Fun Things in Life

… “After started something, you have to finish it” my dad used to tell me…

The Problem: Part 3 was to encrypt a binary file (PDF) in PHP and decrypt it over in Java. It is of course natural to complete it to do it the other way around.

This is actually just flipping some code, real simple, just that I am so busy recently that I have not made time for it.

The Solution:

1. Encrypt a message in Java:

   001	import java.io.*;
   002	import javax.crypto.*;
   003	import javax.crypto.spec.*;
   004
   005	public class encrypt {
   006	  public static void main(String args[]) throws Exception {
   007	    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
   008	    SecretKeySpec keySpec =
   009	      new SecretKeySpec("01234567890abcde".getBytes(), "AES");
   010	    IvParameterSpec ivSpec =
   011	      new IvParameterSpec("fedcba9876543210".getBytes());
   012	    cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec);
   013	    FileInputStream fis   =
   014	      new FileInputStream(new File("plain.pdf"));
   015	    CipherInputStream cis = new CipherInputStream(fis, cipher);
   016	    FileOutputStream fos  =
   017	      new FileOutputStream(new File("encrypted.pdf"));
   018
   019	    byte[] b = new byte[8];
   020	    int i;
   021
   022	    while ((i = cis.read(b)) != -1) {
   023	      fos.write(b, 0, i);
   024	    }
   025	    fos.flush(); fos.close();
   026	    cis.close(); fis.close();
   027	  }

2. The above Java program will encrypted PDF file. It takes the unencrypted PDF file (plain.pdf) and create encrypted.pdf (the encrypted file).
3. Now with the encrypted.pdf, we use a PHP program to decrypt it:

   001	<?php
   002	  $secret_key   = "01234567890abcde";
   003	  $iv           = "fedcba9876543210";
   004	  $infile       = "encrypted.pdf";
   005	  $outfile      = "decrypted.pdf";
   006
   007	  $crypttext = file_get_contents($infile);
   008	  $plaintext = mcrypt_decrypt(MCRYPT_RIJNDAEL_128,
   009	                 $secret_key, $crypttext, MCRYPT_MODE_CBC, $iv);
   010
   011	  header('Content-Type: application/octet-stream');
   012	  header('Content-Length: ' . strlen($plaintext));
   013	  header('Content-Disposition: attachment; filename=' . ($outfile));
   014	  echo $plaintext;
   015	?>

4. The PHP program takes the encrypted.pdf and force download the decrypted.pdf which should be the same as the plain.pdf.

This entry was posted on Saturday, May 19th, 2007 at 5:07 am and is filed under Java, PHP, Programming. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.