Suatu pesan yang tidak disandikan disebut sebagai plaintext ataupun dapat disebut juga sebagai cleartext. Proses yang dilakukan untuk mengubah plaintext ke dalam ciphertext disebut encryption atau encipherment. Sedangkan proses untuk mengubah ciphertext kembali ke plaintext disebut decryption atau decipherment.
Berikut ini adalah contoh enkripsi menggunakan XOR :
Berikut ini Source Code-nya menggunakan Java Applet :
import java.applet.*;
import java.awt.*;
public class EncryptXOR extends Applet
{
// Applet instance variables:
private Dimension dApplet = null;
private Image imOffScreen = null;
private Graphics grOffScreen = null;
private Button btnRandomKey = null;
private Button btnEncrypt = null;
private TextArea taCryptText = null;
private TextArea taPlainText = null;
private TextArea taKeyText = null;
private Label lblOne = null; // First label.
private Label lblTwo = null; // Second label.
private Label lblThree = null; // Third label.
private Label lblMessage = null; // Message label.
// Initialize the applet
public void init()
{
int i = 0;
this.setBackground(Color.lightGray);
GridBagLayout gbl = null;
GridBagConstraints gbc = null;
dApplet = this.size();
gbl = new GridBagLayout();
this.setLayout(gbl);
gbc = new GridBagConstraints();
gbc.insets = new Insets(5, 10, 5, 10); // top, left, bottom, right.
gbc.weightx = 0.0;
gbc.weighty = 0.0;
gbc.gridx = 0;
// First Label
lblOne = new Label("Plain Text", Label.CENTER);
gbc.gridy = 0;
gbl.setConstraints(lblOne, gbc);
this.add(lblOne);
// Add the plain text box:
taPlainText = new TextArea("", 6, 80); // 6 rows and 80 columns.
taPlainText.setEditable(true);
gbc.gridy = 1;
gbl.setConstraints(taPlainText, gbc);
this.add(taPlainText);
// Second Label
lblTwo = new Label("Key Text", Label.CENTER);
gbc.gridy = 2;
gbl.setConstraints(lblTwo, gbc);
this.add(lblTwo);
// Add the Key text box:
taKeyText = new TextArea("", 6, 80); // 6 rows and 80 columns.
taKeyText.setEditable(true);
gbc.gridy = 3;
gbl.setConstraints(taKeyText, gbc);
this.add(taKeyText);
// Add the random button:
btnRandomKey = new Button("Generate Random Key");
btnRandomKey.setForeground(Color.black);
btnRandomKey.setBackground(Color.lightGray);
gbc.gridy = 4;
gbl.setConstraints(btnRandomKey, gbc);
this.add(btnRandomKey);
// Message Label
lblMessage = new Label( "Type or paste text into the upper two text boxes.", Label.CENTER);
gbc.gridy = 5;
gbl.setConstraints(lblMessage, gbc);
this.add(lblMessage);
// Add the encrypt button:
btnEncrypt = new Button("Encrypt the Text");
btnEncrypt.setForeground(Color.black);
btnEncrypt.setBackground(Color.lightGray);
gbc.gridy = 6;
gbl.setConstraints(btnEncrypt, gbc);
this.add(btnEncrypt);
// Third Label
lblThree = new Label("Encrypted Text", Label.CENTER);
gbc.gridy = 7;
gbl.setConstraints(lblThree, gbc);
this.add(lblThree);
// Add the crypt text box:
taCryptText = new TextArea("", 6, 80); // 6 rows and 80 columns.
taCryptText.setEditable(true);
gbc.gridy = 8;
gbl.setConstraints(taCryptText, gbc);
this.add(taCryptText);
} // End of init()
// Execute this code after initialization
public void start()
{
System.out.println("\n" + this.getAppletInfo()); // Identify self to the Java console-aware user
taPlainText.requestFocus();
} // End of start()
// Implements double buffering
public void update(Graphics g)
{
if (imOffScreen == null)
{
// Make sure the offscreen and graphics exist:
imOffScreen = this.createImage(dApplet.width, dApplet.height);
grOffScreen = imOffScreen.getGraphics();
grOffScreen.clearRect(0, 0, dApplet.width, dApplet.height);
}
this.paint(grOffScreen);
g.drawImage(imOffScreen, 0, 0, null);
}
// The applet frame painting function
public void paint(Graphics g)
{
// Code for displaying images or drawing in the applet frame (called by the OS).
g.clearRect(0, 0, dApplet.width, dApplet.height); // Needed for double buffering.
this.setBackground(Color.lightGray); // Ditto.
drawFrame(g); // Draw the frame abound the applet.
} // End of function paint()
private void drawFrame(Graphics g)
{
// Draw a recessed frame around the applet border. Designed for gray-on-gray browser background.
g.setColor(Color.black);
g.drawLine(0, 0, dApplet.width - 1, 0);
g.drawLine(0, 0, 0, dApplet.height - 1);
g.setColor(Color.white);
g.drawLine(0, dApplet.height - 1, dApplet.width - 1, dApplet.height - 1);
g.drawLine(dApplet.width - 1, 1, dApplet.width - 1, dApplet.height - 1);
}
public boolean action(Event e, Object o)
{
if (e.target == btnEncrypt)
{
btnEncrypt.disable();
if (taPlainText.getText().length() == 0)
{
System.out.println("Plaintext Empty");
lblMessage.setText("Plaintext Empty");
}
else
{
if (taKeyText.getText().length() == 0)
{
System.out.println("Keytext Empty");
lblMessage.setText("Keytext Empty");
}
else
{
// We can do the key computation
encrypt();
}
}
btnEncrypt.enable();
}
if (e.target == btnRandomKey)
{
int i = 0;
int iTemp = 0;
int iPlainLength = 0;
StringBuffer sbTemp = null;
sbTemp = new StringBuffer();
iPlainLength = taPlainText.getText().length();
if (iPlainLength > 0)
{
for (i = 0; i < iPlainLength; i++)
{
iTemp = (int) (128 * Math.random());
sbTemp.append(iTemp);
if (i < iPlainLength - 1)
{
sbTemp.append(' ');
}
}
taKeyText.setText(sbTemp.toString());
lblMessage.setText("Generated random key of " + iPlainLength + " characters.");
}
else
{
taKeyText.setText("");
lblMessage.setText("Need some plaintext to generate a key.");
}
}
return true; // Absorb the event;
} // End of action().
public boolean handleEvent(Event e)
{
int iLength = 0;
if (e.target == btnEncrypt && e.id == Event.ACTION_EVENT)
{
btnEncrypt.disable();
if (taPlainText.getText().length() == 0)
{
System.out.println("Plaintext Empty");
lblMessage.setText("Plaintext Empty");
}
else
{
if (taKeyText.getText().length() == 0)
{
System.out.println("Keytext Empty");
lblMessage.setText("Keytext Empty");
}
else
{
// We can do the key computation
encrypt();
}
}
btnEncrypt.enable();
return true;
}
if (e.target == btnRandomKey && e.id == Event.ACTION_EVENT)
{
int i = 0;
int iTemp = 0;
int iPlainLength = 0;
StringBuffer sbTemp = null;
sbTemp = new StringBuffer();
iPlainLength = taPlainText.getText().length();
if (iPlainLength > 0)
{
for (i = 0; i < iPlainLength; i++)
{
iTemp = (int) (128 * Math.random());
sbTemp.append(iTemp);
if (i < iPlainLength - 1)
{
sbTemp.append(' ');
}
}
taKeyText.setText(sbTemp.toString());
lblMessage.setText("Generated random key of " + iPlainLength + " characters.");
}
else
{
taKeyText.setText("");
lblMessage.setText("Need some plaintext to generate a key.");
}
return true;
}
if (e.target == taPlainText)
{
if (e.id != Event.GOT_FOCUS)
{
iLength = taPlainText.getText().length();
lblMessage.setText("Plain text is " + iLength + " characters long.");
}
}
if (e.target == taKeyText)
{
if (e.id != Event.GOT_FOCUS)
{
iLength = taKeyText.getText().length();
lblMessage.setText("Key text is " + iLength + " characters long.");
}
}
return false;
}
private void encrypt()
{
int i = 0;
int iPlainLength = 0;
int iKeyLength = 0;
int iKeyTextLength = 0;
int iDelta = 0;
int iTemp = 0;
char cTemp = 0;
String sTemp = null;
String sPlainText = null;
String sKeyText = null;
String sCryptText = null;
StringBuffer sbTemp = null;
int iKey[] = null;
int iKeyBuffer[] = null;
boolean bNumericKey = false;
sPlainText = taPlainText.getText();
sKeyText = taKeyText.getText();
iPlainLength = sPlainText.length();
iKeyTextLength = sKeyText.length();
System.out.println("\n");
// Find out if the key is numeric:
if (numericP(iKeyTextLength, sKeyText))
{
bNumericKey = true;
System.out.println("The key is numeric.");
// Fill the key array:
iKey = new int[iKeyTextLength];
while (i < iKeyTextLength)
{
cTemp = 0;
sbTemp = new StringBuffer();
while (cTemp != ' ' && i < iKeyTextLength)
{
try
{
cTemp = sKeyText.charAt(i);
}
catch (StringIndexOutOfBoundsException e1)
{
System.out.println("Caught StringIndexOutOfBoundsException in decrypt() (key).");
}
if (cTemp != ' ')
{
sbTemp.append(cTemp);
}
i++;
}
try
{
iTemp = Integer.parseInt(sbTemp.toString());
}
catch (NumberFormatException e2)
{
System.out.println("Caught NumberFormatException in decrypt() (key).");
break;
}
iKey[iKeyLength] = iTemp;
iKeyLength++;
}
}
else
{
System.out.println("The key is not numeric.");
iKeyLength = iKeyTextLength;
}
if (iPlainLength < iKeyLength)
{
// Pad out the crypttext.
System.out.println("Key is longer than plaintext: padding plaintext with spaces.");
lblMessage.setText("Key is longer than plaintext: padding plaintext with spaces.");
sbTemp = new StringBuffer();
iDelta = iKeyLength - iPlainLength;
for (i = 0; i < iDelta; i++)
{
sbTemp.append(" ");
}
sPlainText = sPlainText + sbTemp.toString();
taPlainText.setText(sPlainText);
iPlainLength = sPlainText.length();
}
else
{
if (iKeyLength < iPlainLength)
{
// Repeat the key as necessary to make it long enough.
System.out.println("Key is shorter than plaintext: repeating the key.");
lblMessage.setText("Key is shorter than plaintext: repeating the key.");
if (bNumericKey)
{
iKeyBuffer = new int[iKeyLength]; // Need to stash the key characters someplace
for (i = 0; i < iKeyLength; i++) // while we get more memory for the array.
{
iKeyBuffer[i] = iKey[i];
}
iKey = new int[iPlainLength]; // Expand the key array.
for (i = 0; i < iKeyLength; i++)
{
iKey[i] = iKeyBuffer[i];
}
for (i = iKeyLength; i < iPlainLength; i++)
{
iKey[i] = iKey[i - iKeyLength];
}
}
else
{
// The key is printable text:
sbTemp = new StringBuffer(sKeyText);
for (i = iKeyLength; i < iPlainLength; i++)
{
sbTemp.append(sbTemp.charAt(i - iKeyLength));
}
sKeyText = sbTemp.toString();
iKeyLength = sKeyText.length();
}
}
else
{
// They are equal in length, do nothing.
}
}
// Begin the encryption.
sbTemp = new StringBuffer();
for (i = 0; i < iPlainLength; i++)
{
if (bNumericKey)
{
iTemp = sPlainText.charAt(i) ^ iKey[i]; // XOR encryption
}
else
{
iTemp = sPlainText.charAt(i) ^ sKeyText.charAt(i); // XOR encryption
}
sbTemp.append((char) iTemp);
}
sTemp = sbTemp.toString();
if (unprintableP(iPlainLength, sTemp))
{
System.out.println("Unprintable encrypted text, writing " + iPlainLength + " characters as numeric code.");
lblMessage.setText("Unprintable encrypted text, writing " + iPlainLength + " characters as numeric code.");
sbTemp = new StringBuffer();
for (i = 0; i < iPlainLength; i++)
{
iTemp = sTemp.charAt(i);
if (i == iPlainLength - 1)
{
sbTemp.append(iTemp);
}
else
{
sbTemp.append(iTemp + " ");
}
}
taCryptText.setText(sbTemp.toString());
}
else
{
System.out.println("Printable encrypted text, writing " + iPlainLength + " characters.");
lblMessage.setText("Printable encrypted text, writing " + iPlainLength + " characters.");
taCryptText.setText(sTemp);
}
} // End of function encrypt().
boolean numericP(int iTextLength, String sText)
{
boolean r = true;
int i = 0;
char cTemp = 0;
int iRunLength = 0;
int iMaxRunLength = 0;
for (i = 0; i < iTextLength; i++)
{
try
{
cTemp = sText.charAt(i);
}
catch (StringIndexOutOfBoundsException e7)
{
System.out.println("Caught StringIndexOutOfBoundsException in decrypt() (e7).");
}
if (cTemp != ' ')
{
if (cTemp <> 57)
{
r = false;
break; // Break out of for loop.
}
else
{
if (cTemp > 47 && cTemp < 58)
{
// We have a decimal digit.
iRunLength++;
}
}
}
else
{
// We have a space: // Detect delimiting spaces
if (iRunLength > iMaxRunLength)
{
iMaxRunLength = iRunLength;
}
iRunLength = 0;
}
} // End of for.
if (iRunLength > iMaxRunLength) // Catch the case where the space
{ // comes at the end of the string.
iMaxRunLength = iRunLength;
}
if (iMaxRunLength > 3) // It's not text that happens to to be
{ // a string (or strings) of digits.
r = false;
}
return r;
}
boolean numericKeyP(int iKeyTextLength, String sKeyText)
{
boolean r = true;
int i = 0;
char cTemp = 0;
for (i = 0; i < iKeyTextLength; i++)
{
cTemp = sKeyText.charAt(i);
if (cTemp != ' ')
{
if (cTemp <> 57)
{
r = false;
break; // Break out of for loop.
}
}
}
return r;
}
boolean unprintableP(int iLength, String sText)
{
boolean r = false;
int i = 0;
char cTemp = 0;
for (i = 0; i < iLength; i++)
{
cTemp = sText.charAt(i);
if (cTemp < 32 || cTemp == 127)
{
if (cTemp != 9 && cTemp != 10 && cTemp != 12 && cTemp != 13)
{
r = true;
break; // Break out of for loop.
}
}
}
return r;
}
} // End of Applet class Encrypt
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