Handle InvalidSignature and add to suspicious activities and log the offense

nucypher/network/nodes.py

@@ -852,8 +852,8 @@ class Learner:
         try:
             self.verify_from(current_teacher, node_payload, signature=signature)
         except current_teacher.InvalidSignature:
-            # TODO: What to do if the teacher improperly signed the node payload?  1713
-            raise
+            self.suspicious_activities_witnessed['vladimirs'].append(('Node payload improperly signed', node_payload, signature))
+            self.log.warn(f"Invalid signature ({signature}) received from teacher {current_teacher} for payload {node_payload}")
 
         # End edge case handling.
         fleet_state_checksum_bytes, fleet_state_updated_bytes, node_payload = FleetStateTracker.snapshot_splitter(

tests/learning/test_fault_tolerance.py

@@ -59,6 +59,7 @@ def test_blockchain_ursula_stamp_verification_tolerance(blockchain_ursulas, mock
     # Learn about a node with a badly signed payload
     mocker.patch.object(lonely_blockchain_learner, 'verify_from', side_effect=Learner.InvalidSignature)
     lonely_blockchain_learner.learn_from_teacher_node(eager=True)
+    assert len(lonely_blockchain_learner.suspicious_activities_witnessed['vladimirs']) == 1
 
 @pytest.mark.skip("See Issue #1075")  # TODO: Issue #1075
 def test_invalid_workers_tolerance(testerchain,