AES / CBC / PKCS5Padding在PHP中用Java解密

Question

I have to encrypt one string with given key in PHP.

In Java i've already both metods to decrypt and encrypt.

Here my Java encrypt method:

public static String encriptB64Aes(String value, String aesKey) {
    String result = null;
    try {

       Cipher encryptCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

       //in PHP !?
       SecretKey secretKey = new SecretKeySpec(aesKey.getBytes("UTF-8"), "AES");
       IvParameterSpec ivParameterSpec = new IvParameterSpec(secretKey.getEncoded());

       encryptCipher.init(Cipher.ENCRYPT_MODE, secretKey, ivParameterSpec);

       // Encrypt
       ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
       CipherOutputStream cipherOutputStream = new CipherOutputStream(outputStream, encryptCipher);
       cipherOutputStream.write(value.getBytes());
       cipherOutputStream.flush();
       cipherOutputStream.close();
       byte[] encryptedBytes = outputStream.toByteArray();
       result = encodeBase64(encryptedBytes);

    } catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
       e.printStackTrace();
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (InvalidKeyException e) {
        e.printStackTrace();
    } catch (InvalidAlgorithmParameterException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return result;
}

I need a method like above in PHP code using mcrypt_module_open.

I tried a method like this, but I don't know how to calculate $iv like above

function encrypt($str, $key) { 
      $str = pkcs5_pad($str);
      $iv = ????;                 
      $td = mcrypt_module_open('rijndael-128', '', 'cbc', '');
      mcrypt_generic_init($td, $key, $iv);
      $encrypted = mcrypt_generic($td, $str);
      mcrypt_generic_deinit($td);
      mcrypt_module_close($td);
      return base64_encode($encrypted);
}

function pkcs5_pad ($text) {
      $blocksize = 16;
      $pad = $blocksize - (strlen($text) % $blocksize);
      return $text . str_repeat(chr($pad), $pad);
}

I would greatly appreciate any help you can give me.

Thanks

Answer 1

In the Java code the AES key is used as IV. Respectively, first block of plaintext data is XORed with the AES key which is used after for encryption. .getEncoded() method just returns the byte[] representation of SecretKey. In your case IV = $key

Wbr, Juris