import java.security.*;
import javax.crypto.*;
//
// Public Key cryptography using the RSA algorithm.
public class PublicExample {

  public static void main (String[] args) throws Exception {
    //
    // check args and get plaintext
    if (args.length !=1) {
      System.err.println("Usage: java PublicExample text");
      System.exit(1);
    }
    byte[] plainText = args[0].getBytes("UTF8");
    //
    // generate an RSA key
    System.out.println( "\nStart generating RSA key" );
    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
    keyGen.initialize(1024);
    KeyPair key = keyGen.generateKeyPair();
    System.out.println( "Finish generating RSA key" );
    //
    // get an RSA cipher object and print the provider   
    Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
    System.out.println( "\n" + cipher.getProvider().getInfo() );
    //
    // encrypt the plaintext using the public key
    System.out.println( "\nStart encryption" );
    cipher.init(Cipher.ENCRYPT_MODE, key.getPublic());
    byte[] cipherText = cipher.doFinal(plainText);
    System.out.println( "Finish encryption: " );
    System.out.println( new String(cipherText, "UTF8") );
    //
    // decrypt the ciphertext using the private key
    System.out.println( "\nStart decryption" );
    cipher.init(Cipher.DECRYPT_MODE, key.getPrivate());
    byte[] newPlainText = cipher.doFinal(cipherText);
    System.out.println( "Finish decryption: " );
    System.out.println( new String(newPlainText, "UTF8") );
  }
}