Bitcoin timestamp
Prove that a file existed, exactly as it is, by a certain date, or check a proof someone sent you. It uses OpenTimestamps, a free and open standard. The file is fingerprinted on your device and never uploaded.
Check a proof
Timestamp a file
How it works
Your browser computes the file's SHA-256 fingerprint. To create a proof, the fingerprint is mixed with a random number and hashed again, so what leaves your device reveals nothing about the file. Public OpenTimestamps calendars gather many of these into one Bitcoin transaction, usually within a few hours. The resulting .ots proof links your file's fingerprint to a Bitcoin block, whose date nobody can change.
Checking a proof needs only the proof, the file and the Bitcoin block. Our server fetches that block's
details from a public explorer and passes requests to the calendars, so those services never see your
address. Nothing is stored. Proofs made here work with any OpenTimestamps tool, including the official
ots verify.
What it proves, and what it doesn't
- It proves the file existed, unchanged, no later than the block's time.
- It doesn't prove who made the file, or that it didn't exist earlier.
- Keep the .ots file next to the original. Without the exact original file, the proof proves nothing.
We timestamp our own documents this way: 978 of them so far, with no failures. Only a fingerprint ever goes on the blockchain, never the document.
Want your company's records timestamped automatically?
Everything here is free to use and do yourself. If you'd rather have it designed and built for your company, in accounts you own, that is what makeprivacy.com does.