Why does AES decryption java return extra characters?

Question

Excuse me for bad English. I use mcrypt, which I get from here is MCrypt for php and java . in my android application, I need php and java to communicate securely, so I get the above AES. the problem is when php sends encrypted data, java can decrypt it, but some extra characters are included.

JAVA Code

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; } } 

PHP code

  <?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; } } 

therefore the script is a java-sending data (plain text) in JSON format for PHP, php extracts the data, encrypts them, and finally, an echo in JSON format

Php call:

 <?php $data =json_decode(file_get_contents('php://input'), true); $data=$data["request"]; require_once "encryption.php"; $etool=new MCrypt(); $data=$etool->encrypt($data); $array=array('data'=>$data); echo json_encode($array); 

JAVA Code:

  //sb is StringBuilder JSONObject j=new JSONObject(sb.toString()); encryption etool=new encryption(); result=j.get("data").toString(); result= new String(etool.decrypt( result )); Log.d("success remote ",result ); 

result:

Example

and if I use the Farsi / Arabic word, it gets worse

like this-> درود

In addition, I checked other questions, but I could not get an answer.

AES encryption, extra garbage characters in the decrypted file and
PHP MCRYPT encrypt / decrypt returns invisible weird characters?

Thank you in advance!

Answer 1

AES encrypts in blocks of 16 bytes. If your input is not a multiple of 16 bytes, an additional circuit is needed. Since you did not specify an add-on option for Mcrypt , it uses "zero padding."

In Java code , you specify "NoPadding" when you instantiate your Cipher:

  cipher = Cipher.getInstance("AES/CBC/NoPadding"); 

So, Java believes that the addition made by php is part of the encrypted data.

You just need to make sure your php and Java code uses the same padding scheme.

Answer 2

I think this is binary data that cannot be displayed. Have you tried using base64 to convert it to a regular string before sending it to a php script?

In a php script, you do the following to decode a base64 string.

 $data=base64_decode($data["request"])