How can I extract xades signed content in Java xades4j? - xades4j

Question

I have got xades XML as InputStream. I do not care if certyficates are valid, check sign, etc. I can't provide any CA or any other type of certificate storage/validation. What I need is just get documents embedded in xades file as streams or temporary files on disk so I can process them as they were plain files from disk. Could someone provide snippet that extracts embedded documents? TIA

Answer 1

To extract Base64-encoded signed content from XAdES signed file i use code like below. It doesn't use xades4j at all.
import java.io.InputStream;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import javax.xml.namespace.NamespaceContext;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathFactory;
import org.bouncycastle.util.encoders.Base64;
import org.w3c.dom.Document;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class Utils {
/**
* extract ds:Object from .xades file
*
* #param xadesIn .xades file input stream
* #return base64 decoded bytes
* #throws Exception
*/
public static byte[] extractContentFromXadesSignedFile(InputStream xadesIn) throws Exception {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setNamespaceAware(true);
Document doc = dbf.newDocumentBuilder().parse(xadesIn);
xadesIn.close();
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
xpath.setNamespaceContext(new SimpleNamespaceContext(new HashMap<String, String>() {{
put("ds", "http://www.w3.org/2000/09/xmldsig#");
}}));
XPathExpression expr = xpath.compile("//ds:SignedInfo/ds:Reference");
NodeList referenceNodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
/**
* loop over all Reference nodes
* i need to find Object node with Id that fits URI value of Reference
*/
for(int i=0;i<referenceNodes.getLength();i++){
Node referenceNode = referenceNodes.item(i);
NamedNodeMap attributes = referenceNode.getAttributes();
if(attributes != null) {
Node uri = attributes.getNamedItem("URI");
if(uri != null) {
String objectId = uri.getNodeValue();
XPathExpression expr2 = xpath.compile("//ds:Object[#Id='"+objectId.substring(1)+"']");
Node contentNode = (Node) expr2.evaluate(doc, XPathConstants.NODE);
if(contentNode != null) {
String base64 = contentNode.getFirstChild().getNodeValue();
return Base64.decode(base64);
}
}
}
}
return null;
}
/**
* http://stackoverflow.com/a/6392700/404395
*/
private static class SimpleNamespaceContext implements NamespaceContext {
private final Map<String, String> PREF_MAP = new HashMap<String, String>();
public SimpleNamespaceContext(final Map<String, String> prefMap) {
PREF_MAP.putAll(prefMap);
}
#Override
public String getNamespaceURI(String prefix) {
return PREF_MAP.get(prefix);
}
#Override
public String getPrefix(String uri) {
throw new UnsupportedOperationException();
}
#Override
public Iterator getPrefixes(String uri) {
throw new UnsupportedOperationException();
}
}
}
Sample usage of that:
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import org.apache.commons.io.IOUtils;
import org.junit.Assert;
import org.junit.Test;
public class XadesExtractTest {
#Test
public void extract() throws Exception {
InputStream in = XadesExtractTest.class.getClassLoader().getResourceAsStream("test.xades");
byte[] bytes = Utils.extractContentFromXadesSignedFile(in);
Assert.assertNotNull(bytes);
in.close();
ByteArrayInputStream bin = new ByteArrayInputStream(bytes);
File f = File.createTempFile("test", ".zip");
System.out.println(f.getAbsolutePath());
FileOutputStream fout = new FileOutputStream(f);
IOUtils.copy(bin, fout);
bin.close();
fout.close();
}
}