Make the functions to verify relay descriptors and consensuses into static methods

These static methods check the exact type of their arguments.  We still
want to avoid someone passing us a "consensus" object that has the wrong
type, and a "verify" method that just returns true.  This way, we call
the definitely correct Consensus.verify method, passing it the claimed
consensus.  The method will check the type and verify the signature.

client.py

@@ -52,7 +52,7 @@ class CellClient(relay.CellHandler):
         print("Client %s received msg %s from %s" % (self.myaddr, msg, peeraddr))
         if isinstance(msg, relay.RelayConsensusMsg):
             self.consensus = msg.consensus
-            dirauth.verify_consensus(self.consensus, network.thenetwork.dirauthkeys())
+            dirauth.Consensus.verify(self.consensus, network.thenetwork.dirauthkeys())
             self.consensus_cdf = self.consensus.bw_cdf()
         else:
             return super().received_msg(msg, peeraddr, peer)
@@ -138,7 +138,7 @@ if __name__ == '__main__':
     # Tick the epoch
     network.thenetwork.nextepoch()
 
-    dirauth.verify_consensus(dirauth.DirAuth.consensus, network.thenetwork.dirauthkeys())
+    dirauth.Consensus.verify(dirauth.DirAuth.consensus, network.thenetwork.dirauthkeys())
 
     print('ticked; epoch=', network.thenetwork.getepoch())
 

dirauth.py

@@ -40,10 +40,11 @@ class RelayDescriptor:
         signed = signingkey.sign(serialized.encode("ascii"))
         self.descdict["sig"] = signed.signature
 
-
-def verify_relaydesc(desc):
-    serialized = desc.__str__(False)
-    desc.descdict["idkey"].verify(serialized.encode("ascii"), desc.descdict["sig"])
+    @staticmethod
+    def verify(desc):
+        assert(type(desc) is RelayDescriptor)
+        serialized = desc.__str__(False)
+        desc.descdict["idkey"].verify(serialized.encode("ascii"), desc.descdict["sig"])
 
 
 # A consensus is a dict containing:
@@ -108,14 +109,14 @@ class Consensus:
         idx = bisect.bisect_right(cdf, val)
         return self.consdict['relays'][idx-1]
 
-
-
-def verify_consensus(consensus, verifkeylist):
-    """Use the given list of verification keys to check the
-    signatures on the consensus."""
-    serialized = consensus.__str__(False)
-    for i, vk in enumerate(verifkeylist):
-        vk.verify(serialized.encode("ascii"), consensus.consdict['sigs'][i])
+    @staticmethod
+    def verify(consensus, verifkeylist):
+        """Use the given list of verification keys to check the
+        signatures on the consensus."""
+        assert(type(consensus) is Consensus)
+        serialized = consensus.__str__(False)
+        for i, vk in enumerate(verifkeylist):
+            vk.verify(serialized.encode("ascii"), consensus.consdict['sigs'][i])
 
 
 class DirAuthNetMsg(network.NetMsg):

relay.py

@@ -169,7 +169,7 @@ class CellRelay(CellHandler):
         a = random.choice(self.dirauthaddrs)
         c = network.thenetwork.connect(self, a)
         self.consensus = c.getconsensus()
-        dirauth.verify_consensus(self.consensus, network.thenetwork.dirauthkeys())
+        dirauth.Consensus.verify(self.consensus, network.thenetwork.dirauthkeys())
         c.close()
 
     def received_msg(self, msg, peeraddr, peer):
@@ -267,7 +267,7 @@ class Relay(network.Server):
         descdict["flags"] = self.flags
         desc = dirauth.RelayDescriptor(descdict)
         desc.sign(self.idkey)
-        dirauth.verify_relaydesc(desc)
+        dirauth.RelayDescriptor.verify(desc)
 
         if upload:
             descmsg = dirauth.DirAuthUploadDescMsg(desc)
@@ -337,7 +337,7 @@ if __name__ == '__main__':
     # Tick the epoch
     network.thenetwork.nextepoch()
 
-    dirauth.verify_consensus(dirauth.DirAuth.consensus, network.thenetwork.dirauthkeys())
+    dirauth.Consensus.verify(dirauth.DirAuth.consensus, network.thenetwork.dirauthkeys())
 
     print('ticked; epoch=', network.thenetwork.getepoch())