implement remote assembly loading

Application/Misc/RemoteAssemblyHandler.cs

@@ -0,0 +1,76 @@
+using SharedLibraryCore;
+using SharedLibraryCore.Configuration;
+using SharedLibraryCore.Interfaces;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace IW4MAdmin.Application.Misc
+{
+    public class RemoteAssemblyHandler : IRemoteAssemblyHandler
+    {
+        private const int keyLength = 32;
+        private const int tagLength = 16;
+        private const int nonceLength = 12;
+        private const int iterationCount = 10000;
+
+        private readonly ApplicationConfiguration _appconfig;
+        private readonly ILogger _logger;
+
+        public RemoteAssemblyHandler(ILogger logger, ApplicationConfiguration appconfig)
+        {
+            _appconfig = appconfig;
+            _logger = logger;
+        }
+
+        public IEnumerable<Assembly> DecryptAssemblies(string[] encryptedAssemblies)
+        {
+            return DecryptContent(encryptedAssemblies)
+                .Select(decryptedAssembly => Assembly.Load(decryptedAssembly));
+        }
+
+        public IEnumerable<string> DecryptScripts(string[] encryptedScripts)
+        {
+            return DecryptContent(encryptedScripts).Select(decryptedScript => Encoding.UTF8.GetString(decryptedScript));
+        }
+
+        private byte[][] DecryptContent(string[] content)
+        {
+            if (string.IsNullOrEmpty(_appconfig.Id) || string.IsNullOrWhiteSpace(_appconfig.SubscriptionId))
+            {
+                _logger.WriteWarning($"{nameof(_appconfig.Id)} and {nameof(_appconfig.SubscriptionId)} must be provided to attempt loading remote assemblies/scripts");
+                return new byte[0][];
+            }
+
+            var assemblies = content.Select(piece =>
+            {
+                byte[] byteContent = Convert.FromBase64String(piece);
+                byte[] encryptedContent = byteContent.Take(byteContent.Length - (tagLength + nonceLength)).ToArray();
+                byte[] tag = byteContent.Skip(byteContent.Length - (tagLength + nonceLength)).Take(tagLength).ToArray();
+                byte[] nonce = byteContent.Skip(byteContent.Length - nonceLength).Take(nonceLength).ToArray();
+                byte[] decryptedContent = new byte[encryptedContent.Length];
+
+                var keyGen = new Rfc2898DeriveBytes(Encoding.UTF8.GetBytes(_appconfig.SubscriptionId), Encoding.UTF8.GetBytes(_appconfig.Id.ToString()), iterationCount, HashAlgorithmName.SHA512);
+                var encryption = new AesGcm(keyGen.GetBytes(keyLength));
+
+                try
+                {
+                    encryption.Decrypt(nonce, encryptedContent, tag, decryptedContent);
+                }
+
+                catch (CryptographicException ex)
+                {
+                    _logger.WriteError("Could not obtain remote plugin assemblies");
+                    _logger.WriteDebug(ex.GetExceptionInfo());
+                }
+
+                return decryptedContent;
+            });
+
+            return assemblies.ToArray();
+        }
+    }
+}