Downgrade to net standard 1.2

ModernKeePassLib/Cryptography/Hash/HMAC.cs

@@ -0,0 +1,62 @@
+using System;
+using Org.BouncyCastle.Crypto.Macs;
+
+namespace ModernKeePassLib.Cryptography.Hash
+{
+    public class HMAC : IDisposable
+    {
+        protected HMac Hmac;
+
+        public byte[] Hash
+        {
+            get
+            {
+                var result = new byte[Hmac.GetMacSize()];
+                Hmac.DoFinal(result, 0);
+                return result;
+            }
+        }
+        
+        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, offset, length);
+            Hmac.DoFinal(resBuf, offset);
+
+            return resBuf;
+        }
+
+        public void TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
+        {
+            Hmac.BlockUpdate(inputBuffer, inputOffset, inputCount);
+            if ((outputBuffer != null) && ((inputBuffer != outputBuffer) || (inputOffset != outputOffset)))
+                Buffer.BlockCopy(inputBuffer, inputOffset, outputBuffer, outputOffset, inputCount);
+        }
+
+        public byte[] TransformFinalBlock(byte[] inputBuffer, int inputOffset, int inputCount)
+        {
+            Hmac.BlockUpdate(inputBuffer, inputOffset, inputCount);
+            byte[] outputBytes = new byte[inputCount];
+            if (inputCount != 0)
+                Buffer.BlockCopy(inputBuffer, inputOffset, outputBytes, 0, inputCount);
+            return outputBytes;
+        }
+
+        public void Initialize()
+        {
+            Hmac.Reset();
+        }
+        
+        public void Dispose()
+        {
+            Hmac.Reset();
+        }
+    }
+}