From 4b223b14cd5d719e9378d89710ffa7e6ee11bfea Mon Sep 17 00:00:00 2001
From: Matthew Endsley <mendsley@gmail.com>
Date: Wed, 3 Feb 2021 13:23:33 -0800
Subject: [PATCH] Do not compute HMAC for zero-length cookies

This is a common case since all clients send a non-signed ClientHello
message to initiate a new session. There is no need to perform the
hash+hmac for signatures that will always fail verification due to a
mismatched size.
---
 Hazel/Dtls/Handshake.cs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Hazel/Dtls/Handshake.cs b/Hazel/Dtls/Handshake.cs
index a70af4e..880311b 100644
--- a/Hazel/Dtls/Handshake.cs
+++ b/Hazel/Dtls/Handshake.cs
@@ -452,6 +452,11 @@ namespace Hazel.Dtls
         /// <returns>True if the cookie is valid. Otherwise false</returns>
         public static bool VerifyCookie(ByteSpan cookie, EndPoint peerAddress, HMAC hmac)
         {
+            if (cookie.Length != CookieSize)
+            {
+                return false;
+            }
+
             ByteSpan expectedHash = ComputeAddressMac(peerAddress, hmac);
             if (expectedHash.Length != cookie.Length)
             {
-- 
2.39.5