Dated evidence
- Document
- SHA-256
- Network
- Block
- Transaction
I Did It First · Dated evidence for research PDFs
Establish priority without publishing.
Create an independently verifiable record that your exact PDF existed at a given moment. Your PDF stays on your device unless you choose to save a copy: its fingerprint is computed in your browser, and Ethereum records it mixed with a secret, so it reveals nothing. You do not need a blockchain wallet.You need no account and no blockchain wallet.
Already timestamped? Check a PDF →Your PDF stays on your device: only its fingerprint is sent.Your PDF stays on your device unless you choose to save a copy here.
Records on this device
This browser remembers the records made or opened here, with their private links. It sends nothing to list them.
This browser keeps nothing between visits, so it forgets these records when this tab closes. Keep each record's private link yourself.
Your PDF stays on your device.
Your browser computes the PDF's fingerprint. The service mixes it with a random secret and records only the result on Ethereum, in a transaction it pays for. The PDF itself is never uploadeduploaded only if you choose to save a copy.
- Your deviceThe PDF and its fingerprintThe fingerprint (SHA-256) is computed here. The file is not uploaded.
- BAIF's serviceThe fingerprint and its secretKept with your account, so you can sign in on another device and download the evidence.Kept with the record, so its private link can download the evidence on any device. Never the PDF itself.A PDF copy only if you save one.
- EthereumOne transactionA result that reveals nothing about the PDF without the secret, dated by the block that contains it.
What a timestamp shows, and what it does not
- It shows that these exact PDF bytes existed by the recorded date.
- It does not show who wrote the work, whether the mathematics is correct, or that nobody had the idea earlier.
- Any change to the file, even re-saving it, makes a different PDF. Keep the original you recorded.
Timestamp a PDF
Fingerprint (SHA-256)
We will record a reference to this exact PDF. Selecting a file does not upload it or create a timestamp.
If you want your name or your coauthors' names to be part of the dated document, include them in the PDF before recording it.
- Evidence
- Private: only people with its private link, which you get next, can open the record.
- Your PDF
- Stays on this device. Keep this exact file.
Fingerprint (SHA-256)
Sign in
No account uses yet. Creating one keeps your records available across devices; it does not upload any document.
My papers
Papers
No papers yet. A paper groups the versions of one work and can be shared with collaborators.
Records
Dates match the recorded blockchain date, which only confirmed records have.
No records yet. Timestamp a PDF to start.
No records match these filters.
Your library export holds the evidence of every record you can open, with a list of which are confirmed. Saved PDFs are downloaded from each record.
Export my library
← Home
Request accepted: the website has saved your request.
Keep this exact PDF. We never received it, and an edited or re-saved copy will not match this record.
Your private link
Anyone with this link can manage this record: download its evidence, turn its public check on or off, and delete it. The site keeps only a one-way hash of it, so it cannot send you the link again. If you lose it, you lose control of the record, but never the evidence you already downloaded.
This browser cannot remember this record. Copy the private link and keep it before you leave this page: without it, nobody can manage the record.
A record backup is not a completed timestamp. Download the evidence again after confirmation: that download holds the completed record.
Fingerprint (SHA-256)
- Request accepted
- PDF copy
- Who can see it
Blockchain details
- Network
- Transaction
- Finality
- Blockchain check
Organize
Archive hides this record from your own list only. Other people's access and links stay as they are.
Public check
Publish
With the public check on, anyone with this exact PDF can find this record with Check a PDF, and anyone with its address can open it. They see its fingerprint, recorded date and blockchain transaction. No title, name or PDF is shown. This cannot be recalled: people may keep what they have seen.
Publishing shows the evidence to anyone at once. It cannot be recalled: people may keep what they have seen or downloaded. Publishing does not create a new timestamp, and a pending record is shown as pending.
What saving means:What saving these choices means:
PDF copy
Saving the PDF here lets these people download it, under the paper's existing permissions:
This is a sample: check it without a file.
This PDF
Recorded
Certificate
← My papers
Versions
No versions you can see yet. Open a record and use Organize to move it here.
Members
Invite someone
An invitation is not access: it works only for someone who signs in with the invited address and accepts.
Delete the paper
Deleting the paper deletes every version in it, including those other members added, with their links, shares and public access, public access and saved PDFs. To keep a version, take it out of the paper first.
Deleting this paper from the service:
Paper invitation
Accepting gives your account access to the paper, as the invitation email described. It works only when you are signed in with the address the invitation was sent to.
An invitation opens only for the email address it was sent to. If it went to another of your addresses, sign in with that one: this tab keeps the invitation until then.
Account
Ways to sign in
Any of these signs you in and recovers your account. Keep at least two.
ORCID
Signed-in devices
Close account
Closing deletes your personal records and the papers only you belong to, and ends every way to sign in. Records in other people's papers stay there. Export your library first: the service cannot recreate evidence after deletion.
Lost access to your account?
- Any way to sign in that you registered still works: a code sent to any of your verified email addresses, or any of your passkeys. Sign in.
- Having a PDF, a name, or downloaded evidence does not give control of an account. If every way to sign in is lost, we cannot safely restore the account.
- Evidence that was made publicly checkablewas published, or that you downloaded, can still be checked without the account.
- To avoid this, add a backup email or a passkey under Account.
Check a PDF
Find out whether a PDF matches a timestamp: first among the records on this device, then among those their owners made publicly checkable.
For advanced use: a PDF's SHA-256 fingerprint, 64 hexadecimal characters. The result says whether a fingerprint matches; no PDF is examined.
Public PDF
Download the PDFTo find out whether a PDF matches a timestamp you can see, use Check a PDF.
Public records
Records their authors chose to publish and list. A record that is public but not listed can still be found by checking its exact PDF.
No listed records match.
Opening a shared record
How it works
A timestamp records your PDF's fingerprint, mixed with a secret, on Ethereum: a public ledger that no single party controls, including us.
From file to timestamp
- On your devicepaper.pdfNever uploadedNot uploaded unless you save a copy
- On your deviceSHA-256A one-way function
- Sent to BAIFFingerprint32 bytes
- BAIF's serviceCommitmentThe fingerprint mixed with a random secret
- Public ledgerEthereum blockOne transaction per record
1 · Fingerprint
SHA-256 turns any file into 64 hexadecimal characters. The same bytes always give the same fingerprint; any change gives a completely different one. It cannot be run backwards to recover the file. This happens in your browser.
2 · Record
The service mixes the fingerprint with a random secret and records only the result on Ethereum, in a transaction it pays for. The transaction is included in a block, normally within a block or two (a new one comes every 12 seconds), and its date is provisional; the block becomes final normally 13 to 19 minutes later. Only then is the timestamp confirmed.
3 · Check
The evidence links your fingerprint to that transaction. Anyone with your PDF and the evidence can check it independently against Ethereum, without asking us. On this site, you and the people you share it with can check it, and so can anyone with the PDF if you make it publicly checkable.On this site, anyone with its private link can check it, and so can anyone with the PDF if you turn on its public check.
Precisely what you can claim.
A timestamp establishes
- A file with exactly these bytes existed no later than the time of the Ethereum block.
- The date cannot be changed, not by you and not by BAIF.
- Anyone can check it, now or decades from now, using public data.
It does not establish
- Authorship. If you want your name or your coauthors' names to be part of the dated document, include them in the PDF before recording it.
- Originality or correctness of the ideas, or that the mathematics is right.
- That the file did not exist earlier, or that nobody had the idea earlier: only that this file existed by then.
Your file stays private.
Your PDF stays on your device unless you choose to save a copy: your browser computes its fingerprint, and only that fingerprint is sent to us. A fingerprint cannot be turned back into your document. But anyone who already holds an identical copy can confirm it matches, so treat the fingerprint like the title of an unpublished paper, not like a password.
- The file's contents
- Never uploaded.Not uploaded, unless you choose to save a PDF copy here; then it is kept privately for you and the people you share it with.
- The file name
- Stays in this browser.
- The fingerprint and its secret
- Kept with your record, so that you can sign in on another device and download the evidence.Kept with your record, so that its private link can download the evidence on any device. This is a convenience, not a promise that BAIF cannot see them: BAIF protects them with encryption and access rules that it operates, and could tell whether a PDF it is given matches one of your records. On Ethereum, only the fingerprint mixed with the secret.
- Checking a PDF here
- Sends its fingerprint to BAIF.Compares it with the records on this device first, in this browser, then sends its fingerprint to BAIF to look for publicly checkable records.
- The public check
- Off unless you turn it on for a record. Then anyone with the exact PDF can find the record and see its fingerprint, recorded date and blockchain transaction. No title or name is shown.
- When you delete a record
- Its secret, fingerprint, saved PDF and links are removed from the site. Its private link stops working, and this device forgets it. The Ethereum transaction stays, but without the secret it reveals nothing. Backups keep older copies for a limited time; if one is ever restored, deletions are applied again before the site reopens.
- Analytics and trackers
- None: the site has no analytics or advertising trackers.
Privacy
- What the service keeps
- For each record: its fingerprint, its secret (sealed with encryption), the times of the request and of the block, the Ethereum transaction, whether its public check is on, and a one-way hash of its private link's key, never the key itself.
- What it never receives
- The PDF, its file name, your name or an email address. Nobody signs in.
- Network addresses
- Used in memory to limit how many requests and new records come from one network, and never stored with a record. The service keeps no access log, but its web server's log can keep an address, for instance of a network it turns away for sending too many requests, until that log rotates.
- This device's list
- This browser lists the records made or opened here, with their private links and file names, for anyone who uses it: on a shared computer, forget them when you are done. Browsers may also clear the list themselves: Safari after 7 days without a visit to this site, and private windows when they close. Keep each private link somewhere else too.
Priority, before publication.
In 1676 Robert Hooke published the anagram ceiiinosssttuv. Two years later he revealed it: ut tensio, sic vis. Scientists have long needed to show they had a result before they were ready to share it. A cryptographic fingerprint is the modern anagram: it commits to the exact text without revealing any of it.
That need is growing. As AI systems begin to produce proofs and results at scale, a dated, tamper-evident record lets you show what you had, and when, while you keep refining it, checking it, or waiting for peer review.
Questions
Does re-saving or re-exporting the PDF matter?
Yes. A new export usually changes the bytes (embedded dates, fonts, metadata) even when the text looks identical. Keep the exact file you timestamped, ideally in two places.
What if I lose the PDF?
Your records stay in your account: sign in on any device to download the evidence again.Your record stays on the service: open it with its private link, on any device, to download the evidence again. Download it now and keep it with your PDF as well: it lets you check the timestamp without us. We never receive the PDF, so it cannot be recovered from anything we hold. Without the exact file, there is nothing to check.The PDF cannot be recovered from anything we hold unless you saved a copy here; without the exact file, there is nothing to check.
What if I lose the private link?
Records on this device keeps it in this browser, until you forget it there or the browser clears it. Without the link anywhere, nobody can manage the record any more, and the site cannot send it again: it keeps only a one-way hash of the key. The evidence you downloaded still works with your PDF, without us, and if the record's public check is on, anyone with the exact PDF can still find it with Check a PDF.
Could BAIF backdate or alter a timestamp?
No. The date comes from an Ethereum block, which no single party controls, and checking uses public data. BAIF does keep the secret that checking needs: if it lost or withheld it, a timestamp could no longer be checked from its record here. That is why the evidence you download holds it too; keep it with your PDF.
Why Ethereum?
It is a public ledger that many independent parties keep: a new block comes every 12 seconds and becomes final normally within 13 to 19 minutes, and anyone can check a transaction with public data, without us. Each record is one transaction, which BAIF pays for: you do not need a wallet.
Can I timestamp LaTeX sources, data or code?
Timestamp a PDF takes PDFs. You can timestamp a PDF that contains or describes the other material, and keep that exact PDF.
Ready when your draft is.
Timestamp a PDFConfirm it is you before this change.