Merge pull request #1 from carljohnsen/performance/mac_addr_fix

Performance/Changed the way a device's MAC address is found

Author: kenkendk

src/Constants.cs

@@ -53,4 +53,33 @@ internal static class Constants
     /// </summary>
     /// <remarks>This number is required to be 8192 by the AESCrypt specification</remarks>
     internal const int KEY_HASH_ITERATIONS = 8192;
+
+    /// <summary>
+    /// Helper function for setting the `FIRST_MAC_ADDRESS` varible. It retrieves the first MAC address of the system. If no MAC address is found, or one of the system functions throws an exception, a default MAC address is used.
+    /// </summary>
+    /// <remarks>The default MAC address used is 01:23:45:67:89:ab</remarks>
+    /// <returns>The MAC address of the first network interface that has a MAC address, or the default MAC address if no such interface is found.</returns>
+    private static byte[] GetFirstMacAddress()
+    {
+        byte[] default_mac = [0x01, 0x23, 0x45, 0x67, 0x89, 0xab];
+        try {
+            return System.Net.NetworkInformation.NetworkInterface
+                    .GetAllNetworkInterfaces()
+                    .Select(ni => { try { return ni.GetPhysicalAddress().GetAddressBytes(); } catch { return []; } })
+                    .Where(mac => mac.Length > 0 && !mac.All(b => b == 0))
+                    .FirstOrDefault(default_mac);
+        } catch {
+            return default_mac;
+        }
+    }
+
+    /// <summary>
+    /// The MAC address of the first network interface that has a MAC address.
+    /// </summary>
+    /// <remarks>If no such interface is found, a default MAC address is used (01:23:45:67:89:ab)</remarks>
+    internal static readonly ulong FIRST_MAC_ADDRESS = System.Buffers.Binary.BinaryPrimitives.ReadUInt64BigEndian(
+    [
+        .. GetFirstMacAddress(),
+        .. new byte[2],
+    ]);
 }

src/SetupHelper.cs

@@ -9,12 +9,6 @@ namespace SharpAESCrypt;
 /// </summary>
 internal class SetupHelper : IDisposable
 {
-    /// <summary>
-    /// The MAC adress to use in case the network interface enumeration fails
-    /// </summary>
-    private static readonly ulong DEFAULT_MAC
-        = BinaryPrimitives.ReadUInt64BigEndian([0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef]);
-
     /// <summary>
     /// The encryption algorithm used
     /// </summary>
@@ -145,26 +139,10 @@ private static byte[] EncodePassword(string password)
     /// <returns>A random IV</returns>
     private ReadOnlyMemory<byte> GenerateHeaderIV()
     {
-        var mac = DEFAULT_MAC;
-        try
-        {
-            var interfaces = System.Net.NetworkInformation.NetworkInterface.GetAllNetworkInterfaces();
-            for (int i = 0; i < interfaces.Length; i++)
-                if (i != System.Net.NetworkInformation.NetworkInterface.LoopbackInterfaceIndex)
-                {
-                    mac = BinaryPrimitives.ReadUInt64BigEndian(interfaces[i].GetPhysicalAddress().GetAddressBytes());
-                    break;
-                }
-        }
-        catch
-        {
-            //Not much to do, just go with default MAC
-        }
-
         // Build some initial entropy      
         var iv = new byte[Constants.IV_SIZE];
         BinaryPrimitives.WriteInt64BigEndian(iv.AsSpan(), DateTime.Now.Ticks);
-        BinaryPrimitives.WriteUInt64BigEndian(iv.AsSpan(8), mac);
+        BinaryPrimitives.WriteUInt64BigEndian(iv.AsSpan(8), Constants.FIRST_MAC_ADDRESS);
 
         // The IV is generated by repeatedly hashing the IV with random data.
         // By using the MAC address and the current time, we add some initial entropy,