Timestamp vs digital signature: what each one proves and why you need both
Most people treat a timestamp and a digital signature as interchangeable proofs. They are not. One answers when something existed in a fixed form. The other answers who stood behind it. The confusion matters because a document can carry an impeccable signature and still collapse as evidence years later, simply because nobody could prove the moment it was signed. Understanding timestamp vs digital signature is less about choosing one over the other and more about seeing why a defensible record almost always needs both working together.
The short version: a timestamp anchors data to a precise instant and proves it has not changed since; a digital signature ties that data to a specific signer's identity. Strip either away and you are left with a partial truth. Combine them, and you get evidence that stays enforceable long after certificates expire and software versions are forgotten.
This insight is part of our guide: how qualified electronic timestamps work and their legal value
What a timestamp proves: the "when"
A timestamp proves that a specific set of data existed in a specific form at a specific moment, regardless of who created it. It says nothing about identity. It says everything about time and integrity.
Technically, the process follows RFC 3161, the IETF standard "Internet X.509 Public Key Infrastructure Time-Stamp Protocol". A hash of the original data is generated, sent to a Time Stamping Authority (TSA), and the TSA returns a signed timestamp token binding that hash to a date and time. Because only the hash travels, the content itself never leaves the sender, and any later change to the data breaks the match with the token.
Under eIDAS, a qualified electronic timestamp issued by a qualified trust service provider (QTSP) carries real legal weight. Article 41 grants it a presumption of accuracy: the date, the time, and the integrity of the linked data are assumed correct unless proven otherwise. The practical effect is a reversed burden of proof. In a dispute, the other party has to demonstrate the time is wrong, rather than the holder having to prove it is right. Article 42 sets the bar a qualified timestamp must clear, requiring that the link between data and time makes undetected modification reasonably impossible. And under Article 41(3), a qualified timestamp issued in one EU member state is recognised as qualified across all the others.
What a timestamp does not give you is identity. It can prove a contract existed at 14:32 on a given day in exactly the form you hold. It cannot, on its own, tell you who agreed to it.
What a digital signature proves: the "who"
A digital signature does the opposite job. It binds a document to the identity of the person who signed it and confirms that the signed content has not been altered since. This is the proof of authorship, the who that a timestamp leaves blank.
Under eIDAS, an electronic signature relies on a certificate that links a cryptographic key to a verified individual. When the signer applies the signature, the document is sealed against tampering and tied to that person. For matters of personal commitment, signing a contract, approving a deliverable, accepting terms, this is precisely the assurance you want.
There is a catch that surprises many teams. A signature is only as durable as the certificate behind it. Certificates expire. They can be revoked. Once that happens, a verifier looking at the document later may no longer be able to confirm the certificate was valid at signing time. The signature did not change, but the ability to trust it quietly erodes. A document signed in good faith can become unverifiable a few years on, not because anyone tampered with it, but because the validation material aged out.
This is the structural weakness that a timestamp resolves. Apply a qualified timestamp before the certificate expires, and you lock in proof that the signature existed while the certificate was still valid. The "who" gets a permanent anchor in the "when".
Why you need both: long-term validation and the role of TrueScreen
Long-term validation (LTV) is the mechanism that keeps signed evidence enforceable over time, and it works precisely because it fuses a signature with timestamps. The principle: a qualified timestamp applied before certificate expiry preserves the signature's validity well beyond the certificate's own lifespan, in many cases for twenty years or more.
The ETSI PAdES standard formalises this in a ladder of levels, defined in ETSI EN 319 142-1 for PDF signatures:
- B-B: a baseline signature, valid only while its certificate is valid.
- B-T: adds a timestamp token proving the document existed at a given moment.
- B-LT: embeds all the material needed to validate the signature, including certificates and revocation data, so the document can be checked from its own contents.
- B-LTA: adds archival timestamps that protect long-term integrity and availability, the level closest to the older "LTV" profile, aligned with eIDAS for long-term archival.
The comparison below sets out the two proofs side by side.
| Aspect | Timestamp | Digital signature |
|---|---|---|
| What it proves | When data existed and that it is unchanged since | Who signed and that the signed content is intact |
| What it does NOT prove | The identity of the author | The exact moment of signing, on its own |
| Standard | RFC 3161, eIDAS art. 41-42 | eIDAS electronic signature framework, ETSI PAdES |
| When to use it | Anchoring integrity and time of any file, photo, video, email or web page | A person's signing of a document under their own identity |
This is where TrueScreen fits the picture. The platform captures digital content at the source and certifies it the moment it is acquired, rather than trying to reconstruct authenticity after the fact. At the point of certification it integrates, via API, the qualified electronic seal and qualified timestamp of a third-party QTSP. TrueScreen is not a trust service provider itself: the qualified timestamp and the qualified seal are issued by the QTSP it integrates, and TrueScreen binds them to content that was already secured at capture. The result is a record that pairs the "when" with a verifiable origin from the first instant, which is exactly what long-term validation depends on. For the broader legal background, our guide on qualified electronic timestamps and their legal value covers the eIDAS presumptions in more depth.
The takeaway is practical. If your evidence has to survive a dispute that surfaces years after the fact, neither proof alone carries the weight. The signature names the author; the timestamp fixes the moment and keeps the whole record verifiable once certificates have moved on.
