Proof of existence: evidence a document existed, that anyone can check.
Proof of existence is the simplest, strongest thing a timestamp can give you: independent evidence that an exact file existed at or before a moment in time — and, because it is tied to the file’s fingerprint, that the file has not been altered since.
The idea
Every file has a unique SHA-256 fingerprint. If you publish that fingerprint somewhere permanent and timestamped, you have created a record that the file must have existed by then — because you could not have produced its fingerprint otherwise. Do it on a public blockchain and the record is not only permanent but independently timestamped and tamper-evident: no single party, notaros included, can forge or backdate it.
What it proves
- Existence: this exact file existed no later than the anchoring timestamp.
- Integrity: the file has not changed since — any edit changes the fingerprint.
- Independence: the proof is checkable by anyone, forever, without the issuer.
What it does not prove
Proof of existence is precise, which means it is honest about its limits. It does not establish who authored or owns the file, whether its contents are true, or that anyone signed it. It fixes existence and integrity in time — often exactly the fact in dispute (a priority date, a “we had this before you” claim, an unaltered record) — and nothing more.
How to create one
notaros creates a proof of existence in a minute: fingerprint your file in your browser, anchor it to Base and Bitcoin, and receive a certificate. Then verify it independently — or let anyone else do so.