Added beginning of HMAC verification. Non working

Author: john-h-k

docs/HeaderSpec.md

@@ -16,12 +16,6 @@
         -ITERATIONS:(iterations here)
     }
 
--KEYVERIFICATIONHASH:(hash here, None)
-    {
-        -HASHALGO:(PBKDF2, SHA256, bcrypt),
-        -ITERATIONS:(iterations here)
-    }
-
 -ENCRYPTMODE:(AES, RSA, etc)
     {
         -AESMODE:(ECB, CBC, CFB, CTR),
@@ -41,16 +35,13 @@
 | Argument                                               | Meaning                                                       | Values                                                                                                            |
 | ------------------------------------------------------ |-------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------- |
 | <a href="#HMAC">HMAC</a>                               | The verification hash used to confirm the file hasn't changed | 128 - 512 bit byte array (16-64 bytes)                                                                            |
-| <a href="#KEYVERIFICATIONHASH">KEYVERIFICATIONHASH</a> | A hash of the key to verify if the password is correct        | 128 - 512 bit byte array (16-64 bytes)                                                                            |
 | <a href="#ENCRYPTMODE">ENCRYPTMODE</a>                 | A byte representing the encryption type                       | A string in the table of <a href="#ENCRYPTMODE">ENCRYPTMODE</a> page, and the (undefined ATM -- TODO) enumeration |
 | <a href="IV">IV</a>                                    | The initialization vector used to start the encryption        | 128 - 512 bit byte array (16-64 bytes)                                                                            |
 
 
 ### <p id="HMAC">HMAC</p>
 
-* The HMAC (Hash Message Authentication Code)
-
-### <p id="KEYVERIFICATIONHASH">KEYVERIFICATIONHASH</p>
+The HMAC (Hash Message Authentication Code) is a hash that is used to verify the message hasn't been tampered with. The HMAC is the hashed value of the encrypted message. The receiver can re-hash the received message to verify the message hasn't been tampered with. **IMPORTANT: HMAC construction MUST be actual HMAC algorithm, not just hashing. See [this](https://en.wikipedia.org/wiki/HMAC#Implementation) for details ****
 
 ### <p id ="ENCRYPTMODE">ENCRYPTMODE</P>
 

src/Backend/MessageAuthenticator.cs

@@ -0,0 +1,35 @@
+using System;
+using System.IO;
+using System.Security.Cryptography;
+
+namespace Encryption_App
+{
+    class MessageAuthenticator
+    {
+        public void VerifyHMACFile(byte[] data, byte[] key)
+        {
+            byte[] hashKey;
+
+            using (var hmac = new HMACSHA384(key))
+            {
+                if (key.Length > hmac.InputBlockSize)
+                {
+                    hashKey = hmac.ComputeHash(data);
+                }
+            }
+        }
+
+        public void VerifyHMACFile(byte[] data, byte[] key, Type TypeOfHash)
+        {
+            HMAC hmac;
+            if (TypeOfHash.IsSubclassOf(typeof(HMAC)))
+            {
+                hmac = (HMAC)Activator.CreateInstance(TypeOfHash);
+            }
+            else
+            {
+                throw new ArgumentException("TypeOfHash is not a derivative of \"System.Security.Cryptorgaphy.HMAC\"");
+            }
+        }
+    }
+}

src/EncryptionApp.csproj

@@ -60,7 +60,8 @@
       <SubType>Designer</SubType>
     </Page>
     <Compile Include="Backend\AESCryptoManager.cs" />
-    <Compile Include="UI\App.xaml.cs" >
+    <Compile Include="Backend\MessageAuthenticator.cs" />
+    <Compile Include="UI\App.xaml.cs">
       <DependentUpon>App.xaml</DependentUpon>
       <SubType>Code</SubType>
     </Compile>
@@ -97,4 +98,4 @@
   </ItemGroup>
   <ItemGroup />
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
-</Project>
+</Project>