json_decode возвращает NULL после того, как строка json была расшифрована с помощью mcrypt_decrypt (aes)

//JAVASCRIPT
    var encrypted = CryptoJS.AES.encrypt(
        JSON.stringfy({'message':'message','messageA':'messageA','messageB':'messageB'}),
        key512Bits500Iterations, {iv:iv});

    var data_base64 = encrypted.ciphertext.toString(CryptoJS.enc.Base64);
    var iv_base64 = encrypted.iv.toString(CryptoJS.enc.Base64);
    var key_base64 = encrypted.key.toString(CryptoJS.enc.Base64);

    $.ajax({
		url: 'http://localhost/workspace/messageAppl.php',
		type: 'POST',
		data: {
          'data_base64':data_base64,
          'iv_base64':iv_base64,
          'key_base64':key_base64 //key_base64 will be encrypted with RSA
		},
    	success: function(data){
        	alert(data);
        },
        error: function(){
          alert('Index-Error');
    	}	
    });

//    PHP

    // I can get the jsonString but I can't get the single message like 'message', 'messageA' or 'messageB'
         ...
         
     //Decryption in PHP
         public function jsMessage($data_base64, $iv_base64, $key_base64){
			$data_enc = base64_decode($data_base64); // data_base64 from JS
			$iv        = base64_decode($iv_base64);   // iv_base64 from JS
			$key       = base64_decode($key_base64);  // key_base64 from JS
		
			$plaintext = rtrim( mcrypt_decrypt( MCRYPT_RIJNDAEL_128, $key, $data_enc, MCRYPT_MODE_CBC, $iv ), "\t\0 " );
			return $plaintext;
		}

         
    $json_string = aes_decrypt($_POST['data_base64'], $_POST['iv_base64'], $_POST['key_base64']);


    // json_decode returns NULL but WHY?
    $array=json_decode($json_string);

    $message=$array->message
    $messageA=$array->messageA
    $messageB=$array->messageB