Watermark
Embedded into the content
A party puts an identifier into the content before it spreads, and a decoder reads it back. Content that was never marked carries none.
Tech demo · ISCC soft binding for C2PA · Windows, macOS, Linux
Bind Content Credentials to the content, not just the bytes.
Content Credentials are tied to a file by a hash of its exact bytes. Resize or re-encode the file and they no longer match. This tech demo adds the International Standard Content Code (ISCC, ISO 24138) to the credentials: a code anyone can calculate from the content itself.
To show what each binding sees, we re-encoded a signed image at half size and copied its Content Credentials back in. C2PA says Invalid: the hash no longer matches the bytes. The ISCC Content-Code still matches the pixels at 100%, and at 81% after a crop; unrelated images score around 50%. The credentials stay invalid, but the ISCC shows which content they were made for.
1Inspect
Drop an image, a document or an audio file. See its Content Credentials (who signed it, when, and whether the signature holds) and its ISCC.
2Sign
Save a signed copy. Its Content Credentials carry the ISCC, a timestamp and, if you choose, whether AI training and data mining is allowed.
3Check
Open a signed file, changed or not. The app calculates the ISCC again and compares it with the one in the Content Credentials, unit by unit.
Why soft bindings
A hash breaks when one byte changes. That is the point, and the problem.
C2PA binds a manifest to its file with a cryptographic hash of the exact bytes. That proves nothing has changed. But platforms re-encode files and strip manifests every day: a re-encoded copy no longer matches its credentials, and a stripped copy has lost them. A soft binding connects credentials and content through the content itself, so a service can find the credentials of a copy again. C2PA allows two kinds:
Fingerprint · ISCC
Calculated from the content
Anyone can calculate it from any copy, at any time, with software that implements the open standard. Checking it means calculating it again.
Four codes, one soft binding
Similar content. Similar codes.
An ISCC is made of units, each calculated from a different part of the file. The demo stores them in one
c2pa.soft-binding assertion with the algorithm io.iscc.v0, as
IEP-0020 defines.
Each unit is compared as a percentage: unrelated content scores around 50%, and the closer to 100%, the closer the content. The byte-based Data-Code and Instance-Code drop as soon as a file is re-encoded; that is their job. The Content-Code follows the image, the text or the sound.
- Content-CodeFrom the pixels, the text or the sound. Usually stays close through resizing and re-encoding.
- Data-CodeFrom the raw bytes. Survives small byte edits, not re-encoding.
- Instance-CodeA checksum of the bytes: an exact match, or none.
Why we built it
To show it, not just say it
It runs
io.iscc.v0 has been on the C2PA soft binding algorithm list since 2024. Here it runs end to
end with c2pa-rs, the open source C2PA SDK of the
Content Authenticity Initiative, on 19 file formats.
Anyone can check it
ISCC is an ISO standard with an open source reference implementation, so anyone can calculate it again and compare. The tests check every unit of this app against iscc-core and iscc-sdk, bit for bit.
Download · v0.1.0 · 2026-09-28
Try it with a file you know
Images: JPEG, PNG, WebP, GIF, TIFF, SVG. Documents: EPUB, Word, PowerPoint, Excel, OpenDocument, plain text, Markdown. Audio: MP3, FLAC, WAV, M4A. The builds are not code-signed yet, so each card says how to get past the system's warning at the first start.
Windows
Windows 10 and 11, x64
Installer 6.2 MBiscc-c2pa-demo-0.1.0-windows-x64-setup.exe
SmartScreen shows “Windows protected your PC”. Choose More info, then Run anyway. The installer needs no admin rights.
macOS
macOS 11 or later, Apple silicon and Intel
for Terminal · read the script
curl -fsSL https://c2pa-demo.iscc.codes/install-mac.sh | bashPaste it into Terminal. It downloads the latest release, checks its checksum, installs the app and opens it, with no security warning.
Prefer the disk image (16.5 MB)? Then macOS says it “could not verify” the app: choose Done, not Move to Bin, and Open Anyway in System Settings → Privacy & Security.
Linux
x86_64, WebKitGTK 4.1
AppImage 87.3 MBiscc-c2pa-demo-0.1.0-linux-x86_64.AppImage
Make it executable and run it: chmod +x iscc-c2pa-demo-*.AppImage. Or install the
.deb (Debian, Ubuntu) or the .rpm (Fedora, openSUSE).
Checksums: SHA256SUMS · Release notes · All releases
Good to know
What the demo does not do
- It does not look credentials up yet. Finding the credentials of a stripped copy by its ISCC needs a lookup service, which C2PA specifies as the Soft Binding Resolution API. That is the next step.
- The built-in certificate is a test certificate. Anyone can check the ISCC, but only this app trusts the demo signature. Sign with your own certificate and key for anything real.
- A matching ISCC is a strong signal, not proof. It suggests that two files hold the same or similar content. It says nothing about who made them or who holds the rights.
- Your files stay on your computer. Signing sends only a hash of the signature to a timestamp service, never the file. Inspecting stays offline.
For developers
Rust, Tauri and a little TypeScript
The core is Rust: c2pa-rs for Content Credentials,
iscc-lib for ISCC, and pure Rust readers for every
format. No external tools, no Python. The same core also builds as c2pa-iscc, a command-line tool
that prints JSON, for scripts and agents.
Needs Rust 1.96 or later, Node 22.12 or later and pnpm. On Linux also the Tauri system libraries.
git clone https://github.com/iscc/iscc-c2pa-demo
cd iscc-c2pa-demo
pnpm install
pnpm tauri dev
# the command-line tool
cd src-tauri
cargo run --features cli --bin c2pa-iscc -- sign photo.jpg