I asked a question here why AES java decryption return extra characters? about getting extra characters when I decrypt the encrypted data. Thanks to a comment by user "Ebbe M. Pedersen" I now understand that the problem is not using the same padding mechanism in both the PHP and Android Java code. So I changed the Java code to
Java code
public class encryption {
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 encryption()
{
ivspec = new IvParameterSpec(iv.getBytes());
keyspec = new SecretKeySpec(SecretKey.getBytes(), "AES");
try
{
cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");//"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;
}
}
Then I added the same PKCS5padding functions to my PHP mcrypt class:
PHP mcrypt class
class MCrypt
{
private $iv = 'fedcba9876543210'; #Same as in JAVA
private $key = '0123456789abcdef'; #Same as in JAVA
function MCrypt()
{
}
function encrypt($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 $bindata;
}
function pkcs5_pad ($text, $blocksize)
{
$pad = $blocksize - (strlen($text) % $blocksize);
return $text . str_repeat(chr($pad), $pad);
}
function pkcs5_unpad($text)
{
$pad = ord($text{strlen($text)-1});
if ($pad > strlen($text)) return false;
if (strspn($text, chr($pad), strlen($text) - $pad) != $pad) return false;
return substr($text, 0, -1 * $pad);
}}
Now the current problem is sending/receiving UTF-8 characters, not how to decode/encode UTF-8 characters.
When i send Arabic/Persian words which contain for example more than 3 or less than 3 characters it returns nothing.
For example:
If I send the word "خوب" (which has exactly 3 characters) I get "خوب" which is correct; but
if I send مچکرم (which has 5 characters) I get nothing.
I found that the problem is that I was not using the unpadding function after decrypting the data in my php code, so I fixed that:
PHP code
<?php
$data =file_get_contents('php://input');
$block_size=mcrypt_get_block_size("rijndael-128",'cbc');
require_once "encryption.php";
$etool=new MCrypt();
$data =$etool->decrypt($data);
$data=$etool->pkcs5_unpad($data);// <------ using unpad function
$data =json_decode($data, true);
$data=$data["request"];
$etool=new MCrypt();
$data=$etool->pkcs5_pad($data,$block_size);
$data=$etool->encrypt($data);
$array=array('data'=>$data);
echo json_encode($array);
And here is the Java code to get it
JSONObject j=new JSONObject(sb.toString());//sb is string builder
result=j.get("data").toString();
result= new String(etool.decrypt( result ),"UTF-8");
result = new String(result.getBytes("ISO-8859-1"));
Log.d("success remote ",result);
Now the problem is reversed!! I can get words containing more than or less than 3 Persian/Arabic characters, but not words containing exactly 3 characters.
I think I should check "does unpadding required?" but how if so?
