From f86176f3bd4f77b49795d5f5ec61346328440bc4 Mon Sep 17 00:00:00 2001
From: Jeremy Lakeman <Jeremy.Lakeman@gmail.com>
Date: Wed, 28 Nov 2012 11:18:17 +1030
Subject: [PATCH] Reserve high nonce bit for future use

---
 overlay_mdp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/overlay_mdp.c b/overlay_mdp.c
index 3502dab5..0fdfa884 100644
--- a/overlay_mdp.c
+++ b/overlay_mdp.c
@@ -752,6 +752,8 @@ int overlay_mdp_dispatch(overlay_mdp_frame *mdp,int userGeneratedFrameP,
 	op_free(frame);
 	RETURN(WHY("urandombytes() failed to generate nonce"));
       }
+      // reserve the high bit of the nonce as a flag for transmitting a shorter nonce.
+      nonce[0]&=0x7f;
       fe|= ob_append_bytes(frame->payload,nonce,nb);
       /* generate plain message with zero bytes and get ready to cipher it */
       unsigned char plain[zb+10+mdp->out.payload_length];