RFC 3161 · Time-Stamp Protocol (TSP)
The protocol that proves WHEN a signature happened.
What it is
An IETF standard for requesting and validating cryptographic timestamps from a Time Stamping Authority (TSA). The TSA receives a hash, signs the hash + the current time, and returns a TimeStampToken. The token is proof that a specific document existed at a specific moment in time — without revealing the document itself.
Scope
Built into every credible long-term signature format (PAdES-T, XAdES-T, CAdES-T). eIDAS implementing acts mandate RFC 3161 timestamps for qualified signatures.
What letssign.now does
Every PAdES envelope we produce is countersigned by an independent third-party RFC 3161 TSA. The timestamp authority is qualified under eIDAS — its signature on the time is itself legally binding evidence of when the document was sealed.
Deeper detail
Why a third partyExpandClose
The signer can't be trusted to timestamp their own signature — that would be circular. The TSA is a neutral third party, qualified under eIDAS, whose business is signing the current time. Its own clock is GPS-synced and audited.
Long-term validityExpandClose
Even if our signing certificate expires or our company disappears, the TSA's timestamp is independent evidence that the signature existed at a specific moment. That's the foundation for PAdES-LT and PAdES-LTA archival profiles.
Related standards
The frameworks above interlock. Each linked page covers one in full.
Drop a PDF. See it verified.
Free, no signup. We identify the standard, the issuing authority, and the legal tier in under a second.