add an option to turn off mixing

mixnet/v2/sim/config.py

@@ -62,7 +62,7 @@ class MixnetConfig:
 
     def validate(self):
         assert self.num_nodes > 0
-        assert 0 < self.num_mix_layers <= self.num_nodes
+        assert 0 <= self.num_mix_layers <= self.num_nodes
         assert self.payload_size > 0
         assert self.message_interval > 0
         assert self.real_message_prob > 0

mixnet/v2/sim/config.yaml

@@ -4,6 +4,8 @@ simulation:
 
 mixnet:
   num_nodes: 100
+  # A number of mix nodes selected by a message sender through which the Sphinx message goes through
+  # If 0, the message is broadcast directly to all nodes without being Sphinx-encoded.
   num_mix_layers: 3
   # A size of a message payload in bytes (e.g. the size of a block proposal)
   payload_size: 320

mixnet/v2/sim/node.py

@@ -63,6 +63,9 @@ class Node:
         Creates a real or cover message
         @return:
         """
+        if self.config.mixnet.num_mix_layers == 0:  # if mixing is turned off
+            return self.build_payload()
+
         mixes = self.p2p.get_nodes(self.config.mixnet.num_mix_layers)
         public_keys = [mix.public_key for mix in mixes]
         # TODO: replace with realistic tx