Trusted timestamping is a way to prove that a specific piece of data existed at a specific point in time — and hasn't changed since. It's used for contracts, legal documents, software releases, research, and creative work.
The core idea: hashing
You don't timestamp the whole file. Instead you create a hash — a short, unique fingerprint of the file using an algorithm like SHA-256. Change a single character and the hash changes completely. So if you can prove a particular hash existed at a time, you've proven the exact file existed then, without revealing the file itself.
The classic model: a Time Stamping Authority
Traditional trusted timestamping uses a Time Stamping Authority (TSA) — a trusted third party that signs your hash with the current time. It works, but you're trusting that one authority: its clock, its keys, and its continued existence. If the TSA is compromised or shuts down, the value of its timestamps weakens.
The blockchain model
Blockchain timestamping replaces the single authority with a public, decentralized ledger. You record your hash in a blockchain transaction, and the network's own timestamp becomes your proof. The advantages:
- No single point of trust — the record lives on a distributed network.
- Immutable — once recorded, it can't be altered or back-dated.
- Publicly verifiable forever — anyone can check it on a block explorer, independent of any company.
Why it matters
A timestamp answers two questions at once: did this exact data exist by this date? and has it been changed since? That's exactly what you need to prove authorship, establish a date for intellectual property, show a contract predates a dispute, or demonstrate a file is unmodified.
BlockchainSign uses the Ethereum blockchain and SHA-256: it hashes your file in your browser, records the fingerprint on-chain, and gives you a lifetime certificate you can verify yourself on Etherscan.