How-to · Premium

Open and verify your proof

You received an .ots file: your proof of existence engraved in the Bitcoin blockchain. Here is how to open it, verify it and keep it, entirely on your own, without depending on DfinA.

⚑ In one sentence

The .ots file is the mathematical proof that your document's fingerprint existed at a precise date, engraved in the Bitcoin blockchain. It can be verified anywhere, without us, for a long time to come.

What you received

A tiny file, a strong guarantee

The .ots proof (OpenTimestamps) is a tiny file that accompanies your document. It does not contain your file: only its 64-character digital fingerprint and the path that links that fingerprint to a block of the Bitcoin blockchain. It is this link that establishes the date.

▲ What matters: the content, not the name

You can copy the file as many times as you like and rename it freely: that changes nothing. Only the content must stay strictly identical. Verification recomputes the fingerprint from the content: if it is modified, even by a single byte (re-export, compression, conversion, editing), the fingerprint changes and the proof no longer matches. So keep your original file as is, next to the .ots, ideally in several copies.

The simple method

Verify in four steps

No software to install. Everything happens in your browser, and your file never leaves it.

Gather your two files

Your original file (identical to the one certified) and the .ots received by email.

Open the verifier

Go to opentimestamps.org, the “Stamp & Verify” section.

Drop the .ots, then the file

First drag the .ots file (to verify), then your original file. The fingerprint is recomputed in your browser.

Read the engraved date

The tool shows the block of the Bitcoin blockchain and the date (in UTC) when your fingerprint was recorded. That is your proof.

Which tool to use

Two ways to verify

The proof relies on an open standard: any OpenTimestamps tool works, not only ours.

The simplest: online

On opentimestamps.org, drop the .ots then your file. No account, no installation. The fingerprint is computed in your browser: your file is never uploaded. Recommended.

For the more technical: command line

Install the official client, then verify the proof next to your file:

pip install opentimestamps-client
ots verify my-file.ots

The command ots info my-file.ots shows the details (block, date).

◆ Also check integrity, on the DfinA side

On the Certify page, “Verify a proof” tab, you can confirm that your file matches your certificate's fingerprint. This is a complementary integrity check; the engraved date itself is verified via OpenTimestamps above.

Frequently asked

In case of doubt

Do I need to keep both the .ots and the original file?

Yes, both. The .ots alone is not enough: verification recomputes your original file's fingerprint and compares it to the one recorded in the proof. Without the exact file, the date cannot be confirmed.

The tool shows “pending”?

This should not happen to you: we only send the .ots once the block of the Bitcoin blockchain is confirmed. If you see this message, wait a few hours then try again; the confirmation always ends up appearing.

The fingerprint does not match?

That means the verified file's content is not exactly the one that was certified: it was modified, re-exported, recompressed or converted. Renaming or copying it, on the other hand, changes nothing. Use the intact original, as it was at the time of certification.

Do I need DfinA to verify?

No. The proof is self-contained: it rests on the Bitcoin blockchain and the open OpenTimestamps standard. As long as you keep your two files, it remains verifiable by anyone, in full independence.

Is it confidential?

Yes. The verifier computes the fingerprint locally: your file is not uploaded. And only an anonymous fingerprint was recorded in the blockchain, never the content nor the name of your document.

A question?

We are here to help you open or verify your proof. Write to support@dfina.org.

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