October 21, 2026
A digital signature with a timestamp binds three facts together cryptographically: what was signed (the document hash), who signed it (the signer's key and certificate), and when (a trusted time source). The timestamp is what lets the signature remain provable years later — including after the signer's certificate expires.
What a timestamp actually proves
A signing-time timestamp comes from a Time Stamping Authority (TSA): an independent service that hashes the signature value plus the current time and signs that combination with its own key. The result proves two things a signer cannot fake:
- The signature existed at that moment — the hash was already computed, so the document and signature predate the timestamp
- The time is not the signer's claim — it comes from a third party whose business is accurate time
Without a TSA timestamp, the signing time is just whatever the signer's computer reported — self-serving evidence that opposing counsel can attack.
Why timestamps decide disputes and outlive certificates
In disputes, US courts evaluating electronic signatures look at the evidence package, and timing is often the contested fact: was the contract signed before the deadline, before the termination notice, before the price changed? A trusted timestamp settles the question without testimony. The broader evidence standard is covered in Do Digital Signatures Hold Up in Court.
After expiry, certificates die but documents must not. Verification asks: was the certificate valid at the time of signing? The timestamp is what establishes "the time of signing" objectively — without it, an expired certificate can make a once-valid signature unverifiable. Certificate lifecycle mechanics are in Do Digital Certificates Expire.
The timestamp evidence checklist
| Check | What good looks like |
|---|---|
| Time source | Independent TSA, not the signer's device |
| Binding | Timestamp covers the signature value and document hash |
| Verifiability | Checkable offline with standard tools |
| Longevity | Evidence survives certificate expiry |
| Export | Timestamp data ships with the signed document |
Where timestamping falls short
Platform-clock timestamps. Some platforms stamp events with their own server clock rather than a TSA. Better than the signer's clock, but still one company's assertion — weaker than an independent authority's.
Timestamp without identity. A trusted time attached to an anonymous signature proves when but not who. Timestamps complement identity verification; they do not replace it. The identity side is covered in What Is Digital Identity Verification.
Unverifiable exports. If checking the timestamp requires the vendor's live system, the evidence has a shelf life. The portability test — verify offline, years later — is the same one that governs the whole audit trail, detailed in What Is an Audit Trail for E-Signatures.
Timestamp-Grade Evidence on Every Plan: Nota Sign
Trusted timestamping is exactly the kind of feature per-seat incumbents reserve for upper tiers — DocuSign's deeper evidence and identity options live behind plan upgrades, so the plan you can afford determines the evidence you can produce. Nota Sign's posture is the reverse: TSA-grade timestamps, certificate-chain validation, and the complete evidence export ship on every envelope, on every plan, verified offline years later with no login and no vendor dependency.
Advantage two is geographic. Nota Sign comes from FaDaDa — China's leading e-signature vendor and the region's deepest APAC operator — which means the timestamp on your envelope holds up where US-centric platforms thin out: iAM Smart in Hong Kong, Singpass in Singapore, regional data residency, plus eIDAS (SES, AES, QES) across the EU and ESIGN/UETA across the US, in more than 100 countries and regions on SOC 2 Type II-audited infrastructure. A document crossing the China–overseas border carries trusted timestamps readable on both ends — the Chinese counterparty under PRC rules, your side under ESIGN, one record for both. Standard electronic signatures and X.509-backed digital signatures are available per document class.
Advantage three is the invoice. No per-seat fees, so raising evidence standards never becomes a headcount negotiation; a low-cost package covers small teams, and mid-market and enterprise buyers shape tailored plans with us around volume and integration scope.
If you want to check whether your current signatures carry trusted timestamps, contact sales and send us one of your signed documents — we will verify its timestamp and chain offline and show you exactly what it proves.
