BlockchainSign is a blockchain timestamping service for people holding documents they cannot hand over.

Conventional options all require custody: a copyright office wants a deposit copy, a notary wants to see the paper, an e-signature platform wants the file on its servers. BlockchainSign never receives the file at all. The document is hashed with SHA-256 in the user's own browser using the Web Crypto API, and only the resulting hash is written to the Ethereum blockchain.

The result is a certificate file recording the hash, the transaction and the timestamp. Because each certificate is its own Ethereum L1 transaction, with the payload hash readable as UTF-8 on a public block explorer, verification does not run through the vendor's portal: if BlockchainSign shut down, existing certificates would still verify.

There is no subscription and no cryptocurrency wallet involved. Certificates are bought as credits with a card and spent when needed. Credits are valid for 12 months; an issued certificate never expires.

Key points

• The file is never uploaded — only its SHA-256 hash is transmitted
• Recorded on Ethereum L1, one transaction per certificate
• Verifiable on a public block explorer, independently of us
• No subscription, no renewal, no wallet, no crypto knowledge needed
• A free SHA-256 file hash generator is available with no account
• Available in English, French, German, Spanish and Portuguese

What it does not do. A timestamp proves that a file existed in that exact form at that time — existence and integrity. It does not prove authorship or ownership, and it is not a substitute for copyright registration. There is no API or integrations yet, and no eIDAS qualified timestamp.