How to convert XML-Information into RSAPrivateKey

Question

Hi,
how can I convert PrivateKey-data issued as XML-document into a valid RSAPrivateKey that can be used for signature and encryption? For X509Certificates and PublicKey-data this seems to be no problem, but I could not find any function that does it for PrivateKey-data.
Please see http://www.w3.org/TR/xkms2/#XKMS_2_0_Section_C_3 for an example XML-PrivateKey.
After converting it into a valid RSAPrivateKey System.out.println(privateKey); should output something like this:
Sun RSA private CRT key, 1024 bits
  modulus:          1149848018...
  public exponent:  65537
  private exponent: 3967455520...
  prime p:          1210859164...
  prime q:          9496133427...
  prime exponent p: 4043649185...
  prime exponent q: 6250868914...
  crt coefficient:  2246802223but with:
         BigInteger mod = new BigInteger(Base64.decode(modulus));
         BigInteger exp = new BigInteger(Base64.decode(exponent));
          KeyFactory keyFactory = KeyFactory.getInstance("RSA");
          RSAPrivateKeySpec keySpec = new RSAPrivateKeySpec(mod, exp);
          RSAPrivateKey privateKey = (RSAPrivateKey) keyFactory.generatePrivate(keySpec);I only got the following:
Sun RSA private CRT key, 1024 bits
  modulus:          1149848018...
  private exponent: 3967455520...Please help!

Answer 1

at no charge for you:
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.RSAPrivateCrtKeySpec;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
public class DotNetXMLPrivateKeyReader {
     private Document privateKeyDocument;
     private InputStream xmlInputStream;
     public DotNetXMLPrivateKeyReader(InputStream xmlInputStream) throws SAXException, IOException{
          this.xmlInputStream = xmlInputStream;
          parseDocument();
     public DotNetXMLPrivateKeyReader(byte xmlBytes[]) throws SAXException, IOException{
          this(new ByteArrayInputStream(xmlBytes));
     public DotNetXMLPrivateKeyReader(String xmlString) throws SAXException, IOException{
          this(xmlString.getBytes());
     public PrivateKey getPrivateKey() throws IOException, InvalidKeySpecException {
          KeyFactory keyFactory;
          try {
               keyFactory = KeyFactory.getInstance("RSA");
          } catch (NoSuchAlgorithmException e) {
               throw new RuntimeException("Error loading RSA KeyFactory", e);
          RSAPrivateCrtKeySpec keySpec = loadKeySpec();
          return keyFactory.generatePrivate(keySpec);
     private void parseDocument() throws SAXException, IOException {
          DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
          DocumentBuilder builder;
          try {
               builder = dbf.newDocumentBuilder();
          } catch (ParserConfigurationException e) {
               throw new RuntimeException("Error creating DocumentBuilder from DocumentBuilderFactory", e);
          privateKeyDocument = builder.parse(xmlInputStream);
     private RSAPrivateCrtKeySpec loadKeySpec() throws IOException {
          String modulusStr = getNodeContent("Modulus");
          String publicExpStr = getNodeContent("Exponent");
          String primePStr = getNodeContent("P");
          String primeQStr = getNodeContent("Q");
          String primeEPStr = getNodeContent("DP");
          String primeEqStr = getNodeContent("DQ");
          String crtCoefficientStr = getNodeContent("InverseQ");
          String privateExpStr = getNodeContent("D");
          RSAPrivateCrtKeySpec keySpec = new RSAPrivateCrtKeySpec(
                    decodeBigDecimal(modulusStr), decodeBigDecimal(publicExpStr),
                    decodeBigDecimal(privateExpStr), decodeBigDecimal(primePStr),
                    decodeBigDecimal(primeQStr), decodeBigDecimal(primeEPStr),
                    decodeBigDecimal(primeEqStr), decodeBigDecimal(crtCoefficientStr));
          return keySpec;
     private String getNodeContent(String nodeName) {
          NodeList elementsByTagName = privateKeyDocument.getElementsByTagName(nodeName);
          Node node = elementsByTagName.item(0);
          String modulusStr = node.getTextContent();
          return modulusStr;
     private byte[] b64Decode(String data) throws IOException {
          return Base64Util.decode(data);
     private BigInteger decodeBigDecimal(String str) throws IOException {
          byte decodedMod[] = b64Decode(str);
          byte positiveMod[] = new byte[decodedMod.length + 1];
          System.arraycopy(decodedMod, 0, positiveMod, 1, decodedMod.length);
          return new BigInteger(positiveMod);
Marcus Vin�cius Travassos Haickel de Oliveira
Software Architect
Live Source IT Solutions