how to encrypt and decrypt a quire string c# asp.net

sender page
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.IO;//used for streams support
using System.Security.Cryptography;//used for security
using System.Text;//used for encoding
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    public static string Encrypt_QueryString(string str)
    {
        string EncrptKey = "god you are great";
            //"2013;[pnuLIT)WebCodeExpert";
        byte[] byKey = { };
        byte[] IV = { 18, 52, 86, 120, 144, 171, 205, 239 };
        byKey = System.Text.Encoding.UTF8.GetBytes(EncrptKey.Substring(0, 8));
        DESCryptoServiceProvider des = new DESCryptoServiceProvider();
        byte[] inputByteArray = Encoding.UTF8.GetBytes(str);
        MemoryStream ms = new MemoryStream();
        CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(byKey, IV), CryptoStreamMode.Write);
        cs.Write(inputByteArray, 0, inputByteArray.Length);
        cs.FlushFinalBlock();
        return Convert.ToBase64String(ms.ToArray());
    }
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string val = Encrypt_QueryString(TextBox1.Text.Trim());
        Response.Redirect("Default2.aspx?EmpId=" + val);
    }
  }
redirecting page
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Security.Cryptography;
using System.IO;
using System.Text;

public partial class Default2 : System.Web.UI.Page
{
    public static string Decrypt_QueryString(string str)
    {
        str = str.Replace(" ", "+");
        string DecryptKey = "god you are great";
            //"2013;[pnuLIT)WebCodeExpert";
        byte[] byKey = { };
        byte[] IV = { 18, 52, 86, 120, 144, 171, 205, 239 };
        byte[] inputByteArray = new byte[str.Length];

        byKey = System.Text.Encoding.UTF8.GetBytes(DecryptKey.Substring(0, 8));
        DESCryptoServiceProvider des = new DESCryptoServiceProvider();
        inputByteArray = Convert.FromBase64String(str);
        MemoryStream ms = new MemoryStream();
        CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(byKey, IV), CryptoStreamMode.Write);
        cs.Write(inputByteArray, 0, inputByteArray.Length);
        cs.FlushFinalBlock();
        System.Text.Encoding encoding = System.Text.Encoding.UTF8;
        return encoding.GetString(ms.ToArray());
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        string Id = Decrypt_QueryString(Request.QueryString["EmpId"]);
        Response.Write("Emp Id =:" + Id);
    }
}