Issue with validation of signature

Question

Hello,
I am facing a problem in producing a correct signature and I hope someone can help me understand the root of the problem. Most of us are familiar with the Java (Sun) examples of GenDetached, GenEnveloped, GenEnveloping, and Validate code samples. The code below is a small variation of the GenDetached:
public class GenerateDetachedWithManifest {
  public static void main(String[] args) throws Exception {
    // First, create a DOM XMLSignatureFactory that will be used to
    // generate the XMLSignature and marshal it to DOM.
    String providerName = System.getProperty("jsr105Provider",
        "org.jcp.xml.dsig.internal.dom.XMLDSigRI");
    XMLSignatureFactory fac = XMLSignatureFactory.getInstance("DOM",
        (Provider) Class.forName(providerName).newInstance());
    // Create a Reference to an external URI that will be digested
    // using the SHA1 digest algorithm
    Reference ref = fac.newReference("http://www.w3.org/TR/xml-stylesheet", fac
        .newDigestMethod(DigestMethod.SHA1, null));
    Reference xref = fac.newReference("#object", fac.newDigestMethod(
        DigestMethod.SHA1, null), null, "http://www.w3.org/2000/09/xmldsig#Object", null);
    Manifest manifest = fac.newManifest(Collections.singletonList(ref));
    List<XMLObject> objs = new ArrayList<XMLObject>();
    objs.add(fac.newXMLObject(Collections.singletonList(manifest), "object", null, null));
    // Create the SignedInfo
    SignedInfo si = fac.newSignedInfo(fac.newCanonicalizationMethod(
        CanonicalizationMethod.INCLUSIVE,
        (C14NMethodParameterSpec) null), fac.newSignatureMethod(
        SignatureMethod.DSA_SHA1, null), Collections.singletonList(xref));
    // Create a DSA KeyPair
    KeyPairGenerator kpg = KeyPairGenerator.getInstance("DSA");
    kpg.initialize(512);
    KeyPair kp = kpg.generateKeyPair();
    // Create a KeyValue containing the DSA PublicKey that was generated
    KeyInfoFactory kif = fac.getKeyInfoFactory();
    KeyValue kv = kif.newKeyValue(kp.getPublic());
    // Create a KeyInfo and add the KeyValue to it
    KeyInfo ki = kif.newKeyInfo(Collections.singletonList(kv));
    // Create the XMLSignature (but don't sign it yet)
    XMLSignature signature = fac.newXMLSignature(si, ki, objs, "SignatureIdValue", null);
    // Create the Document that will hold the resulting XMLSignature
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    dbf.setNamespaceAware(true); // must be set
    Document doc = dbf.newDocumentBuilder().newDocument();
    // Create a DOMSignContext and set the signing Key to the DSA
    // PrivateKey and specify where the XMLSignature should be inserted
    // in the target document (in this case, the document root)
    DOMSignContext signContext = new DOMSignContext(kp.getPrivate(), doc);
    // Marshal, generate (and sign) the detached XMLSignature. The DOM
    // Document will contain the XML Signature if this method returns
    // successfully.
    signature.sign(signContext);
    // output the resulting document
    OutputStream os;
    if (args.length > 0) {
      os = new FileOutputStream(args[0]);
    } else {
      os = System.out;
    TransformerFactory tf = TransformerFactory.newInstance();
    Transformer trans = tf.newTransformer();
    trans.transform(new DOMSource(doc), new StreamResult(os));
}If you wonder why I am doing this the answer is that I am trying to sign a format based on OPC. Anyway, the problem I have is that the output of the above program fails to validate when running the Validate sample. I don't think the issue is with the Validate program because it correctly validates output of a .NET signing application whose behavior I am trying to replicate in Java.
So the question is: why does the above code produce an incorrect signature?
Thanks,
Luis

Answer 1

Can you post relevant sections of the OPC standard (or a link to it) that describes the requirement? Its possible that they have written the requirements differently from the examples. Its also possible that the DSIG library in the JDK only does things in a specifc way (I'll let Sean Mullan weigh in on this part of the discussion if he's monitoring this list/thread - he's the developer from Sun who wrote the library).
Here's the wording from the W3C spec on the Object element:
+"The Object's Id is commonly referenced from a Reference in SignedInfo, or Manifest. This element is typically used for enveloping signatures where the object being signed is to be included in the signature element. The digest is calculated over the entire Object element including start and end tags."+
What you have is neither an Enveloping Signature nor Detached - but a combination of the two. So its possible that the JDK library doesn't work with Object references in this manner (although in theory is should). Based on this thread (XML dsig: Can I sign a SignatureProperty of the Signature? it appears that this theory holds up for child-elements of Object , but not for the Object element itself.
Arshad Noor
StrongAuth, Inc.