A cryptographic seal, not just a picture of a signature
sign.yt does more than paste a drawn signature onto a page. Each signature is embedded in the PDF as a PAdES signature, so any later edit to the file is detectable.
One PAdES signature per signer
When a recipient finishes, sign.yt applies an incremental PAdES signature with a certificate issued for that signer by the platform certificate authority. Signatures are added one after another, so earlier ones stay valid.
New keys use ECDSA P-384 with SHA-384. When all parties have signed, a final platform seal closes the document.
Each signer has their own entry in the PDF signature panel, with their name and signing time, instead of one anonymous stamp for the whole document.
Trusted time and long-term validation
sign.yt can add an RFC 3161 timestamp from a timestamping authority to each signature. With a timestamp configured, the final seal is extended with validation data and a document timestamp (PAdES-B-LTA), so the signature can still be checked years from now.
Without a timestamping authority the signatures are produced at the baseline PAdES-B-B level. Either way, the signature covers every byte of the document as it looked at that moment.
Verifiable outside sign.yt
The signed file is a standard PDF. Adobe Acrobat Reader and other PDF readers with signature support list the signatures and flag any modification made after signing.
Anyone can also drop the PDF into the public sign.yt verifier, no account needed, to see who signed, when, and whether the bytes are intact.
The verifier checks whether the signature covers the whole file and whether the document carries the sign.yt platform seal. Where the EU DSS validator is enabled, it also shows an eIDAS verdict for each signature.
Every completed document gets a QR code and a short verify.sign.yt address on its certificate of completion. It opens a public page with masked signer names, signing dates, the final hash, the seal and the Bitcoin anchor status, and lets anyone check that their copy of the file is identical.
Evidence attached to the document
A certificate of completion is appended to the signed PDF. For every signer it lists the email, verification method, timestamps of sending, viewing and signing, IP address and user agent, plus the consent statement they ticked before signing. The evidence travels with the file, not only in our database.
The hash of the final PDF is also anchored in Bitcoin through OpenTimestamps, and the whole package can be downloaded as one evidence ZIP.
If a signature is ever questioned, you have everything in one file that you can hand to a lawyer, an auditor or a court.
Frequently asked questions
Is a sign.yt signature legally binding?
Under eIDAS an electronic signature cannot be denied legal effect just because it is electronic. Where the law requires written form, use a qualified electronic signature from a qualified trust service provider. Profil Zaufany and e-dowód signatures through Węzeł Podpisu are also available where enabled.
Will Adobe Reader show the signatures?
Yes. The signatures are standard PAdES and appear in the signature panel. Whether Adobe marks the signer identity as trusted depends on its own trust list.
What happens if someone edits the PDF after signing?
The edit falls outside the signed byte range, so PDF readers and the sign.yt verifier report the document as modified.
Do I need my own certificate?
No. sign.yt issues per-signer certificates automatically. Qualified signatures are available as a separate signing method.
More features
- Public verification
Each signed document carries a QR code and short link to a public check page. Masked names, signing dates, seal status and a file comparison.
- Profil Zaufany and qualified signatures
Let Polish signers use Profil Zaufany, e-dowód or mObywatel via Węzeł Podpisu, or sign with a qualified electronic signature from a trust service provider.
- Audit trail
Every action is logged in an append-only, hash-chained audit log. Signatures are chained per document and a certificate of completion is added to each PDF.