The short answer
That this exact file, byte for byte, existed no later than the time of a Bitcoin block. That time is accurate to within a few hours.
Who made the file, whether it is true or original, or anything about an edited copy. It is not a signature or a notarisation.
Admissible in many places, and accepted by courts in China and France so far. The judge decides how much it weighs, so pair it with other evidence.
What courts and laws have said
No court has yet named OpenTimestamps, the protocol we use, by name. These decisions and laws are about the same mechanism: a file's fingerprint anchored in a blockchain.
- 2018 · ChinaHangzhou Internet Court, Huatai Yimei v. Daotong. This was the first court to accept blockchain evidence. The judges checked the Bitcoin anchor themselves, recomputed the fingerprint, and admitted the evidence, holding that the standard should not be raised just because the technology is new. English translation
- 2021 · ChinaOnline Litigation Rules, Arts. 16–19. Courts presume that blockchain data was not changed after it went on-chain, but can still ask whether it was genuine before that. Text
- 2014 → 2026 · EUeIDAS Art. 41 (and Art. 45k for ledgers): a court can't reject an electronic timestamp just because it's electronic or not "qualified". Only a qualified timestamp from a supervised provider carries a legal presumption, and ours isn't one. eIDAS · Qualified ledgers, 2025/2531
- 2025 · FranceTribunal judiciaire de Marseille, 20 March 2025. A fashion designer proved copyright ownership partly with Bitcoin-anchored timestamps of their designs, which a bailiff had recorded. It was the first French ruling of its kind, a first-instance decision with brief reasons. Judgment · EUIPO note
- Spain · GermanyNon-qualified electronic evidence is weighed freely by the judge (LEC 326; ZPO §371a for when a presumption does apply).
- United StatesVermont presumes the date a record was added to a blockchain, though not that its content is true (12 V.S.A. §1913). Illinois and Arizona forbid excluding a record only because it's on a blockchain (205 ILCS 730, A.R.S. §44-7061). Federal courts can authenticate data by its hash (FRE 902(13)–(14)).
- 2026 · IndiaThe Supreme Court upheld the rule that electronic evidence comes with a certificate stating its hash values (BSA s.63(4)). Report
The case law is still thin, and every decision so far is first-instance. Treat a stamp as strong supporting evidence, not a certificate. Read the full research, with every source and what we couldn't verify.
When a stamp is worth it
Stamp when you might one day need to show that this exact content existed by a date.
Drawings, photos, music, code and designs: priority if someone copies you. This is the Marseille case.
Also keep: drafts, publication recordsWhich version existed when, during a negotiation.
Also keep: the parties' signaturesLab notes and results, without revealing them. A stamp doesn't count as publication, and it's not a patent.
Also keep: lab records, witnessesShows a dataset, model or output wasn't changed after a date.
Also keep: a manifest of every file's hashShows audit or security logs weren't rewritten afterwards.
Also: stamp at regular intervals, not each lineShows material existed before a date, without disclosing it.
Also: talk to a lawyer before you publishWhen you need something more
| If you need… | Use |
|---|---|
| A legal presumption of the date (EU, UK, Spain), or time to the minute | A qualified electronic timestamp from a provider on the EU trusted list |
| Proof of who signed or agreed | An electronic signature, ideally qualified |
| Proof of what a website showed, or of an event | A notary or bailiff record |
| Deeds, wills, property: anything with a required legal form | A notary. A stamp can't satisfy formalities. |
| A dispute that has already started | A lawyer, first |
Keep your stamp useful
- Never change the original. Even re-saving it, or stripping its metadata, changes the fingerprint. Keep it read-only.
- Keep the .ots proof next to the file, backed up in two places.
- Download the proof again after a few hours. Your first proof is pending. Once Bitcoin confirms it, the complete proof no longer depends on anyone. Check it with Verify.
- Write down the context: who made the file, what it is, and where the original lives. The stamp can't record that for you.
- Stamp early, when you create or finish something. A stamp made once a dispute has started looks self-serving.
- Many files? Stamp a list of their fingerprints (a manifest), and keep the list with the files.
- Need to show who? Sign the file, then stamp it.
Questions
Will it hold up in court?
It's admissible evidence in many countries, and courts have accepted similar Bitcoin timestamps. How much it counts is up to the judge, so pair it with signatures, records and, if needed, a qualified timestamp or a notary.
Is this a notarisation or a certificate?
No. Nobody vouches for you or for the content. It's a mathematical proof that the exact bytes existed by a certain time, which anyone can check.
How precise is the time?
A few hours. The proof says the file existed no later than a Bitcoin block, and block times can be off by about two hours. It says nothing about when the file was created.
Do you see my file?
No. Your browser computes the fingerprint (SHA-256) and only that is sent. A fingerprint can't be turned back into the file.
What if you disappear?
Your complete proof doesn't need us. It's a standard OpenTimestamps file that can be checked at opentimestamps.org, or with your own Bitcoin node.
Is a pending proof enough?
Not on its own: it still relies on the timestamp calendars. Download the proof again a few hours after stamping to get the complete version anchored in Bitcoin.
This page is general information, not legal advice. It was last reviewed in October 2026. For agents, the same guidance is at /evidence.md. The research, with every source and what we couldn't verify, is at /evidence/report.md.