Add clearer indication of "self encryption"

libp2p/security/secio/exceptions.py

@@ -2,6 +2,15 @@ class SecioException(Exception):
     pass
 
 
+class SelfEncryption(SecioException):
+    """
+    Raised to indicate that a host is attempting to encrypt communications
+    with itself.
+    """
+
+    pass
+
+
 class PeerMismatchException(SecioException):
     pass
 

libp2p/security/secio/transport.py

@@ -28,6 +28,7 @@ from .exceptions import (
     InvalidSignatureOnExchange,
     PeerMismatchException,
     SecioException,
+    SelfEncryption,
 )
 from .pb.spipe_pb2 import Exchange, Propose
 
@@ -195,9 +196,8 @@ def _select_encryption_parameters(
     elif second_score < first_score:
         order = 1
 
-    # NOTE: if order is 0, "talking to self"
+    if order == 0:
-    # TODO(ralexstokes) nicer error handling here...
+        raise SelfEncryption()
-    assert order != 0
 
     return (
         _select_parameter_from_order(