Free service: indisputable proof of when your file existed, and that it's unchanged.

Prove that your file existed, and that nobody changed it

Have you ever needed to show that you wrote something first, or that a document hasn't been changed? Think of a song, design, contract, logfile, photo, video or business idea. A date on a file is easy to fake, so it often isn't enough. This free service gives you indisputable proof.

How it works

Your file and filename stay private and never leave your computer. Your browser only creates a digital fingerprint of it, called a SHA-256 hash. If even one character in your file changes, the fingerprint becomes completely different.

We save all submitted fingerprints in a public viewable record. Every day at 00:01 UTC, we collect all the fingerprints from that day into one file. We then record the fingerprint of that file in the Bitcoin, Ethereum and Cardano blockchains, public records that nobody can change or delete.

You can prove it later. You can then show that your data existed on or before that date and hasn't changed since. To do that, you need three things: your original, unchanged file; the file with all the fingerprints from that day; and the transaction IDs. With that information, anyone can verify that the file existed on a specific date and has not been changed since.