How the seal works

Proof it's the same file

A trust badge only means something if it sticks to the exact recording we checked. The seal is how anyone can prove that, without trusting us.

What we seal

• The file fingerprint: the SHA-256 of the exact bytes we checked.
• The stream fingerprint: the same for the audio and video inside the file. Matching a re-labelled copy by it is coming later.
• A speech fingerprint of the recording, so later we can recognise the same recording even after it is converted.
• The result: the exact bytes of the published check, so nobody can quietly change it.
• How it was checked: the method version, the reading mode and the software version for each step.

Signed, logged, stamped

We sign this record with our Ed25519 key and add it to a public log that can only grow. Every hour we sign the latest state of the log. Once a day that state is stamped into the Bitcoin blockchain through OpenTimestamps, so its date can be proven by anyone, forever.

Each record is named like fct1:7K3M9QX2:2: the public page code and the check number. Only checks on public pages can be looked up; private reports are never revealed.

How to check it yourself

1. Drop a file on our seal check page. Your browser computes its fingerprint. The file never leaves your computer.
2. Or download the signed record from any public page and check its signature against our public keys: factunion-keys.json. We will publish a verifier here.

Coming later

Recognising the same recording after it has been converted or trimmed, checking which words changed, and Content Credentials embedded in files.