# ASL/COMMON-WITNESS-ROTATION/1 -- Common Witness Rotation Artifact

Status: Draft
Owner: Architecture
Version: 0.1.0
SoT: No
Last Updated: 2025-01-17
Tags: [common, witness, rotation, governance]

**Document ID:** `ASL/COMMON-WITNESS-ROTATION/1`
**Layer:** L2 -- Common witness governance (no transport)

**Depends on (normative):**

* `ASL/DAM/1`
* `ASL/POLICY-HASH/1`
* `ASL/LOG/1`

**Informative references:**

* `ASL/OCS/1` -- certificate semantics
* `ASL/OFFLINE-ROOT-TRUST/1`
* `ASL/SYSTEM/1` -- system view

---

## 0. Conventions

The key words **MUST**, **MUST NOT**, **REQUIRED**, **SHOULD**, and **MAY** are to be interpreted as in RFC 2119.

ASL/COMMON-WITNESS-ROTATION/1 defines the artifact used to rotate the Common witness emitter. It does not define transport, storage layout, or quorum transport mechanisms.

---

## 1. Purpose

This document defines the **Witness Rotation Artifact (WRA)** for the Common domain. The WRA is the only mechanism that authorizes a change of the active Common witness emitter while preserving a single linear Common history.

---

## 2. Roles and Terms

* **Witness Emitter:** The single domain authorized to emit the next Common snapshot.
* **Witness Authority:** A domain whose principals may endorse a witness rotation.
* **Rotation Snapshot:** The first Common snapshot emitted by the new witness emitter.

---

## 3. Artifact Identity

* **Artifact type tag:** `asl.common.witness-rotation`
* **Artifact key:** content-addressed (ASL/1-CORE)
* **Visibility:** published within the Common domain

---

## 4. Canonical Structure (Logical)

```text
WitnessRotationArtifact {
    version                 : u32
    common_domain_id         : DomainID
    previous_snapshot_id     : SnapshotID
    previous_snapshot_hash   : Hash
    old_witness_domain_id    : DomainID
    old_witness_pubkey_id    : KeyID
    new_witness_domain_id    : DomainID
    new_witness_pubkey_id    : KeyID
    policy_ref               : ArtifactRef
    endorsements             : EndorsementSet
    created_at_logseq        : u64
    reserved0                : u32
}

EndorsementSet {
    threshold                : u32
    endorsements[]           : Endorsement
}

Endorsement {
    endorser_domain_id       : DomainID
    endorser_pubkey_id       : KeyID
    signature                : Signature
}
```

Notes:

* `policy_ref` MUST reference the policy artifact governing the Common domain at the time of rotation.
* `reserved0` MUST be 0.

---

## 5. Signing Payload (Normative)

Each endorsement signature MUST cover the canonicalized payload:

```
H(
  version
  || common_domain_id
  || previous_snapshot_id
  || previous_snapshot_hash
  || new_witness_domain_id
  || new_witness_pubkey_id
  || policy_ref
)
```

* `H` is the hash function used by the Common domain.
* The signature algorithm MUST be allowed by the endorser's DAM and policy.

---

## 6. Validation Rules (Normative)

A Common domain implementation MUST accept a witness rotation artifact if and only if:

1. `previous_snapshot_id` and `previous_snapshot_hash` match the current trusted Common snapshot.
2. The endorsement set meets or exceeds `threshold` with valid signatures.
3. Each endorser is authorized as a witness authority by the Common domain's policy.
4. `policy_ref` matches the policy hash recorded for the Common domain at the time of rotation.
5. `created_at_logseq` is monotonic and consistent with the Common log ordering.

If any rule fails, the WRA MUST be rejected and MUST NOT affect witness authority.

---

## 7. Rotation Semantics (Normative)

* The WRA authorizes exactly one transition from `old_witness_*` to `new_witness_*`.
* The new witness emitter MUST begin emitting snapshots at the next log sequence after the rotation is admitted.
* Only one witness emitter MAY be active at a time.
* A rotation does not grant broader authority beyond emitting Common snapshots.

---

## 8. Non-Goals

ASL/COMMON-WITNESS-ROTATION/1 does not define:

* How endorsements are collected or transported
* Network replication or consensus protocols
* Storage or encoding formats for the artifact
* Automated governance workflows beyond validation rules