The trust model first: you do not have to trust kysigned. Your signature is your own email provider's cryptographic stamp on the message you send, and anyone can re-check it with math. We are not part of what proves your signature.
The whole thing in 53 seconds. Prefer to read? It is all below.
When someone sends you a document to sign, you will receive an email with the document attached. After you have read it, forward that email back to the address shown and type “I sign this document” as the first line. Press Send. That is it: no account, no password, no app to install.
Every email your provider sends carries an invisible digital stamp that proves the message really left your account. When you forward your “I sign this document” email, that stamp becomes your signature, and because only your email provider can produce it, no one else can fake a message in your name. This is why the trust lives with your provider and the math, never with us.
Once everyone has signed, we email every party a single PDF, and that PDF is your signing record: it holds the document, a signature page, and each signer's original stamped email. Your signing record is your permanent proof, and it lives in your own inbox. No account and no website are needed to keep it.
Anyone you show your signing record to can confirm it is genuine by dropping the PDF onto our verify page. The check runs entirely on their own computer, even with no internet, and even if kysigned no longer exists. For every signer it confirms three things: that the email really came from that person's email provider, that they signed this exact document with nothing changed, and when they signed.
The verify page is the easy way, made for anyone. For people who would rather check it themselves, the very same check is also an open-source command-line tool, and a second, independent tool that double-checks the first, so no one has to take our word for what “verified” means. The technical page walks through all of it.
And if you have the original file, our hash-check tool confirms it is exactly the document inside a signing record, also right in your browser.
Want to try both before you sign anything? Ready-made sample files, including a genuine signed record and tampered ones that must fail, ship in the open-source repository.
The proof lives only with the people involved: the signing records in your inboxes. It is yours to keep, and yours to show to whomever you choose.
We keep the PDF only long enough for everyone to receive their signing record. After that it is permanently deleted from our servers. The lasting copy is the signing record in your inbox, yours to keep.
For almost everyone, forwarding the email and typing the line just works, on Gmail, Apple Mail, or Outlook, on a computer or a phone. There is nothing to switch on and nothing to install.
If your signature did not go through, open the signing-request email in a different mainstream email app, or your email provider's website in a web browser, and forward it from there. That is the only fix you should ever need.
Questions? Contact the person who sent you the document. Want the cryptographic details? How it works (technical) →
