StackOverflow - Q13271184 - Example

package stackoverflow;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;

/**
 * @author TheLima
 */
public class Q_13271184 {

    private static final File DESKTOP =
                    new File(System.getProperty("user.home") + "/Desktop");
    private static final File BASE_PDF = new File(DESKTOP, "Placas_teste.pdf");
    private static final byte[] SALT = {
        (byte) 0xde, (byte) 0x33, (byte) 0x10, (byte) 0x12,
        (byte) 0xde, (byte) 0x33, (byte) 0x10, (byte) 0x12,};
    private static final char[] KEY = "Just A Key For Testing".toCharArray();

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws GeneralSecurityException, IOException {
        byte[] content = readFile(BASE_PDF);
        System.out.println("ORIGINAL: " + new String(content).substring(0, 8));
        byte[] encrypted = encrypt(content);
        System.out.println("ENCRYPTED: " + new String(encrypted).substring(0, 8));
        File encryptedFile = new File(DESKTOP, "EncryptedPDF.pdf");
        saveFile(encrypted, encryptedFile);
        content = readFile(encryptedFile);
        byte[] decrypted = decrypt(content);
        System.out.println("DECRYPTED: " + new String(decrypted).substring(0, 8));
        File decryptedFile = new File(DESKTOP, "DecryptedPDF.pdf");
        saveFile(decrypted, decryptedFile);
    }

    private static byte[] encrypt(byte[] bytes) throws GeneralSecurityException {
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
        SecretKey key = keyFactory.generateSecret(new PBEKeySpec(KEY));
        Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
        pbeCipher.init(Cipher.ENCRYPT_MODE, key, new PBEParameterSpec(SALT, 20));

        //Encrypt and save to temporary storage.
        byte[] encrypted = pbeCipher.doFinal(bytes);

        //Cleanup data-sources - Leave no traces behind.
        for (int i = 0; i < bytes.length; i++) {
            bytes[i] = 0;
        }
        bytes = null;
        System.gc();

        //Return encryption result.
        return encrypted;
    }

    private static byte[] decrypt(byte[] bytes) throws GeneralSecurityException {
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
        SecretKey key = keyFactory.generateSecret(new PBEKeySpec(KEY));
        Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
        pbeCipher.init(Cipher.DECRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
        return pbeCipher.doFinal(bytes);
    }

    private static byte[] readFile(File file) {
        byte[] content = null;
        InputStream is;
        try {
            is = new FileInputStream(file);
            BufferedInputStream vf = new BufferedInputStream(is);
            content = new byte[(file.length() <= Integer.MAX_VALUE)
                            ? (int) file.length() : Integer.MAX_VALUE];
//          content = new byte[is.available()];

            System.out.printf("file.length() : %d\nis.available() : %d",
                            file.length(), is.available());

            vf.read(content);
            is.close();
        } catch (FileNotFoundException ex) {
            Logger.getLogger(Q_13271184.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(Q_13271184.class.getName()).log(Level.SEVERE, null, ex);
        }
        return content;
    }

    public static void saveFile(byte[] bytes, File file) throws IOException {
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(file));
        bos.write(bytes);
        bos.flush();
        bos.close();
    }
}