xml dsig, how to save and hash reference elements?

[AK]

Hello,

I need to do the following with an xml document which has a list of
assets:
1. Hash the assets
2. Hash the element describing the assets
3. Create a digital signature (using X.509 certificate) over the
hashes from step 1 and 2

Most of the examples I've been looking at are doing a digital
signature in one go, and I'm not sure how to write the references with
the digest to the xml file without also creating a signature.

This is the code I currently have:

// Create a key container
CspParameters cspParameters = new CspParameters() ;
cspParameters.K eyContainerName = "XML_DSIG_RSA_K EY";

// Create an RSA key and save it in the container
RSACryptoServic eProvider rsaKey = new
RSACryptoServic eProvider(cspPa rameters);

// Create a new XML document and load the manifest into it
XmlDocument xmlDoc = new XmlDocument();
//xmlDoc.Preserve Whitespace = true;
xmlDoc.Load(man ifestPath);

hashAssets(xmlD oc, rsaKey);

// Save the manifest
xmlDoc.Save(man ifestPath);


public void hashAssets(XmlD ocument Doc, RSA Key)
{
// Create a SignedXml object
SignedXml signedXml = new SignedXml(Doc);

// Add the key
signedXml.Signi ngKey = Key;

// Get urls to assets with signed = true
assetUris = getAssetUris();

foreach (string assetUri in assetUris)
{
// Create a reference to be signed
Reference reference = new Reference(); reference.Uri = assetUri;

//// Add an enveloped transformation to the reference
//XmlDsigEnvelope dSignatureTrans form env = new
XmlDsigEnvelope dSignatureTrans form();
//reference.AddTr ansform(env);

// Add the reference to the SignedXml object
signedXml.AddRe ference(referen ce);
}

// Compute the signature
signedXml.Compu teSignature();

// Get the XML representation of the signature and save it to an
XmlElement object
XmlElement xmlDigitalSigna ture = signedXml.GetXm l();

// Append the element to the XML document
Doc.DocumentEle ment.AppendChil d(Doc.ImportNod e(xmlDigitalSig nature,
true));
}

Is there any way of saving the reference to the xmldoc without also
creating a signature? And then hash the reference elements and create
a signature over them? Or am I taking the wrong approach with this
code to start with?

Many thanks,

AK