SignedXml.CheckSignature fails in .NET 4 but it works in .NET 3.5, 3 or 2

Question

I have a response from a 3-rd party web service. I load an XmlDocument with that response.

  string txt = readStream.ReadToEnd();
  response = new XmlDocumen         


        

Answer 1

// Assume the data to sign is in the data.xml file, load it, and

// set up the signature object.
XmlDocument doc = new XmlDocument();

doc.Load(@"D:\Example.xml");
SignedXml sig = new SignedXml(doc);

// Make a random RSA key, and set it on the signature for signing.
RSA key = new RSACryptoServiceProvider();

sig.SigningKey = key;

// Create a Reference to the containing document, add the enveloped
// transform, and then add the Reference to the signature
Reference refr = new Reference("");refr.AddTransform(new XmlDsigEnvelopedSignatureTransform());

sig.AddReference(refr);

// Compute the signature, add it to the XML document, and save
sig.ComputeSignature();

doc.DocumentElement.AppendChild(sig.GetXml());
doc.Save("data-signed.xml");

// Load the signed data

//XmlDocument doc = new XmlDocument();
doc.PreserveWhitespace = true;

doc.Load("data-signed.xml");

// Find the Signature element in the document
XmlNamespaceManager nsm = new XmlNamespaceManager(new NameTable());

nsm.AddNamespace("dsig", SignedXml.XmlDsigNamespaceUrl);
XmlElement sigElt = (XmlElement)doc.SelectSingleNode("//dsig:Signature", nsm);

// Load the signature for verification

//SignedXml sig = new SignedXml(doc);

sig.LoadXml(sigElt);

// Verify the signature, assume the public key part of the

// signing key is in the key variable
if (sig.CheckSignature(key))
    Console.WriteLine("Signature verified");
else
    Console.WriteLine("Signature not valid");