Implementing Qualified Timestamps and Long-Term Signature Validation

Why a signature without a timestamp has an expiry date

A certificate-backed signature depends on evidence that the certificate and signature were valid at the relevant time. Qualified timestamps and preserved revocation information can strengthen that historical proof. Long-term validation requires an operating process for collecting, validating, retaining, and, where needed, augmenting the evidence; it should not be described as automatically indefinite.

RFC 3161

Standard for trusted timestamps

TSA

Time Stamping Authority

Level T / LT / LTA

PAdES/XAdES LTV levels

Defined by the archival and evidence-maintenance policy

Validation period with LTV

Signatures with and without trusted timestamps

	Without timestamp	With qualified timestamp
Validation period	Only during certificate validity	Indefinite — verifiable after expiry
Proof of timing	Server log (weak evidence)	TSA cryptographically sealed timestamp
Court admissibility	Diminishes after certificate expiry	Maintained indefinitely
Best for	Short-term transactions	Contracts, compliance records, archival

How a trusted timestamp works

A TSA timestamp is not just a date string — it is a cryptographic proof that specific signed data existed at a specific time.

After the signer applies their digital signature, the signing platform computes a cryptographic hash of the signed data (document + signature).

The hash is sent to a Time Stamping Authority. The TSA does not see the document — only the hash. This preserves document confidentiality.

The TSA creates a timestamp token (RFC 3161 format) that binds the hash to the TSA's clock. The token is signed by the TSA's qualified certificate.

The timestamp token is embedded in the signed document (e.g. as a PAdES Level T signature). Future validators can verify that the signature existed at the TSA's timestamped time.

Qualified timestamp vs advanced timestamp

Advanced electronic timestamp

An advanced timestamp binds the data to a time in a way that prevents undetected alteration. It does not require a qualified TSA certificate. Acceptable as evidence but does not carry the eIDAS legal presumption.

Qualified electronic timestamp

A qualified timestamp is issued by a qualified TSA (QTSP-accredited) using a qualified certificate. Under eIDAS Article 41, a qualified electronic timestamp enjoys the presumption of the accuracy of the date and time it indicates, and the integrity of the data to which the date and time are bound.

Why qualified matters for legal evidence

For contracts that may need enforcement in EU courts years after signing, a qualified timestamp ensures the timing evidence holds up. Non-qualified timestamps are admissible but may be challenged on the accuracy of timing.

Implementing LTV in your signing workflow

To ensure signatures remain verifiable for the full retention period, configure your signing platform with these settings.

Enable TSA timestamping

Configure the signing platform to request a timestamp from a qualified TSA for every signed document. Most platforms support TSA configuration out of the box.

Set PAdES/XAdES level to LT or LTA

Level LT embeds validation material (certificates, CRLs, OCSP responses) in the document. Level LTA adds periodic archival timestamps for ultra-long-term records.

Configure revocation checking

Ensure the platform fetches and embeds CRL or OCSP responses at signing time. This proves the certificate was not revoked when the signature was applied.

Test long-term validation

Use a validation tool (e.g. DSS Demo WebApp, Adobe Reader signature validation) to verify the signed document passes LTV checks. The validation report should confirm the timestamp and embedded validation material.

Set retention policy

Define how long signed documents must be retained. For regulated industries, this may be 7-10 years or longer. Ensure storage can accommodate signed documents with embedded LTV material.

How eSign.AI implements trusted timestamps and LTV

eSign.AI can be configured to request RFC 3161 timestamps and preserve LTV material for supported signature profiles. The implementation must specify the TSA, qualification status, revocation checking, retention period, and archival testing.

Timestamp from accredited TSA

For workflows configured with timestamping, eSign.AI records the timestamp token returned by the selected TSA. Verify the provider's status, certificate chain, time source, service availability, and validation behaviour before treating it as qualified evidence.

PAdES B-LT by default

Supported PDF workflows can be configured for an appropriate PAdES baseline profile, including LT material where required. Confirm the actual profile in a sample signed file and test offline or future-date validation before production rollout.

Frequently asked questions

Without a trusted timestamp, the signature may become unverifiable after certificate expiry — a validator cannot confirm the signature was created during the certificate's validity window. With a qualified timestamp, the validator can confirm the signature predated expiry, so it remains valid indefinitely.

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