Waqas Sadiq

In Java, The KeyPairGenerator class is used to create a pair of private/public keys. Java supports below three basic types of algorithms with keysize in parenthesis:

1. DiffieHellman (1024)
2. DSA (1024)
3. RSA (1024, 2048)

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.PrivateKey;
import java.security.PublicKey;

public class GenerateKeysEncoded {

 private KeyPairGenerator keyGen;
 private KeyPair pair;
 private PrivateKey privateKey;
 private PublicKey publicKey;

 public GenerateKeysEncoded(int keylength, String algorithm) throws NoSuchAlgorithmException, NoSuchProviderException {
  this.keyGen = KeyPairGenerator.getInstance(algorithm);
  this.keyGen.initialize(keylength);
 }

 public void createKeys() {
  this.pair = this.keyGen.generateKeyPair();
  this.privateKey = pair.getPrivate();
  this.publicKey = pair.getPublic();
 }

 public PrivateKey getPrivateKey() {
  return this.privateKey;
 }

 public PublicKey getPublicKey() {
  return this.publicKey;
 }

 public void writeToFile(String path, byte[] key) throws IOException {
  File f = new File(path);
  f.getParentFile().mkdirs();

  FileOutputStream fos = new FileOutputStream(f);
  fos.write(key);
  fos.flush();
  fos.close();
 }

 public static void main(String[] args) {
  GenerateKeysEncoded gk;
  try {
   gk = new GenerateKeysEncoded(1024, "RSA");
   gk.createKeys();
   gk.writeToFile("publicKey", gk.getPublicKey().getEncoded());
   gk.writeToFile("privateKey", gk.getPrivateKey().getEncoded());
  } catch (NoSuchAlgorithmException | NoSuchProviderException e) {
   System.err.println(e.getMessage());
  } catch (IOException e) {
   System.err.println(e.getMessage());
  }

 }

}