.com/c2pa-org/conformance-public/tree/main/trust-list](https://github.com/c2pa-org/conformance-public/tree/main/trust-list)).

### Writing C2PA Metadata

The `asset_write` tool generates a C2PA manifest store, signs it with the
provided claim signer key, and embeds it into a copy of the input asset. The
media type is inferred from the input file extension.

#### Creating Test Keys and Certificates

`asset_write` needs an EC P-256 key and certificate for the claim signer, and
optionally another pair for the Time Stamping Authority (TSA). For local
testing, [`tools/create_test_pki.sh`](tools/create_test_pki.sh) creates a
private root CA and issues both certificates from it. It requires OpenSSL 1.1.1
or later:

```bash
tools/create_test_pki.sh test_pki
```

The script refuses to overwrite existing keys. It produces:

*   `claim_signer_key.pem` and `claim_signer_cert.pem`: pass to
    `--claim_signer_key` and `--claim_signer_cert`.
*   `tsa_key.pem` and `tsa_cert.pem`: pass to `--tsa_key` and `--tsa_cert`.
*   `root_ca_cert.pem`: pass to `--claim_signer_trust` and `--tsa_trust` when
    validating.

#### Writing a Manifest Store

```bash
bazel-bin/tools/asset_write \
  --input=/path/to/input.jpg \
  --output=/path/to/output.jpg \
  --claim_signer_key=/path/to/claim_signer_key.pem \
  --claim_signer_cert=/path/to/claim_signer_cert_chain.pem \
  --tsa_key=/path/to/tsa_key.pem \
  --tsa_cert=/path/to/tsa_cert.pem
```

Flags:

*   `--claim_signer_key`: PEM-encoded EC P-256 private key of the claim signer.
*   `--claim_signer_cert`: PEM-encoded claim signer certificate chain, leaf
    first.
*   `--claim_signer_ocsp` (optional): DER-encoded OCSP response for the claim
    signer certificate.
*   `--tsa_key`, `--tsa_cert` (optional): PEM-encoded EC P-256 private key and
    certificate used to timestamp the claim signature locally. If omitted,
    timestamping is disabled.
*   `--disable_timestamping` (optional): Disables timestamping.
*   `--request_txtpb` (optional): Text-format
    [`GenerateManifestStoreRequest`](proto/generator.proto) describing the
    manifest to generate. Defaults to a single `c2pa.created` action.

#### End-to-End Example

Using the files from
[Creating Test Keys and Certificates](#creating-test-keys-and-certificates),
sign an asset and validate it against the test root CA. Run these commands from
the repository root:

```bash
tools/create_test_pki.sh test_pki

bazel-bin/tools/asset_write \
  --input=/path/to/input.jpg \
  --output=signed.jpg \
  --claim_signer_key=test_pki/claim_signer_key.pem \
  --claim_signer_cert=test_pki/claim_signer_cert.pem \
  --tsa_key=test_pki/tsa_key.pem \
  --tsa_cert=test_pki/tsa_cert.pem

bazel-bin/tools/c2pa_validate \
  --asset=signed.jpg \
  --claim_signer_trust=test_pki/root_ca_cert.pem \
  --tsa_trust=test_pki/root_ca_cert.pem
```

The validation result should report `claimSignature.validated`,
`signingCredential.trusted` and `timeStamp.trusted` with no failures.

> **Note:** `asset_write` signs with locally supplied keys and is intended for
> development and testing. Manifest stores it produces are only trusted by
> validators that trust the supplied certificates.

## Building & Testing

To build the entire project:

```bash
bazel build ...
```

To execute all unit tests:

```bash
bazel test ...
```

## Support & Releases

Credentio recommends that users **live-at-head** (updating to the latest commit
on the main branch as often as possible). We are actively developing this
project and may introduce breaking changes without notice.

## License & Disclaimer

Credentio is licensed under the terms of the Apache 2.0 License. See
[LICENSE](LICENSE) for more information.

### Disclaimer

This is not an officially supported Google product. This project is not eligible
for the
[Google Open Source Software Vulnerability Rewards Program](https://bughunters.google.com/open-source-security).

## Contact

For questions, feedback, or inquiries, please contact:
`credentio-team@google.com`.