Updating D2D protocol to v1 to support separate sequence numbers.

components/cryptauth/proto/securemessage.proto

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Definitions related to the SecureMessage format, used by CryptAuth. Do not
 // edit unless transcribing from server definitions.
 syntax = "proto2";
 
 package securemessage;
 
@@ skipping 88 matching lines @@
   // The payload of the message.
   optional bytes message = 1;
 
   // The sequence number of the message - must be increasing.
   optional int32 sequence_number = 2;
 }
 
 // Sent as the first message from initiator to responder in an unauthenticated
 // Diffie-Hellman Key Exchange.
 message InitiatorHello {
+  // The session public key to send to the responder.
   optional GenericPublicKey public_dh_key = 1;
+
+  // The protocol version.
+  optional int32 protocol_version = 2 [default = 0];
 }
 
 // Sent inside the header of the first message from the responder to the
 // initiator in an unauthenticated Diffie-Hellman Key Exchange.
 message ResponderHello {
+  // The session public key to send to the initiator.
   optional GenericPublicKey public_dh_key = 1;
+
+  // The protocol version.
+  optional int32 protocol_version = 2 [default = 0];
 }