I'm signing part of an XML document using the Java XML DSig api. I'm trying to understand how it is arriving at the Digest value.
My document is:
<?xml version=\"1.0\" encoding=\"UTF-8\"?><PurchaseOrder><foo>bar</foo></PurchaseOrder>
My xpath expression is:
PurchaseOrder/foo/text()
What I attempt to do is:
- Call the Java DSIG library and view the value of the generated digest.
- Use the MessageDigest (SHA-1) class to digest the value "bar".
- Verify that the digests from 1 and 2 match.
When I do this, 1 and 2 produce different digest values. Either I'm doing something totally wrong with my DSIG code, or I don't understand how DSIG works. Any ideas?
Here is my test code (sorry it is so long ... I should go back to perl):
public class GenerateXmlSignature2 {
private static final String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><PurchaseOrder><foo>bar</foo></PurchaseOrder>";
private static final String xpath = "PurchaseOrder/foo/text()";
public static void main(String[] args) throws Exception {
Base64 base64 = new Base64();
// Create a DOM XMLSignatureFactory that will be used to
// generate the enveloped signature.
final XMLSignatureFactory fac = XMLSignatureFactory.getInstance("DOM");
// Create a Reference to the enveloped document (in this case,
// you are signing the whole document, so a URI of "" signifies
// that, and also specify the SHA1 digest algorithm and
// the ENVELOPED Transform.
final List<XPathType> xpaths = new ArrayList<XPathType>() {
{
add(new XPathType(xpath, XPathType.Filter.UNION));
}
};
List<Transform> transforms = new ArrayList<Transform>() {{
add(fac.newTransform(
Transform.XPATH2,
new XPathFilter2ParameterSpec(xpaths)
)
);
}};
Reference ref = fac.newReference
("", fac.newDigestMethod(DigestMethod.SHA1, null),
transforms,
null, null);
// Create the SignedInfo.
SignedInfo si = fac.newSignedInfo
(fac.newCanonicalizationMethod
(CanonicalizationMethod.INCLUSIVE,
(C14NMethodParameterSpec) null),
fac.newSignatureMethod(SignatureMethod.RSA_SHA1, null),
Collections.singletonList(ref));
// Load the KeyStore and get the signing key and certificate.
KeyStore ks = KeyStore.getInstance("JKS");
ks.load(new FileInputStream("mykeystore.jks"), "changeit".toCharArray());
KeyStore.PrivateKeyEntry keyEntry =
(KeyStore.PrivateKeyEntry) ks.getEntry
("mykey", new KeyStore.PasswordProtection("changeit".toCharArray()));
X509Certificate cert = (X509Certificate) keyEntry.getCertificate();
// Create the KeyInfo containing the X509Data.
KeyInfoFactory kif = fac.getKeyInfoFactory();
List x509Content = new ArrayList();
x509Content.add(cert.getSubjectX500Principal().getName());
x509Content.add(cert);
X509Data xd = kif.newX509Data(x509Content);
KeyInfo ki = kif.newKeyInfo(Collections.singletonList(xd));
// Instantiate the document to be signed.
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setNamespaceAware(true);
Document doc = dbf.newDocumentBuilder().parse
(new ByteArrayInputStream(xml.getBytes()));
// Create a DOMSignContext and specify the RSA PrivateKey and
// location of the resulting XMLSignature's parent element.
DOMSignContext dsc = new DOMSignContext
(keyEntry.getPrivateKey(), doc.getDocumentElement());
// Create the XMLSignature, but don't sign it yet.
XMLSignature signature = fac.newXMLSignature(si, ki);
// Marshal, generate, and sign the enveloped signature.
signature.sign(dsc);
// Output the resulting document.
TransformerFactory tf = TransformerFactory.newInstance();
Transformer trans = tf.newTransformer();
trans.transform(new DOMSource(doc), new StreamResult(System.out));
System.out.println("\n\n*** SHA-1 Digest ***");
XPathExpression xpathExpression = XPathFactory.newInstance().newXPath().compile(xpath);
String data = xpathExpression.evaluate(new InputSource(new StringReader(xml)));
System.out.println("Xpath: " + data);
MessageDigest md;
md = MessageDigest.getInstance("SHA");
byte[] sha1hash;
md.update(data.getBytes(), 0, data.length());
sha1hash = md.digest();
String base64Sha1OfCanonicalXml = new String(base64.encode(sha1hash));
System.out.println("Digest: " + base64Sha1OfCanonicalXml);
}
}