/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.xml.security.samples.encryption;

import java.io.File;
import java.io.FileOutputStream;

import java.security.Key;

import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESedeKeySpec;

import org.apache.xml.security.encryption.XMLCipher;
import org.apache.xml.security.utils.JavaUtils;
import org.apache.xml.security.utils.EncryptionConstants;

import org.w3c.dom.Document;
import org.w3c.dom.Element;

import javax.xml.transform.TransformerFactory;
import javax.xml.transform.Transformer;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.OutputKeys;

/**
 * This sample demonstrates how to decrypt data inside an xml document.
 *
 * @author Vishal Mahajan (Sun Microsystems)
 */
public class Decrypter {

    static org.slf4j.Logger log =
        org.slf4j.LoggerFactory.getLogger(
            Decrypter.class.getName());

    static {
        org.apache.xml.security.Init.init();
    }

    private static Document loadEncryptionDocument() throws Exception {
        String fileName = "build/encryptedInfo.xml";
        File encryptionFile = new File(fileName);
        javax.xml.parsers.DocumentBuilderFactory dbf =
            javax.xml.parsers.DocumentBuilderFactory.newInstance();
        dbf.setNamespaceAware(true);
        javax.xml.parsers.DocumentBuilder db = dbf.newDocumentBuilder();
        Document document = db.parse(encryptionFile);
        System.out.println(
            "Encryption document loaded from " + encryptionFile.toURI().toURL().toString()
        );
        return document;
    }

    private static SecretKey loadKeyEncryptionKey() throws Exception {
        String fileName = "build/kek";
        String jceAlgorithmName = "DESede";

        File kekFile = new File(fileName);

        DESedeKeySpec keySpec =
            new DESedeKeySpec(JavaUtils.getBytesFromFile(fileName));
        SecretKeyFactory skf =
             SecretKeyFactory.getInstance(jceAlgorithmName);
        SecretKey key = skf.generateSecret(keySpec);

        System.out.println(
            "Key encryption key loaded from " + kekFile.toURI().toURL().toString()
        );
        return key;
    }

    private static void outputDocToFile(Document doc, String fileName) throws Exception {
        File encryptionFile = new File(fileName);
        FileOutputStream f = new FileOutputStream(encryptionFile);

        TransformerFactory factory = TransformerFactory.newInstance();
        Transformer transformer = factory.newTransformer();
        transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        DOMSource source = new DOMSource(doc);
        StreamResult result = new StreamResult(f);
        transformer.transform(source, result);

        f.close();
        System.out.println(
            "Wrote document containing decrypted data to " + encryptionFile.toURI().toURL().toString()
        );
    }

    public static void main(String unused[]) throws Exception {
        Document document = loadEncryptionDocument();

        Element encryptedDataElement =
            (Element) document.getElementsByTagNameNS(
                EncryptionConstants.EncryptionSpecNS,
                EncryptionConstants._TAG_ENCRYPTEDDATA).item(0);

        /*
         * Load the key to be used for decrypting the xml data
         * encryption key.
         */
        Key kek = loadKeyEncryptionKey();

        String providerName = "BC";

        XMLCipher xmlCipher =
            XMLCipher.getInstance();
        /*
         * The key to be used for decrypting xml data would be obtained
         * from the keyinfo of the EncrypteData using the kek.
         */
        xmlCipher.init(XMLCipher.DECRYPT_MODE, null);
        xmlCipher.setKEK(kek);
        /*
         * The following doFinal call replaces the encrypted data with
         * decrypted contents in the document.
         */
        xmlCipher.doFinal(document, encryptedDataElement);

        outputDocToFile(document, "build/decryptedInfo.xml");
    }
}