DigestValue in XMLSignature in Java is different from C#

Question

I have a program running in C# which applies an XMLSignature to an xml document. I have the same XML documents in both cases (C# and Java), but I am not getting the same digest and signature values. I know that the results from my C program are correct, but I dont get to get them correctly in Java.

Here the C# code:

      public void SignXml(XmlDocument xmlDoc, RSA Key)
        {
            // Check arguments.
            if (xmlDoc == null)
                throw new ArgumentException("xmlDoc");
            if (Key == null)
                throw new ArgumentException("Key");

            // Create a SignedXml object.
            SignedXml signedXml = new SignedXml(xmlDoc);

            // Add the key to the SignedXml document.
            signedXml.SigningKey = Key;

            // Create a reference to be signed.
            Reference reference = new Reference();
            reference.Uri = "";

            // Add an enveloped transformation to the reference.
            XmlDsigEnvelopedSignatureTransform env = new XmlDsigEnvelopedSignatureTransform();
            reference.AddTransform(env);

            // Add the reference to the SignedXml object.
            signedXml.AddReference(reference);

            KeyInfo ki = new KeyInfo();
            KeyInfoX509Data clause = new KeyInfoX509Data();
            clause.AddCertificate(x509_2);
            clause.AddIssuerSerial(x509_2.Issuer, x509_2.GetSerialNumberString());
            ki.AddClause(clause);
            signedXml.KeyInfo = ki;

            // Compute the signature.
            signedXml.ComputeSignature();

            // Get the XML representation of the signature and save
            // it to an XmlElement object.
            XmlElement xmlDigitalSignature = signedXml.GetXml();

            //xmlDoc.Save("antes_firma.xml");
            // Append the element to the XML document.
            xmlDoc.DocumentElement.AppendChild(xmlDoc.ImportNode(xmlDigitalSignature, true));


        }

The Java code is the following:

DOMSignContext dsc = new DOMSignContext (pk, doc.getDocumentElement()); 
            XMLSignatureFactory fac = XMLSignatureFactory.getInstance("DOM");

            Reference ref = fac.newReference ("", fac.newDigestMethod(DigestMethod.SHA1, null), 
                        Collections.singletonList
                        (fac.newTransform(Transform.ENVELOPED,
                        (TransformParameterSpec) null)), null, null);

            SignedInfo si = fac.newSignedInfo
                      (fac.newCanonicalizationMethod
                        (CanonicalizationMethod.INCLUSIVE,
                          (C14NMethodParameterSpec) null),
                        fac.newSignatureMethod(SignatureMethod.RSA_SHA1, null),
                        Collections.singletonList(ref)); 

            KeyInfoFactory kif = fac.getKeyInfoFactory();
            X509IssuerSerial issuerSerial = kif.newX509IssuerSerial(cert2.getIssuerDN().getName(), cert.getSerialNumber());
            List x509Content = new ArrayList();
            x509Content.add(issuerSerial);
            x509Content.add(cert2);
            X509Data xd = kif.newX509Data(x509Content);
            KeyInfo ki = kif.newKeyInfo(Collections.singletonList(xd));

            XMLSignature signature = fac.newXMLSignature(si, ki);

            signature.sign(dsc);

With the same xml document, certificate and private key I am getting the following Digest Values in each one:

• Java: EZTMZuMvR9D0WSUgbT2AdFYTBh4=

• C#: EsJDdWiUMIOaQp9CC26wQWA6kJ0=

Why does this happen?

Answer 1

I dont know why this happens, but the solution to this problem was converting the Document to String and then to Document again and by doing that I got the expected digest and signature values.

TransformerFactory transfac = TransformerFactory.newInstance();
            Transformer trans = transfac.newTransformer();


            //CREAR STRING DEL ARBOL XML
            StringWriter sw = new StringWriter();
            StreamResult result = new StreamResult(sw);
            DOMSource source = new DOMSource(doc);
            trans.transform(source, result);
            String xmlString = sw.toString();
            System.out.println(xmlString);

            dbfac = DocumentBuilderFactory.newInstance();
            dbfac.setNamespaceAware(true);
            doc = dbfac.newDocumentBuilder().parse(new InputSource(new StringReader(xmlString)));

Answer 2

Just to add what I did to solve this problem:

String thisLine = "";
String xmlString = "";
BufferedReader br = new BufferedReader(new FileReader(xmlFile));
while ((thisLine = br.readLine()) != null) {
    xmlString = xmlString + thisLine.trim();
}
br.close();

ByteArrayInputStream xmlStream = new ByteArrayInputStream(xmlString.getBytes());
xmlDocument = docBuilder.parse(xmlStream);

So, before computing digest and signature, you need to strip whitespace and CRLF when loading xml from file. Otherwise, signature and digest compared to .Net result would be different.

Answer 3

You should canonicalize the xml before calculate digest and signature. for the C# codes.

XmlDsigC14NTransform canonicalization = new XmlDsigC14NTransform(); reference.AddTransform(canonicalization);