About BlockchainSign
A small, deliberately narrow service: we prove a file existed at a point in time, without ever receiving the file. This page covers how that works, who runs it, and what we will not claim.
What we do
BlockchainSign records a permanent, independently verifiable proof that a specific file existed at a specific time and has not changed since.
You choose a file. Your browser computes its SHA-256 hash. We write that hash into its own transaction on the Ethereum mainnet and send you a certificate naming the hash, the transaction, and a public link anyone can open.
That is the whole product. It is deliberately narrow.
Why it works this way
Most ways of proving a document existed require giving the document to someone. A copyright office wants a deposit copy. A notary wants to see the paper. An e-signature platform wants the file on its servers. A national deposit service archives the content.
For a great many documents that is fine. For a pre-patent design, an unannounced brand, a client deliverable under NDA or a confidential financial document, handing over the file is the problem the proof was supposed to solve.
So the file never leaves your machine. The hash is computed in your browser with the Web Crypto API and only the hash is transmitted — there is no endpoint that accepts the file, because nothing would use it. Our free SHA-256 hash generator runs the same code with nothing sent anywhere, so you can watch it happen in your browser's network tab rather than take our word for it.
Why a dedicated transaction
Each certificate gets its own Ethereum transaction, with the payload hash written into the input data as readable text. Open the transaction on Etherscan, choose "View as UTF-8", and it is there.
This is more expensive than the alternative. Services that batch many hashes into one transaction through a Merkle tree can charge cents or nothing, and their designs are sound — OpenTimestamps is genuinely good software. The trade is that with aggregation the proof lives in a separate file you must keep and sometimes upgrade, and explaining it to a non-technical person is your problem.
We took the more expensive option because the person who eventually has to be convinced by your evidence is usually not a cryptographer.
What a certificate is worth
A blockchain timestamp is evidence of one narrow fact, and courts in several jurisdictions have accepted it as such — see is a blockchain timestamp valid in court for what has actually been decided.
It is not a registration, not a right, and not proof that you created the work. That last distinction matters enough that we wrote a whole page about it: proof of existence vs proof of authorship.
How it is priced
Certificates are bought outright, not subscribed to: 1 for $9.99, down to $2.99 each in the 100-pack. There is no monthly fee and nothing to cancel. Unused credits stay spendable for 12 months from purchase; a certificate, once created, does not expire at all.
Every competitor worth comparing against is a monthly subscription. That is better value if you timestamp constantly and worse value if you do it four times a year.
About this content
The guides, comparisons and articles on this site are researched and written in-house. Comparison pages quote other companies' public prices and features and carry the date they were last verified, because those facts go stale and become wrong rather than merely old. Where we cite a court decision or a regulation, we name it — the date, the court, the article number — so you can check it rather than trust us.
Nothing here is legal advice. If a decision matters, take advice from someone who knows your jurisdiction and your facts.
Corrections are genuinely welcome: [email protected].