/*	MessageDigestComputer.java
*	@author: Charles Bell
*	@version: Apr 20, 2002
*/

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.security.*;

import javax.swing.*;

/**	Computes the Message Digest of the Text contained in the text area and displays it
*	in the TextField when the Compute button is clicked.
*	Message Digest Algorithms:
*	MD2: The MD2 message digest algorithm as defined in RFC 1319.
*	MD5: The MD5 message digest algorithm as defined in RFC 1321. 
*	SHA-1: The Secure Hash Algorithm, as defined in Secure Hash Standard, NIST FIPS 180-1. 
*	SHA-256, SHA-384, and SHA-512: New hash algorithms for which the draft Federal Information
*	Processing Standard 180-2, Secure Hash Standard (SHS) is now available. SHA- 256 is a 256-bit 
*	hash function intended to provide 128 bits of security against collision attacks, while SHA-512 is 
*	a 512-bit hash function intended to provide 256 bits of security. A 384-bit hash may be obtained 
*	by truncating the SHA-512 output.
*/
public class MessageDigestComputer extends Applet implements ActionListener{

	JFrame frame;
	JTextArea editor;
	JTextField digestdisplay;
	MessageDigest messagedigest;
	boolean inanapplet = true;


	
	/**	Creates an instance of this class and initiates it. The variable
	*	inanapplet is only set to false when main is invoked, i.e. when 
	*	this is run as an application. 
	*/
	public static void main(String[] args){
		MessageDigestComputer computer = new MessageDigestComputer();
		computer.inanapplet = false; //otherwise in an applet it will be true
		computer.init();
	}

	/**	Initiates the user interface and initializes the Digest Algorithm
	*/
	public void init(){
		frame = new JFrame("MessageDigest");
		frame.setSize(450,450);
		if (!inanapplet){
			frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		}else{
			frame.setDefaultCloseOperation(WindowConstants.HIDE_ON_CLOSE);
		}
		JButton md5button = new JButton("Compute MD5");
		JButton sha1button = new JButton("Compute SHA-1");

		JButton exitbutton = new JButton("Exit");
		
		JPanel buttonpanel = new JPanel();
		md5button.addActionListener(this);
		sha1button.addActionListener(this);
		buttonpanel.add(md5button);
		buttonpanel.add(sha1button);
		
		exitbutton.addActionListener(this);
		buttonpanel.add(exitbutton);
		
		frame.getContentPane().add(buttonpanel,"North");
		editor = new JTextArea();
		frame.getContentPane().add(editor,"Center");
		digestdisplay = new JTextField();
		Font myfont = new Font("Monospaced",Font.PLAIN,12);
		editor.setFont(myfont);
		digestdisplay.setFont(myfont);
		frame.getContentPane().add(digestdisplay,"South");
		frame.show();
	}

	/**	initializes the Digest Algorithm
	*/
	public void setDigestAlgorithm(String algorithm){
		try{
			messagedigest = MessageDigest.getInstance(algorithm);
			displayDigest("");
		}catch(NoSuchAlgorithmException nsae){
			System.out.println("NoSuchAlgorithmException: " + nsae.getMessage());
			System.out.println("Should be SHA-1, MD2, or MD5.");
		}
	}

	/**	Gets the byte array corresponding to the text in the digestdisplay text area.
	*/
	public byte[] getDigestDisplayBytes(){
		return digestdisplay.getText().getBytes();
	}

	/**	Computes the message digest of the input string.
	*/
	public String computeDigestText(String s){
		messagedigest.reset();
		messagedigest.update(s.getBytes());
		byte[] digestarray = messagedigest.digest();
		String digesttext = "";
		for (int i = 0;i< digestarray.length;i++){
			int j = digestarray[i] & 0xFF;
			if (j < 16) digesttext = digesttext + "0";
			digesttext = digesttext + Integer.toString(j,16).toUpperCase() + " ";
		}
		return digesttext;
	}


	/**	Computes the message digest from the byte array given as input.
	*/
	public String computeDigestText(byte[] bytearray){
		messagedigest.reset();
		messagedigest.update(bytearray);
		byte[] digestarray = messagedigest.digest();
		String digesttext = "";
		for (int i = 0;i< digestarray.length;i++){
			int j = digestarray[i] & 0xFF;
			if (j < 16) digesttext = digesttext + "0";
			digesttext = digesttext + Integer.toString(j,16).toUpperCase() + " ";
		}
		return digesttext;
	}

	/**	Outputs the computed Message Digest to the digestdisplay JTextField.
	*/
	public void displayDigest(String text){
		digestdisplay.setText(text);
	}

	/**	Implemants the ActionListener interface providing response to buttons
	*	used in user interface.
	*/
	public void actionPerformed(ActionEvent actionevent){
		String commandstring = actionevent.getActionCommand();

		if (commandstring.compareTo("Compute MD5")==0){
			setDigestAlgorithm("MD5"); 
			byte[] bytearray = getDigestDisplayBytes();
			displayDigest(computeDigestText(bytearray));			
		}else if (commandstring.compareTo("Compute SHA-1")==0){
			setDigestAlgorithm("SHA-1"); 
			byte[] bytearray = getDigestDisplayBytes();
			displayDigest(computeDigestText(bytearray));			
		}else if (commandstring.compareTo("Exit") ==0){
			if (!inanapplet){
				System.exit(0);	
			}else{
				frame.hide();
			}
		}
	}
}