test timestamp fast-forward attack recovery

This test simulates the timestamp fast-forward attack recovery.
It simulates that the timestamp keys were compromised, the attacker
generated a new high version of the timestamp.

The repository generates a new key and rollbacks the timestamp
version to the initial version.

Signed-off-by: Kairo de Araujo <kdearaujo@vmware.com>

tests/test_updater_top_level_update.py

@@ -339,6 +339,37 @@ def test_new_timestamp_expired(self) -> None:
 
  self._assert_files_exist([Root.type])
 
+ def test_new_timestamp_fast_foward_recovery(self) -> None:
+ """Test timestamp fast-forward recovery using key rotation.
+
+ The timestamp recovery is made by the following steps
+ - Remove the timestamp key
+ - Create and add a new key for timestamp
+ - Bump and publish root
+ - Rollback the timestamp version
+ """
+
+ # attacker updates to a higher version
+ self.sim.timestamp.version = 99999
+
+ # client refreshes the metadata and see the new timestamp version
+ self._run_refresh()
+ self._assert_version_equals(Timestamp.type, 99999)
+
+ # repo add new timestamp keys and recovers the timestamp version
+ self.sim.root.roles["timestamp"].keyids.clear()
+ self.sim.signers["timestamp"].clear()
+ key, signer = self.sim.create_key()
+ self.sim.root.add_key("timestamp", key)
+ self.sim.add_signer("timestamp", signer)
+ self.sim.root.version += 1
+ self.sim.publish_root()
+ self.sim.timestamp.version = 1
+
+ # client refresh the metadata and see the initial timestamp version
+ self._run_refresh()
+ self._assert_version_equals(Timestamp.type, 1)
+
  def test_new_snapshot_hash_mismatch(self) -> None:
  # Check against timestamp role’s snapshot hash