IT Certificaions

Google Cloud Platform

Monday, May 21, 2012

encyption-decryption using DES

 Example of encyption-decryption using DES
 ----------------------------------------------------------
package com.example.des;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESKeySpec;

public class CipherExample {

    public static void main(String[] args) {
        try {
            String key = "y1$ab??x";            // your key , needs to be at least 8 characters for DES
           

            FileInputStream fis = new FileInputStream("OriginalFile.txt");
            FileOutputStream fos = new FileOutputStream("encryptedFile.txt");
            System.out.println("Going to encrpyt this file using DES.......");
            encrypt(key, fis, fos);

            FileInputStream fis2 = new FileInputStream("encryptedFile.txt");
            FileOutputStream fos2 = new FileOutputStream("decryptedFile.txt");
            System.out.println("Going to decrypt this file using DES.......");
            decrypt(key, fis2, fos2);
        } catch (Throwable e) {
            e.printStackTrace();
        }   
       
    }

    public static void encrypt(String key, InputStream is, OutputStream os) throws Throwable {
        encrypt_Or_Decrypt(key, Cipher.ENCRYPT_MODE, is, os);
    }

    public static void decrypt(String key, InputStream is, OutputStream os) throws Throwable {
        encrypt_Or_Decrypt(key, Cipher.DECRYPT_MODE, is, os);
    }

    public static void encrypt_Or_Decrypt(String key, int mode, InputStream is, OutputStream os) throws Throwable {
        System.out.println("encryptOrDecrypt this file using DES.......");
        DESKeySpec dks = new DESKeySpec(key.getBytes());
        SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
        SecretKey desKey = skf.generateSecret(dks);
        Cipher cipher = Cipher.getInstance("DES"); // DES/ECB/PKCS5Padding for SunJCE

        if (mode == Cipher.ENCRYPT_MODE) {
            cipher.init(Cipher.ENCRYPT_MODE, desKey);
            CipherInputStream cis = new CipherInputStream(is, cipher);
            doCopy(cis, os);
        } else if (mode == Cipher.DECRYPT_MODE) {
            cipher.init(Cipher.DECRYPT_MODE, desKey);
            CipherOutputStream cos = new CipherOutputStream(os, cipher);
            doCopy(is, cos);
        }
    }

    public static void doCopy(InputStream is, OutputStream os) throws IOException {
        byte[] bytes = new byte[64];
        int numBytes;
        while ((numBytes = is.read(bytes)) != -1) {
            os.write(bytes, 0, numBytes);
        }
        os.flush();
        os.close();
        is.close();
    }

}