Why your signature stays valid for decades

There is an awkward fact underneath every electronic signature: the certificate that made it expires. Usually within a year or two. A twenty-year lease signed today outlives its own signing certificate many times over.

If nothing is done about that, opening the file in 2032 gives you "signature validity unknown", not because anything is wrong, but because the evidence needed to check it has aged out. Handling this properly is what separates a real signature platform from a tool that draws a picture of a signature on a page.

The problem, concretely

To verify a signature, a reader has to answer three questions: whose certificate made this, was that certificate valid at the time, and has the file changed since. Ordinarily it answers the middle one by asking the certificate authority, which works right up until the certificate expires, the authority retires the check, or both.

So the answer has to be captured at signing time and carried inside the file, rather than looked up later.

What swipesign puts in the file

Standard

PAdES B-LTA (ETSI EN 319 142)

Timestamp source

A qualified timestamping authority, currently A-Trust

Applied

After every signature, and once more when the last signer is done

Works in

Adobe Reader and any PAdES-aware reader

• The certificate chain: every certificate from the signer up to the root, so the reader never has to fetch one.
• Revocation evidence: proof, captured at the moment of signing, that the certificate had not been revoked. This is the part that stops working later if you do not save it.
• A qualified timestamp after every signature: independent proof from a trusted authority of exactly when each signature was made, so "was it valid then" has an answer that does not depend on today.
• An archive timestamp, laid over the finished document once everyone has signed. It seals everything above, including the earlier timestamps, and is what lifts the file to the highest archival level.

Why the last step happens at the end

Each signature gets its own qualified timestamp the moment it is made. The archive timestamp comes once more at the end, over the finished document. That last step is provider-agnostic: whether your signers used ID Austria, a Baltic Smart-ID, or a mix of half a dozen different services, the finished document ends up sealed the same way.

What this means in practice

Open a completed swipesign document in Adobe Reader in ten years, offline, with the signing certificate long expired, and it should still verify: because everything needed to check it is inside the file. See Check a signature in Adobe Reader.

Keeping the file is still your job

A signature engineered to last decades is no use if the document is gone. swipesign deletes completed documents after 14 days: download and archive your copy. See How long we keep your documents.