XML Digests using Xerces and XML Security Suite

[Iwan Eising <java@i-ware.net>]

Hi,

I'm writing an application that generates an XML document and saves it to a
file. Later when the file is read again, I want to make sure that it is the
same file. I want to use an MD5 digest to check this, the digest is stored
in the XML document it self, so when I send it to a different location
(possibly over the Internet) I can still check if it is the original file I
created in the first place.
I downloaded IBM's XML Security Suite and I created the following two
methods (full code below):

	boolean checkSignature(Node node,String signature);
	String generateSignature(Node node);

I store the signature in the XML document it self. The XML document has the
following structure:

<Document>
	<signature>
		<!-- signature-value in BASE64 -->
	</signature>
	<ActualContents>
	</ActualContents>
</Document>

I made sure that in both case the Digest is generated from ActualContents
node (The System.out shows me this). I'm using DOM, so the complete document
is read before it is being processed.

For some reason when I read the DOM from file and take the node and feed it
to checkSignature, I get a different Digest than when I create the DOM from
scratch and generate the digest.

Does anybody know what I'm doing wrong, or have a better/easier/working way
of solving this problem?

Thanks,
Iwan


    protected boolean checkSignature(Node node,String signature)
    {
        boolean result = false;

        System.out.println("Start hash at: " + node.getNodeName());
        try
        {
            byte[] digest =
Digest.getDigest(MessageDigest.getInstance("MD5"), node);
            BASE64Encoder encoder = new BASE64Encoder();
            String genSignature = encoder.encode(digest);
            result = signature.equals(genSignature);
        }
        catch(NoSuchAlgorithmException exc)
        {
            exc.printStackTrace();
        }

        return (result);
    }

    protected String generateSignature(Node node)
    {
        String id="";

        System.out.println("Start hash at: " + node.getNodeName());
        try
        {
            byte[] digest =
Digest.getDigest(MessageDigest.getInstance("MD5"), node);
            BASE64Encoder encoder = new BASE64Encoder();
            id = encoder.encode(digest);
        }
        catch(NoSuchAlgorithmException exc)
        {
            exc.printStackTrace();
        }

        return (id);
    }


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