What is a blockchain timestamp?
A blockchain timestamp is the inscription of a document's hash in a transaction of a blockchain whose block header carries a timestamp covered by the proof of work. Because altering that timestamp would invalidate the work already spent, the date does not rest on anyone's word: anyone holding the proof file can verify it. In the European Union it is a non-qualified electronic time stamp (Arts. 3(33) and 41 of Regulation (EU) 910/2014).
How it works
The chain of custody of the date has four links. If one fails, the proof establishes nothing; if all four hold, the date is nobody's declaration but a physical quantity already spent.
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Hash
The document is digested with SHA-256 on the user's device. Only the 32-byte fingerprint travels; the content cannot be reconstructed from it.
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Transaction
The fingerprint is placed in a network transaction and broadcast to every node. From here on the issuer no longer controls it.
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Header with timestamp
A block accepts the transaction and commits to it (Merkle tree) in its header, which includes the block timestamp.
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Proof of work
Miners spend energy finding a hash of that header below the difficulty target. The timestamp is inside what was hashed: changing it means redoing the work, and the work of every later block.
The full specification of what is checked, with formulas and a real example, is in how to verify a PVK-PROOF/1 proof.
How it differs from a qualified stamp and from a notary
All three fix a date, but not in the same way nor with the same effects. A qualified stamp is issued by a provider on the EU trusted list and enjoys the presumption of Art. 41(2); a notary gives public faith and identifies the parties; a blockchain timestamp gives neither presumption nor identity, but it is the only one of the three anyone can check without trusting the issuer.
| Aspect | Blockchain timestamp (non-qualified) | Qualified time stamp (eIDAS) | Notary |
|---|---|---|---|
| Who fixes the date | The consensus of a public proof-of-work network | A qualified provider with a synchronised, audited clock | The notary, who attests the day and time |
| Legal presumption of date (Art. 41(2)) | No; admissible as evidence (Art. 41(1)) | Yes | Not an eIDAS stamp; public deed with public faith |
| Verification without the issuer | Yes: anyone, with the proof file and a copy of the chain | Depends on the certificate chain and the trusted lists | Depends on the notarial records |
| The document leaves the device | No: only the hash | No: normally only the hash | Yes: it is deposited or shown |
| Attests identity or authorship | No | No (that is what the electronic signature does) | Yes, it identifies the parties |
| Cost | Low or free | Per stamp or subscription | Fee per record |
OpenTimestamps, Proovik and a qualified TSA, compared
An honest comparison: each option suits a different case. OpenTimestamps is the free, open reference on Bitcoin; a qualified time-stamping authority (TSA) is the only one with a legal presumption; Proovik sits in between, with fast confirmation, a readable certificate and an API.
| Criterion | OpenTimestamps | Proovik | Qualified TSA (eIDAS) |
|---|---|---|---|
| Where it anchors | Bitcoin (proof of work) | Kaspa (proof of work, BlockDAG) | The provider's server; no blockchain |
| Cost to the user | Free (public calendars) | Free plan and paid plans | Fee per stamp or subscription |
| Time until the proof is complete | Hours: calendars aggregate many hashes into one transaction and its Bitcoin confirmation must be awaited | Seconds: the network confirms the transaction and the proof is completed by capturing the header | Seconds |
| Proof format | .ots file (binary) that is upgraded once the transaction confirms | PVK-PROOF/1 package (JSON) attached to a PDF certificate; public specification | RFC 3161 token signed by the provider |
| Independent verification | Yes, with the open-source client and access to Bitcoin headers | Yes, with the specification and a Kaspa header (included in the package); online tool on the verification page | By validating the token signature against the EU trusted list |
| Legal presumption (Art. 41(2)) | No (non-qualified) | No (non-qualified) | Yes |
| Reliance on the provider | None to verify; calendars only aggregate | None to verify; Proovik only issues | High: validity rests on the provider's certificate and its preservation |
| Human-readable certificate and API | No certificate; libraries and a command line | PDF certificate with QR to the explorer; REST API | Depends on the provider |
Times describe the usual behaviour of each network and provider, not a service commitment. Proovik's prices are on its pricing page; other services' prices, on theirs.
What it proves and what it does not
It proves that some bytes with a specific SHA-256 existed before the block timestamp and have not changed. It does not prove who created them, whether their content is true or that they did not exist earlier. It is a proof of existence and prior date, not of authorship or truthfulness. If you need to fix the date of a document and want to see the five possible methods, read how to prove that a document existed on a date.
What happens if Proovik disappears
Nothing that affects your proof. The transaction lives on the Kaspa network, the PDF certificate carries the PVK-PROOF/1 package with everything needed to recompute the chain, and the procedure is published on the verification page. Keep the PDF next to the original document: the two together are the proof, with or without Proovik.
Frequently asked questions
Is a blockchain timestamp legally valid?
How is it different from an electronic signature?
What is OpenTimestamps and how does it differ from Proovik?
Why Kaspa and not Bitcoin or Ethereum?
Is my document uploaded to the blockchain?
What happens if Proovik disappears?
Time-stamp a document on Kaspa
No account needed to start. The hash is computed in your browser and you receive a PDF certificate with the PVK-PROOF/1 proof. To integrate it into your systems, see the API.