JceSecretCipher.java - Secret Key Encryption Sample Program

Cryptography Tutorials - Herong's Tutorial Examples

∟Cipher - Secret Key Encryption and Decryption

∟JceSecretCipher.java - Secret Key Encryption Sample Program

This section provides a tutorial example on how to write a secret key encryption and description program using the javax.crypto.Cipher class.

The following sample program shows you how to do encryption and decryption with a secret key using the javax.crypto.Cipher class:

/* JceSecretCipher.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.io.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
class JceSecretCipher {
   public static void main(String[] a) {
      if (a.length<5) {
         System.out.println("Usage:");
         System.out.println("java JceSecretCipher algorithm mode"
            +" keyFile input output");
         return;
      }
      String algorithm = a[0];
      String mode = a[1];
      String keyFile = a[2];
      String input = a[3];
      String output = a[4];
      try {
         SecretKey ky = readKey(keyFile,algorithm);
         secretCipher(algorithm, mode, ky, input, output);
      } catch (Exception e) {
         System.out.println("Exception: "+e);
         return;
      }
   }
   private static SecretKey readKey(String input, String algorithm) 
      throws Exception {
      String fl = input;
      FileInputStream fis = new FileInputStream(fl);
      int kl = fis.available();
      byte[] kb = new byte[kl];
      fis.read(kb);
      fis.close();
      KeySpec ks = null;
      SecretKey ky = null;
      SecretKeyFactory kf = null;
      if (algorithm.equalsIgnoreCase("DES")) {
         ks = new DESKeySpec(kb);
         kf = SecretKeyFactory.getInstance("DES");
         ky = kf.generateSecret(ks);
      } else if (algorithm.equalsIgnoreCase("DESede")) {
         ks = new DESedeKeySpec(kb);
         kf = SecretKeyFactory.getInstance("DESede");
         ky = kf.generateSecret(ks);
      } else {
         ks = new SecretKeySpec(kb,algorithm);
         ky = new SecretKeySpec(kb,algorithm);
      }
      System.out.println();
      System.out.println("KeySpec Object Info: ");
      System.out.println("Saved File = "+fl);
      System.out.println("Length = "+kb.length);
      System.out.println("toString = "+ks.toString());
      System.out.println();
      System.out.println("SecretKey Object Info: ");
      System.out.println("Algorithm = "+ky.getAlgorithm());
      System.out.println("toString = "+ky.toString());
      return ky;
   }

   private static void secretCipher(String algorithm, String mode,
      SecretKey ky, String input, String output) throws Exception {
      Cipher cf = Cipher.getInstance(algorithm);
      if (mode.equalsIgnoreCase("encrypt")) 
         cf.init(Cipher.ENCRYPT_MODE,ky);
      else if (mode.equalsIgnoreCase("decrypt"))
         cf.init(Cipher.DECRYPT_MODE,ky);
      else
         throw new Exception("Invalid mode: "+mode);
      System.out.println();
      System.out.println("Cipher Object Info: ");
      System.out.println("Block Size = "+cf.getBlockSize());
      System.out.println("Algorithm = "+cf.getAlgorithm());
      System.out.println("Provider = "+cf.getProvider());
      System.out.println("toString = "+cf.toString());

      FileInputStream fis = new FileInputStream(input);
      FileOutputStream fos = new FileOutputStream(output);
      int bufSize = 1024;
      byte[] buf = new byte[bufSize];
      int n = fis.read(buf,0,bufSize);
      int fisSize = 0;
      int fosSize = 0;
      while (n!=-1) {
         fisSize += n;
         byte[] out = cf.update(buf,0,n);
         fosSize += out.length;
         fos.write(out);
         n = fis.read(buf,0,bufSize);
      }
      byte[] out = cf.doFinal();
      fosSize += out.length;
      fos.write(out);
      fis.close();
      fos.close();
      System.out.println();
      System.out.println("Cipher Process Info: ");
      System.out.println("Input Size = "+fisSize);
      System.out.println("Output Size = "+fosSize);
   }
}

Note that:

This sample program requires a secret key file as described in the previous section.
If want to, you could also create a secret key by yourself as any byte array. But the size of the key should meet the requirement of the encryption algorithm. For example, DES requires that the key to be 8 bytes long.