Key Pair Sample Program - JcaKeyPair.java

Cryptography Tutorials - Herong's Tutorial Examples

∟Private key and Public Key Pair Generation

∟Key Pair Sample Program - JcaKeyPair.java

This section provides a tutorial example on how to write simple program to generate a pair of private key and public key for the RSA or DSA algorithm.

The following sample program shows you how to invoke the key pair generation algorithms implemented by the default provider, Sun, and generate key pairs.

/* JcaKeyPair.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.io.*;
import java.math.*;
import java.security.*;
import java.security.interfaces.*;
class JcaKeyPair {
   public static void main(String[] a) {
      if (a.length<3) {
         System.out.println("Usage:");
         System.out.println("java JcaKeyPair keySize output"
            +" algorithm");
         return;
      }
      int keySize = Integer.parseInt(a[0]);
      String output = a[1];
      String algorithm = a[2]; // RSA, DSA
      try {
         getKeys(keySize,output,algorithm);
      } catch (Exception e) {
         System.out.println("Exception: "+e);
         return;
      }
   }
   private static void getKeys(int keySize, String output, 
         String algorithm) throws Exception {
      KeyPairGenerator kg = KeyPairGenerator.getInstance(algorithm);
      kg.initialize(keySize);
      System.out.println();
      System.out.println("KeyPairGenerator Object Info: ");
      System.out.println("Algorithm = "+kg.getAlgorithm());
      System.out.println("Provider = "+kg.getProvider());
      System.out.println("Key Size = "+keySize);
      System.out.println("toString = "+kg.toString());
      KeyPair pair = kg.generateKeyPair();
      PrivateKey priKey = pair.getPrivate();
      PublicKey pubKey = pair.getPublic();
      String fl = output+".pri";
      FileOutputStream out = new FileOutputStream(fl);
      byte[] ky = priKey.getEncoded();
      out.write(ky);
      out.close();
      System.out.println();
      System.out.println("Private Key Info: ");
      System.out.println("Algorithm = "+priKey.getAlgorithm());
      System.out.println("Saved File = "+fl);
      System.out.println("Size = "+ky.length);
      System.out.println("Format = "+priKey.getFormat());
      System.out.println("toString = "+priKey.toString());
      fl = output+".pub";
      out = new FileOutputStream(fl);
      ky = pubKey.getEncoded();
      out.write(ky);
      out.close();
      System.out.println();
      System.out.println("Public Key Info: ");
      System.out.println("Algorithm = "+pubKey.getAlgorithm());
      System.out.println("Saved File = "+fl);
      System.out.println("Size = "+ky.length);
      System.out.println("Format = "+pubKey.getFormat());
      System.out.println("toString = "+pubKey.toString());
   }
}

Note that:

KeyPairGenerator.getInstance(algorithm) method is called to get default key pair generator of the specified algorithm.
generateKeyPair() method is called to return a new pair of private key and public key.
getPrivate() method is called to return the private key from the key pair.
getPublic() method is called to return the public key from the key pair.
getEncoded() method is called to convert the key to an encoded byte stream.