Java decrypt error: data not block size aligned

Question

I'm trying to encrypt data between my android application and a PHP webservice.

I found the next piece of code in this website: http://schneimi.wordpress.com/2008/11/25/aes-128bit-encryption-between-java-and-php/

But when I try to decrypt I get the Exception of the title "data not block size aligned"

This are the method in my MCrypt class

public String encrypt(String text) throws Exception
{
    if(text == null || text.length() == 0)
        throw new Exception("Empty string");

    Cipher cipher;
    byte[] encrypted = null;

    try {
        cipher = Cipher.getInstance("AES/CBC/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivspec);

        encrypted = cipher.doFinal(padString(text).getBytes());
    } catch (Exception e)
    {           
        throw new Exception("[encrypt] " + e.getMessage());
    }

    return new String( encrypted );
}

public String decrypt(String code) throws Exception
{
    if(code == null || code.length() == 0)
        throw new Exception("Empty string");

    Cipher cipher;
    byte[] decrypted = null;

    try {
        cipher = Cipher.getInstance("AES/CBC/NoPadding");
        cipher.init(Cipher.DECRYPT_MODE, keyspec, ivspec);
        decrypted = cipher.doFinal(hexToBytes(code));
    } catch (Exception e)
    {
        throw new Exception("[decrypt] " + e.getMessage());
    }
    return new String( decrypted );
}


private static byte[] hexToBytes(String hex) {
  String HEXINDEX = "0123456789abcdef";
  int l = hex.length() / 2;
  byte data[] = new byte[l];
  int j = 0;

  for (int i = 0; i < l; i++) {
    char c = hex.charAt(j++);
    int n, b;

    n = HEXINDEX.indexOf(c);
    b = (n & 0xf) << 4;
    c = hex.charAt(j++);
    n = HEXINDEX.indexOf(c);
    b += (n & 0xf);
    data[i] = (byte) b;
  }

  return data;
}

private static String padString(String source)
{
  char paddingChar = ' ';
  int size = 16;
  int x = source.length() % size;
  int padLength = size - x;

  for (int i = 0; i < padLength; i++)
  {
      source += paddingChar;
  }

  return source;
}

And this is how I'm using it in my activity to test:

String encrypted = mcrypt.encrypt(jsonUser.toString());
String decrypted = mcrypt.decrypt(encrypted);

the encrypt method works fine, but the second throws an exception.

SERPRO · Accepted Answer · 2011-07-01 20:42:41Z

At last! I made it work! Thanks for all your suggestion. I would like to share the code just in case somebody get stuck like me:

JAVA

import java.security.NoSuchAlgorithmException;

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

public class MCrypt {

    private String iv = "fedcba9876543210";//Dummy iv (CHANGE IT!)
    private IvParameterSpec ivspec;
    private SecretKeySpec keyspec;
    private Cipher cipher;

    private String SecretKey = "0123456789abcdef";//Dummy secretKey (CHANGE IT!)

    public MCrypt()
    {
        ivspec = new IvParameterSpec(iv.getBytes());

        keyspec = new SecretKeySpec(SecretKey.getBytes(), "AES");

        try {
            cipher = Cipher.getInstance("AES/CBC/NoPadding");
        } catch (NoSuchAlgorithmException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (NoSuchPaddingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public byte[] encrypt(String text) throws Exception
    {
        if(text == null || text.length() == 0)
            throw new Exception("Empty string");

        byte[] encrypted = null;

        try {
            cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivspec);

            encrypted = cipher.doFinal(padString(text).getBytes());
        } catch (Exception e)
        {           
            throw new Exception("[encrypt] " + e.getMessage());
        }

        return encrypted;
    }

    public byte[] decrypt(String code) throws Exception
    {
        if(code == null || code.length() == 0)
            throw new Exception("Empty string");

        byte[] decrypted = null;

        try {
            cipher.init(Cipher.DECRYPT_MODE, keyspec, ivspec);

            decrypted = cipher.doFinal(hexToBytes(code));
        } catch (Exception e)
        {
            throw new Exception("[decrypt] " + e.getMessage());
        }
        return decrypted;
    }



    public static String bytesToHex(byte[] data)
    {
        if (data==null)
        {
            return null;
        }

        int len = data.length;
        String str = "";
        for (int i=0; i<len; i++) {
            if ((data[i]&0xFF)<16)
                str = str + "0" + java.lang.Integer.toHexString(data[i]&0xFF);
            else
                str = str + java.lang.Integer.toHexString(data[i]&0xFF);
        }
        return str;
    }


    public static byte[] hexToBytes(String str) {
        if (str==null) {
            return null;
        } else if (str.length() < 2) {
            return null;
        } else {
            int len = str.length() / 2;
            byte[] buffer = new byte[len];
            for (int i=0; i<len; i++) {
                buffer[i] = (byte) Integer.parseInt(str.substring(i*2,i*2+2),16);
            }
            return buffer;
        }
    }



    private static String padString(String source)
    {
      char paddingChar = ' ';
      int size = 16;
      int x = source.length() % size;
      int padLength = size - x;

      for (int i = 0; i < padLength; i++)
      {
          source += paddingChar;
      }

      return source;
    }
}

HOW TO USE IT (JAVA)

mcrypt = new MCrypt();
/* Encrypt */
String encrypted = MCrypt.bytesToHex( mcrypt.encrypt("Text to Encrypt") );
/* Decrypt */
String decrypted = new String( mcrypt.decrypt( encrypted ) );

====================================================

PHP

<?php 

class MCrypt
{
    private $iv = 'fedcba9876543210'; #Same as in JAVA
    private $key = '0123456789abcdef'; #Same as in JAVA


    function __construct()
    {
    }

    function encrypt($str) {

      //$key = $this->hex2bin($key);    
      $iv = $this->iv;

      $td = mcrypt_module_open('rijndael-128', '', 'cbc', $iv);

      mcrypt_generic_init($td, $this->key, $iv);
      $encrypted = mcrypt_generic($td, $str);

      mcrypt_generic_deinit($td);
      mcrypt_module_close($td);

      return bin2hex($encrypted);
    }

    function decrypt($code) {
      //$key = $this->hex2bin($key);
      $code = $this->hex2bin($code);
      $iv = $this->iv;

      $td = mcrypt_module_open('rijndael-128', '', 'cbc', $iv);

      mcrypt_generic_init($td, $this->key, $iv);
      $decrypted = mdecrypt_generic($td, $code);

      mcrypt_generic_deinit($td);
      mcrypt_module_close($td);

      return utf8_encode(trim($decrypted));
    }

    protected function hex2bin($hexdata) {
      $bindata = '';

      for ($i = 0; $i < strlen($hexdata); $i += 2) {
        $bindata .= chr(hexdec(substr($hexdata, $i, 2)));
      }

      return $bindata;
    }

}

HOW TO USE IT (PHP)

<?php 

$mcrypt = new MCrypt();
#Encrypt
$encrypted = $mcrypt->encrypt("Text to encrypt");
#Decrypt
$decrypted = $mcrypt->decrypt($encrypted);

Femi · Accepted Answer · 2011-07-01 11:20:09Z

1

I'm guessing your keyspec and ivspec are not valid for decryption. I've typically transformed them into PublicKey and PrivateKey instances and then use the private key to decrypt.

answered Jul 1, 2011 at 11:20

Femi

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14 Comments

SERPRO Over a year ago

this are my ivspec and keyspec: ivspec = new IvParameterSpec(iv.getBytes()); keyspec = new SecretKeySpec(SecretKey.getBytes(), "AES");

Femi Over a year ago

Ah. You're using AES, not RSA. My mistake. What is the exception you are receiving?

SERPRO Over a year ago

this is the exception: javax.crypto.IllegalBlockSizeException: data not block size aligned

Sunil Kumar Sahoo Over a year ago

@Femi, we cannot encrypt big data using RSA

Sunil Kumar Sahoo Over a year ago

@Femi, I think we can encrypt a data of max size 256byte using RSA

|

Explosion Pills · Accepted Answer · 2011-07-01 12:04:38Z

I looked at the comments in the other answer. I ran into a similar problem trying to encrypt a large block of text using open SSL in php (on both sides). I imagine the same issue would come up in Java.

If you have a 1024 bit RSA key, you must split the incoming text into 117 byte chunks (a char is a byte) and encrypt each (you can concatenate them together). On the other end, you must split the encrypted data into 128 byte chunks and decrypt each. This should give you your original message.

Also note that http may not play friendly with the non-ASCII encrypted data. I base64 encode/decode it before and after transmission (plus you have to worry about additional urlencoding for the base64 change, but it is easy).

I'm not sure of your AES key length, but if it's 1024 bits the chunk length is probably the same. If it's not, you will have to divide the bits by 8 to find the byte chunk length coming out. I'm actually not sure how to get it coming in, unfortunately (maybe multiply by 117/128 ?)

Here's some php code:

class Crypto {
   public function encrypt($key, $data) {
      $crypto = '';
      foreach (str_split($data, 117) as $chunk) {
         openssl_public_encrypt($chunk, $encrypted, $key);
         $crypto .= $encrypted;
      }
      return $crypto;
   }

   //Decrypt omitted.  Basically the same, change 117 to 128.

   /**#@+
    * Update data for HTTP transmission and retrieval
    * Must be used on encrypted data, but also useful for any binary data
    * (e.g. zip files).
    */
   public function base64_encode($value) {
      return rtrim(strtr(base64_encode($value), '+/', '-_'), '=');
   }
   //String length must be padded for decoding for some reason
   public function base64_decode($value) {
      return base64_decode(str_pad(strtr($value, '-_', '+/')
         , strlen($value) % 4, '=', STR_PAD_RIGHT));
   }
   /**#@-*/
}

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