JcePublicCipher.java - Private and Public Key Encryption

JDK Tutorials - Herong's Tutorial Examples

∟Cipher - Secret Key Encryption and Decryption

∟JcePublicCipher.java - Private and Public Key Encryption

This section provides a sample program on how the javax.crypto.Cipher class could be used to perform private and public key encryption with DSA or RSA algorithm.

The following sample program shows you how to do encryption and decryption with a private and public key pair:

/* JcePublicCipher.java
 - Copyright (c) 2014, HerongYang.com, All Rights Reserved.
 */
import java.io.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
class JcePublicCipher {
   public static void main(String[] a) {
      if (a.length<5) {
         System.out.println("Usage:");
         System.out.println("java JcePublicCipher 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 {
         Key ky = readKey(algorithm, mode, keyFile);
         publicCipher(algorithm, mode, ky, input, output);
      } catch (Exception e) {
         System.out.println("Exception: "+e);
         return;
      }
   }
   private static Key readKey(String algorithm, String mode,
      String input) throws Exception {
      KeyFactory keyFactory = KeyFactory.getInstance(algorithm);
      System.out.println();
      System.out.println("KeyFactory Object Info: ");
      System.out.println("Algorithm = "+keyFactory.getAlgorithm());
      System.out.println("Provider = "+keyFactory.getProvider());
      System.out.println("toString = "+keyFactory.toString());

      FileInputStream fis = new FileInputStream(input);
      int kl = fis.available();
      byte[] kb = new byte[kl];
      fis.read(kb);
      fis.close();
      Key ky = null;
      if (mode.equalsIgnoreCase("encrypt")) {
         X509EncodedKeySpec pubKeySpec 
            = new X509EncodedKeySpec(kb);
         ky = keyFactory.generatePublic(pubKeySpec);
      } else if (mode.equalsIgnoreCase("decrypt")) {
         PKCS8EncodedKeySpec priKeySpec 
            = new PKCS8EncodedKeySpec(kb);
         ky = keyFactory.generatePrivate(priKeySpec);
      } else
         throw new Exception("Invalid mode: "+mode);
      System.out.println();
      System.out.println("Key Object Info: ");
      System.out.println("Algorithm = "+ky.getAlgorithm());
      System.out.println("Saved File = "+input);
      System.out.println("Length = "+kl);
      System.out.println("Format = "+ky.getFormat());
      System.out.println("toString = "+ky.toString());
      return ky;
   }
   private static void publicCipher(String algorithm, String mode,
      Key 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);
   }
}

See the next section for test result of this sample program.

Last update: 2014.

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