From e922df23b1115a714ebeda31af4a479f822d7c8a Mon Sep 17 00:00:00 2001
From: Matthew Endsley <mendsley@gmail.com>
Date: Fri, 22 Jan 2021 10:39:08 -0800
Subject: [PATCH] Add null record protection implementation

---
 Hazel/Dtls/NullRecordProtection.cs | 66 ++++++++++++++++++++++++++++++
 Hazel/Hazel.csproj                 |  1 +
 2 files changed, 67 insertions(+)
 create mode 100644 Hazel/Dtls/NullRecordProtection.cs

diff --git a/Hazel/Dtls/NullRecordProtection.cs b/Hazel/Dtls/NullRecordProtection.cs
new file mode 100644
index 0000000..76fa132
--- /dev/null
+++ b/Hazel/Dtls/NullRecordProtection.cs
@@ -0,0 +1,66 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Hazel.Dtls
+{
+    /// <summary>
+    /// Passthrough record protection implementaion
+    /// </summary>
+    public class NullRecordProtection : IRecordProtection
+    {
+        public readonly static NullRecordProtection Instance = new NullRecordProtection();
+
+        public void Dispose()
+        {
+        }
+
+        public int GetEncryptedSize(int dataSize)
+        {
+            return dataSize;
+        }
+
+        public int GetDecryptedSize(int dataSize)
+        {
+            return dataSize;
+        }
+
+        public void EncryptServerPlaintext(ByteSpan output, ByteSpan input, ref Record record)
+        {
+            CopyMaybeOverlappingSpans(output, input);
+        }
+
+        public void EncryptClientPlaintext(ByteSpan output, ByteSpan input, ref Record record)
+        {
+            CopyMaybeOverlappingSpans(output, input);
+        }
+
+        public bool DecryptCiphertextFromServer(ByteSpan output, ByteSpan input, ref Record record)
+        {
+            CopyMaybeOverlappingSpans(output, input);
+            return true;
+        }
+
+        public bool DecryptCiphertextFromClient(ByteSpan output, ByteSpan input, ref Record record)
+        {
+            CopyMaybeOverlappingSpans(output, input);
+            return true;
+        }
+
+        private static void CopyMaybeOverlappingSpans(ByteSpan output, ByteSpan input)
+        {
+            // Early out if the ranges `output` is equal to `input`
+            if (output.GetUnderlyingArray() == input.GetUnderlyingArray())
+            {
+                if (output.Offset == input.Offset && output.Length == input.Length)
+                {
+                    return;
+                }
+            }
+
+            input.CopyTo(output);
+        }
+    }
+}
diff --git a/Hazel/Hazel.csproj b/Hazel/Hazel.csproj
index 18e7fa0..9becc82 100644
--- a/Hazel/Hazel.csproj
+++ b/Hazel/Hazel.csproj
@@ -82,6 +82,7 @@
     <Compile Include="Dtls\Handshake.cs" />
     <Compile Include="Dtls\IHandshakeCipherSuite.cs" />
     <Compile Include="Dtls\IRecordProtection.cs" />
+    <Compile Include="Dtls\NullRecordProtection.cs" />
     <Compile Include="Dtls\PrfSha256.cs" />
     <Compile Include="Dtls\Record.cs" />
     <Compile Include="Dtls\X25519EcdheRsaSha256.cs" />
-- 
2.39.5