---
title: "Timestamps for agent receipts: plain, anchored, qualified"
url: https://knowyouragent.ch/en/knowledge/timestamps-and-trust-anchors
lang: en
updated: 2026-10-12
license: © Innopulse Consulting GmbH
---

# Timestamps for agent receipts: plain, anchored, qualified

A receipt without a point in time can be rewritten afterwards. A timestamp prevents that – but how well depends on whom you believe.

[Leutrim Miftaraj](https://knowyouragent.ch/en/about/leutrim-miftaraj), Founder, Innopulse Consulting GmbH
Published 12 October 2026

Key points

- An RFC 3161 timestamp fixes a hash in time.
- How much it proves is decided by the verifying party's trust anchor.
- A timestamp is only qualified according to an official trust list.

## Key points

- A [timestamp](https://knowyouragent.ch/en/knowledge/glossary/rfc-3161-timestamp) following RFC 3161 proves that data existed at a point in time.
- Only the hash is timestamped; the authority never sees the content.
- Only a [trust anchor](https://knowyouragent.ch/en/knowledge/glossary/trust-anchor) proves which authority a timestamp belongs to.
- Qualified timestamps carry a legal presumption; simple ones are suitable for tests.

## What a timestamp proves

An RFC 3161 timestamp is a timestamp authority's signed response to a hash. It confirms: this hash existed no later than this time. Anyone who changes the receipt afterwards gets a different hash, and the binding breaks. The content itself never leaves your own system; the authority only sees the hash.

## Three levels of evidential weight

| Level | What is proven | What remains open |
|---|---|---|

| Validly signed | The timestamp is genuine and unchanged | Who the authority is and whether to trust it |

| Traced to an anchor | The authority is one the verifying party trusts | The legal classification |

| Qualified | The authority is a recognized provider, with a legal presumption | – |

## Why the anchor decides

A timestamp usually brings its authority's certificate along. That certificate can never be its own proof, because anyone can create a certificate called “timestamp authority”. Only when the path leads to a [trust anchor](https://knowyouragent.ch/en/knowledge/glossary/trust-anchor) that the verifying party explicitly recognizes is the timestamp proven. That is why level A4 requires an anchor provided by the verifying party itself.

## Qualified timestamps

In the EU, the eIDAS Regulation governs qualified electronic timestamps. They enjoy the presumption that date and time are accurate and the data has not changed since. In Switzerland, the Federal Act on Electronic Signatures (ZertES) provides for qualified timestamps from recognized certification service providers. Whether an authority is qualified can only be determined through the official trust lists.

KYA does not load a trust list in this version and therefore reports the qualification status as “not checked”, even at level A4. A [verifier](https://knowyouragent.ch/en/knowledge/glossary/verifier) claiming “qualified” without a trust list would be overclaiming.

## What operators should do

- Stamp the manifest or the chain head rather than every single receipt when volumes are large.
- Compute the entry hash without the timestamp field, otherwise every correctly stamped receipt breaks its own binding.
- Publish the timestamp authority's anchor so auditors can adopt it.
- Choose a qualified provider for cases with legal effect.

[Mandact](https://mandact.com/en/protocol?utm_source=knowyouragent.ch&utm_medium=referral&utm_campaign=knowledge-timestamps) applies timestamps according to these rules.

## Timestamps in practice

A timestamp following [RFC 3161](https://knowyouragent.ch/en/knowledge/glossary/rfc-3161-timestamp) takes only a few steps: a hash is computed from the data, sent to a timestamp authority and returned signed. The authority never sees the content. For receipt chains, it is enough to timestamp the chain's current hash regularly; this also secures all earlier entries.

How this works in concrete terms with OpenSSL and the freely accessible FreeTSA service is shown in the [guide to verifying timestamps](https://knowyouragent.ch/en/knowledge/guides/verify-timestamp).

## Qualified and simple timestamps

Technically, timestamps hardly differ. The difference lies in the provider's recognition. A [qualified timestamp](https://knowyouragent.ch/en/knowledge/glossary/qualified-timestamp) comes from a recognized trust service, in the EU under the eIDAS Regulation and in Switzerland under the Federal Act on Electronic Signatures. For it, the law presumes the accuracy of time and integrity.

For internal purposes and tests, simple timestamps often suffice. For high-value disputes, a qualified provider is advisable. KYA verifies both kinds the same way; which provider is trustworthy is decided by the verifying party through the anchor it provides.

## Maintaining anchors

Trust anchors are not a one-time setting. Certificates expire, providers change keys, and occasionally an anchor is replaced. Verifying parties should document their anchors, review them regularly and keep old anchors only as long as older evidence must be verified.

KYA loads no anchors itself. This is deliberate: the decision whom to trust stays with the verifying party and is traceable in the certificate.

## Avoiding typical mistakes

In practice, the same mistakes keep occurring. Timestamps are created over content instead of a stable hash and can no longer be matched later. The timestamp authority's root certificate is not kept, so a verification fails years later. Or only the server time is logged, which cannot be proven independently in a dispute. Whoever keeps hash, timestamp and anchor together and verifies them regularly avoids all three mistakes.

## Frequently asked questions

### Why does a timestamp need a trust anchor?

Because the signature alone only shows that timestamp and key match. Who owns the key is proven only by the path to an anchor the verifying party trusts.

### How often should a receipt chain be timestamped?

That depends on the risk. For payments, a timestamp per transaction or per hour is common; the shorter the interval, the more precisely a point in time can be proven.

### Is a qualified timestamp more expensive?

Usually yes, because the provider must meet legal requirements. For internal purposes, simple timestamps often suffice; for disputes, a qualified provider is worthwhile.

### What happens when an anchor expires?

New timestamps must be verified against the new anchor. Older evidence remains verifiable as long as the old anchor is documented and available.

### Can I verify a timestamp without internet access?

Yes. KYA verifies locally as soon as the timestamp and the anchor are available. A connection to the timestamp authority is not needed for verification.

### Can I create my own timestamps?

Technically yes, but a timestamp from one's own system proves little toward third parties. The value of a timestamp lies in the independence of the authority that issues it.

## Sources

- RFC 3161, Time-Stamp Protocol: [https://www.rfc-editor.org/rfc/rfc3161](https://www.rfc-editor.org/rfc/rfc3161)

---
Quelle: https://knowyouragent.ch/en/knowledge/timestamps-and-trust-anchors · KYA – Know Your Agent