Stamp a file

Put a file's fingerprint on the public record.

Pick a file. Your browser computes its SHA-256 fingerprint right here. The file itself never leaves your machine: only the fingerprint and the file size are sent. Stamping records that fingerprint, with a time, in a public repository anyone can read.

3 free stamps a day. Checking whether a file is already stamped is free and does not use a stamp.

What a stamp means

It proves when. It does not prove who, or whether it is true.

A stamp proves that a file in this exact form existed no later than the stamp time. Change one byte and the fingerprint changes, so the stamp no longer matches.

It does not prove who made the file. It does not prove that anything the file says is true. It does not prove the file is older than the stamp by any amount.

The fingerprint is public. It does not reveal the file's contents, but a very short or easy to guess file could be guessed from it. The first stamp of a fingerprint wins: stamping the same file again returns the original record and its original time.

Where the record lives: one public repository, written by one operator and hosted by one code host. That is an outside party, but it is not an independent one. If the repository is deleted, or its history is rewritten, the record goes with it. The record is public, so anyone can save or mirror a copy, and a copy you hold yourself is the strongest form of this.

The exact wording of what each stamp proves comes from the stamp service in every response and is shown above as it arrives. See also what Arcaeon proves, and what it does not. New to this? How to prove a file is yours walks through every option, including the ones that are not us.