Write a Java program to implement the DES algorithm logic.

HARDWARE AND SOFTWARE REQUIREMENT:

1. Intel based Desktop PC: - RAM of 512 MB

2. Notepad/Notepad ++ editor

3. Net beans / Eclipse

THEORY:

DES is a block cipher technique which encrypts data in blocks (64 bit size), i.e. 64 bits of PLAINTEXT  message goes as the input to DES, which produces 64 bits of CIPHERTEXT message. DES uses a 56 bit key. DES is actually based on the two fundamental concepts of cryptography: substitution  and transposition. It consists of 16 steps called as a rounds. Each round is responsible for performing the steps of substitution and transposition.

STEP-1:

The 64 bit PLAINTEXT message is given to an initial Permutation (IP).

STEP-2:

Initial permutation (IP) divides 64-bit PLAINTEXT into two halves ;say Left    PLAINTEXT (LPT) and Right PLAINTEXT (RPT).

STEP-3:

         Now each LPT and RPT  go through 16 rounds of encryption process.

STEP-4:

  In the end, LPT and RPT are re-joined and a Final Permutation (FP) is performed     on the combined 64-bit block.

 STEP-5:

         The result of this process produces 64 bit CIPHERTEXT.

SOURCE CODE:

import javax.swing.*;

import java.security.SecureRandom;

import javax.crypto.Cipher;

import javax.crypto.KeyGenerator;

import javax.crypto.SecretKey;

import javax.crypto.spec.SecretKeySpec;

import java.util.Random ;

class DES {

byte[] skey = new byte[1000];

String skeyString;

static byte[] raw;

String inputMessage,encryptedData,decryptedMessage;

public DES()

{

try

{

generateSymmetricKey();

inputMessage=JOptionPane.showInputDialog(null,"Enter message to encrypt");

byte[] ibyte = inputMessage.getBytes();

byte[] ebyte=encrypt(raw, ibyte);

String encryptedData = new String(ebyte);

System.out.println("Encrypted message "+encryptedData);

JOptionPane.showMessageDialog(null,"Encrypted Data "+"\n"+encryptedData);

byte[] dbyte= decrypt(raw,ebyte);

String decryptedMessage = new String(dbyte);

System.out.println("Decrypted message "+decryptedMessage);

JOptionPane.showMessageDialog(null,"Decrypted Data  "+"\n"+decryptedMessage);

}

catch(Exception e)

{

System.out.println(e);

}

}

void generateSymmetricKey() {

try {

Random r = new Random();

int num = r.nextInt(10000);

String knum = String.valueOf(num);

byte[] knumb = knum.getBytes();

skey=getRawKey(knumb);

skeyString = new String(skey);

System.out.println("DES Symmetric key = "+skeyString);

}

catch(Exception e)

{

System.out.println(e);

}

}

private static byte[] getRawKey(byte[] seed) throws Exception

{

KeyGenerator kgen = KeyGenerator.getInstance("DES");

SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");

sr.setSeed(seed);

kgen.init(56, sr);

SecretKey skey = kgen.generateKey();

raw = skey.getEncoded();

return raw;

}

private static byte[] encrypt(byte[] raw, byte[] clear) throws

Exception {

SecretKeySpec skeySpec = new SecretKeySpec(raw, "DES");

Cipher cipher = Cipher.getInstance("DES");

cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

byte[] encrypted = cipher.doFinal(clear);

return encrypted;

}

private static byte[] decrypt(byte[] raw, byte[] encrypted)

throws Exception

{

SecretKeySpec skeySpec = new SecretKeySpec(raw,

"DES");

Cipher cipher = Cipher.getInstance("DES");

cipher.init(Cipher.DECRYPT_MODE, skeySpec);

byte[] decrypted = cipher.doFinal(encrypted);

return decrypted;

}

public static void main(String args[]) {

DES des = new DES();

}

}

OUTPUT: