and how to encrypt the json again, it give me error i can't put json directly to the code ?
the problem been solved

:
before you put json directly to c# code you have to escape json with this tool ;
https://www.browserling.com/tools/json-escapethis my code :
Code:
using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
public class Program
{
private static string key = "Fotoable";
public static string DesEncrypt(string encryptString)
{
string result;
try
{
byte[] bytes = Encoding.UTF8.GetBytes(key.Substring(0, 8));
byte[] rgbIV = bytes;
byte[] bytes2 = Encoding.UTF8.GetBytes(encryptString);
DESCryptoServiceProvider descryptoServiceProvider = new DESCryptoServiceProvider();
MemoryStream memoryStream = new MemoryStream();
CryptoStream cryptoStream = new CryptoStream(memoryStream, descryptoServiceProvider.CreateEncryptor(bytes, rgbIV), CryptoStreamMode.Write);
cryptoStream.Write(bytes2, 0, bytes2.Length);
cryptoStream.FlushFinalBlock();
string text = Convert.ToBase64String(memoryStream.ToArray());
cryptoStream.Close();
memoryStream.Close();
result = text;
}
catch (Exception exception)
{
result = encryptString;
}
return result;
}
public static void Main()
{
Console.WriteLine(DesEncrypt("{\"data\": [{\"answer\": \"ten\", \"isHorizontal\": 1, \"firstLetterRow\": 2, \"firstLetterCol\": 1}, {\"answer\": \"net\", \"isHorizontal\": 0, \"firstLetterRow\": 1, \"firstLetterCol\": 2}], \"size\": 5}"));
}
}