AES 128 encryption in Java Decryption in PHP

Question

I have been trying to decrypt a string using AES-128 CBC which was originally crypted using JAVA AES encryption. In java PKCS7 padding is used. And I have tried to encrypt and decrypt using similar PHP code. But I am getting different result.

My Java code

import java.security.MessageDigest;
import java.security.spec.AlgorithmParameterSpec;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import android.util.Base64;

/**
 * @author vipin.cb , [email protected] <br>
 *         Sep 27, 2013, 5:18:34 PM <br>
 *         Package:- <b>com.veebow.util</b> <br>
 *         Project:- <b>Veebow</b>
 *         <p>
 */
public class AESCrypt {

    private final Cipher cipher;
    private final SecretKeySpec key;
    private AlgorithmParameterSpec spec;
    public static final String SEED_16_CHARACTER = "U1MjU1M0FDOUZ.Qz";

    public AESCrypt() throws Exception {
        // hash password with SHA-256 and crop the output to 128-bit for key
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        digest.update(SEED_16_CHARACTER.getBytes("UTF-8"));
        byte[] keyBytes = new byte[32];
        System.arraycopy(digest.digest(), 0, keyBytes, 0, keyBytes.length);

        cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
        key = new SecretKeySpec(keyBytes, "AES");
        spec = getIV();
    }

    public AlgorithmParameterSpec getIV() {
        byte[] iv = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, };
        IvParameterSpec ivParameterSpec;
        ivParameterSpec = new IvParameterSpec(iv);

        return ivParameterSpec;
    }

    public String encrypt(String plainText) throws Exception {
        cipher.init(Cipher.ENCRYPT_MODE, key, spec);
        byte[] encrypted = cipher.doFinal(plainText.getBytes("UTF-8"));
        String encryptedText = new String(Base64.encode(encrypted,
                Base64.DEFAULT), "UTF-8");

        return encryptedText;
    }

    public String decrypt(String cryptedText) throws Exception {
        cipher.init(Cipher.DECRYPT_MODE, key, spec);
        byte[] bytes = Base64.decode(cryptedText, Base64.DEFAULT);
        byte[] decrypted = cipher.doFinal(bytes);
        String decryptedText = new String(decrypted, "UTF-8");

        return decryptedText;
    }

}

And the equivalent PHP code I am using.

<?php

class MCrypt {

    private $iv = '0000000000000000'; #Same as in JAVA              
    private $key = 'U1MjU1M0FDOUZ.Qz'; #Same as in JAVA

    function __construct() {
        $this->key = hash('sha256', $this->key, true);
    }

    function encrypt($str) {
        $iv = $this->iv;
        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
        mcrypt_generic_init($td, $this->key, $iv);
        $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
        $pad = $block - (strlen($str) % $block);
        $str .= str_repeat(chr($pad), $pad);
        $encrypted = mcrypt_generic($td, $str);
        mcrypt_generic_deinit($td);
        mcrypt_module_close($td);
        return base64_encode($encrypted);
    }

    function decrypt($code) {
        $iv = $this->iv;
        $td = mcrypt_module_open('rijndael-128', '', 'cbc', '');
        mcrypt_generic_init($td, $this->key, $iv);
        $str = mdecrypt_generic($td, base64_decode($code));
        $block = mcrypt_get_block_size('rijndael-128', 'cbc');
        mcrypt_generic_deinit($td);
        mcrypt_module_close($td);
        return $str;
        //return $this->strippadding($str);             
    }

    /*
      For PKCS7 padding
     */
    private function addpadding($string, $blocksize = 16) {
        $len = strlen($string);
        $pad = $blocksize - ($len % $blocksize);
        $string .= str_repeat(chr($pad), $pad);
        return $string;
    }

    private function strippadding($string) {
        $slast = ord(substr($string, -1));
        $slastc = chr($slast);
        $pcheck = substr($string, -$slast);
        if (preg_match("/$slastc{" . $slast . "}/", $string)) {
            $string = substr($string, 0, strlen($string) - $slast);
            return $string;
        } else {
            return false;
        }
    }

}

$encryption = new MCrypt();
echo $encryption->encrypt('123456') . "<br/>";
echo $encryption->decrypt('tpyxISJ83dqEs3uw8bN/+w==');

In Java
Plain text = 123456
Cipher text = tpyxISJ83dqEs3uw8bN/+w==

In PHP

Plain text = 123456
Cipher text = IErqfTCktrnmWndOpq3pnQ==

When I tried to decrpt the Java encrypted text "tpyxISJ83dqEs3uw8bN/+w==" using PHP decryption I am getting an empty array if I removed the padding . Without removing the padding I am getting "::::::::::"

I think there is some mistake with the IV bytes used in PHP and Java Can anyone help me on this. I have tried many combinations . Still no result. I am very new to Java concepts.

------Solution-------

I have modified my php class according to the comments given by owlstead. may be there is a better way. I am posting it here so that someone may find it helpful in future and your comments are welcome for further improvement.

<?php

class MCrypt {

    private $hex_iv = '00000000000000000000000000000000'; # converted Java byte code in to HEX and placed it here               
    private $key = 'U1MjU1M0FDOUZ.Qz'; #Same as in JAVA

    function __construct() {
        $this->key = hash('sha256', $this->key, true);
        //echo $this->key.'<br/>';
    }

    function encrypt($str) {       
        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
        mcrypt_generic_init($td, $this->key, $this->hexToStr($this->hex_iv));
        $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
        $pad = $block - (strlen($str) % $block);
        $str .= str_repeat(chr($pad), $pad);
        $encrypted = mcrypt_generic($td, $str);
        mcrypt_generic_deinit($td);
        mcrypt_module_close($td);        
        return base64_encode($encrypted);
    }

    function decrypt($code) {        
        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
        mcrypt_generic_init($td, $this->key, $this->hexToStr($this->hex_iv));
        $str = mdecrypt_generic($td, base64_decode($code));
        $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
        mcrypt_generic_deinit($td);
        mcrypt_module_close($td);        
        return $this->strippadding($str);               
    }

    /*
      For PKCS7 padding
     */

    private function addpadding($string, $blocksize = 16) {
        $len = strlen($string);
        $pad = $blocksize - ($len % $blocksize);
        $string .= str_repeat(chr($pad), $pad);
        return $string;
    }

    private function strippadding($string) {
        $slast = ord(substr($string, -1));
        $slastc = chr($slast);
        $pcheck = substr($string, -$slast);
        if (preg_match("/$slastc{" . $slast . "}/", $string)) {
            $string = substr($string, 0, strlen($string) - $slast);
            return $string;
        } else {
            return false;
        }
    }
function hexToStr($hex)
{
    $string='';
    for ($i=0; $i < strlen($hex)-1; $i+=2)
    {
        $string .= chr(hexdec($hex[$i].$hex[$i+1]));
    }
    return $string;
}
}

$encryption = new MCrypt();
echo $encryption->encrypt('123456') . "<br/>";
echo $encryption->decrypt('tpyxISJ83dqEs3uw8bN/+w==');

Answer 1

Your IV is different, a byte with value zero is different from a character '0' which would translate into a byte with value 30 in hexadecimals or 48 in decimals (if you presume ASCII or UTF-8 encoding).