Prove that a file existed, down to the date.
A dispute, a project milestone, a record, an archive: when a moment must be fixed beyond ambiguity, inscribe the file’s SHA-256 fingerprint on the Bitcoin blockchain. Any third party can verify the proof themselves, without ever depending on btc3r.
What the proof shows — and what it does not
A proof is only valuable if its limits are precisely known. Here are ours, plainly.
Existence by a date at the latest
A file whose fingerprint appears in a block necessarily existed before that block was mined. The block’s date is a certain upper bound.
Integrity since that date
If the fingerprint of the file presented today matches the one in the block, the file has not changed by a single byte since the inscription.
Authorship of the content
The inscription does not say who created the file. It corroborates other elements: being the only one able to produce the original of an old fingerprint is a strong indication, not proof of authorship in itself.
Truthfulness of the content
Inscribing a document does not make its content true or lawful: the blockchain dates, it does not certify substance. It is for the judge or the parties to assess the content itself.
When fixing a moment becomes decisive
Disputes & pre-litigation
The state of a deliverable at handover, the exact content of an exchange, the version of a document at the time of the facts: build the evidence before the disagreement sets in.
Project milestones
End of phase, tender submission, software version freeze: each timestamped milestone becomes indisputable, for you and for your partners.
Archives & records
A backup of personal or professional archives, a capture of online content, an inventory: date the state of things at the moment you recorded it.
How anyone verifies your proof
The strength of proof of existence comes from this: verifying it requires no trust in btc3r. Here is what an expert, a lawyer or an opposing party will do.
Open the transaction
With the TXID from the certificate, they view the transaction on a public explorer such as mempool.space or blockstream.info.
Read the inscribed fingerprint
The transaction’s OP_RETURN output contains the SHA-256 fingerprint, as well as the date of the block that holds it.
Recompute the fingerprint
They compute the SHA-256 of the file you produce themselves, with the tool of their choice — the function is a public standard (NIST, FIPS 180-4).
Compare
If the two fingerprints are identical, the conclusion is inescapable: this exact file existed no later than the block’s date. Otherwise, the proof does not apply to this file.
The detailed procedure, with screenshots and tools, is described step by step on our Understand inscription page.
Proof of existence: what people ask us
What is the difference between proof of existence and proof of anteriority?
Both rely on the same mechanism: a dated fingerprint on the blockchain. Proof of existence answers the question “did this file exist on this date?”; proof of anteriority uses it in a priority relationship, to establish that a creation precedes another event (a filing, a publication, a dispute). Existence is the raw fact; anteriority, its comparative use.
How does a third party verify the proof without going through btc3r?
With the TXID shown on the certificate, they view the transaction on any public block explorer (mempool.space, blockstream.info…), read the fingerprint inscribed in the OP_RETURN output, recompute the SHA-256 of the file you present, and compare. If the two fingerprints match, the file existed no later than the block’s date. No trust in btc3r is needed.
Does the proof show that I am the author or owner of the file?
No. It shows that the file existed on a given date and that whoever produces the original holds it. Authorship or ownership are proven by other means, which the proof of existence corroborates — for instance if you are the only one able to produce the original matching an old fingerprint.
Is the block’s date accurate to the second?
The timestamp of a Bitcoin block is set by the miner within the limits tolerated by the protocol; it should be considered reliable at the scale of the hour, not the second. For a proof of existence, this precision is more than enough: the demonstration is about the day, rarely the minute.
What happens if btc3r disappears?
Nothing for your proof. The fingerprint is inscribed on the Bitcoin blockchain, replicated across thousands of independent nodes worldwide: it remains viewable via any public explorer, with only the TXID from your certificate. This is one of the founding principles of the service.
Other ways to use inscription
Proof of anteriority
Date a creation — manuscript, invention, code — before showing it to the world.
Learn more →Document timestamping
Contracts, minutes, reports: freeze the exact state of a professional document.
Learn more →Understand inscription
OP_RETURN, SHA-256, independent verification: the foundations explained simply.
Learn more →A fact, a date, a witness that nothing erases.
Build your proof of existence for 9.60 € : inscribed on Bitcoin, verifiable by anyone, independent of btc3r.