security: reject reused recovery approval keys

yuqei-infra/deploy/plan-first-release-snapshot-restore.py

@@ -681,6 +681,7 @@ def _validate_keyring(
     if not isinstance(raw_keys, list) or len(raw_keys) < 2:
         raise SnapshotRestorePlanError("recovery keyring has insufficient keys")
     result: dict[str, dict[str, Any]] = {}
+    public_keys: set[bytes] = set()
     for raw in raw_keys:
         item = _exact(
             raw,
@@ -708,6 +709,11 @@ def _validate_keyring(
             public_key = Ed25519PublicKey.from_public_bytes(public_raw)
         except (TypeError, ValueError) as exc:
             raise SnapshotRestorePlanError("recovery public key is invalid") from exc
+        if public_raw in public_keys:
+            raise SnapshotRestorePlanError(
+                "recovery keyring reuses an Ed25519 public key across identities"
+            )
+        public_keys.add(public_raw)
         not_before = _timestamp(item.get("not_before"), label="key not_before")
         not_after = _timestamp(item.get("not_after"), label="key not_after")
         if not_after <= not_before:

yuqei-infra/tests/test_first_release_snapshot_restore_planner.py

@@ -105,6 +105,7 @@ def _case(
     database_downgrade_performed: bool = False,
     successful_release_count: int = 0,
     same_approver_person: bool = False,
+    reused_approval_public_key: bool = False,
     restore_bindings_match: bool = True,
     empty_image_map: str | None = None,
 ) -> dict[str, Any]:
@@ -414,9 +415,14 @@ def _case(
     restore_path = _write_json(evidence_root / "independent-restore-test.json", restore_test)
 
     root_private = Ed25519PrivateKey.generate()
+    release_manager_key = Ed25519PrivateKey.generate()
     role_keys = {
-        "release_manager": Ed25519PrivateKey.generate(),
-        "database_owner": Ed25519PrivateKey.generate(),
+        "release_manager": release_manager_key,
+        "database_owner": (
+            release_manager_key
+            if reused_approval_public_key
+            else Ed25519PrivateKey.generate()
+        ),
     }
     approver_ids = {
         "release_manager": "approver-release-manager",
@@ -1024,6 +1030,25 @@ def test_approvals_require_two_different_people_and_keys(
         _validate(case)
 
 
+def test_keyring_rejects_public_key_reused_across_approval_identities(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    case = _case(tmp_path, reused_approval_public_key=True)
+    key_records = case["keyring"]["keys"]
+    assert len({item["key_id"] for item in key_records}) == 2
+    assert len({item["approver_id"] for item in key_records}) == 2
+    assert len({item["role"] for item in key_records}) == 2
+    assert len({item["public_key_base64"] for item in key_records}) == 1
+
+    _provision_test_pins(monkeypatch, case)
+    with pytest.raises(
+        planner.SnapshotRestorePlanError,
+        match="reuses an Ed25519 public key across identities",
+    ):
+        _validate(case)
+
+
 def test_cli_has_no_apply_or_caller_supplied_trust_pin() -> None:
     options = {
         option