Verifiable digital proof
When you need to show that a file already existed, you will have a proof you can keep and verify. The timestamp adds a legal presumption of date and integrity across the EU (eIDAS).
How it works
Select the exact version you want to protect.
Sellat calculates its digital fingerprint and creates the evidence tied to that file.
Keep the proof and use it later to verify that the file matches.
The whole circuit
One concrete case: you move into a rented flat, photograph the state it is handed to you in, and when you leave your deposit is withheld for damage that was already there. This is what happens in between. The circuit is the same for a contract, a report or a record from your system: the file changes, the steps do not.
Day 0
The day you pick up the keys you photograph the blind, the floor and the rest of the flat. For now it is one more photo on your phone, carrying whatever date your phone says.
Day 0, two minutes later
You drag the photos into Sellat. Your browser computes each file fingerprint and only that fingerprint is sent. Add the qualified seal and the date comes from a timestamping authority, not from your phone and not from us.
Day 0, in your inbox
The PDF certificate and the full package arrive as a ZIP. You store it next to the tenancy agreement and forget about it. No account and no subscription are needed to keep it.
Two years later
Your deposit is withheld over the blind. You open the ZIP: inside is the exact photo you took on day one, its fingerprint and the sealed date, with checking instructions in Spanish and English.
The same day
You pass that ZIP to your lawyer, to an expert witness or to the insurer. Any of them can check the date and that the file is untouched without asking us for anything and without taking your word or ours.
Sellat does not decide who caused the damage, what it costs to repair or how much deposit you get back. A settlement, an arbitrator or a judge decides that. What the package adds is a date that does not depend on you.
Seal my photosInside the package
Not a promise and not a screenshot: the real list of files Sellat puts in your ZIP. What you see here is generated by the same module that builds the package.
original/<archivo> If the original is kept The exact photo you sealed, in a folder of its own so no other file in the package can be mistaken for it. It travels inside when the original is available: the upload that created the proof, or custody.
certificado-<id>.pdf Always The PDF you show a person or attach to a filing. It is an informative document: what actually gets checked is the file, not the PDF. If the file carried Content Credentials (C2PA), the certificate records them too — who signed, with which tool and whether they declare AI use — exactly as your browser read them when you protected it.
proof.json Once the batch is anchored Your file fingerprint, its Merkle leaf and inclusion path, the batch root and the public transaction that records it. This is the piece that lets anyone check everything without Sellat.
sello-cualificado-<id>.tsr With a qualified seal The RFC 3161 response from the qualified timestamping authority, exactly as it was issued. This is the file that fixes the date under eIDAS.
autoridad-sellado.pem With a qualified seal That authority signing certificate, with its SHA-256 written into the README. It travels inside so the check works offline and nobody has to go looking for it.
anclaje-bitcoin.ots Once the batch is anchored The OpenTimestamps proof of the batch root. It may still be waiting for a block: it is a valid file and whoever receives it can upgrade it themselves.
LEEME.txt / README.txt Always What each file is, what it proves and what it does not, and the exact commands to check it. In Spanish and English, so an expert or a lawyer never has to ask you anything.
With the seal and the authority certificate inside the ZIP, the date is verified with standard tools on the machine of whoever receives it. If Sellat disappeared tomorrow, your package would still check out.
The package proves that this exact file existed on that date and has not been modified. It does not prove who created it, who took the photo, or what happened in front of the camera.
When the claim arrives
The day somebody claims something from you, you do not have to explain how anything works. You send a link. Whoever opens it sees which files existed, on what date, and that they have not been touched.
Qualified (eIDAS) timestamp
Add to your proof a qualified timestamp issued by the FNMT-RCM (the Spanish Royal Mint), a qualified trust service provider under Regulation (EU) 910/2014. It is issued over your file’s fingerprint and stays inside your proof.
Protect a fileYour first qualified timestamp is free. One per account, on the proof you choose. After that, €6 per timestamp.
See all plans →A qualified timestamp enjoys a legal presumption of the accuracy of the date and time it indicates and of the integrity of the data it is bound to, across the European Union.
Anyone can verify it with standard tools (RFC 3161) against the EU trusted list, without relying on Sellat. The timestamp shows that this exact file existed at that moment; not who its author is nor the content of any agreement.
Content Credentials and Sellat
Sellat is the layer that survives when the metadata does not.
C2PA / Content Credentials keeps provenance in a signed manifest, normally embedded in the file itself: which tool produced it, who signed it, which edits it carries. It is the file’s history, and it travels with the file.
Sellat anchors existence outside the file: its SHA-256 fingerprint and the moment, on Polygon and on Bitcoin. It depends on nothing the file carries inside, so nothing that happens to the metadata erases it.
C2PA was never the problem. Screenshots, format conversions and platforms that strip metadata are: not all of them do, but it happens often and you do not get to choose. The fingerprint Sellat anchors does not live inside the file, so none of that erases it. What does change is the file: a screenshot or a recompression is a different file with a different fingerprint, and checking the proof needs the exact version you sealed.
C2PA protects the history inside the file. Sellat anchors existence outside it. Your proof stops depending on nobody touching your metadata — only on you keeping the exact version, which is precisely what arrives in the ZIP.
Check an image’s credentials → Read: what Content Credentials are and why they can disappear →The same idea, at any scale
The same proof logic can be part of applications and workflows that handle large volumes.
See the API →Optional custody
If you want it, Sellat keeps the original too, not only the proof. It is optional, the proof does not depend on it, and you can withdraw it whenever you like.
See Custody and pricing →Protect the exact version of the file you want to be able to recognise later.
Protect files