Question

I would like to read/write encrypted XML files using LINQ to XML. Does anyone know how to use encryption algorithms built into the .NET Framework to encrypt the Stream used by the XDocument object?

I did try it, but you can’t set the CryptoStream to Read/Write access. It only support Read or Write, which causes LINQ to XML to throw an exception.

Update: It would be nice to read/write the document ‘on the fly’, but I am only required to read the encrypted xml file, manipulate it, then write it back out encrypted again.

Answer 1

The easiest approach is probably an XDocument.Load(), Linq around, then XDocument.Save(). From a quick test app (go easy on non-disposed resources):

XDocument writeContacts = new XDocument(    new XElement('contacts',       new XElement('contact',          new XElement('name', 'Patrick Hines'),          new XElement('phone', '206-555-0144',              new XAttribute('type', 'home')),          new XElement('phone', '425-555-0145',              new XAttribute('type', 'work')),          new XElement('address',             new XElement('street1', '123 Main St'),             new XElement('city', 'Mercer Island'),             new XElement('state', 'WA'),             new XElement('postal', '68042')          )       )    ) );  Rijndael RijndaelAlg = Rijndael.Create();  FileStream writeStream = File.Open('data.xml', FileMode.Create); CryptoStream cStream = new CryptoStream(writeStream,     RijndaelAlg.CreateEncryptor(RijndaelAlg.Key, RijndaelAlg.IV),     CryptoStreamMode.Write);  StreamWriter writer = new StreamWriter(cStream);  writeContacts.Save(writer);  writer.Flush(); writer.Close();  FileStream readStream = File.OpenRead('data.xml');  cStream = new CryptoStream(readStream,   RijndaelAlg.CreateDecryptor(RijndaelAlg.Key, RijndaelAlg.IV),   CryptoStreamMode.Read);  XmlTextReader reader = new XmlTextReader(cStream);  XDocument readContacts = XDocument.Load(reader);  //manipulate with Linq and Save() when needed 

Swap your favorite ICryptoTransform into the CryptoStream.