From: Matthew Endsley <mendsley@gmail.com>
Date: Wed, 3 Feb 2021 21:23:33 +0000 (-0800)
Subject: Do not compute HMAC for zero-length cookies
X-Git-Tag: 1.0.0~20^2~4^2~1
X-Git-Url: https://git.deb.at/?a=commitdiff_plain;h=4b223b14cd5d719e9378d89710ffa7e6ee11bfea;p=rhonda%2Fimpostor.hazel.git

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.
---

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)
             {