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.
- KYA-A0Unverified
A0Format recognized, nothing proven
- KYA-A1Integrity Verified
A1Signatures and hashes match
- KYA-A2Authority Verified
A2Mandate valid, action in scope
- KYA-A3Provenance Verified
A3Not revoked, delegation unbroken
- KYA-A4Time-Anchored Evidence
A4Point in time independently fixed
The rules
| Level | Label | Minimum requirement |
|---|---|---|
KYA-A0 | Unverified Unverified | Only readable or syntactically recognized. |
KYA-A1 | Integrity Verified Integrity Verified | Format and cryptographic integrity proven. |
KYA-A2 | Authority Verified Authority Verified | A1, plus issuer, agent and principal, and validity proven; scope neither disproven nor unknown. |
KYA-A3 | Provenance Verified Provenance Verified | A2, plus revocation proven; delegation proven or absent. |
KYA-A4 | Time-Anchored Evidence Time-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. 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 is valid, bound to the content and traceable to a trust anchor provided by the 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
Unproven delegation
For A3 the delegation chain may be absent – then the 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.