Updating D2D protocol to v1 to support separate sequence numbers.

components/cryptauth/proto/securemessage.proto

Index: components/cryptauth/proto/securemessage.proto
diff --git a/components/cryptauth/proto/securemessage.proto b/components/cryptauth/proto/securemessage.proto
index c086145a06a8d5a258c5e47019bc8b69599efb35..58ec3bd37c721458e8810edc32c816ea20638718 100644
--- a/components/cryptauth/proto/securemessage.proto
+++ b/components/cryptauth/proto/securemessage.proto
@@ -106,11 +106,19 @@ message DeviceToDeviceMessage {
 // 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];
 }