Made signature verification time constant

Author: TwoTenPvP

MLAPI/NetworkingManagerComponents/Core/InternalMessageHandler.Receive.cs

@@ -129,23 +129,14 @@ internal static void HandleHailResponse(uint clientId, Stream stream, int channe
                             {
                                 byte[] clientHash = rsa.Decrypt(diffieHellmanPublicSignature, false);
                                 byte[] serverHash = sha.ComputeHash(diffieHellmanPublic);
-                                if (clientHash.Length != serverHash.Length)
+                                
+                                if (!CryptographyHelper.ConstTimeArrayEqual(clientHash, serverHash))
                                 {
                                     //Man in the middle.
-                                    if (LogHelper.CurrentLogLevel <= LogLevel.Normal) if (LogHelper.CurrentLogLevel <= LogLevel.Normal) LogHelper.LogWarning("Signature length doesnt match for the key exchange public part. Disconnecting");
+                                    if (LogHelper.CurrentLogLevel <= LogLevel.Normal) if (LogHelper.CurrentLogLevel <= LogLevel.Normal) LogHelper.LogWarning("Signature doesnt match for the key exchange public part. Disconnecting");
                                     netManager.DisconnectClient(clientId);
                                     return;
                                 }
-                                for (int i = 0; i < clientHash.Length; i++)
-                                {
-                                    if (clientHash[i] != serverHash[i])
-                                    {
-                                        //Man in the middle.
-                                        if (LogHelper.CurrentLogLevel <= LogLevel.Normal) if (LogHelper.CurrentLogLevel <= LogLevel.Normal) LogHelper.LogWarning("Signature doesnt match for the key exchange public part. Disconnecting");
-                                        netManager.DisconnectClient(clientId);
-                                        return;
-                                    }
-                                }
                             }
                         }
                         else

MLAPI/NetworkingManagerComponents/Cryptography/CryptographyHelper.cs

@@ -78,6 +78,23 @@ public static byte[] GetServerKey()
                 return NetworkingManager.Singleton.clientAesKey;
             }
         }
+
+        internal static bool ConstTimeArrayEqual(byte[] a, byte[] b)
+        {
+            if (a.Length != b.Length)
+                return false;
+            
+            int i = a.Length;
+            int cmp = 0;
+            
+            while (i != 0)
+            {
+                --i;
+                cmp |= (a[i] ^ b[i]);
+            }
+            
+            return cmp == 0;
+        }
     }
 }
 #endif