DsaKeyGenerator.java - Generating DSA Key Pair

Cryptography Tutorials - Herong's Tutorial Examples

∟DsaKeyGenerator.java - Generating DSA Key Pair

This section provides a tutorial example on how to using the Java default implementation of DSA (Digital Signature Algorithm) to generate DSA key pair, public key and private key.

Implementing the DSA digital signature algorithm from scratch is not easy. What we can do is to use the default implementation of DSA in Java SE 6.0.

The first Java program I wrote is to generate a DSA key pair, public key and private key:

/* DsaKeyGenerator.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.io.*;
import java.math.*;
import java.security.*;
import java.security.interfaces.*;
class DsaKeyGenerator {
   public static void main(String[] a) {
      if (a.length<2) {
         System.out.println("Usage:");
         System.out.println("java DsaKeyGenerator keySize output");
         return;
      }
      int keySize = Integer.parseInt(a[0]);
      String output = a[1];
      String algorithm = "DSA";
      try {
         genKeyPair(keySize,output,algorithm);
      } catch (Exception e) {
         System.out.println("Exception: "+e);
         return;
      }
   }
   private static void genKeyPair(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());
   }
}

Some notes on DsaKeyGenerator.java:

The java.security.KeyPairGenerator.getInstance(algorithm) method is used to create a key pair generator object for the specified algorithm, "DSA".
The java.security.KeyPairGenerator.initialize() method is used to initialize the key pair generator with the specified key size.
The java.security.KeyPairGenerator.generateKeyPair() method is used to generate a new key pair.
The java.security.Key.getEncoded() method is used to convert the key to a byte array using the default encoding.
The java.io.FileOutputStream.write() method is used to dump the byte array to a file.