Java tutorial
/* * Copyright (c) 2000 David Flanagan. All rights reserved. * This code is from the book Java Examples in a Nutshell, 2nd Edition. * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied. * You may study, use, and modify it for any non-commercial purpose. * You may distribute it non-commercially as long as you retain this notice. * For a commercial use license, or to purchase the book (recommended), * visit http://www.davidflanagan.com/javaexamples2. */ import java.io.DataInputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.security.InvalidKeyException; import java.security.NoSuchAlgorithmException; import java.security.Provider; import java.security.Security; import java.security.spec.InvalidKeySpecException; import javax.crypto.BadPaddingException; import javax.crypto.Cipher; import javax.crypto.CipherOutputStream; import javax.crypto.IllegalBlockSizeException; import javax.crypto.KeyGenerator; import javax.crypto.NoSuchPaddingException; import javax.crypto.SecretKey; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.DESedeKeySpec; /** * This class defines methods for encrypting and decrypting using the Triple DES * algorithm and for generating, reading and writing Triple DES keys. It also * defines a main() method that allows these methods to be used from the command * line. */ public class TripleDES { /** * The program. The first argument must be -e, -d, or -g to encrypt, * decrypt, or generate a key. The second argument is the name of a file * from which the key is read or to which it is written for -g. The -e and * -d arguments cause the program to read from standard input and encrypt or * decrypt to standard output. */ public static void main(String[] args) { try { // Check to see whether there is a provider that can do TripleDES // encryption. If not, explicitly install the SunJCE provider. try { Cipher c = Cipher.getInstance("DESede"); } catch (Exception e) { // An exception here probably means the JCE provider hasn't // been permanently installed on this system by listing it // in the $JAVA_HOME/jre/lib/security/java.security file. // Therefore, we have to install the JCE provider explicitly. System.err.println("Installing SunJCE provider."); Provider sunjce = new com.sun.crypto.provider.SunJCE(); Security.addProvider(sunjce); } // This is where we'll read the key from or write it to File keyfile = new File(args[1]); // Now check the first arg to see what we're going to do if (args[0].equals("-g")) { // Generate a key System.out.print("Generating key. This may take some time..."); System.out.flush(); SecretKey key = generateKey(); writeKey(key, keyfile); System.out.println("done."); System.out.println("Secret key written to " + args[1] + ". Protect that file carefully!"); } else if (args[0].equals("-e")) { // Encrypt stdin to stdout SecretKey key = readKey(keyfile); encrypt(key, System.in, System.out); } else if (args[0].equals("-d")) { // Decrypt stdin to stdout SecretKey key = readKey(keyfile); decrypt(key, System.in, System.out); } } catch (Exception e) { System.err.println(e); System.err.println("Usage: java " + TripleDES.class.getName() + " -d|-e|-g <keyfile>"); } } /** Generate a secret TripleDES encryption/decryption key */ public static SecretKey generateKey() throws NoSuchAlgorithmException { // Get a key generator for Triple DES (a.k.a DESede) KeyGenerator keygen = KeyGenerator.getInstance("DESede"); // Use it to generate a key return keygen.generateKey(); } /** Save the specified TripleDES SecretKey to the specified file */ public static void writeKey(SecretKey key, File f) throws IOException, NoSuchAlgorithmException, InvalidKeySpecException { // Convert the secret key to an array of bytes like this SecretKeyFactory keyfactory = SecretKeyFactory.getInstance("DESede"); DESedeKeySpec keyspec = (DESedeKeySpec) keyfactory.getKeySpec(key, DESedeKeySpec.class); byte[] rawkey = keyspec.getKey(); // Write the raw key to the file FileOutputStream out = new FileOutputStream(f); out.write(rawkey); out.close(); } /** Read a TripleDES secret key from the specified file */ public static SecretKey readKey(File f) throws IOException, NoSuchAlgorithmException, InvalidKeyException, InvalidKeySpecException { // Read the raw bytes from the keyfile DataInputStream in = new DataInputStream(new FileInputStream(f)); byte[] rawkey = new byte[(int) f.length()]; in.readFully(rawkey); in.close(); // Convert the raw bytes to a secret key like this DESedeKeySpec keyspec = new DESedeKeySpec(rawkey); SecretKeyFactory keyfactory = SecretKeyFactory.getInstance("DESede"); SecretKey key = keyfactory.generateSecret(keyspec); return key; } /** * Use the specified TripleDES key to encrypt bytes from the input stream * and write them to the output stream. This method uses CipherOutputStream * to perform the encryption and write bytes at the same time. */ public static void encrypt(SecretKey key, InputStream in, OutputStream out) throws NoSuchAlgorithmException, InvalidKeyException, NoSuchPaddingException, IOException { // Create and initialize the encryption engine Cipher cipher = Cipher.getInstance("DESede"); cipher.init(Cipher.ENCRYPT_MODE, key); // Create a special output stream to do the work for us CipherOutputStream cos = new CipherOutputStream(out, cipher); // Read from the input and write to the encrypting output stream byte[] buffer = new byte[2048]; int bytesRead; while ((bytesRead = in.read(buffer)) != -1) { cos.write(buffer, 0, bytesRead); } cos.close(); // For extra security, don't leave any plaintext hanging around memory. java.util.Arrays.fill(buffer, (byte) 0); } /** * Use the specified TripleDES key to decrypt bytes ready from the input * stream and write them to the output stream. This method uses uses Cipher * directly to show how it can be done without CipherInputStream and * CipherOutputStream. */ public static void decrypt(SecretKey key, InputStream in, OutputStream out) throws NoSuchAlgorithmException, InvalidKeyException, IOException, IllegalBlockSizeException, NoSuchPaddingException, BadPaddingException { // Create and initialize the decryption engine Cipher cipher = Cipher.getInstance("DESede"); cipher.init(Cipher.DECRYPT_MODE, key); // Read bytes, decrypt, and write them out. byte[] buffer = new byte[2048]; int bytesRead; while ((bytesRead = in.read(buffer)) != -1) { out.write(cipher.update(buffer, 0, bytesRead)); } // Write out the final bunch of decrypted bytes out.write(cipher.doFinal()); out.flush(); } }