Stamp a file
Put a file's fingerprint on the public record.
Pick a file. Your browser computes its SHA-256 fingerprint right here. The file itself never leaves your machine: only the fingerprint and the file size are sent. Stamping records that fingerprint, with a time, in a public repository anyone can read.
3 free stamps a day from each internet address. Checking whether a file is already stamped is free and does not use a stamp.
What it costs
Three stamps a day are free.
Free: the first 3 stamps each day (UTC) from each internet address. Stamping a file that is already stamped is free and does not use one, and so is checking a stamp.
After that: each stamp costs 0.25 credit from the prepaid balance on a witness key. The page asks for a key only once the free stamps are used up, and it shows the price the service sends back.
The current terms are on the pricing page and in offers.json.
1. Pick a file
File: ()
SHA-256 fingerprint, computed in your browser:
2. Result
Top up this key: . Each link adds pins to the key you already have. No new key is made.
No key yet? Get one.
- Fingerprint
- Size
- Stamped at
- What it proves
- What it does not prove
- The witness
Check it yourself
How to test what this page says.
The fingerprint. Work it out on your own machine and compare it with the one this page shows. Windows: certutil -hashfile yourfile SHA256. Mac: shasum -a 256 yourfile. Linux: sha256sum yourfile.
What leaves your computer. Open your browser's developer tools, choose the Network tab, pick a file and press Stamp it. The page sends one request, to witness.arcaeon.io/api/stamp, and its body holds only sha256 and size. Check without stamping sends only the fingerprint, in the address.
The record. Ask the service directly, with no page in between: curl "https://witness.arcaeon.io/api/stamp?sha256=FINGERPRINT". A stamped file returns its record. Your internet address is not in it.
The date. Each stamp links to its commit history: the public history that holds the record. The commit date is our clock.
The first stamp wins. Stamp the same file again. You get the original date back, and nothing new is written.
The price. Stamp four new files in one day from one connection. The fourth asks for a witness key and names the price.
What a stamp means
It proves when. It does not prove who, or whether it is true.
A stamp proves that a file in this exact form existed no later than the stamp time. Change one byte and the fingerprint changes, so the stamp no longer matches.
It does not prove who made the file. It does not prove that anything the file says is true. It does not prove the file is older than the stamp by any amount.
The fingerprint is public. It does not reveal the file's contents, but a very short or easy to guess file could be guessed from it. The first stamp of a fingerprint wins: stamping the same file again returns the original record and its original time.
Where the record lives: one public repository, written by one operator and hosted by one code host. That is an outside party, but it is not an independent one. If the repository is deleted, or its history is rewritten, the record goes with it. The record is public, so anyone can save or mirror a copy, and a copy you hold yourself is the strongest form of this.
The exact wording of what each stamp proves comes from the stamp service in every response and is shown above as it arrives. See also what Arcaeon proves, and what it does not. New to this? How to prove a file is yours walks through every option, including the ones that are not us.