---
title: "KYA assurance levels A0 to A4 explained"
url: https://knowyouragent.ch/en/method/levels
lang: en
updated: 2026-10-12
license: CC BY 4.0
---

# Assurance levels A0 to A4

A readable language of trust for what is technically proven. Not a legal classification, but a summary of the checks.

In short

Five cumulative levels from A0 (unverified) to A4 (time-anchored). Disproven evidence always sits at A0.

- A0

KYA-A0**Unverified**Format recognized, nothing proven

- A1

KYA-A1**Integrity Verified**Signatures and hashes match

- A2

KYA-A2**Authority Verified**Mandate valid, action in scope

- A3

KYA-A3**Provenance Verified**Not revoked, delegation unbroken

- A4

KYA-A4**Time-Anchored Evidence**Point in time independently fixed

## The rules

| Level | Label | Minimum requirement |
|---|---|---|
| KYA-A0 | UnverifiedUnverified | Only readable or syntactically recognized. |
| KYA-A1 | Integrity VerifiedIntegrity Verified | Format and cryptographic integrity proven. |
| KYA-A2 | Authority VerifiedAuthority Verified | A1, plus issuer, agent and principal, and validity proven; scope neither disproven nor unknown. |
| KYA-A3 | Provenance VerifiedProvenance Verified | A2, plus revocation proven; delegation proven or absent. |
| KYA-A4 | Time-Anchored EvidenceTime-Anchored Evidence | A3, plus timestamp proven and traced to an anchor of the verifying party. |

The levels are cumulative. Reaching A3 means A1 and A2 are already proven.

## Disproven evidence always sits at A0

If a single check is disproven, the verdict is “invalid” and the level is A0 – even if other checks are proven. A high level next to a disproven check would be skimmed and misread.

## A blanket authority does not get past A1

A mandate without scope is a [blanket authority](https://knowyouragent.ch/en/knowledge/glossary/blanket-authority). Whether an action falls within it cannot be checked, so the scope is “unknown”. Since policy 1.0 this blocks level A2: an unlimited authority is not a verified authority.

## What A4 means and what it doesn't

A4 means: all checks up to A3 are proven, and an [RFC 3161 timestamp](https://knowyouragent.ch/en/knowledge/glossary/rfc-3161-timestamp) is valid, bound to the content and traceable to a [trust anchor](https://knowyouragent.ch/en/knowledge/glossary/trust-anchor) provided by the [verifying party](https://knowyouragent.ch/en/knowledge/glossary/verifying-party).

A4 does not mean the timestamp is qualified within the meaning of ZertES or eIDAS. That requires a trust list, which this version does not load. The report therefore states the qualification status as “not checked”. [More on timestamps and anchors](https://knowyouragent.ch/en/knowledge/timestamps-and-trust-anchors)

## Unproven delegation

For A3 the [delegation chain](https://knowyouragent.ch/en/knowledge/glossary/delegation-chain) may be absent – then the [principal](https://knowyouragent.ch/en/knowledge/glossary/principal) mandated directly. If a chain is present but cannot be proven, that is not enough: an unprovable chain is not a proven chain.

## Versioning of the levels

Every level has a public rule, test vectors and a policy version. A report keeps the version under which it was produced. If a rule is tightened, a new version is created, not a retroactive re-evaluation.

---
Quelle: https://knowyouragent.ch/en/method/levels · KYA – Know Your Agent