◫ The concept
Create the proof now, so it can be proven later.
Anyone can run this check without us — the record is public, and verifying it needs nothing from Quantum Notary.
Today
You record the file
Your file
Hashed locally in browser. Not uploaded.
Its fingerprint
a3f9c21d…2a6df85b
Fingerprint written to a dated Base block
Public, readable by anyone, and not ours to edit or withdraw.
Later
You need to prove it
The file in question
Anyone can hash the file again using the same algorithm, SHA-256.
Same fingerprint
a3f9c21d…2a6df85b
The file has not changed since the date it was recorded.
Different fingerprint
f41b09ce…77d2e8a0
The file has been edited, tampered with, or is not the same file as the original.
One edit anywhere changes the fingerprint, which is what makes a change visible. Placing the original fingerprint on a blockchain proves the file existed in an exact state on that date — and has not changed since.
Learn More with Interactive Demos →See your file’s hash
Drop a file to hash
computed in your browser · we only ever see the digest
Digest · SHA-256
—
Visual fingerprint
Nothing hashed yet.
▤ With an account
Every record you've notarized, in one place.
- Search by filename or digest
- Track anchoring status
- View transaction and block references
- Download your proof
◆ Once made, proofs are independent of us
If we stop existing, your record does not.
We cannot edit it.
The record is a transaction in Base’s public history — a ledger we do not run and cannot write to twice.
We cannot delete it.
Not on request, not by mistake, not under a subpoena. No mechanism exists by which we could, and there is none we could build.
We cannot take it back.
Not if you cancel, not if you stop paying, not if you fall out with us entirely. It was never ours to withdraw.
We cannot stand in the way of a check.
Reading it back needs a Base explorer or an RPC provider, and neither of those is us. You do not need our page or our permission.
That is not a policy we chose. It is how the mechanism works. Your file's fingerprint went into Base's public transaction history, and nobody needs to come through us to read it there. Keep the exact original file. Where to look is on the receipt: block number, transaction hash, and which slot in that transaction holds your fingerprint. Any Base explorer will take it from there, and our database never comes into it.
▸ How it works
Drag it in. Click once.
We deal with the chain.
No wallet, no gas, no keys, nothing to install. The browser file flow computes a fingerprint from the exact bytes on your machine, sends only that, and hands back the references a checker needs.
Drag the file in
Or click to browse. The bytes are read on your machine and the file itself does not leave it.
Click Notarize
Use the public one-file page while the guest offer is available, or sign in and spend one account credit. Either way we pay the gas and sign the transaction.
The proof comes back
Transaction and block references, an explorer link, and a receipt to keep beside the file.
◈ Why anchor on a public chain
A chain record outside our database.
Hash-only privacy
The browser file flow hashes exact file bytes locally and sends the digest plus selected metadata. A public digest is not encryption or automatic anonymization.
Public-chain anchored
New records use a zero-value Base transaction whose calldata is a 32-byte-aligned array of raw digests, holding your own 32 digest bytes at a named slot. The service marks a record finalized after observing a successful Base L2 receipt; it does not monitor Ethereum L1 settlement.
Verifiable without us
A receipt includes Base transaction and block references. Direct verification can avoid our application, but it still depends on retained input, the processing rule, and suitable historical Base access.
▸ Step by step
How to prove a file existed on a date
Record a fingerprint of the exact file in a public Base transaction, and keep the file. Later, anyone holding that same file can recompute the fingerprint and read the transaction back from Base without going through us.
What you need
- The exact file, kept unchanged. The comparison is byte for byte, so a re-saved copy will not match.
- The public guest offer must be available, or you can use a signed-in account and one credit.
- A card for the guest Stripe checkout. An account is not required for the guest path.
- Somewhere private to keep the receipt link. You need the exact file and receipt together later.
The whole procedure, start to finish
◇ The limits, stated plainly
A matching digest and chain record support tamper-evident chronology evidence, and nothing wider than that. It dates the submission of a file — never the moment a shutter fired, never who created, owned, signed or supplied it, and never whether its contents are true. No identity is checked and nobody witnesses anything, so there is no legal presumption for it anywhere, and admissibility remains a question for the court and its rules. Your file stays on your computer, and a public digest is not encryption. A transaction carrying several digests discloses that those records were submitted around the same time. And the later check needs the exact bytes you kept, the processing rule, the receipt, and Base history through somebody.
Find the one nearest to yours
▸ Questions people ask
The questions that come up first.
How do I prove a file existed on a date?
Record a fingerprint of the file — its SHA-256 digest — in a public Base transaction, and keep the file itself. Anyone holding that same file can later recompute the fingerprint and read the transaction back from Base. If the two agree, that exact file existed no later than the transaction that carries it.
Do I need an account?
Not to check a file or use the one-file guest offer when it is available. The verify page is public — no sign-in, nothing to install — and the public notarize page can send one browser-computed digest to checkout without an account. An account opens the signed-in console once you have verified your email address.
How much does it cost?
Checking a file is free: no account, no card. The public notarize page shows the current server-authoritative price for one guest anchor when sales are available, without a hard-coded fallback. Signed-in customers use credits bought in packs; see /pricing for the current catalog.
Will a court accept this?
Treat it as evidence, not as a status. It carries no legal presumption in any country: no jurisdiction’s law says a Base transaction shifts a burden of proof. The US rules people ask about, Federal Rules of Evidence 902(13) and 902(14), turn on a written certification signed by someone qualified to give it — the receipt data is material such a certification could describe, and it does not replace the person who signs it. Whether a court accepts anything depends on that court, its rules, and a witness who can speak to how the record was made. What you get is a dated record the other side can check for themselves, which usually ends the argument before anyone instructs a lawyer.
Is this the same as a notary public?
No. A notary public checks the identity of a person in front of them and witnesses an act. Nobody’s identity is checked here and nothing is witnessed. The name is a metaphor: what you get is an independent, dated record that this exact file existed.
Does this prove I own the file, or that I made it?
No. A fingerprint carries no information about who. It shows this exact file existed by this date; who made it and who owns it are separate questions, answered by your raw files, your delivery emails and your contracts.
Does it show when the photo was taken?
No, and nothing here can. The record dates the submission of a file, never the moment the shutter fired. Capture time comes from the camera and its metadata, both of which are editable, and neither of which we see.
Do you see my file?
The file body stays on your computer — the browser hashes it locally and sends the digest. Guest filename, size, and content type are off by default and reach us only if you opt to include them. A digest is not encryption: if a file’s contents are predictable, someone can test a guess against the published digest and learn whether it matches.
What actually goes on the blockchain?
Thirty-two bytes: the raw SHA-256 digest of your file, at a named slot in the transaction’s input. Nothing else travels with it — not the filename, not the topic, not your name, not your account. One transaction can carry several digests, and that discloses exactly one thing: those records were submitted around the same time.
What if I lose the original file, or re-save it?
Then the check cannot be run. The comparison is byte for byte, so a re-exported PDF, a re-compressed image, or a copy a platform has processed produces a different fingerprint and will not match. That is the mechanism working rather than failing — but it does mean the file you keep has to be the exact one you recorded.
What happens if Quantum Notary disappears?
The transaction is in Base’s public history and we cannot alter or delete it. You can check a record without us: recompute the digest from the file you kept and read the transaction through any Base explorer or RPC provider. That still depends on things — the exact bytes, the processing rule, the receipt, and someone serving Base history — but none of them is our database.
Isn’t there a free way to do this?
Yes, and it is worth knowing about before you pay for anything. OpenTimestamps has anchored hashes on Bitcoin free for over a decade, and several certificate authorities run free timestamp services. It is a command line, and confirmation takes hours rather than minutes. What is being sold here is the layer above the anchor: a page a third party uses with no account and nothing to install, a portable receipt, a proof PDF, and a public verifier.
Is this a qualified electronic timestamp under eIDAS?
No. An EU qualified electronic timestamp carries a presumption about the accuracy of its date and the integrity of the data, and it is issued by a qualified trust service provider on a supervised list. We are not on that list and do not issue qualified timestamps; they cost a few cents. If you need the EU presumption, buy one — what we sell is the part that is not in the box with it.