wip single-pass circuit extension

relay.py

@@ -878,11 +878,36 @@ class RelayChannelManager(ChannelManager):
         elif isinstance(msg, SinglePassCreateCircuitMsg):
             # A new circuit has arrived
             circhandler = channel.new_circuit_with_circid(msg.circid)
-            # Create the ntor reply using Sphinx
-            #TODO what is the correct domain seperater here to indicate using
-            #Sphinx?
+            # Create the ntor reply for the circuit-extension key
             reply, secret = NTor.reply(self.onionkey, self.idpubkey,
-                    msg.ntor_request, self.perfstats,  b'data')
+                    msg.ntor_request, self.perfstats,  b'circuit')
+
+            # Set up the circuit to use the shared secret established from the
+            # circuit extension key
+            enckey = nacl.hash.sha256(secret + b'downstream')
+            deckey = nacl.hash.sha256(secret + b'upstream')
+            circhandler.add_crypt_layer(enckey, deckey)
+
+            # here, we will directly extend the circuit ourselves, after doing
+            # the following:
+            # 1. determining the next relay using the client's path selection
+            #    key in conjunction with our own
+            # 2. blinding each of the client's public keys to send to the next
+            #    hop.
+
+            # Add a handler for once the next relay replies to say that the
+            # circuit has been created
+            # be at most one on this circuit).
+            # TODO add the proper interface for the handler
+            circhandler.replace_celltype_handler(
+                    SinglePassCreatedCircuitCell,
+                    SinglePassCreatedCircuitHandler())
+
+            # Send the next create message to the next hop
+            # TODO add the correct interface here
+            self.send_msg(CircuitCellMsg(msg.circid,
+                    SinglePassCreateCircuitCell()), peeraddr)
+
             sys.exit("have not yet implemented circuit handling for single-pass in relays")
         else:
             return super().received_msg(msg, peeraddr, channel)