title: ProtectedData.Unprotect (DPAPI) stops working after password change
body: <p>Suppose I encrypt data and write it to a file like this:</p>
  
  <pre><code>byte[] encrypted =
      ProtectedData.Protect(plain, null, DataProtectionScope.CurrentUser);
  File.WriteAllBytes(filename, encrypted);
  </code></pre>
  
  <p>Decrypting is as straightforward:</p>
  
  <pre><code>byte[] encrypted = File.ReadAllBytes(filename);
  byte[] decrypted =
      ProtectedData.Unprotect(encrypted, null, DataProtectionScope.CurrentUser);
  </code></pre>
  
  <p>Now when I change my windows password between the calls to Protect and Unprotect, Unprotect will throw an exception. I do want the encrypted data to be linked to my user account, but I also want it to survive password changes.</p>
  
  <p>I guess I have to hand the data over to Windows rather than writing it to my own file, so that Windows can re-encrypt it on password changes. I just can't find the documentation that tells me how. Does anyone know?</p>