created a builder class for creating a crypto provider from an xml element

mRemoteNGTests/Security/XmlCryptoProviderBuilderTests.cs

@@ -0,0 +1,66 @@
+using System;
+using System.Xml.Linq;
+using mRemoteNG.Security;
+using mRemoteNG.Security.SymmetricEncryption;
+using NUnit.Framework;
+
+
+namespace mRemoteNGTests.Security
+{
+    public class XmlCryptoProviderBuilderTests
+    {
+        [Test]
+        public void BuildsCorrectEncryptionEngine()
+        {
+            var element = BuildValidElement();
+            var builder = new XmlCryptoProviderBuilder(element);
+            var cryptoProvider = builder.Build();
+            Assert.That(cryptoProvider.CipherEngine, Is.EqualTo(BlockCipherEngines.Serpent));
+        }
+
+        [Test]
+        public void BuildsCorrectCipherMode()
+        {
+            var element = BuildValidElement();
+            var builder = new XmlCryptoProviderBuilder(element);
+            var cryptoProvider = builder.Build();
+            Assert.That(cryptoProvider.CipherMode, Is.EqualTo(BlockCipherModes.EAX));
+        }
+
+        [Test]
+        public void BuildsCorrectKdfIterations()
+        {
+            var element = BuildValidElement();
+            var builder = new XmlCryptoProviderBuilder(element);
+            var cryptoProvider = builder.Build();
+            Assert.That(cryptoProvider.KeyDerivationIterations, Is.EqualTo(1234));
+        }
+
+        [Test]
+        public void CantPassNullIntoConstructor()
+        {
+            Assert.Throws<ArgumentNullException>(() =>
+            {
+                // ReSharper disable once ObjectCreationAsStatement
+                new XmlCryptoProviderBuilder(null);
+            });
+        }
+
+        [Test]
+        public void ReturnsOldProviderTypeIfXmlIsntValid()
+        {
+            var badElement = new XElement("BadElement");
+            var builder = new XmlCryptoProviderBuilder(badElement);
+            var cryptoProvider = builder.Build();
+            Assert.That(cryptoProvider, Is.TypeOf<LegacyRijndaelCryptographyProvider>());
+        }
+
+        private static XElement BuildValidElement()
+        {
+            return new XElement("TestElement",
+                new XAttribute("EncryptionEngine", "Serpent"),
+                new XAttribute("BlockCipherMode", "EAX"),
+                new XAttribute("KdfIterations", "1234"));
+        }
+    }
+}

mRemoteNGTests/mRemoteNGTests.csproj

@@ -137,6 +137,7 @@
     <Compile Include="Security\Authentication\PasswordAuthenticatorTests.cs" />
     <Compile Include="Security\KeyDerivation\Pkcs5S2KeyGeneratorTests.cs" />
     <Compile Include="Security\SecureStringExtensionsTests.cs" />
+    <Compile Include="Security\XmlCryptoProviderBuilderTests.cs" />
     <Compile Include="Tools\ExternalToolsArgumentParserTests.cs" />
     <Compile Include="Tree\ClickHandlers\TreeNodeCompositeClickHandlerTests.cs" />
     <Compile Include="Tree\ConnectionTreeDragAndDropHandlerTests.cs" />

mRemoteV1/Security/CryptographyProviderFactory.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Xml.Linq;
 using mRemoteNG.Security.SymmetricEncryption;
 using Org.BouncyCastle.Crypto;
 using Org.BouncyCastle.Crypto.Engines;
@@ -20,6 +21,12 @@ namespace mRemoteNG.Security
             return new LegacyRijndaelCryptographyProvider();
         }
 
+        public static ICryptographyProvider BuildFromXml(XElement element)
+        {
+            var builder = new XmlCryptoProviderBuilder(element);
+            return builder.Build();
+        }
+
         private IBlockCipher ChooseBlockCipherEngine(BlockCipherEngines engine)
         {
             switch (engine)

mRemoteV1/Security/XmlCryptoProviderBuilder.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Xml.Linq;
+
+
+namespace mRemoteNG.Security
+{
+    public class XmlCryptoProviderBuilder
+    {
+        private readonly XElement _element;
+
+        public XmlCryptoProviderBuilder(XElement element)
+        {
+            if (element == null)
+                throw new ArgumentNullException(nameof(element));
+
+            _element = element;
+        }
+
+        public ICryptographyProvider Build()
+        {
+            ICryptographyProvider cryptoProvider;
+            try
+            {
+                var engine = (BlockCipherEngines)Enum.Parse(typeof(BlockCipherEngines), _element?.Attribute("EncryptionEngine")?.Value ?? "");
+                var mode = (BlockCipherModes)Enum.Parse(typeof(BlockCipherModes), _element?.Attribute("BlockCipherMode")?.Value ?? "");
+                cryptoProvider = new CryptographyProviderFactory().CreateAeadCryptographyProvider(engine, mode);
+
+                var keyDerivationIterations = int.Parse(_element?.Attribute("KdfIterations")?.Value ?? "");
+                cryptoProvider.KeyDerivationIterations = keyDerivationIterations;
+            }
+            catch (Exception)
+            {
+                return new CryptographyProviderFactory().CreateLegacyRijndaelCryptographyProvider();
+            }
+
+            return cryptoProvider;
+        }
+    }
+}

mRemoteV1/mRemoteV1.csproj

@@ -220,6 +220,7 @@
     <Compile Include="Security\ICryptographyProvider.cs" />
     <Compile Include="Security\SecureStringExtensions.cs" />
     <Compile Include="Security\CryptographyProviderFactory.cs" />
+    <Compile Include="Security\XmlCryptoProviderBuilder.cs" />
     <Compile Include="Tools\ExternalToolArgumentParser.cs" />
     <Compile Include="Tools\CmdArgumentsInterpreter.cs" />
     <Compile Include="Tools\ConnectionsTreeToMenuItemsConverter.cs" />