satsamidlet.java

Mobile Phone JSR 177 midlet example

//Copyright 2005 Nokia Corporation.
//
// THIS SOURCE CODE IS PROVIDED 'AS IS', WITH NO WARRANTIES WHATSOEVER,
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// FOR ANY PARTICULAR PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE
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// BY THIRD PARTIES
//
// Furthermore, information provided in this source code is preliminary,
// and may be changed substantially prior to final release. Nokia Corporation
// retains the right to make changes to this source code at
// any time, without notice. This source code is provided for informational
// purposes only.
//
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// Corporation.
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// Sun Microsystems, Inc.
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// trade names of their respective owners.
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// source code. The licensee has the right to market, sell, distribute and
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package satsa;

import java.security.GeneralSecurityException;
import javax.crypto.BadPaddingException;
import javax.microedition.lcdui.Display;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;

// Main SATSA MIDlet class
// It controls the state of the user interface
// and handles the encryption and decryption process
public class SATSAMIDlet extends MIDlet {
  private Display display;    
  private MessageStore messageStore;
  private ListScreen listScreen;
  private EncryptScreen encryptScreen;
  private PasswordScreen passwordScreen;
  private DecryptScreen decryptScreen;
  private InfoScreen infoScreen;
  private NewScreen newScreen;
  private Codec codec;

  public SATSAMIDlet() {}

  protected void destroyApp(boolean unconditional)
    throws MIDletStateChangeException
  {
    exitMIDlet();
  }

  protected void pauseApp()
  {
  }

  protected void startApp()
    throws MIDletStateChangeException
  {
    if (display == null)
    {
      initMIDlet();
    }
  }

  // Initialize all the internal fields
  private void initMIDlet()
  {
    // Init the user interface
    display = Display.getDisplay(this);
    listScreen = new ListScreen(this);
    encryptScreen = new EncryptScreen(this);
    passwordScreen = new PasswordScreen(this);
    decryptScreen = new DecryptScreen(this);
    infoScreen = new InfoScreen();
    newScreen = new NewScreen(this);
    
    // Initialize the Cryptographic Codec and the message store
    codec = new Codec(this);
    messageStore = new MessageStore(this);
    
    // Startup the UI
    showMessageList();
  }

  // Shows the list of existing messages
  void showMessageList()
  {
    messageStore.fillList(listScreen);
    display.setCurrent(listScreen);
  }

  // Shows an encrypted message in HEX format
  void showEncryptedMessage(int index)
  {
    encryptScreen.setIndex(index);
    encryptScreen.setMessage(codec
        .byteToHex(messageStore.getMessage(index+1)));
    display.setCurrent(encryptScreen);
  }

  // Displays the password screen
  void showPasswordScreen(int index)
  {
    passwordScreen.setIndex(index);
    display.setCurrent(passwordScreen);
  }

  // Shows a decrypted messages
  void showDecryptedMessage(int index, String password)
  {
    // 128bit (16 characters) key is needed for AES
    // just fill with blanks if too short
    while (password.length() <16 )
    {
      password = password.concat(" ");
    }
    decryptScreen.setIndex(index);
    byte message[] = messageStore.getMessage(index+1);
    // Do the decryption and validation in a separate thread
    new Thread(new CryptoRunnable(message,
        password.getBytes(),
        false)).start();
  }

  // Display an error message
  void showError(String messageString)
  {
    infoScreen.showError(messageString, Display.getDisplay(this));
  }

  // Delete a message
  void deleteMessage(int index)
  {
    messageStore.deleteMessage(index+1);
    messageStore.fillList(listScreen);
  }

  // Shows the new message
  void showNewMessage()
  {
    newScreen.createForm();
    display.setCurrent(newScreen);
  }

  // adds a new message encrypting it an storing in the record store
  void addNewMessage(String message, String password)
  {
    // 128bit (16 characters) key is needed for AES
    // just fill with blanks if too short
    while (password.length() <16 )
    {
      password = password.concat(" ");
    }
    // Do the encryption in a separate thread
    new Thread(new CryptoRunnable(message.getBytes(),
        password.getBytes(),
        true)).start();      
  }

  void exitMIDlet()
  {
    if (messageStore != null) {
  	messageStore.close();
    }   
    notifyDestroyed();
  }
  
  // Internal class to handle the decryption and encryption
  // process in a separate thread as recommended in SATSA-CRYPTO
  private class CryptoRunnable implements Runnable {
    private byte[] message, password;
    private boolean encryption;
    
    CryptoRunnable(byte[] message, byte[] password, boolean encryption) {
      this.message = message;
      this.password = password;
      this.encryption = encryption;
    }
    
    public void run() {
      if (encryption) {
        try
        {
          // Encrypt the message
          byte[] encryptedMessage = codec.encrypt(password, message);
          // Calculate the digest of the encrypted message
          byte[] digest = codec.digest(encryptedMessage);
          // Compose the overall message
          byte[] messageBytes = 
            new byte[encryptedMessage.length + digest.length];
          System.arraycopy(digest, 0, messageBytes, 0, digest.length);
          System.arraycopy(encryptedMessage,
              0,
              messageBytes,
              digest.length,
              encryptedMessage.length);
          // Store the encoded message
          messageStore.addMessage(messageBytes);
        }
        catch (GeneralSecurityException gse)
        {
          // Use of generic Exception type since mutiple
          // exceptions may be thrown at this point
          showError("General Security Exception while encrypting: "
              + gse.toString());
        }
        showMessageList();
      } else {
        try
        {
          // Get the cipher text and the digest
          // SHA-1 digest is 160 bits long
          byte[] digest = new byte[20];
          byte[] cipherText = new byte[message.length-digest.length];
          // Decompose the message
          System.arraycopy(message, 0, digest, 0, digest.length);
          System.arraycopy(message,
              digest.length,
              cipherText,
              0,
              cipherText.length);
          
          // Verify the cipher's text digest
          if (codec.isDigestValid(cipherText, digest)) {
            // If digest is ok, let's decrypt
            byte[] plainText = codec.decrypt(password, cipherText);        
             
            // Display the message on screen
            decryptScreen.setMessage(new String(plainText));
            display.setCurrent(decryptScreen);
          } else {
            showError("Digest of message is not valid");
          }            
        }
        catch (BadPaddingException bpe)
        {
          // This is a particular exception when the password is incorrect
          showError("Incorrect password.");
        }
        catch (GeneralSecurityException gse)
        {
          // Handles all other exceptions
          showError("General Security Exception while decrypting: "
              + gse.toString());
        }
      }
    }
  }
}