ModernKeePassLib implements HMAC correctly

Blake2b also implemented, but not tested
ModernKeePass app better implements focus on database password box (but still not working correctly)

ModernKeePassLib/Cryptography/Hash/HMAC.cs

@@ -0,0 +1,31 @@
+using System;
+using Org.BouncyCastle.Crypto.Macs;
+
+namespace ModernKeePassLib.Cryptography.Hash
+{
+    public class HMAC : IDisposable
+    {
+        protected HMac _hmac;
+        
+        public byte[] ComputeHash(byte[] value)
+        {
+            return ComputeHash(value, 0, value.Length);
+        }
+
+        public byte[] ComputeHash(byte[] value, int offset, int length)
+        {
+            if (value == null) throw new ArgumentNullException(nameof(value));
+
+            byte[] resBuf = new byte[_hmac.GetMacSize()];
+            _hmac.BlockUpdate(value, 0, length);
+            _hmac.DoFinal(resBuf, 0);
+
+            return resBuf;
+        }
+
+        public void Dispose()
+        {
+            _hmac.Reset();
+        }
+    }
+}