title: Can't find `DataProtectionScope` and `ProtectedData` classes in System.Security.Cryptography
body: <p>I've referred the file <code>System.Security.dll</code> as described in <a href="http://msdn.microsoft.com/en-us/library/system.security.cryptography.dataprotectionscope%28v=vs.100%29.aspx">this article</a> but according to my IDE, the line <code>using System.Security.Cryptography;</code> can be safely removed as it's not being used.</p>
  
  <p>The same IDE tells me that I've got an error with <code>DataProtectionScope</code> and <code>ProtectedData</code>. Those are supposed to be in <strong>that</strong> namespace. However, when I dot my way through the packages, I can't see them in there.</p>
  
  <p>Is the article wrong? How can I access the two classes?</p>