Guide · Proof of existence and prior date

How to prove that a document existed on a date?

To prove that a document existed on a date you must fix its content in a record that nobody can alter or backdate: a notary, a qualified electronic time stamp (eIDAS), registered mail with certified content, a public registry, or a time stamp on a proof-of-work blockchain. What gets fixed is the document or its fingerprint (SHA-256 hash); how strong the evidence is depends on who controls the clock and whether the record can be rewritten later.

This guide explains what a proof of existence and prior date exactly is, compares the five methods, shows how it is done with blockchain in four steps and quotes what Regulation (EU) 910/2014 (eIDAS) says.

What a proof of existence and prior date is

It is evidence that a specific content, with those exact bytes, already existed at a given instant and has not changed since. Technically it is built in two steps: a cryptographic fingerprint of the document is computed (SHA-256 hash, 64 hexadecimal characters that change completely if a single bit changes) and that fingerprint is fixed in a dated record that neither the requester nor the custodian can rewrite.

What it proves

That the document existed on that date (existence), that it existed before any later fact (prior date) and that the file you present today is identical to the one back then (integrity).

What it does NOT prove

Who created it (authorship), whether what it says is true (truthfulness), whether the signer was entitled to sign, or that it did not already exist earlier. Other means of evidence are needed for that.

The five methods, compared

Cost is indicative and qualitative; it varies by country and provider. The legal presumption column refers to Regulation (EU) 910/2014: only qualified time stamps enjoy the presumption of accuracy of Art. 41(2).

Comparison of methods to prove that a document existed on a date
Method	Indicative cost	Time to obtain the proof	In person?	Legal presumption (Art. 41(2) eIDAS)	Reliance on a third party	Future verifiability
Notary (deposit or notarial record)	High: fee per record	Days (appointment)	Yes, generally	Not an eIDAS time stamp; the record is a public deed with notarial public faith	On the notary and the preservation of their records	As long as the notarial records are preserved
Qualified electronic time stamp (provider on the EU trusted list)	Medium: fee per stamp or subscription	Seconds	No	Yes: presumption of accuracy of date and time (Art. 41(2))	On the provider and its certificate chain; long-term preservation requires re-stamping	Yes, as long as the certificate chain can be checked
Registered mail with certified content	Medium: fee per dispatch	Hours or days	In person or online, depending on the operator	Not an eIDAS time stamp; certifies date, dispatch and content per the operator	On the postal operator	Limited to the operator's retention period
Public registry (intellectual property, companies, administrative)	Low to medium: fee	Weeks or months	In person or online	Not an eIDAS time stamp; each registry has its own effects (e.g. Art. 145 of the Spanish IP Act)	On the registry body	Yes: public archive
Time stamp on a proof-of-work blockchain (Proovik, OpenTimestamps)	Low or free	Seconds to hours, depending on the network	No	No: non-qualified stamp. Admissible as evidence (Art. 41(1)), without the presumption (Art. 41(2))	None to verify (public network); a service only to issue	Yes: anyone with the proof file, without the issuer

How it is done with blockchain, in four steps

This is how a time stamp on a proof-of-work blockchain such as Kaspa works. The key point is that the timestamp is part of the data the mining work was spent on: changing it would require redoing that work.

Compute the document's fingerprint on your device

The file's SHA-256 hash is computed in the browser. The document is not uploaded anywhere; it cannot be reconstructed from the hash.
Record the hash in a blockchain transaction

The hash is placed in a transaction on the Kaspa network. The block that accepts it carries a timestamp in its header, and the proof of work is executed over that header.
Keep the certificate next to the original document

The PDF certificate includes the hash, the transaction id, the timestamp and the PVK-PROOF/1 proof package. Document and certificate together are the proof.
When needed, verify without relying on anyone

Recompute the document's hash, compare it with the certificate and check the transaction, the header and the proof of work against the public specification. Proovik does not need to exist.

The detail of what exactly is checked (transaction, Merkle tree, header, proof of work) is in the public PVK-PROOF/1 verification specification; the comparison with OpenTimestamps and with qualified time stamps is in what a blockchain time stamp is.

What the law says

Literal quotes from Regulation (EU) No 910/2014 of the European Parliament and of the Council of 23 July 2014 (eIDAS), consolidated version.

Article 3(16) — "trust service"

"an electronic service normally provided for remuneration which consists of: (a) the creation, verification, and validation of electronic signatures, electronic seals or electronic time stamps, electronic registered delivery services and certificates related to those services […]"

Article 3(33) — "electronic time stamp"

"data in electronic form which binds other data in electronic form to a particular time establishing evidence that the latter data existed at that time"

Article 41(1) — legal effects

"An electronic time stamp shall not be denied legal effect and admissibility as evidence in legal proceedings solely on the grounds that it is in an electronic form or that it does not meet the requirements of the qualified electronic time stamp."

Article 41(2) — presumption (qualified only)

"A qualified electronic time stamp shall enjoy the presumption of the accuracy of the date and the time it indicates and the integrity of the data to which the date and time are bound."

What this means for a blockchain time stamp. It is a non-qualified electronic time stamp: it fits the definition of Art. 3(33), it is admissible as evidence under Art. 41(1) and it lacks the presumption of Art. 41(2). If challenged, the party presenting it must show that the date is correct; that is why it matters that the check is arithmetic and reproducible by anyone, rather than a provider's declaration.

In Spain. Art. 326 of the Civil Procedure Act (LEC) governs the evidential weight of private documents. Paragraph 3 (introduced by Law 6/2020) provides that, when the authenticity, integrity or accuracy of date and time of an electronic document that a non-qualified trust service can establish is challenged, evidence is taken under paragraph 2 and Regulation (EU) 910/2014; paragraph 4 reserves the presumption for qualified services listed in the trusted list. Hence a non-qualified time stamp such as Proovik's does not by itself confer the Spanish Civil Code status of "fecha cierta" (Art. 1227): it provides a proof of existence and prior date that the court weighs freely.

This page is general information, not legal advice. Outside the European Union, treatment depends on each jurisdiction.

Frequently asked questions

Is a screenshot enough to prove the date?

Not on its own. Anyone can fabricate or edit a screenshot, and the date it shows is the device clock, which can be changed in seconds. It works as circumstantial evidence if something fixes its existence in time: for instance, time-stamping the hash of the screenshot itself the moment you take it.

Does emailing the document to myself work?

It is weak evidence. Email headers are generated by the sender's server and can be altered; the message sits in a mailbox you control; and the provider certifies nothing. It may support a narrative, but it does not fix the content in a way a third party cannot dispute.

What about the date in the PDF or file metadata?

Metadata (creation date, modification date, author) is written by the program that generates the file and can be edited with free tools without a trace. It proves nothing against someone who challenges it. A time stamp fixes the hash of the file's full bytes, metadata included, in an external record you do not control.

What does a time stamp NOT prove?

It does not prove who created the document (authorship), that its content is true (truthfulness), that the signer was entitled to sign it, or that the document did not exist before the stamp date. It proves existence and prior date: that those exact bytes already existed at that instant and have not changed since. Authorship and truthfulness are established by other means.

Which method should I choose?

It depends on what is at stake. If you need the legal presumption of date and time of Art. 41(2) or public faith, go to a qualified provider or a notary. If you need to fix many versions, at low cost, without the document leaving your computer and with a proof anyone can check twenty years from now, a blockchain time stamp is appropriate. Methods can be combined: you can time-stamp on blockchain today and notarise later if the matter requires it.

Fix the existence of your document today

The hash is computed in your browser; the document never leaves your device. You get a certificate anyone can verify without Proovik.

Certify a document Verify a proof

Product traceability? What EPCIS 2.0 is